Enhancing communities’ adaptive capacity to climate change in drought-prone hotspots of the Blue Nile Basin in Ethiopia

ILRI-UNEP-Wollo University pilot project

TRAINING MANUAL ON PLANTING INDIGENOUS TREE SPECIES FOR FOREST RESTORATION; AND AGROFORESTRY SYSTEMS AND PRACTICES FOR EXTENSION WORKERS AT KABE

WATERSHED, WEREILU, SOUTH WOLLO, ETHIOPIA

Compiled by:

Tsegaye Gobezie and Worku Belayhun

March 2012

Dessie, Ethiopia

ACKNOWLEDGEMENT We would like to thank Wollo University, ILRI, UNEP, Mr. Derbew Kefyalew (coordinator), Mr. Teklemariam Bekele and a number of people from various departments who have been part of the Kabe watershed management for mitigation of climate change.

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TABLE OF CONTENTACKNOWLEDGEMENT............................................................................................................................... ii

TABLE OF CONTENT................................................................................................................................. iii

LIST OF FIGURES...................................................................................................................................... v

INTRODUCTION TO THE MODULE...........................................................................................................1

PART I: PLANTING INDIGENOUS TREE SPECIES FOR FOREST RESTORATION................................2

1 WHY FOREST RESTORATION?........................................................................................................3

1.1 Why plant forest tree.................................................................................................................... 3

1.2 Need and Purpose for Planting....................................................................................................4

1.3 Area and Tree Species Selection.................................................................................................5

1.4 Matching species with site...........................................................................................................6

2 FOREST TREE ESTABLISHMENT AND MANAGEMENT..................................................................8

2.1. Procedure of Plantation Establishment........................................................................................8

2.1.1. Lay-out plantation................................................................................................................. 8

2.1.2. Marking.............................................................................................................................. 10

2.1.3. Site preparation.................................................................................................................. 10

2.1.4. Plantation establishment....................................................................................................11

2.2. Preparation of Planting Pits........................................................................................................11

2.3. Time of tree planting.................................................................................................................12

2.4. Tree Planting.............................................................................................................................. 12

2.4.1. Tree planting method.........................................................................................................12

2.5. Planting tree at Buffer Zones.....................................................................................................12

2.6. Planting Tree on a steep slope..................................................................................................12

3. PLANTATION MAINTENANCE.........................................................................................................14

3.1. Beating- up............................................................................................................................... 14

3.2. Retention of Moisture (Mulching)...............................................................................................14

3.3. Water Supply (Watering/reduce evaporation).......................................................................15

3.4. Fertilization................................................................................................................................. 15

3.5. Protecting seedling from Frost attack.........................................................................................15

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3.5.1. Cover it Up......................................................................................................................... 15

3.5.2. Stone mound......................................................................................................................15

3.6. Weeding..................................................................................................................................... 16

3.7. Protection.................................................................................................................................. 16

4. Reference.......................................................................................................................................... 18

PART II: AGROFORESTRY SYSTEMS AND PRACTICES......................................................................19

1. OVERVIEW OF AGROFORESTRY...................................................................................................20

1.1. Concept and definition of agroforestry.......................................................................................20

1.2. Benefits of agroforestry..............................................................................................................21

1.2.1. Soil fertility improvement and soil conservation.........................................................................21

1.2.2. Fuel wood (Energy)....................................................................................................................22

1.2.3. Carbon sequestration................................................................................................................. 22

1.2.4. Fodder....................................................................................................................................... 23

2. CLASSIFICATION OF AGROFORESTRY SYSTEMS AND DESCRIPTION OF SOME AGROFORESTRY PRACTICES...............................................................................................................24

2.1. Classification of Agroforestry systems.......................................................................................24

2.1.1. Agrisilvicultural systems.....................................................................................................24

2.1.2. Silvopastoral systems........................................................................................................24

2.1.3. Agrosilvopastoral systems.................................................................................................25

2.2. Description of agroforestry practices..........................................................................................25

2.2.1. Improved fallows........................................................................................................................ 25

2.2.2. Alley Cropping............................................................................................................................ 26

2.2.3. Scattered trees on cropland.......................................................................................................28

2.2.4. Live fences................................................................................................................................. 29

2.2.5. Windbreaks................................................................................................................................ 30

2.2.6. Trees on boundaries.................................................................................................................. 31

2.2.7. Contour vegetation strips...........................................................................................................32

2.2.8. Trees and shrubs on terraces....................................................................................................33

3. REFERENCE..................................................................................................................................... 35

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LIST OF FIGURES Figure 1: Calculation of number of tree per ha for different plantation types......................................9

Figure 2: The benefits of agroforestry in nutrient cycling and erosion control............................................21

Figure 3: An improved fallow with Sesbania sesban..................................................................................25

Figure 4: The different phases of improved fallow and subsequent cropping phase.................................25

Figure 5: Tree spacing in alley cropping....................................................................................................27

Figure 6: (Left) Schematic presentation of dispersed trees on cropland; (Right) Scattered Faidherbia albida trees in Teff crop land in Central Rift Valley (CRV) of Ethiopia.......................................................28

Figure 7: : Live fences.............................................................................................................................. 29

Figure 8: Good and bad windbreaks..........................................................................................................31

Figure 9: A line of trees along a boundary.................................................................................................32

Figure 10: Contour hedgerows of Leucaena leucocephala on a hill-farming demonstration site (A) and closely spaced contour hedgerows of Leucaena leucocephala (B)...........................................................33

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INTRODUCTION TO THE MODULEEthiopia is situated in the horn of Africa, which is the second most populous country from the continent with about 85 million people. Agriculture accounts for almost 40 percent of the country’s gross domestic product and 80 percent of exports. The majority of the population is engaged in subsistence farming. Trees and forests play vital role in improving rural livelihoods by providing construction materials and fuel wood, generate cash income, control soil erosion, enhance ground water development, regulate stream flow, and provide shelter and other services. Currently, these benefits are becoming less available due to deforestation. Deforestation is recognized as the most severe environmental problem in Ethiopia, which results severe land degradation. A report on the forest resources of Ethiopia indicates, there is alarming deforestation that goes on an accelerating rate.

Ninety-four percent of the Ethiopian population relies on wood-based and biomass fuel for household energy. Scarcity of firewood has become acute in many parts of the country causing a continuous rise in prices, and thus increasing the economic burden on the household budget. Animal dung and crop residues are increasingly being used for household fuel rather than being added to the soil to improve soil fertility, thus further exacerbating the problems of environmental degradation.

To mitigate such problems launching intensive forestry programs can be solution through the following strategies:

Planting tree (establish forest plantations) Promote community woodlots and natural regeneration on degraded sites to reclaim denuded

areas and also supply wood products Initiate management plan for remnant woodlands/forests Integrate tree growing with other land use system such as:

Crop production livestock husbandry etc

The main focus of this training manual is on the first and last strategy. The writers hope that the trainee will give good information about tree planting and different agroforestry practices. The module have two parts; part one is about ‘planting indigenous tree species for forest restoration’ and part two is about ‘agroforestry systems and practices’. First part of the training manual consists of three chapters, and the second one contains two chapters. Each of them focuses on various aspects of forestry and agroforestry practices.

Tsegaye Gobezie (MSc) Worku Belayhun (MSc)

Wollo University Wollo University

P.O.Box: 1145 P. O. Box - 1145

E-mail: tsegaye_gobezie@yahoo.com E-mail: workubelayhun@yahoo.com

Mobile: +251-920787787 Mobile: +251-911574255

PART I: PLANTING INDIGENOUS TREE SPECIES FOR FOREST RESTORATION

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CHAPTER ONE

1 WHY FOREST RESTORATION?

INTRODUCTION

The highly rugged and majestic mountains of Ethiopia, that were once covered by lush montane forests, which are presently denuded and eroded. The surrounding steep slopes were once covered with indigenous species including Olea africana Mill. (syn:Olea europaea L. subsp. cuspidata Wall ex. Dc.) cifferi, Podocarpus gracilior Pilg. (syn: Podocarpus falcatus Thunb. (Mirb.), Cordia africana Lam., Hagenia abyssinica (Bruce) J.F. Gamel., Juniperus procera Hochst. ex. A. Rich., and Ekebergia capensis Sparrm.

At present because of deforestation much of the highlands are covered with wooded grasslands in which secondary tree species like Acacia abyssinica, A. negrii and A. pilispina occur. Forest plantations in the Ethiopian highlands, apart from providing economically and socially valued forest products and services, also facilitate the restoration of floristic and faunal diversity and eventually also the productivity of degraded lands. Tree planting can play an important role in restoring the productivity, ecosystem stability, and biological diversity of degraded tropical lands.

Objectives of the Chapter At the end of this chapter the trainee are able:

o to identify the prerequisite for plantation establishmentso to list the steps of tree planting o to know the needs and Purpose for Planting

Methods of delivery Gap Lecture /Power point presentation Group discussion

1.1 Why plant forest treeThe direct benefits of forest on the value of the land are forest products such as saw timber, fuel wood, charcoal, poles, food products, and fodder for livestock, medicinal products and shade for agricultural crops.

From an ecological point of view, the reconstruction of a vegetation cover through forest plantation restores the productivity of the land in terms of reduction of air pollution, regulation of water quality and regime, control of potential soil erosion, improvement of soil fertility and creation of habitat for wildlife. The socio-economic effects are enhancement of the beauty of the landscape, creation of an environment beneficial to the health and increase in the value of the land.

Forests play an important role in the function and management of our watersheds. They

Stabilize soil; minimize soil loss and landslides by slowing down and spreading out water flow. Maintain a sustained water supply. Provide a seed bank for plants. are a source of cultural and economic services (i.e. food, medicine, construction materials,

totems) Habitats for other organisms. Maintain the surrounding environment, woody vegetation can trap water from fog or ameliorate

frosts.

In addition, Forests play a major role in global carbon (C) cycle, and the carbon density (CD) could reflect its ecological function of C sequestration.

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This day Ethiopians are facing rapid deforestation and degradation of land resources. The increasing population has resulted in extensive forest clearing for agricultural use, overgrazing, and exploitation of existing forests for fuel wood, fodder, and construction materials.

To reduce these problems, Forests need to be conserved and restored to prepare them for the impacts of climate change. Communities working in collaboration with key government and non-government partners play an important part and help create a better future for forest restoration. This training manual explains the what, where and how of restoring forests. It further elaborates on how we can repair the degraded land that we have created through tree planting and identify needs and purposes for replanting, species to site selection, planting techniques, and monitoring & maintenance.

The diagram below show the steps of tree planting explained in this training manual.

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1.2 Need and Purpose for PlantingIn order to select the most appropriate tree species for replanting, you will need to identify your main purpose for wanting to replant trees.Listed are some questions you need to consider:

Is it for food security? For economic development? Greater biodiversity? Do you want to make the soil fertile again? Is it to stop soil erosion and sediments entering your waterways (cleaner water)? Is it mainly for food source or cultural connection (e.g. medicinal)? Do you want to look at some timber species for longer-term economic gains? It will usually be a combination of the above factors.

Purpose of the intended plantationPlantations are established for one of four main purposes:

i. Industrial uses: fuelwood, pulpwood, saw timber, panel products such as plywood and other boards.

ii. Domestic uses: notably firewood, but also rough round wood for poles, stakes, etc. iii. Environmental protection: check soil erosion and water runoff, stabilize soil surface, windbreaks,

rehabilitation of wasteland/industrial sites. iv. Tree-planting as an integral part of rural development for amenity, shade, shelter, food, fruits and

nuts, animal fodder and browse, and to enrich the soil through leaf fall, nitrogen fixation, other agroforestry, etc.

What is the most suitable species to plant will differ between each of these purposes and between different end-uses. Where plantations are established to satisfy more than one objective species choice will depend on priorities or be varied to suit different purposes

Though, in general, the purpose for growing trees dictates species choice, this is not always so. Tree-planting may occasionally be done to promote rural employment, with the assumption that forest produce will always be of value, and often the most readily available species is used.

1.3 Area and Tree Species Selection

Identify Species potentially availableOnce the purpose of a plantation is known the choice of species is narrowed. The approach to find the right species lies in the axiom of matching species with site - to select the species that grows best on the sites in question. The factor of site is considered later, considered here are the possibilities and limitations in species selection under the headings indigenous species, exotics and species introduction, and genetic variation and tree improvement.

Indigenous species An indigenous species is one that grows naturally in the country concerned, though not necessarily in all parts and certainly not suited to all sites. With such species there are no political or quaran tine problems to obstruct its use in a plantation programme, and there are some important biological advantages of using indigenous species:

1. Growth of natural stands provide some indication of possible performance in plantation, 2. The species is adapted to the environment and already filling an ecological niche, this may

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render it less susceptible to serious damage from diseases and pests since controlling agents (predators, viruses, climatic factors) are already present.

3. Indigenous species, even in monoculture, are generally considered more ecologically valuable than exotics for conservation of native fauna and flora.

4. The timber is likely to be known to local wood using industries and may be preferred as a firewood source.

As a rule where a native species meets the need there is no reason to choose an alternative. Indeed, for reasons of conservation, if the choice lies between two species of comparable growth and quality, one of which is native and one exotic, the native species is to be preferred. Of course , where no suitable native species exists trials of introduced species must be laid down.

Exotics speciesThe majority of successful plantations in the tropics consist of exotic species. There are several factors which can lead to great success if a carefully chosen exotic is used. According to Evans, 1992 advantages of growing exotic forests are mentioned as follow

1. The much wider choice of species, in theory from anywhere in the world, increases the chance of finding a species well suited to the planting site.

2. An exotic species, away from its natural habitat, is often free from diseases and pests, for the first rotation at least, since insects and fungal pathogens in the recipient region may not find the 'alien' species a suitable host.

3. When exotics are used world-wide, already-existing research and experience allows them to be used with some degree of certainty. From the outset seed is available and dependable silvicultural methods can be used, and mistakes and problems avoided which so easily occur with a little known species.

1.4 Matching species with siteOnce you have considered your purpose for planting, you will then need to identify your area or site for your replanting. Much land, ill-suited to agriculture, is potentially available for forest plantations; land shortage is unlikely to be a problem in the foreseeable future. The area requiring restoration is initially assessed for the various types of “land units” found within. Factors to consider are soil type, slope, existing trees and vegetation (in the immediate area and similar areas nearby), current and potential land–use practices.

The tree species are then selected based on the above conditions. This is an important step because it will determine which trees are best suited to the above conditions.

The third component in the triangle of factors influencing choice of species is the site itself; a tree must grow well where it is to be planted. Much of silviculture is concerned with achieving the best match between species (variety and provenance) and the planting site. Most species grow naturally over a range of sites and localities. This wide separation and often isolation of stands may lead to genetically different populations within one species. Where the difference exhibits distinctive phenotypes, the term “variety” is used. Even within a variety, owing to differences in adaptation to local conditions, there will be variation between stands; this variation is recognized as differences of provenance.

And, it is now clear that individual trees or provenances may sometimes respond differently relative to each other in different environments. This is known as genotype (provenance) x environment interaction (GEl). At provenance and variety level, interactions are principally with climatic parameters; at family or clonal level they are with edaphic factors. This knowledge underlines the need to define site accurately, as well as knowing as exactly as possible the genetic origin of what is to be planted. Relatively few descriptors of the environment (rainfall, temperatures, frost occurrence, soil type, etc.) broadly define a site's potential, and the environmental conditions in the species' natural habitat are the best guide, at least to begin with, to the sort of conditions the planting site should have.

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Making the choiceOne question now remains, how is a species selected in practice. Assuming the unlikely situation that nothing is known about which species are suitable for planting the land available, the following summary indicates the steps to take.

1. Gather information Data are needed about all the above factors:

a. Purpose of plantation. b. Knowledge of species potentially available.c. Site conditions.

2. Laying down trials Species and provenance selection cannot be made exclusively from study of literature and site data, a trial of more promising ones must be carried out. These normally take four forms.

1. Species elimination: evaluate many species, eliminate failures and identify promising ones. 2. Species refinement: examine genetic variation within promising species, in particular compare

provenances. 3. Industrial scale trials: large-scale trials to provide stand growth data, to test methods of

cultivation, and to evaluate the likely species on the range of sites encountered in the project. 4. Tree improvement; identification of land races, breeding, clonal propagation, etc., to create better

forest stands for later plantings and subsequent rotations.SUMMARY

The highly rugged and majestic mountains of Ethiopia, that were once covered by lush montane forests, which are presently denuded and eroded inspired me to study ways of rehabilitating these degraded ecosystems.

Forests play an important role in the function and management of our watersheds. In order to select the most appropriate tree species for replanting, you will need to identify your

main purpose for wanting to replant trees. Once you have considered your purpose for planting, you will then need to identify your area or

site for your replanting. Species elimination: evaluate many species, eliminate failures and identify promising ones. Species refinement: examine genetic variation within promising species, in particular compare

provenances. Industrial scale trials: large-scale trials to provide stand growth data, to test methods of

cultivation, and to evaluate the likely species on the range of sites encountered in the project. Tree improvement; identification of land races, breeding, clonal propagation, etc., to create better

forest stands for later plantings and subsequent rotations. Much land, ill-suited to agriculture, is potentially available for forest plantations; land shortage is

unlikely to be a problem in the foreseeable future.

Check listSelf evaluation: Read the following review questions and give your answer by using right √ Mark accordingly.

No Review question yes No 1 Can you list the role of forest that plays in the function and management of

our watersheds?2 Do you know the role of forest plantation establishment at Kabe watershed?3 Have understand the steps of forest plantation establishments?4 Do you know the species selection criteria for plantation? 5 Can you list the objectives of forest plantation?6 Do you know the method of matching species with area plantation?

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CHAPTER 2

2 FOREST TREE ESTABLISHMENT AND MANAGEMENT Introduction

A plantation is defined as a forest crop or stands raised artificially, either by sowing or planting (Ford-Robertson 1971). Based on the type of land use where forests are established, Man-made forests may be defined as:Afforestation: forests established artificially on land that previously did not carry forest within the last 50 years,Reforestation: forests established artificially on land that carried forest within the previous 50 years, including the replacement of the previous crop by a new and essentially different crop. The term forestation is used to denote both afforestation and reforestation.

The first variable influencing planting is timing. Throughout the tropics the occurrence of the rainy season usually determines the planting time. Evapotranspiration stress at planting is one of the main causes of initial death. To minimize planting stress, seedlings should be planted when the soil moisture level has returned to field capacity, ie, after approximately 100 mm of steady rain has fallen; during cloudy days; and using well-watered seedlings.

In South Wollo, Planting tree seedlings has been done during the beginning of rainy season (July). There is no restriction about the planting time during cloudy days but the best time is before noon on sunny days. If the planting is done during the rainy season, watering is not necessary. However, the local community should plan for watering in case no rain falls in the first week after planting.

Objectives of Chapter two At the end of this chapter the trainee are able to

o List procedures of plantation establishmento Identify the tree planting methods o know how to plant seedlings at buffer zoneo Know how to tree planting on a steep slope

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Methods of delivery Gap Lecture /Power point presentation Group discussion Field demonstration

2.1.Procedure of Plantation Establishment

2.1.1. Lay-out plantationFor large-scale forest plantations, planning the plantation lay-out is complex. For small-scale village/community forest plantations, lay-out planning consists of four activities:

A. spacing decisionB. area survey and marking operationC. establishment of firebreak line around the forest plantation as boundary protection line, andD. mapping the location of the plantation

Table -2 Provides guidelines on how to lay-out a forest plantation

Activity Methodology

Area survey Instruments: Compass (or GPS) and tape

Annual planting area(ha)= Total area of planting project/rotation

Fire break Cleaning of width 2-10 m of area square or rectangular spacing on flat land ; triangular spacing on sloping land

Tree spacing 1-2 M : Fuel wood, 1 M: Environmental rehabilitation

Square or Rectangular spacing on flat land ; Triangular spacing on sloping land

Making planting line and pit

On slopes <15 degree, establish base line parallel to convenient track

Mark the location of the start of planting lines along the baseline with poles use compass and rope marked with fixed intervals to trace the planting line , at right angle to base line

Mark the planting pits with sticks/pegs along the rope

In steep terrain, use a simple level to mark planting pit along contour lines

Mapping Scale 1:10 000: General planning of the location of forest plantation areas

Scale 1:5 000 Activity planning for forest plantation of area < 10 ha

Adapted : Evans,1992

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The lay-out defines the exact location and the shape of the forestation area as well as the road network and subdivision into area units. Precondition for the lay-out is the legal and practical availability of land.

There is room for choice, the shape of the forestation area should be compact and rectangular. This makes protection, utilization, planning and operation more efficient. When laying out the forestation area, the road network, as well as the subdivision into compartments, has to be planned simultaneously.

2.1.1.1. Determination of seedling per hectare

To calculate the number of seedling per hectare the following procedure is followed:

Insert figure 1 hereFigure 1: Calculation of number of tree per ha for different plantation types

A. Squared spacing: if the lateral side is r, then the number of seedlings will be:

Number of seedlings = per hectare

B. Rectangular spacing: if the distance between the lines = r, and the distance within the line = p, then the number of seedlings will be:

Number of seedlings = per hectare

C. Triangular spacing: if the distance within the line = p, and the height of the triangle = h, where; h= p*sin600 then the number of seedlings will be:

Number of seedlings = per hectare or It can also be calculated using the following

formulae: A = P2 * sin600

E.g. in the triangular spacing, three seedlings form a triangle with equal sides where the lateral side is p. In this case, the seedlings are in rows with distance between them is p x 0.866 (i.e. the height of the triangle with equal sides). Example: if the distance within the line (p) = 1.2 m, and the height

of the triangle (h) = 1.039 m, then the number of seedlings = = = 8019 plants

per hectare or A = P2 * sin600 = (1.2)2 * 0.866 = 1.247, then seedlings per ha will be 10000/1.247 = 8019.

Calculation of spacing when number of trees per ha is given in squared planting arrangement: E.g. if the number of per ha is 2500, what would be the spacing?

Given: Number of plants (N) per ha = 2500

Required spacing (S) in meters, S = = = 100m/50 = 2m

Calculation of spacing in triangular arrangement with equal sides when number of trees per ha is given, E.g. suppose there are 618 trees per ha, what is the average equilateral spacing?

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Area per tree (A) = 10000/618 = 16 m2 then, S2 = = S= = 4.62m

2.1.2. MarkingAfter the forestation area is determined and the lay-out of access roads and boundaries of the compartments is known, the planting lines and planting pits are marked within each plot. Wherever possible, the planting should be carried out along straight lines. In all other circumstances it will be necessary to advise upon the procedure of marking and to train the staff involved. Row alignment should be planned to fit into the planned extraction system and be at right angles to the main roads and tracks in a compartment.

2.1.3. Site preparationThe extent of preparation needed for the planting site depends on four factors: namely purpose of plantation, species to be planted, existing vegetative cover, and soil conditions. Site preparation comprises two main field activities: systematic removal of the existing weed species and ground preparation to improve water retention and provide optimal soil conditions for the plantation’s initial phase.

Among vegetation clearance methods manual can be employed. Pre-planting harrowing, preparation planting pits and construction of terracing are the major activities that needs to be performed under site preparation.

Terracing

To stabilize endangered sites and to reduce erosion, terracing is proved to be a successful means to establish a forest. It is also applied on sites with a pronounced dry season where water harvesting is essential for the success of the plantation. Some of the purposes of constructing terraces are it provide the site for plantations on slopes steeper than 15°, halt ongoing soil erosion, conserve the existing soil cover, it can harvest runoff water for the benefit of the seedlings on the structures and for the catchment.

2.1.4. Plantation establishment

2.1.4.1. Direct sowing of seeds as an option Plantation establishment It was the first artificial technique used to establish forests. When deciding whether direct seeding should be applied, the following points should be taken into consideration. The factors favoring the choice of direct sowing are: if raising seedling is not necessary, and thus the whole nursery operation can be avoided, if species difficult to grow in the nurseries can be successfully established ,if species that produce a long tap root at an early stage are generally difficult to transplant.

However direct sowing can have the following disadvantages: there will be losses from seed-eating birds, rodents and insects as well as losses due to climate, soil and competing weed growth and animals that browse or trample seedlings, Costs of obtaining seed are high (e.g. when using imported seeds, or those from special provenances, or from orchards) , Irregular stocking results (especially with broadcast sowing) and therefore a less efficient use of the growing space compared with planting methods, The success is very uncertain because it depends on many unpredictable factors, Species selection is concentrated on easy-to-handle species with abundant and light seeds, therefore local, lesser known and often valuable species are avoided.

Sowing Methods; Broadcast, line seedling and spot sowing:

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Broadcast sowing: is used for many tree species. It is used in circumstances where the seed supply is abundant and cheap and presupposes that only a relatively small percentage (30%) of the germinating seeds survives.

Line seeding: uses one-half to one-third of the quantities of seeds required for broadcasting. It is also the method best suited to sow large seeds. Hand sowing in lines is still commonly used in many countries, particularly for small-scale afforestations. A shallow furrow is drawn, into which the seeds are dropped before closing the furrow in with a hoe or rake. Wherever possible, the seed should be covered for protection with a thin layer of soil of a depth to two or three times the diameter of the seed. Very large seeds can be dibbled in holes made in the soil by a pointed stake.

Spot Sowing: In this method seed is sown in relatively small cultivated patches spaced at regular intervals corresponding to the desired crop spacing.

2.2.Preparation of Planting Pits The preparation of planting pits is importance on sites with a pronounced dry period. It could be decisive for the survival of the plants. In order to reduce competition for nutrient and water clear vegetation from an area of about 1m2 around the planting pit. The planting pit must be at least as big as the pot or the root system of the pant. In general, a pit needs to be 40 cm deep and 40 cm wide. When digging the plating pit, keep the topsoil that you have dug up separate from the subsoil. The subsoil is of poorer quality than the topsoil. When the seedling has been plated fill the pit with the fertile topsoil first, so that this surrounds the roots. If conditions permit, the pits should be prepared well in advance of the planting activity.

2.3.Time of tree plantingThe first variable influencing planting is timing. Throughout the tropics the occurrence of the rainy season usually determines the planting time. Evapotranspiration stress at planting is one of the main causes of initial death. To minimize planting stress, seedlings should be planted when the soil moisture level has returned to field capacity, ie, after approximately 100 mm of steady rain has fallen; during cloudy days; and using well-watered seedlings.

In South Wollo, Planting tree seedlings has been done during the beginning of rainy season. There is no restriction about the planting time during cloudy days but the best time is before noon on sunny days. If the planting is done during the rainy season, watering is not necessary. However, the local community should plan for watering in case no rain falls in the first week after planting.

2.4.Tree Planting

2.4.1. Tree planting methodBare-rooted plants and stumps can be planted in a hole or slit dug with a spade, mattock or even opened up with a crow bar. Container plants are planted in a small pit. Planting is an important operation and deserves being done carefully. For all planting the following general rules apply.

1. Insert roots into the soil up to the root collar (transition b/n root & stem, often there is a light swelling).

2. Avoid damaged roots by breaking, bending or crushing3. Firm soil around the roots using the heel or ball of the foot4. Remove impervious containers before planting5. On dry sites the planting position should maximize water retention e.g. furrow bottom, base of

mound or micro catchment6. Stump plants should not be forced into the ground. They should be placed in specially deep

to ensure that roots reach moist soil and only a small part of the shoot is above ground and subject to transpiration stress.

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2.5.Planting tree at Buffer ZonesNative forest tree species should be used for planting along the waterways. The main purpose for using the indigenous species in the buffer zones is for the management of the watershed and maintaining the waterways for continuous supply of quality water and purification. The buffer zone of 20 to 30 meters on either side of the waterways must be maintained (Dayal, 2011)

2.6.Planting Tree on a steep slopePrior to the preparing planting pits appropriate soil conservation structure should be constructed. Among this a construction of hill side terraces, an embankment and etc helps to support the growth of trees in area closures.

Just like preparing a planting hole on flat land, a planting hole on a slope should be at least twice as wide and just the same depth as the plant’s root ball (though the hole can be a bit elongated to fit the contour of the slope as opposed to the typical round hole on a flat ground).

Post planting begins by first leveling out a terrace or table on the hillside where you want to plant. Carve away the slope above the planting hole with a pick and shift the resulting soil to build up a table area level with the eventual planting hole.

Summary

For large-scale forest plantations, planning the plantation lay-out is complex. For small-scale village/community forest plantations, lay-out planning consists of four activities that should be carried out.

Two types of planting material are commonly used: bare rooted plants, including stumps, and container plants most commonly grown in plastic bags.

Native forest tree species should be used for planting along the waterways The buffer zone of 20 to 30 meters on either side of the waterways must be maintained. Prior to the preparing planting on a steep slope appropriate soil conservation structure should be

constructed.

Check listSelf evaluation: Read the following review questions and give your answer by using right √ Mark accordingly.No Review question yes No 1 Can you list the procedures of plantation establishment?2 Do you know the type of planting material?3 Have you understand the tree planting methods?4 Do you know how to plant seedlings at buffer zone? 5 Can you establish forest plantation on a steep slope?

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CHAPTER 3

3. PLANTATION MAINTENANCE Introduction

The first maintenance activity for a successful plantation is the protection and guarding of the planted area from frost attack, animal damage by grazing/browsing and human trespass for cultivation/theft of trees. The second maintenance activity is weeding & other tending activities. Annual weeding requirements will be high if the spacing between planted seedlings is large enough to allow sufficient light to penetrate and facilitate the rapid growth of weed plants.

If the initial seedling survival rate is too low, the most important rule is to carry out replanting (beating up) within the first year of plantation establishment, i.e., the following planting season, to ensure minimum variation of plantation ages. Replanting represents an added cost; therefore relatively high losses can be acceptable, provided the dead seedlings are evenly distributed.

Initial survival of seedlings can be affected by many factors (Pancel, 1993; Evans, 1992). Some of them are: improper planting skill especially on firmness of soil around the roots and improper planting depth, unfavorable immediate post-planting weather, poor quality of seedlings, high intensity of shock during transportation, Poor soil conditions especially water logging or eroding surface and insects such as termites etc can be mentioned.

In general, the survival and successful growth performance of the established plantation will largely depend on the follow-up activities. This includes weeding, beating up, mulching thinning, pruning and protection of the plantation will be discuss under this chapter.

Completing this chapter will help you to

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o Identify the factors that affect initial survival of seedlings.o List plantation maintenance that can be applied to their area.o Know the methods of protecting seedling from frost attack.

Methods of delivery Gap lecture /Power point presentation Group discussion Case study

3.1.Beating- upIf deaths after planting are unacceptably high, the failures are replaced. In the tropics blanking must be done within a few weeks of planting for fast growing broad leaved species such as Eucalyptus grandis and E. deglupta etc. Within a few months for slow growing species. Any delay in blanking permanently puts the replacement trees at a disadvantage and the resulting stand will show great variation in tree sizes. Seedlings used for blanking should be healthy, robust and little larger than average with good root development (Evans, 1992). 3.2.Retention of Moisture (Mulching) Newly planted trees will perform better with mulching. Mulches placed on the soil over the rooting zone provide several benefits. Mulch suppresses growth of turf grass and weeds that compete with the tree for soil moisture and nutrients; elimination of vegetation near the tree thwarts potential injury to the trunk from lawnmowers and string trimmers.

Mulch help conserve soil moisture and reduce soil erosion while lessening soil temperature extremes. Some mulch may also increase soil fertility, improve soil structure, and reduce soil compaction. Although increased rooting may occur in the mulch layer, mulches are also thought to improve depth of rooting. Mulches not only benefit newly planted trees but also established trees.

The most often used mulches are organic materials such as shredded hard woods bark, wood chips, pine bark, cypress bark, organic compost, conifer needles and leaves. Other types of mulching materials include sand, gravel, rubber mats, plastic sheeting and landscape fabrics, Mulches should generally be applied 2-4 inches (5.08 to 16 cm) thick in as wide a circle as possible over the root system.

3.3.Water Supply (Watering/reduce evaporation)In many parts of Ethiopia, the dry season may last up to three to six months. In such areas, as the Northern part of the country, success in the establishment forest will depend to a great extent on the supply of water to the seedlings during their first two dry seasons.

Adequate mulching and establishment of cover crops helps to economize on the application of water. You should carry out your watering during the cool hours of the day, preferably in the mornings or the evenings, and you should not allow water to collect around the seedlings in order to prevent water logging while could lead to diseases or even death of the seedlings.

3.4.Fertilization For good development a tree needs an adequate quantity of each macronutrient (N, P, K, Ca, Mg and S) and each micronutrient (Fe, Mn, Zn, Cu, Cl, B and Mo). The required amount of each micronutrient is very small compared to the macronutrients. The primary macronutrients are nitrogen (N), phosphorus (P) and potassium (K) which are the main elements of fertilizers used in forestry and agriculture.

Those can be getting from two sources such as from natural (organic) & synthetic (artificial, inorganic) fertilizer. Both sources has they own advantage & limitation. Preferring the types of fertilizer uses depends on different factor.For example, a common fertilizer referred to as 5-10-5 fertilizer contains 5% N, 10% P2O5, 5% K2O per kilogram. Some fertilization can be done after the start of the plantation but the best time is to fertilize is at

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planting (Wadsworth, 1997). If there are indications of mineral deficiencies in the planting site, the plantation manager should plan for a fertilization operation.

Nitrogen contributes chiefly to vegetative growth, ie, the formation of stems and leaves. Phosphorus encourages root development and hastens seed ripening. Potassium is necessary for assimilation and increases disease resistance. In tropical areas, low P availability is one of the main soil factors limiting forest productivity.

3.5.Protecting seedling from Frost attack In the cold night time hours, moisture is squeezed out of the air, decorating your trees and plants in glittering splendor. But once the sun comes up, the frost starts to melt, and evaporate, both of which steal heat from the leaves and bark, lowering their temperature below even that of the chill morning air. Frost attack may bite is hard for young seedling.

3.5.1. Cover it Up The simplest answer to frost is to not let it condense on young plants in the first place. Row covers on young seedling during time of coldly months provide both insulation and a barrier to frost. Painter's plastic, drop cloths, tarps, or even blankets can be pressed into service to cover your young seedling. Remember to never place plastic directly in contact with leaves and plant material for more than a single night because it will encourage fungus and disease, which plants are especially vulnerable to in the cold anyway.

3.5.2. Stone mound Putting stone mound around a seedling can be an option in providing insulation, a barrier to frost and prevent grazing animals. Standardized design for the construction of stone mound is lacking. However, it good to perform the height of the stone mound is greater than the height of seedling. The distance of from the seedling to the mound is good to be 50 cm. Practicality of this technology depends on the availability stone near the plantation area & commitments of implementers. If the two is maintained at initial stages mounding stone slightly higher than the height of the seedling is very important. Incrementing the height of the stone as the height of seedling increase until the seedling get well established. Putting stone mound around a seedling needs a special consideration. It should be mounded on assuring stability of a stone mound. This is because inappropriate stone mound may lead to cause death of seedlings.

3.6.WeedingIn a cause where the site conditions are better in terms of high precipitation and better soils condition the greater the problem of weeds will be to seedlings. The threat consists of competition for light, water and nutrients and also of suffocating the trees. Therefore, the main objective of the undertaking weeding operation is to promote the growth and development of the plantation within the framework of a reasonable utilization of resources. Weeding methods: The existing weeding methods can be separated into manual, mechanical and chemical. They intend to suppress or eliminate the existing weeds. Manual weeding: The simplest method of weed suppression is to trample or beat the weeds down away from the planted trees. The most common manual weeding method is to cut them back using a variety of cutting tools such as sickles, brush hooks and scythes. Manual weeding is done mainly by short-handled hoes. The operation is usually more effective if the hoe is used for actual cultivation involving turning over of the soil rather than scraping off of the weeds. Mechanical weeding: Machineries used for mechanical weeding are tractor- powered machines for brush cutting, mainly rear-mounted and operated from the power take-off. These are horizontally rotating chain swipe machines, horizontally rotating blade machines and vertically rotating flail machines. The main weeding equipment for larger-scale work includes: agricultural tractors with rear-mounted

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heavy-duty offset disk harrows and agricultural tractors with rear-mounted rotavators. The disk harrows are widely used and, except in areas of exceptionally heavy weed growth, have proven satisfactory in practice.

Chemical weed control: Use of herbicides to control weeds is a valuable method in conifer plantations, since chemicals that kill grasses and herbs are unlikely to damage conifer trees, at least at normal dosage rates. However, their use in broadleaved plantations is much more difficult since a chemical that kills an angiosperm weed is equally likely to kill an angiosperm tree. Present-day herbicides are not specific enough to discriminate between different families of angiosperms. 3.7.Protection The protection of the planting site starts with the planting operation. Protection includes preventing damage by fire, pests, domestic animals wildlife grazing and man. Any plantation project can only assure its sustained success if the local population cooperates in the difficult and diverse task of protection.

. Summary The survival and successful growth performance of the established plantation will largely

depend on the follow-up activities. Follow up activities includes weeding, beating up, mulching thinning, pruning and protection

of the plantation. For good development a tree needs an adequate quantity of each macronutrient (N, P, K, Ca,Mg,

S) and each micronutrient (Fe, Mn, Zn, Cu, Cl, B, Mo) are vital. Mulch help conserve soil moisture and reduce soil erosion while lessening soil temperature

extremes. Protection includes preventing damage by fire, pests, domestic animals wildlife grazing and

man. The simplest answer to frost is to not let it condense on young plants in the first place. Row

covers on young seedling during time of coldly months provide both insulation and a barrier to frost.

The simplest method of weed suppression is to trample or beat the weeds down away from the planted trees.

Check listSelf evaluation: Read the following review questions and give your answer by using right √ Mark accordingly. No Review question yes No 1 Can you List the factors that affect initial survival of seedlings?2 Do you know the plantation maintenance that can be applied to your area?3 Do you know the methods of protecting seedling from Frost attack?4 Do you know the effects of weeding on tree seedlings?5 Can you list the weeding method?

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4. Reference Brown, A.G., Nambiar, E.K.S. and Cossalter, C. 1997. Plantations for the tropics – Their role, extent and

nature. In Nambiar, E.K.S. and Brown, A.G. (eds.). Management of soil, nutrients and water in tropical plantation forests. ACIAR Monograph No. 43, Canberra, pp. 1-23.

Eshetu Yirdaw, 2002. Restoration of the native woody-species diversity, using plantation species as foster trees, in the degraded highlands of Ethiopia. Helsinki.

Evans, J. 1992. Plantation forestry in the tropics. 2nd Edition, Clarendon Press, Oxford, 403 p. Germany, pp. 645-725.

IFSP, 2000. Visual presentation of extension material. Indonesia Forest Seed Project (IFSP). Bandung, Indonesia.

Lal, R. 1997. Soils of the tropics and their management for plantation forestry. In Nambiar, E.K.S. andMarika, T. 2011. Training manual: a guide to planting local tree species for forest restoration. COWRIE

Project No. 43, Canberra, pp. 97-123.Pancel, L. 1993. Forestation. In Pancel, L. (ed.). Tropical forestry handbook. Vol. 1, Springer-Verlag,

Service, Washington, 563 p.Wadsworth, F.H. 1997. Forest production for Tropical America. Agriculture handbook 710, USDA ForestZhang, M., Wang, M., & Liang, X., 2008. Quantitative classification and carbon density of the forest

vegetation in Lu¨liang Mountains of China. Journal Plant Ecology, Volume 201, No. 1, 1–9.

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PART II: AGROFORESTRY SYSTEMS AND PRACTICES

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CHAPTER 1

1. OVERVIEW OF AGROFORESTRYAgroforestry has received much attention in recent development efforts. It can deliver a wide range of benefits. It can enhance food security and improve rural livelihoods; increase soil fertility; absorb atmospheric carbon, a major greenhouse gas; and provide farmers with the technologies to restore degraded land. As a one solution to mitigate different problems, the Ethiopian government has developed the “Climate Resilient Green Economy” initiative which promotes agroforestry among other environment conservation activities. Former Prime Minister Meles Zenawi declared at the Durban Climate Change Convention in December 2011 that his government would implement a Faidherbia program that seeks to establish 100 million Faidherbia albida trees on smallholder cereal croplands across the country within the next three years to improve food production and livelihoods of smallholder farmers. (Faidherbia albida is a good agroforestry tree which is compatible to grow in the farm land together with crops).

Module objective

The overall objective of this training manual is to provide information on the concept and definition of agroforestry, its benefit; and provide description about some agroforestry practices which can be applicable at Kabe watershed.

Mode of delivery:

- presentation

- Slide picture show

- Case studies

- Discussion

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1.1.Concept and definition of agroforestry Agroforestry is a new name for a set of old practices. Cultivating trees and agricultural crops in intimate combination with one another is an ancient practice that farmers have used throughout the world. Farmers have always grown trees on their land and this had useful effects on the soil and crop yields. The World Agroforestry Centre (ICRAF) defines agroforestry as a dynamic, ecologically based natural resource management system that, through the integration of woody perennials (trees or shrubs) with agricultural crops, pastures or livestock diversifies and sustains production for increased social, economic and environmental benefits for land users.

Agroforestry is a science and art of producing trees, crops and animals in combination. It shouldn’t be seen merely as an arrangement of trees and crops or particular combination of certain species but rather as an approach to land use that seeks to meet the specific needs of the community or individuals (soil fertility, fodder, fuel, construction, wood, food, etc). Generally agroforestry is a practical, low-cost alternative for food production as well as environmental protection. However, the benefits from agroforestry will only be realized through a combination of the right tree species with the right crops in the right spatial arrangements with the right management practices.

There are two important features that identify agroforestry from other land-use systems: There must be a tree component deliberately grown or retained in the land-use system There must be significant interaction, positive and/ or negative, between the woody and non-

woody components of the system.

Agroforestry, therefore, involves two or more species of plants and /or animals at least one of which is a woody perennial and with two or more outputs. Owing to the variety of mixtures, therefore, even the simplest agroforestry system is more complex both ecologically and economically than a mono-cropping system. The aim and basis of agroforestry lies in optimizing production based on the interactions between the components and their physical environment. This will lead to higher sum total and a more diversified and /or sustainable production than from a monoculture of agriculture or forestry alone.

1.2.Benefits of agroforestryAgroforestry combines production and service roles. Nair (1993) indicated that the combination of several types of products which are both subsistence and income generating, helps farmers to meet their basic needs and minimizes the risk of the production system’s total failure. Generally, agroforestry has the potential to solve many land-use problems. Some of the benefits that agroforestry offers are: soil-fertility improvement, provision of wood products (fuelwood, poles, timber, fruits, medicines, etc.), improved beekeeping, control of erosion, stabilizing of river and stream banks (i.e. prevention of siltation), improvement of water infiltration in to the soil, shrubs can act as live fences against livestock and human beings, trees and shrubs can contribute to better microclimate (shade, windbreak, etc,) and provision of fodder, especially in the dry season.

1.2.1. Soil fertility improvement and soil conservationLand degradation and declining soil fertility create a major threat to agricultural productivity and affecting human welfare in most of African countries. Particularly it is serious in tropical and subtropical regions where many soils lack plant nutrients and organic matter and top soil erodes by intense rainfall. Use of artificial fertilizers to replenish soil nutrients fails to provide adequate solution. Incorporation of trees in the farm can help in maintaining the nutrient pool and enhance soil fertility both under sequential and simultaneous agroforestry. Soil fertility can be improved or sustained by the addition of vegetative organic matter, i.e. decomposition of leafy biomass and roots. Further, integrating leguminous trees is common in agroforestry, which have ability of fix atmospheric nitrogen and contributes to better soil fertility. Nitrogen fixing tree, under agroforestry significantly increased nutrient pool, organic biomass, and activities of organisms in the soil. This would not only be beneficial to the soil, but would also be cheaper for resource-poor farmers and provide fodder or firewood.

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On the other hand, erosion is the primary cause of reduction of crop yield due to loss of organic matter, associated nutrients and soil fertility. So, restoration and maintenance of fertility is essential. Root systems of woody perennials enable to adapt to steeply sloping sites that are unsuited to conventional cropping or grazing. Nitrogen fixing trees (legumes) in agroforestry have the capacity to grow in difficult sites subject to erosion and low soil fertility. They have also potential to restore degraded areas and control of soil erosion. Once established, they can create favorable conditions for the growth of other species. Additionally, tree legumes improve soil structure, which help to decrease erosion.

Due to its long lived nature, trees and shrubs can remain throughout the year in the farmland and serve as better resources to control of erosion and soil conservation. They reduce the wind speed and runoff (through enhancing percolation of rain water in to the ground through ground litter). The tree root protects the soil from erosion and the litter serves as a buffer to direct rain drops and runoff and the tree crown reduces the wind speed and slows the direct force of the rain drops.

Generally agroforestry is relevance to control soil erosion in the following aspects: (1) the initial cost of establishing erosion-control is frequently lower than that of terracing or bunds. (2) In addition to the benefit from maintenance of crop yields through control of soil loss, some trees (e.g. Faidherbia albida) can have the potential to increase crop yields. In addition, there are benefits from the tree products. (3) For degraded land, the cost of reclamation can be reduced if soil improving trees are combined. Erosion control allows rejecting the mass of soil removed and it permits maintenance of fertility. Agroforestry practices like barrier hedges, hedgerow intercropping and multistory tree gardens have the potential to control of erosion even in the place of cropping in the sloppy areas.

Insert figure 2 hereFigure 2: The benefits of agroforestry in nutrient cycling and erosion control

1.2.2. Fuel wood (Energy)Over 90% of the populations in Ethiopia depend on fuel wood for their energy needs. Increased tree growing and better management of existing resources could provide for products such as fuel wood, poles, fruits and timber which have not only become scarce but increasingly expensive. Thus, such commodities could be produced both for subsistence and for cash. Scarcity of fuel wood may influence both the amount of food cooked and its type. Further, since fuel wood collection is women’s work further away the source of fuel wood the greater their workload becomes. Consequently, they have less and less time and energy to spend on other activities such as caring for children or engaging in income-generating activities. Thus, the scarcity of fuel wood has a direct impact on the family’s nutrition.

Within an ox culture where mono-cropping is predominantly practiced poor farmers use dung and crop residue for fuel. Cow-dung and crop residue use for fuel is the most land degrading practices. Burning crop residue and cow dung is the most nutrient depleting tasks of all wrong acts in conventional agriculture in Ethiopia. In the Northern part of Ethiopia in Menz for example where there is no tree at all and the entire land is covered with grass, fuel is cow dung and some crop residue. Under agro-ecology potential production classification, it is a high potential cereal zone with a high rainfall area. In Mono-cropping cereals of ox culture system long term gestation of perennial tree growth is the constraint. Agroforestry enables rural households to produce firewood in near and accessible places (homestead, farm, etc). It has potential to solve shortage of construction poles and timber, fuelwood problems, shortage of fodder during the dry season, silting and flooding of rivers and streams, declining soil fertility and soil erosion.

1.2.3. Carbon sequestration Now current global-climate change (global warming) is the most serious environmental problem affecting human lives on a global scale and it is because of primarily by the increase in atmospheric concentrations of greenhouse gases (GHGs) mainly carbon dioxide (CO2). CO2 is the most abundant and is responsible for more than half of the greenhouse effect. Besides fossil fuel burning, deforestation and forest

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ecosystem degradation are also significant causes of the global warming recorded in the past century. They account for 17% of global greenhouse gas emissions, more than the entire transport sector. This increment of GHG has significant impact on human health, food security and other environmental degradation.

Forests play an important role in the global carbon cycle because they store a large amount of carbon in vegetation biomass and soil. It also sinks CO2 from the atmosphere. Conversion of especially high-biomass tropical forest to other land-uses like agriculture could lead to increased atmospheric CO2 via biomass burning, increased soil respiration and decrease in CO2 uptake by plants. So, this decrease in forest area reduces the carbon stock in the forest ecosystem. In the past three decades, agroforestry has become recognized as an integrated approach to sustainable land use because of its production and environmental benefits and it received attention as a strategy for biological carbon sequestration. The potential of agroforestry in sequestering carbon is based on the premise that the greater effectiveness of integrated systems in resource captures and use than single species. The density of carbon storage in agroforestry is low in comparison with forests; the woody biomass of agroforestry systems could provide a source of local fuel. Through providing fuel, agroforestry would reduce pressure on forests and at the same time, provide a substitute for fossil fuel.

On the other hand, because of their capacity to give economic and environmental benefits, intervention of agroforestry are considered to be the best measures in making communities adapt and become resilient to the impacts of climate change. The other important elements of agroforestry systems that can play a significant role in the adaptation to climate change include changes in the microclimate, protection through provision of permanent cover, opportunities for diversification of the agricultural systems, improving efficiency of use of soil, water and climatic resources, contribution to soil fertility improvement and reducing carbon emissions and increasing sequestration. Greater agro-biodiversity, which is the characteristics of agroforestry, may ensure longer term stability of C storage in fluctuating environments. Trees represent the most important C pool in aboveground biomass of perennial plants growing on-farm. Generally, integrating more trees in the agricultural landscapes has a higher potential to sequester carbon.

1.2.4. Fodder Grasses and cereal crop residues are the most important feed resources for livestock and which account for more than 70% of the dry matter in the animal feeds. But they are deficient in protein. On the other hand, there is an acute shortage of green fodder in many parts during the dry season. To overcome those problems, forages from leguminous trees (which mostly common in agroforestry) have a great potential to supply protein-rich fodder and play an important role in the supplementary feeding of livestock during the dry season or in times of drought. A huge percentage of fodder trees are legumes and most of those are rich in protein and digestible. Farmers and pastoralists have long experience in feeding fodder trees and shrubs to their livestock to increase the benefits of the output gained from the animals, either by browsing or by cut and carry system. Faidherbia albida, sesbania sesban, Chamaecytisus proliferus, etc are a woody perennial which can provide fodder. Sesbania sesban and Chamaecytisus proliferus are potential fodder species for Kabe area.

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CHAPTER 2

2. CLASSIFICATION OF AGROFORESTRY SYSTEMS AND DESCRIPTION OF SOME AGROFORESTRY PRACTICES

This section will give information about classification of agroforestry systems and brief description of some common agroforestry practices which can be applicable at the Kabe watershed. For each agroforestry practice points like a short description, criteria for selection of species, spatial arrangement, areas where each practice may be most relevant, establishment and spacing, management aspects, benefits and examples of species are discussed.

2.1.Classification of Agroforestry systemsThe most common set of criteria used to classify agroforestry systems and practices are (Nair 1993):

Structural basis—refers to the composition and arrangement of the components, both spatial and temporal.

Functional basis—refers to the main function or role of the components especially the woody components as for soil conservation and soil fertility improvement (i.e. productive or protective).

Socioeconomic basis—refers to the intensity or scale of management and goals of the system.

Ecological basis—refers to the environmental and ecological suitability of systems. There can be separate sets of agroforestry systems for arid and semi-arid lands or humid and sub-humid tropics.

There are three important components of agroforestry systems namely, the woody perennials (trees/shrubs), the herbaceous plants (crops, pasture plants), and the animals. Based on these three

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basic components, agroforestry systems can also be classified for all practical purposes according to their component composition.

Agrisilvicultural systems

Silvopastoral systems

Agrosilvopastoral systemsOther systems: e.g. apiculture with trees, aquaculture involving trees and shrubs

2.1.1. Agrisilvicultural systemsThis is an agroforestry system where agronomic crops are combined with shrubs/trees on the same unit of land for higher or better-sustained production of annual crops, fodder, and wood. The combination of components can be arranged in time (e.g. taungya practice), and in space (e.g. scattered trees on cropland, alley cropping, etc).

2.1.2. Silvopastoral systemsThis is an agroforestry system where trees and range crops and/or animals are combined for better production of grasses and fodder. This combination can be arranged as a pure stand with fodder trees/shrubs planted as a protein bank (with cut-and-carry fodder production) and/or mixed in different configurations such as living fences of fodder trees and hedges. The trees and shrubs and grass components are arranged in such a way that their healthy coexistence is not disrupted. The acacia-dominant system in the arid parts of Ethiopia, Kenya, and Somalia are good examples of this system.

This system can be practiced on both range and forest lands for the production of both feed and woody materials. This system could also be practiced on sloping ground by growing grasses and trees/shrubs together for soil conservation purposes. The main objective of this practice is to supply feed for livestock during the dry season with high quality tree leaves and pods. This will substantially increase the productive capacity of poor and scarce pasture lands common on the Hararghe Highlands. Fuelwood and construction poles can also be produced with this system.

2.1.3. Agrosilvopastoral systemsThis is an agroforestry practice by which food, pasture, and tree/shrub crops are combined on the same unit of land for the production of fodder, biomass for fuelwood and green manure, and food for human consumption. This system is practiced when the farmer needs all the benefits that would be obtained from silvipasture and agrisilviculture systems from a unit of land. Usually, such a system is practiced on cultivated land. Alternative rows of hedges, grass strips and/or crops would form such a system, a form of alley cropping. This system has potential for use in various regions of the country.

The above definition and discussions of agroforestry systems and practices encompasses many well-known land-use systems long practiced in the Ethiopian highlands. Thus, it is apparent that agroforestry is only a new word for an old practice: it is based on forestry, agriculture, animal husbandry, land resource management, and other disciplines that all form the systematic background of land use. Furthermore, it encompasses an awareness of interactions between humans and the environment and between demand and available resources in a given area. Although science can improve agroforestry practices, an important aspect of the problem of Ethiopia is to mobilize and implement what is already known.

2.2.Description of agroforestry practices

2.2.1. Improved fallows One method in which resource-poor farmers combats soil infertility is by leaving degraded land without cultivation. This abandoned land is referred to as ‘fallow’, and it is an option for improving soil fertility and it has been practiced for many generations. Improved fallow is defined as enrichment of a natural fallow with leguminous trees or shrubs planted at high density to improve soil fertility. The primary aim of

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improved fallow is promotion of food security through increased soil productivity. The improved fallow technology involves deliberate planting or sowing of nitrogen-fixing leguminous tree or shrub species. This technology has potential to restore soil fertility more rapidly than the traditional fallows and, hence, allow shortening of the fallow period. This practice has a potential to cut down fertilizer costs. However, the effect of improved fallow depends on the fallow period and the type of tree species.

Insert figure 3 here

Figure 3: An improved fallow with Sesbania sesban

Research results indicated that a fallow land that is left for one to three years planted with small trees Sesbania sesban has shown good results. Usually a tick carpet of litter has built up on the soil and the soil has become “soft”. The litter and the remaining roots of the fallow trees fertilize the soil and the crop yields are better than those fields fertilized with recommended amounts of inorganic fertilizer.

Insert figure 4 here

Figure 4: The different phases of improved fallow and subsequent cropping phase

Establishment and spacingSince very many individual shrubs are required, all with a relatively short life span, a simple and cheap propagation method is necessary. Sesbania sesban has such characteristics. Use of seedlings is expensive; direct sowing is the best option. Planting short-lived shrubs at 1 m x 1 m or 90 cm x 90 cm is recommended. The denser the spacing the more effectively will weeds be suppressed. Improved fallows can be sown with a mix of species to obtain more benefits, e.g. Sesbania sesban with Cajanus cajan.

Management aspectsThe shrubs require little management once they are well established. Weed during establishment to improve growth of the shrubs and protection from livestock is necessary. If the shrubs are very densely spaced some thinning can be done. When land is to be brought back under cultivation, some shrubs can be left to supply propagation material for the next fallow period. Cut short-lived shrubs after 2-3 years and thereafter let the crops grow.

Criteria for selection of species Various trees or shrubs are suitable for agroforestry, but only a few are currently used in improved fallows. Some of the attributes used in selecting and screening species for improved fallows are:

Rate of tree growth and biomass production: fast growing tree species with high biomass production are best suited for improved fallows.

Capacity to fix nitrogen: nitrogen fixing leguminous woody species with high potential to fix nitrogen. Quality of residues: the tree residues should be high in nitrogen content and low in lignin allowing

the residues to rapidly decompose and release nutrients for use by associated crops. Ease of propagation: must take a short time to germinate and for those materials that are planted

vegetatively, they should sprout easily. Compatibility of the tree in a cropping system: both the trees and the associated crops must be able

to grow easily in the same system. Manageability: must be easy to manage. Potential for weediness: the species used should not be a threat to the environment by becoming a

noxious weed. Noxious plants as revealed in literature should be avoided. Pest and disease tolerance: species must not easily give way to disease and pests. Adaptability: must grow easily in targeted ecosystem.

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Benefits Quick restoration of soil fertility and wood production Nutrient recycling from deeper soil horizons Improve soil physical and chemical properties Protect the soil from erosion. Suppress weeds Increase the nutrient and organic-matter content of the soil thereby improving its fertility and

structure, including aeration, water-holding capacity and tilth. Production of fuelwood, reduces pressure on the natural forests and saves household labour

Examples of recommended speciesFast-growing nitrogen-fixing shrubs which are easy to propagate and which have a short lifespan and relatively small root system are desirable. Acacia mearnsii, Leucaena leucocephala, Sesbania spp., Gliricidia sepium, Cajanus cajan and Calliandra calothyrsus are promising.

2.2.2. Alley Cropping Alley cropping is a simultaneous agroforestry practice where crops are grown between lines of planted trees and/or shrubs, preferably leguminous species, which are pruned periodically during the crop’s growth to provide green manure (which, when returned to the soil, enhances soil nutrient status and physical properties) and to prevent shading of the growing crop(s). This technology helps increase production and land productivity by maintaining and improving soil moisture and fertility. This practice has received much research attention and is regarded as having promise for solving problems of declining soil fertility in situations where farmers cannot afford to use inorganic fertilizers at the recommended rates. Alley cropping is suited to humid and sub-humid tropics, and there is great potential for use of the system in Ethiopia, particularly to improve soil and water conservation in the hilly and mountain areas.

Criteria for selection of species This practice is suited mainly to humid and sub-humid tropics. The multipurpose tree species in this agroforestry practice should bear the following important characteristics:

Fast growing – benefits became available to the farm family as soon as possible; Good coppicing ability (re-sprouting) High biomass production Deep rooting habit Freedom from pests and diseases Nitrogen fixing ability (leguminous) Adaptable to close spacing

Areas where the practice is relevantResearch findings indicate that alley cropping is not feasible where average rainfall is less than 800 mm annually. The practice has its major potential in humid lowlands. Since the technology is labour demanding, it is relevant mainly in areas with small farms and a high population density or, in other words, where labour is not a limiting factor.

Establishment and spacingThe establishment of alley cropping requires many trees or shrubs and therefore a cheap propagation tree spp. is preferable. Direct seeding or use of cuttings would be ideal, but so far seedlings have been used in most research experiments. If seedlings are to be raised, on-farm nurseries are recommended since growing the relevant species does not require much skill.

The spacing used in field trials has ranged from 4 to 8 m between rows and from upto 2.00 m within rows. In humid areas, close spacing can be tolerated, but in drier conditions a wider spacing is required if competition for moisture is not to be too severe. On flat land, hedgerows should be oriented in an east-west direction to reduce shading. On sloping land, hedgerows must be oriented along the contours.

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Insert figure 5 hereFigure 5: Tree spacing in alley cropping

Criteria for selection of species Trees used in alley cropping must have (1) deep roots; so that they do not compete with food crops for water and nutrients. (2) They should be fast growing (3) they should be able to re-sprout easily after pruning, coppicing or pollarding (4) they should ideally be multipurpose, i. e. capable of producing poles, wood, food, fodder, medicinal and other products. (5) They should preferably be leguminous; able to fix their own nitrogen, so they provide protein rich leaves for livestock and nitrogen-rich organic matter for the soil.

Management aspectsIntensive management is required. The first coppicing is done 6-18 months after establishment, depending mainly on growth rate. The frequency of cutting depends on what type of wood is preferred, and on whether or not some reduction in crop yield due to shade can be tolerated. If the leaves are to be used for green manuring or fodder, frequent (up to monthly) prunings are required, but if firewood or staking material is the desired output, cutting should perhaps be only yearly. With yearly cuttings one would, however, expect some loss in crop yield due to shade unless the shrubs are regularly pruned.

BenefitsTrees and shrubs in the alley cropping system have the following benefits:

Provision of green manure or mulch for companion food crops i.e. plant nutrients are recycled from deeper soil layers;

Provision of pruning applied as mulch, and shade during the fallow to suppress weeds, Provision of favorable conditions for soil microorganisms, When planted along the contours of sloping lands, provide a barrier to control soil erosion, Provision of pruning for browse (to feed livestock), staking materials and firewood, and Provision of biologically fixed nitrogen to the companion crop(s).

Examples of recommended species Chamaecytisus palmensis, Sesbania sesban, Cajanus cajan, Calliandra calothyrisus, Leuceana leucocephala and Cassia siamea are some of the recommended plant species for alley cropping.

2.2.3. Scattered trees on cropland This practice involves the growing of individual trees and shrubs in wide spaces in the farmland, while field crops are grown in the understorey. The practice of growing trees dispersed on cropland may be based on protection and careful management of naturally regenerated trees, and it also involves planting new trees. Dispersed trees grown in farmlands characterize a large part of the Ethiopian agricultural landscape and it is an age-old practice. Some good examples of this practice include Cordia africana intercropping with maize in Bako and western Ethiopia; Faidherbia albida-based agroforestry in the Hararghe Highlands and Debrezeit area; scattered Croton macrostachys trees into the cropland at Finote-selam in West Gojam Zone, Acacia nilotica, Ehretia cymosa, Cordia africana and Croton macrostachys in the farmland in North shoa and South Wollo zones, which all share the characteristics of Weyna-dega and Dega agroclimatic zones.

Insert figure 6 hereFigure 6: (Left) Schematic presentation of dispersed trees on cropland; (Right) Scattered Faidherbia albida trees in Teff crop land in Central Rift Valley (CRV) of Ethiopia

Criteria for selection of species

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The ideotype for tree species for scattered trees in cropland should bear the following characteristics: • Deep rooting habit• A canopy that produces only light shade• A capacity to improve the soil through nitrogen-fixation and litter fall• No tendency to harbor crop pests

Areas where the practice is relevantIn most situations, it is feasible to have trees in cropland. It can be applied from wet Dega to dry Kola agro-climatic zones. There are limited possibilities in irrigation schemes. The benefits to be obtained from the trees, in terms of soil fertility and soil structure, are normally more clearly seen in areas where little or no inorganic fertilizer is used.

Establishment and spacingMany methods of tree propagation are possible. However, the most convenient method is to leave desirable trees when clearing land for agriculture, or if they are too few, to protect naturally growing seedlings, suckers or coppice shoots. Spacing is determined by the size and property of tree species in order to fit the tree component in to the farming system in a way that maximizes positive effects to food crops. A population of up to 100 trees per hectare, corresponding to a spacing of 10 m x 10 m, is appropriate in high-potential areas. If trees are to be planted, a better option than square spacing may be to plant trees in lines with close spacing in the rows and a wider between-row space resulting in a similar overall density. A spacing of 5 m within rows and 20m between rows can be suggested. The tree and crop species and management methods chosen are factors that will influence decisions on spacing. In arid and semi-arid areas, lower tree populations are recommended, e.g. 40-70 trees per hectare, corresponding to a square spacing of 12-15 m. If trees in cropland are to be established from seedlings, a greater number than that ultimately required need to be planted since there will always be some mortality.

Management aspectsTree-management practices will depend on the tree and crop species concerned and the need for tree products, but generally there is need to protect the young seedlings from livestock and fires, especially during dry seasons. With a light-demanding crop, pollarding or pruning is essential, but this does not apply to shade-tolerant crops or to trees that naturally only have light shade. Species that need and tolerate pollarding are Albizia spp., Balanites aegyptiaca, Cassia siamea, Croton macrostachyus, Terminalia spp., and Grevillea robusta. Timber production and light reduction both call for pollarding high up, at 12-15 m, but shade tolerance and pole production call for lower and less frequent pollarding. It is important to consider the land-use pattern throughout the year before recommending tree planting in cropland. Post-harvest grazing and burning of crop residues are other factors that need to be taken into account.

Benefit The benefits that may be obtained by having trees in the fields are:

Improved soil fertility by converting atmospheric nitrogen to a form usable by plants and the decomposition of leaves and other residues to organic matter

Reduction of soil erosion because leaf litter acts as mulch, conserves soil moisture, improves water infiltration and suppresses weeds

Provision of fodder for livestock Provision of poles and timber Provision of fuelwood and medicine Improvement of the microclimate on cropped land. Advantageous to maintain indigenous tree species that are at the verge of extinction.

Examples of recommended speciesRecommended species for this agroforestry practice should preferably be leguminous, with deep root system, having light branches, deciduous, with decomposable leaves like: Croton macrostchyus,

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Grevillea robusta, Acacia abyssinica, Cordia africana, Erythrina brucei, Faidherbia albida, Acacia polyacantha, Ehretia cymosa.

2.2.4. Live fencesLive fences are barriers of closely spaced trees or shrubs to protect crops or structures against livestock and human interference. It may be established all around the farm, but it is commonly established around the homesteads and gardens. It is commonly practiced in Ethiopia. Live fences can be combined with other trees for production of wood and fruits. They can be made of single or multiple densely planted rows. Alternatively, one row of living fence posts can be planted widely spaced, with wire, sticks or dead branches between the trees.

The use of live fences is a cheap method of fencing large areas because once the live fences become established they are permanent. Their establishment requires no expensive materials to be purchased and they are easy to maintain. Living fences may also give produce, e.g. fruits.

Insert figure 7 hereFigure 7: : Live fences

Criteria for selection of speciesThe species which are to be used for live fencing should be:

- Able to keep off livestock (thorny and/or densely branched)- Easy to establish and maintain- Able to withstand temporary water logging - Resistant to fire– act as firebreak - Tolerant to minor injuries: it is susceptible to frequent injuries from pruning or animals- Able to provide useful by-products.

Areas where the practice is relevantThis practice is relevant for most farming systems except on irrigation schemes and in the most arid areas. Fences are more important where livestock graze and hedges elsewhere.

Establishment and spacingVery many individual shrubs are required to make a fence. Thus the propagation method must be simple and cheap. Direct seed sowing or use of cuttings (depending on species) is primarily recommended. It is best to plant seeds, seedlings or cuttings in two staggered rows so that an impenetrable fence or hedge is formed. The distance between the rows can be 15-30 cm with the same space within the rows. Directly sown fences must be well looked after and protected initially.

Management• Protect the young seedlings against livestock and fires.• Weed young seedlings.• Replant the dead seedlings as quickly as possible to minimize gaps in the fence.• Trim or prune to make a dense fence. Most species make a better fence if trimmed to a pyramidal

shape so that even the lowest branches can get some light.• Apply manure/fertilizer if seedlings do not grow well or show other signs of nutrient deficiency.

BenefitsLive fences are often multipurpose and have several advantages. Some of the uses are:

- Once established and regularly managed, live fences are permanent- Live fences can produce by-products, e.g. poles, fruits, fodder, and fuel wood;

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- Live fences can provide mulch for gardens, bee forage or wood- Provide shade, protection and can also serve as a windbreak for the compound- Control movement of cattle- Be ornamental- Provide protection for chickens against birds of prey- Help in soil conservation.

Examples of recommended speciesAcacia brevispica, Acacia nilotica, Acacia tortilis, Balanites spp., Caesalpinia decapetala, Calliandra calothyrsus, Carissa edulis, Cupressus lusitanica, Casuarina spp., Dovyalis abyssinica, Euphorbia tirucalli, Gliricidia sepium, Morus alba, Parkinsonia aculeata, Pithecellobium dulce, Prosopis spp., Psidium guajava, Ziziphus spp.

2.2.5. Windbreaks Windbreaks are lines of trees or shrubs planted to protect fields, homes, institutions, etc from wind damage. Where wind is a major cause of soil erosion and moisture loss, windbreaks can make a significant contribution to sustainable production. It plays an important role in preserving soil and its fertility as well as improving the microclimate for crops. Well-designed windbreaks, i.e. ones that are not too dense, not only reduce wind speed but may also increase humidity and reduce water loss from the soil. When establishing new fields, some protection from runoff and wind can be obtained by leaving a shelterbelt. A good windbreak “wears down” the wind which has to force its way between the leaves, pushing past them and making-float like flags. A properly designed windbreak can protect a field at least 10 times as long as the height of the tallest trees, so 10 meters tall trees protect a crop field of up to 100 meters long downwind. Not all trees slow down the wind with the same efficiency. Trees with very dense broadleaved foliage form an impenetrable wall on which the wind tends to rebound rather than slow down. On the other hand, trees with plenty of foliage consist of light, fairly penetrable leaves, filter the wind and exhaust it at the same time.

Areas where the practice is relevantLarge windbreaks are most relevant in large-scale farming areas since otherwise they would extend over many small farms thus causing complicated planning and requiring good co-operation between the farmers. Boundary planting of trees and live fences is usually sufficient as windbreaks in small-scale farming areas.

Insert figure 8 here Figure 8: Good and bad windbreaks

Criteria for selection of speciesTrees that would be suitable for windbreaks should be:

Easy to propagate, to establish and to manage: minimize labour inputs Not harbour pests and diseases Deep rooted: add stability by making the trees less susceptible to wind damage Provide minimum competition for light, water and nutrients to adjacent crops Not spread on their own Wind resistant – withstand strong winds Small open crown: reduces the risk of wind damage

Establishment and spacingAny propagation method is suitable, but the main method of establishing windbreaks is by seedlings. A windbreak should be planted at right angles to the prevailing wind direction. It can either consist of a single line of trees with a spacing of 1.5-2.0 m, or two lines with a spacing of 4-5 m within the line and 2-4

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m between the lines. In addition to one or two lines of trees, a line of shrubs spaced at approximately 1 m can be planted on the side facing the prevailing wind. The spacing between trees may vary with species.

The windbreak must not be too dense. If the wind is blocked completely, it will cause turbulence over crops. Windbreak must be semi-permeable by the wind to slow it (dramatically reduced wind speeds).

Management Protect young trees against livestock and fires. Careful weeding and replacement of dead seedlings Termite control is necessary for trees that are susceptible to termite attack. Mature trees can be selectively pruned or pollarded to maintain a suitable density and to reduce

the shading effect on the adjacent agricultural crops.Benefits

Reduced wind damage and increased retention of moisture Protection of crops and soil against wind, which increases yield minimize the amount of moisture the winds evaporate from soils It will produce wood.

2.2.6. Trees on boundariesCertain multipurpose trees and shrubs can be planted along boundaries of fields and structures for demarcation purposes. The most common form of boundary planting consists of a single line of widely spaced trees and shrubs. If trees are to be planted along a property line affecting more than one land owner, it requires agreement between the neighbours involved to avoid conflicts. Consensus of all stakeholders is needed to agree on how to use the boundary area, whether jointly or separately. There are different ways of sharing trees planted on a boundary. Sometimes two rows of trees are planted, one on each side of the boundary, and then each farmer grows and manages his own trees. A disadvantage with this system is that it occupies more land than a single row. If trees are grown in a single row, the neighbours can agree on ownership of every second tree, for example. In such cases it is recommended that trees of the same species are grown, although it may be difficult to keep track of which tree belongs to which farmer. If different species are chosen, one species may outcompete the other and one of the two farmers be disadvantaged. Another option is for the neighbours to agree to own trees in different sections of the boundary. This may be easier than owning every second tree and it is then possible to choose different species for different sections according to the farmers' preferences. When only one owner wants to plant trees near his boundary bordering with other owners, it must not affect the crops and pasture lands of others.

Insert figure 9 hereFigure 9: A line of trees along a boundary

Areas where the practice is relevantThis technology is relevant for all farming areas except irrigation schemes.

Establishment and spacingThe spacing for smaller and medium sized fruit trees is normally 3 m. Other multipurpose tree species can be spaced between 2 and 4 m depending on species. With double rows the spacing between the rows should not be less than 2 m. The tree propagation method will depend on the species, but use of seedlings or transplantation of wildings is common.

Management aspects Protect young trees against livestock and fires.

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Tend the trees by pruning and pollarding to reduce shade on the adjacent crops. The prunings and pollarded branches can be used as construction materials or firewood.

Benefits Production of fuelwood, poles, fruits, fodder and timber. Marking of field or farm boundaries effectively. Protection of crops and soil against wind (yields are known to increase when windbreaks are

established in areas with strong winds).

Examples of recommended speciesTree species, e.g. Azadirachta indica, Cordia abyssinica, Grevillea robusta and Croton macrostachyus, can be used as boundary markers. Trees with a short lifespan, e.g. Sesbania spp. are less suitable unless they are combined with more permanent trees. Competitive trees such as eucalypts and pines should be avoided. Many other non-competitive trees are suitable.

2.2.7. Contour vegetation stripsIn many traditional African farming systems, living barriers of grasses, lines of stone or wood, are placed across hillsides to control runoff and soil erosion. Combinations of trees, shrubs, grasses and creeping vines planted along the contour can serve the same purpose. They result in greater structural stability and can provide a higher yield and diversity of useful products. The contour strip is also known as a barrier strip or hedge, horizontal vegetation strip, contour hedge or horizontal hedgerow. It is an erosion-control measure for sloping farmland, which provides useful products and enriches the soil. The establishment and maintenances of horizontal strips of vegetation on sloping ground is one of the most direct, cost-effective and ecologically sound erosion control interventions.

Contour vegetation strips may be planted or they may consist of natural vegetation left to grow across the slope. If the strips are dense and wide enough, they can stop water from flowing downhill and trap soil particles in a web of vegetation and litter. If the soil is permeable, water can then soak slowly into the ground.

Insert figure 10 hereFigure 10: Contour hedgerows of Leucaena leucocephala on a hill-farming demonstration site (A) and closely spaced contour hedgerows of Leucaena leucocephala (B)

The effectiveness of contour vegetation strips depends in large part on slope, rainfall intensity and soil conditions. For conserving soil and water, the two most important factors are the width of the strips and the interval between them. In general steeper slopes require wider strips spaced closer together (table 1). Contour strips usually range from 3 to 8 meters wide and cover about 10% of the total area under cultivation. If no specific design methods are available, the table given here can be used to estimate proper spacing.

The strips consists of one or two rows of shrubs and trees with at least one line of tightly spaced grasses planted on the down slope side to trap eroding soil. Trees and shrub species used on contour strips must be compatible with surrounding crops and cultivation practices. Some of the recommended species are: Dichrostachys cinerea, Lablab purpureus and Pennesetum purpureum.

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Table 3.1: Relationships among slope percent, strip width and distance between strips

2.2.8. Trees and shrubs on terraces The term ‘terrace’ is popularly used to describe any soil conservation measure introduced on slopes to change the natural course of runoff. Terraces are built mainly to conserve the soil and stabilize the slopes of steep land, while providing level areas for sustained cropping. The construction of terraces frequently increases yields and makes possible a wider variety of crops by improving soil-moisture conditions. Trees and shrubs used to stabilize a terrace and provide leaf mulch, shade and shelter from wind. In most cases, pre-existing trees and shrubs can be maintained on undisturbed parts of a slope or by adjusting terrace design and construction. Terraces may also improve site conditions for introducing valuable tree crops. Terraces with trees may evolve over time by forming behind contour vegetation strips.

Trees can either be placed at the toe of the terrace riser or along its edge. In areas where soil moisture is scarce, tree roots find better growing conditions along the toe. In fact, the soil immediately behind the edge the terrace is drier than anywhere else on the structure. In areas where rains and winds are heavy, trees planted along the terrace edge will protect crops and increase yields, although there may be a risk that trees will blow over and damage the terrace. The greater portion of the leaf litter will fall near the edge of the terrace if the trees are planted along the edge. Thus, in terms of site improvement and effect on crops, the best place for trees is at the edge of a terrace, where as in terms of the tree’s own requirements, the toe of the riser is best.

Insert figure 11 hereFigure 11 - Planting alternatives of trees on terraces

Trees may help stabilize rock-wall terraces and the earth behind them, fastening themselves by sending roots into rock crevices deep below the surface and acting as anchors to tie different soil layers together, thus reducing the chance of mass earth movements such as mudslides. Trees planted on any slope which is unstable due to high level of soil moisture, may improve stability by absorbing some of the excessive water that reduce water pressure and help prevent soil slippage down the slope.

Many farming communities who have used terrace systems for generations have also practiced a kind of agroforestry by leaving and protecting trees of certain species in their fields (e.g. Konso landscape). The farmers of the Kabe watershed also plants tree lucern (Chamaecytisus proliferus) in the summer. They know the benefit of this species as fodder, soil fertility improvement, etc. Trees such as Grevillea robusta may be scattered on terraced fields spaced widely enough not to shade the crops but closely enough to contribute significant amounts of leaf litter. Fruit trees are usually planted along the edges of terraces. Ziziphus spinachristii, olea species, Prunus amygdales are some of the classic examples of tree crops planted on rock-wall terraces. Other trees such as Persea Americana, Carica papaya, Citrus species, Mangifera indica and Psidium guajava are also recommended. Many farmers in Africa have also experimented with hedges of Leucaena leucocephala and similar trees on terrace risers to produce fodder and fuel wood on these previously underutilized sites.

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3. REFERENCEBadege, B. and Abdu, A. (2003). Agroforestry and Community Forestry for Rehabilitation of Degraded Watersheds on the Ethiopian Highlands. Paper presented at the International Symposium on Contemporary Development Issues in Ethiopia, July 11-12, 2003, Addis Ababa, Ethiopia.

Bekele-Tesemma, A. (2007). Useful trees of Ethiopia: identification, propagation and management in 17 agroecological zones. Nairobi: RELMA in ICRAF Project, 552p.Brown, S. (1997). Estimating biomass and biomass change of tropical forests: a primer. FAO Forestry Paper No. 134. Rome.

International Union for Conservation of Nature (IUCN) (2008). Reduced emissions from deforestation and degradation (REDD) in developing countries. Fourteenth session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP14), Poznan, Poland.

Nair, P. K. R., (1993): An introduction to agroforestry. Kluwer academic publishers, Dordrecht, the Netherlands.

Nair, P. K. R., Kumar, B. M., and Nair, V. D. (2008). “Agroforestry as a strategy for carbon sequestration”. J. Plant Nutr. Soil Sci., 172: 10–23.

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Nakakaawa, C., Aune, J. and Vedeld, P. (2009). Changes in carbon stocks and tree diversity in agro-ecosystems in south western Uganda: what role for carbon sequestration payments? Springer Science+Business Media B.V. New Forests DOI 10.1007/s11056-009-9180-5.

Rao, K.P.C., Verchot., L.V. and Laarman, J. (2007). Adaptation to Climate Change through Sustainable Management and Development of Agroforestry Systems. International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Nairobi, Kenya.

Reed, J.D., Rittner, U., Tanner, J., and Wiegand, O. (1992). Nutritive Value of Leaves and Fruits of Faidherbia albida and their Use for Feeding Ruminants. In: Faidherbia albida in the West African semi-arid tropics: proceedings of a workshop, 22-26 Apr 1991, Niamey, Niger.

Simute, S., Phiri, C. L. and Tengnäs, Bo (1990). Agroforestry Extension Manual for Eastern Zambia. Nairobi, Kenya.

Singh, B. R., Wele, A. D. and Lal, R. (2010). Soil carbon sequestration under chronosequences of agroforestry and agricultural lands in Southern Ethiopia. 19th World Congress of Soil Science, Soil Solutions for a Changing World, 1 – 6 August 2010, Brisbane, Australia.

Singh, S. P. (1994): Hand book of agroforestry. Agrotech puplishing academy, Hiran Mangri.

Sulistyawati, E., Ulumuddin, Y. I., Dudung M. Hakim, D. M., Harto, A. B. And Ramdhan, M. (2006). Estimation of Carbon Stock at Landscape Level using Remote Sensing: a Case Study in Mount Papandayan. Environmental Technology and Management Conference, 7-8 September 2006 Bandung, West Java, Indonesia.

Tengnas B. (1994). Agroforestry extension manual for Kenya. Nairobi: International Centre for Research in Agroforestry.

Unruh, J. D., Houghton, R. A., Lefebvre, P. A. (1993). Carbon storage in agroforestry: an estimate for sub-Saharan Africa. Climate Research vol. 3: 39-52.

Young, A. (1989). Agroforestry for soil conservation. ICRAF CAB international, Wallingford, UK.

Pictures

Figure 1. Calculation of number of tree per ha for different plantation types

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Figure 2. The benefits of agroforestry in nutrient cycling and erosion control

Figure 3. An improved fallow with Sesbania sesban

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Figure 4. The different phases of improved fallow and subsequent cropping phase

Figure 5. Tree spacing in alley cropping

Figure 6. (Left) Schematic presentation of dispersed trees on cropland

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Figure 7. Live fences

Figure 8. Good and bad windbreaks

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Figure 9. A line of trees along a boundary

Figure 10. Contour hedgerows of Leucaena leucocephala on a hill-farming demonstration site (A) and closely spaced contour hedge

Figure 11 - Planting alternatives of trees on terraces

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