texto agroforestería martin crawford

7/29/2019 Texto agroforestera MARTIN CRAWFORD

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Agroforestry (Martin Crawford)

Agroforestry is the growing of both trees and agricultural / horticulturalcrops on the same piece of land. They are designed to provide tree and

other crop products and at the same time protect, conserve, diversify andsustain vital economic, environmental, human and natural resources.

Agroforestry differs from traditional forestry and agriculture by its focus onthe interactions amoung components rather than just on the individualcomponents themselves.

Research over the past 20 years has confirmed that agroforestry can bemore biologically productive, more profitable, and be more sustainablethan forestry or agricultural monocultures. Many otherbenefits have beenshown. Temperate agroforestry systems are already widespread in manyparts of the world and are central to production in some regions.

Success of agroforestry is largely determined by the extent to whichindividual forest and agricultural components can be integrated to helprather than hinder each other. The choice of tree and crop speciescombinations is critically important when setting up systems.
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The main agroforestry types are:

Silvopasture (Wood-pasture) - mixing trees and pasture/forage.

Silvoarable (Wood/field crop, intercropping or alley cropping) - mixing

trees and arable or horticultural crops.

Forest farming- cultivating high-value products within forested areas.

Forest gardening - imitating complex forest ecosystems to producemany products.

Multi-purpose windbreaks, riparian buffer strips, contour plantings forerosion control, and fertility plantings of nitrogen-fixing trees are alsooptions both on their own and incorporated into the three main

agroforestry types.

Benefits of agroforestry

Research over the past 20 years has confirmed that agroforestry can bemore biologically productive, more profitable, and be more sustainablethan forestry or agricultural monocultures. Temperate agroforestrysystems are already widespread in many parts of the world and arecentral to production in some regions.

Research has also confirmed that agroforestry systems can include thefollowing benefits:
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They can control runoff and soil erosion, thereby reducing losses ofwater, soil material, organic matter and nutrients.

They can maintain soil organic matter and biological activity atlevels satisfactory for soil fertility. This depends on an adequateproportion of trees in the system - normally at least 20% crown

cover of trees to maintain organic matter over systems as a whole. They can maintain more favourable soil physical properties than

agriculture, through organic matter maintenance and the effects oftree roots.

They can lead to more closed nutrient cycling than agriculture andhence to more efficient use of nutrients. This is true to animpressive degree for forest garden/farming systems.

They can check the development of soil toxicities, or reduceexisting toxicities - both soil acidification and salinization can bechecked, and trees can be employed in the reclamation of pollutedsoils.

They utilise solar energy more efficiently than monocultural systems- different height plants, leaf shapes and alignments all contribute.

They can lead to reduced insect pests and associated diseases. They can be employed to reclaim eroded and degraded land. They can create a healthy environment - interactions from

agroforestry practices can enhance the soil, water, air, animal andhuman resources of the farm. Agroforestry practices may use only5% of the farming land area yet account for over 50% of the

biodiversity, improving wildlife habitat and harbouring birds andbeneficial insects which feed on crop pests. Tree biodiversity addsvariety to the landscape and improves aesthetics.

They can moderate microclimates. Shelter given by trees improvesyields of nearby crops and livestock. Shade in summer can bebeneficial for livestock, reducing stress.

Agroforestry can augment soil water availability to land-usesystems. In dry regions, though, competition between trees andcrops is a major problem.

Nitrogen-fixing trees & shrubs can substantially increase nitrogen

inputs to agroforestry systems. Trees can probably increase nutrient inputs to agroforestry systems

by retrieval from lower soil horizons and weathering rock. ('Mining'minerals and trace elements)

The decomposition of tree litter and prunings can substantiallycontribute to maintenance of soil fertility. The addition of high-


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quality tree prunings (ie high in Nitrogen but which decay rapidly)leads to large increases in crop yields.

The release of nutrients from the decomposition of tree residuescan be synchronised with the requirements for nutrient uptake ofassociated crops. While different trees and crops will all have

different requirements, and there will always be some imbalance,the addition of high-quality prunings to the soil at the time of cropplanting usually leads to a good degree of synchrony betweennutrient release and demand.

In the maintenenace of soil fertility under agroforestry, the role ofroots is at least as important as that of above-ground biomass.

Agroforestry can provide a more diverse farm economy andstimulate the whole rural economy, leading to more stable farmsand communities. Economic risks are reduced when systemsproduce multiple products.

Silvopasture

These systems comprise trees deliberately introduced into a forageproduction system (or, rarely, forage introduced into a tree productionsystem), the whole designed to produce a high-value tree component,while continuing to produce the forage and livestock componentindefinitely or for a significanttime.

Forage system: usuallypermanent pasture, grazedrotationally. Other options arepasture cut for hay or silage.White clover (especially wildtypes) is more shade-tolerantthan other pasture legumesand should be included inmixtures. Browsing animals aremore likely to damage treesthan large grazing animals or poultry. Deciduous trees are more readilybrowsed than conifers.

Tree component: may be timber or fuelwood trees, or a fruit or nut crop.Nitrogen-fixing trees can also be used to supply nitrogen for the foragecrop. Trees are grown as standards or as pollards.


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For more information on tree species choice in Britain, see Selectingtimber tree species.

Fruit crops as the tree component are usually grown as standards toallow for grazing beneath. Apples, cider apples and plums are some of

the possibilities.

Nut crops can include chestnuts and hazelnuts. Walnuts are slow growingand are only suitable if animals are excluded or if a cheap form of treeprotection is available.

Design & establishment

Trees can be planted evenly at wide spacing (eg. 10 x 10 m), in rows withforage alleys (of 10-30 m width) between, or in clusters. All methods

necessitate some form of weed control - black plastic mulches producethe best tree growth.

Even wide spacing: means that trees have to be individuallyprotected from stock - expensive - unless the forage is cut forhay/silage for the first few years until trees are large enough. Treesalso have to have individual weed control measures. Researchsuggests that deciduous trees planted this way into pasture haveno detrimental effect on pasture and livestock production for at least
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10 years. Forage production falls off rapidly, though, once treesexceed about 35% canopy cover.

Row planting: allows trees to be planted more closely, if desired, forlater thinning. Also allows for block weed control measures, eg.black polythene strip. Tree protection against stock can be

significantly cheaper by using straight fences or electricwire/netting. Also allows for easier access for mowing etc. Bothsingle and double rows of crop trees can be used; a furtheralternative is a triple row, with high-value crop trees sandwichedbetween rows of nurse trees (usually coniferous) which help trainstraight crop trees and are themselves thinned at a later stage.Rows are best aligned North-South.

Cluster planting: has the same potential advantages as rowplanting. Also, shade effects on the forage crop are more localised.Good where exposure is a problem, as trees within the cluster willbe more sheltered.

Silvoarable systems (eg. with walnut or other trees not suited tosilvopasture when young) can be converted to silvopasture when arableyields start to reduce from competition after 10-20 years.

Livestock management is crucial to avoid tree damage by grazing,trampling and rubbing. This may involve seasonal exclusion when treesare most vulnerable, locating salt/mineral licks to encourage uniformlivestock distribution, rotational grazing in sub-units etc. Grazing cancontrol grass competition with trees for moisture and nutrients and reducehabitat for gnawing rodents.

Benefits:

Trees provide shade and wind protection, which reduce heat stressand windchill of livestock; performance is improved and mortalityreduced.

Economic returns from forage/livestock production continue whilecreating a sustainable system with environmental benefits.

Can be designed for little or no long-term reduction of forageproduction whilst growing other crop(s) on the same site.

The combined tree plus forage productivity of silvopastures cansubstantially exceed that of pastures or forests grown alone.


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Drawbacks:

Main one is the cost of protecting trees from livestock, which inwide plantings can be more than the trees themselves. If trees aresubsequently pollarded, this will remove the time and cost involved

in restocking the tree component. Many high-value deciduous timber trees grow with poor (crooked)

form without the sideways light pressure of a forest. Correctionpruning and/or the use of nurse trees can overcome some of thisproblem.

Silvoarable - intercropping & alleycropping

Here, agricultural or horticultural crops are grown simultaneously with along-term tree crop toprovide annual incomewhile the tree cropmatures. Trees aregrown in rows with widealleys in-between forcultivating crops.

Alley component: Anyarable or horticulturalcrop is possible.Overwintering crops (ieautumn-sown) are veryefficient users of the almost full light available over the dormant season ofdeciduous trees, and may be the best choices for narrow alleys wheretrees are quite large. It is important that the alleys are physicallycultivated (or at least ripped with deep tines) - horticultural no-dig raisedbeds are likely to fill with fine tree roots.

Tree component: may be timber or fuelwood trees, or a fruit or nut crop.Pollards and coppiced trees are both possible, the former interfering leastwith arable operations.

For more information on tree species choice in Britain, see Selectingtimber tree species.
http://www.agroforestry.co.uk/agrotree.htmlhttp://www.agroforestry.co.uk/agrotree.htmlhttp://www.agroforestry.co.uk/agrotree.htmlhttp://www.agroforestry.co.uk/agrotree.html


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Fruit crops can be used as the tree component. Apples, cider apples andplums are all possibilities.

Nut crops can include walnuts, chestnuts and hazelnuts.

Poplar silvoarable system in England

Design & establishment

Tree rows are spaced at a minimum of 10-14 m apart to allow enoughroom for cultivation operations. Usually a whole number of cultivationequipment widths is chosen for efficient operations. Rows are bestaligned North-South.

Both single and double rows of timber crop trees can be used; a furtheralternative is a triple row, with high-value timber crop trees sandwichedbetween rows of nurse trees (usually coniferous) which help train straightcrop trees and are themselves thinned at a later stage. Shrubs and otherplants can also be planted to the side of main trees for better windprotection and other uses. Trees can be planted in the rows at finalspacing or at a closer spacing to allow for thinning at a later date. Thelatter allows for more selection of good quality timber trees.


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Weed control is essential. Black plasticmulches give best tree establishment andgrowth, and will soon be covered withleaf mold. Cultivations up to a few inchesof the plastic edge are possible.

3 row tree strip Single row treewith training trees strip

Yields (per unit area) of alley crops are not reduced by shading until thetree height reaches the alley width (at which stage the system can beconverted to silvopasture.) Competition between trees and alley crop forwater does not appear to be a big problem in Britain; it is possible someproblems may occur in drier areas (ie the East) during droughty summers.

Benefits

Wood or tree products are produced in addition to agronomic crops,with no reduction in crop yields per unit area for many years.

Crop quality and yields can be increased by enhancingmicroclimatic conditions, offsetting any reduction by the removal oftree strips from cultivation.

Utilisation and recycling of soil nutrients is improved. Wildlife habitat and corridors are created. Aesthetic diversity - improvement to open monocropped areas.

Drawbacks

Many high-value deciduous timber trees grow with poor (crooked)form without the sideways light pressure of a forest. Correctionpruning and/or the use of nurse trees can overcome some of thisproblem.

Arable farmers in particular often have an aversion to trees inarable fields, citing single trees which get in the way. Alleys,however, if properly designed, should present no problems with

machinery and cultivations.


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Forest farming

In forest farming, high-value speciality crops are cultivated under theprotection of a forest canopy that has been modified and managed to

provide the appropriate conditions. It is a way of utilising forests for short-term income while high-quality trees are being grown for wood products.The amount of light in the stands is altered by thinning, pruning, or addingtrees; 5-40% crown cover is usually desirable. Existing stands of treescan be intercropped with annual, perennial, or woody plants.

Five main categories of speciality crops are:

FOODS:

mushrooms, eg. Shiitake, matsuki (grown on logs, insawdust/chipped wood beds etc.)

nuts, eg. hazelnuts, small chestnut species; note that the canopytrees could also be nut producers, eg. walnuts, chestnuts, pecans,pine nuts

vegetables, eg. radish, beetroot, Swiss chard honey from bee plants, eg. plum, black locust herbs, eg. mints fruits, eg. blueberries, elderberries, blackberries, raspberries,

strawberries, currants, gooseberries edible flowers, eg. elderflowers sap products - eg. maple syrup, birch sap wine etc.


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BOTANICAL PRODUCTS: Many medicinal plants are used in herbalmedicine and are used to give clinically useful drugs, such as:

Adonis vernalis (Spring adonis) Agrimonia eupatoria (Agrimony) Ammi majus (QueenAnnes lace) Anabasis aphylla Anisodus tanguticus Artemesia annua (Annual wormwood) Artemisia maritima (Sea wormwood) Atropa belladonna (Belladonna) Berberis vulgaris (Barberry) Brassica nigra (Blck mustard) Colchicum autumnale (Autumn crocus) Convallaria majalis (Lily of the valley) Coptis japonica Corydalis ambigua Cynara scolymus (Globe artichoke) Cytisus scoparius (Broom) Daphne genkwa Digenia simplex (Makuri) Digitalis lanata & D. purpurea (Foxgloves) Gaultheria procumbens (Wintergreen) Ginkgo biloba Glaucium flavum (Horned poppy) Glycyrrhiza glabra (Liquorice) Hemsleya amabilis Hydrangea macrophylla Hydrastis canadensis (Goldenseal) Hyoscyamus niger (Henbane) Larrea divaricata Lobelia inflata Lycoris squamigera Mentha spp. (Mints)

Panax spp. (Ginseng) Podophyllum peltatum (May apple) Potentilla fragarioides Rhododendron molle Salix alba (White willow) Sambucus spp. (Elders - flowers) Sanguinaria canadensis (Bloodroot)


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Silybum marianum (Milk thistle) Sophora pachycarpa Stephania sinica Taxus brevifolia (Pacific yew) Thymus vulgaris (Thyme) Trichosanthes kirilowii (Snake gourd) Urgenia maritima (Squill) Valeriana officinalis (Valerian) Veratrum album (White hellebore) Vinca minor (lesser periwinkle) essential oil crops can also be cultivated, eg. Eucalyptus leaves,

mints, lemon balm, thyme

DECORATIVES

floral greenery (mosses, ferns, beargrass, salal, Eucalyptus etc) Christmas trees dye plants

HANDICRAFTS

basketry materials (willows etc.) short-term coppice, eg. hazel poles, energy coppice

WOOD PRODUCTS

charcoal from understorey trees fuelwood special woods, eg. for carving, incense garden mulches from chipped wastes & coppice; pine needle

mulches

An existing British system which falls into the latter two categories iscoppice with standards - eg. hazel coppice with standards of oak.

Typically, a system can be established by thinning an existing forest toleave the best trees for continued wood production and to createconditions for the understorey crop to be grown. The understorey crop isthen planted and managed intensively to provide short-term income.

Areas used for forest farming are usually small (5 acres or less), andsystems usually focus on a single crop plus timber, but can be designed


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to produce several products. Examples of such systems in North Americainclude:

ginseng (medicinal) + maple syrup + bee products + timber shiitake mushrooms (grown on cut logs) + timber ferns & beargrass (decorative) + mushrooms + timber ginseng + walnuts + black walnut veneer logs Christmas trees + timber

Before investing time and money in growing speciality forest products,entrepreneurs should :

1. Obtain production and processing information. Proper harvest, storageand transport will maximise returns.

2. Locate sources of technical expertise.

3. Locate or develop potential markets, often local stores or co-operatives.

All these can be quite difficult, especially in Britain where there is littleculture of utilising forests in this way. However, products such asmedicinal plants are increasingly in demand and there is no reason whymany (for example, elder flowers or annually coppiced yews or gingkos)cannot be grown in British forest farms. The internet is an increasingly

good source of locating non-local buyers of such crops. In North America,Co-operative Extension Services and the USDA Forest Service can oftenprovide expertise.

Benefits:

Economic benefits can be significant. Logs can produce shiitakemushrooms worth 5-10 times the value of the logs themselves, andforest-cultivated ginseng averages 122-245 per pound in North

America. Other medicinal plants provide a lower but steady

supplemental income. Markets for floral decoratives have beensteadily increasing.

Forest farming modifies the forest ecosystem but does notsignificantly interfere with its crucial contributions of water filtering,soil erosion control, microclimate moderation, and wildlife habitat.

Forest farming provides opportunities to generate short-termincome from existing woodlands, with minimum capital investment.


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Especially on small family farms, this can contribute significantly todiversification and rural economic development.

Drawbacks:

Requires more of an entrepreneurial attitude from farmers andlandowners.

Likely to need to conduct research to locate potential buyers ofspeciality products.

Forest farming systems are often labour intensive - oftenacceptable if family labour is available.

Forest gardening

A forest garden is a designed agronomic system based on trees, shrubsand perennial plants. These are mixed in such a way as to mimic thestructure of a natural forest - the most stable and sustainable type ofecosystem in this climate.

The primary aims for the system are:

to be biologically sustainable, able to cope with disturbances suchas climate change

it should be productive, yielding a number (often large) of different

products it should require low maintenance.


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The crops which are produced will often include fruits, nuts, edible leaves,spices, medicinal plant products, poles, fibres for tying, basketrymaterials, honey, fuelwood, fodder, mulches, game, sap products.

Forest gardens (often called home gardens) have been used for millennia

in tropical regions, where they still often form a major part of the foodproducing systems which people rely on, even if they work elsewhere formuch of the time. They may also provide useful sources of extra income.Their use is intimately linked with prevailing socio-economic conditions.They are usually small in area, often 0.1-1 hectares (0.25-2.5 acres).

In temperate regions, forest gardens are a more recent innovation, manyinspired by Robert Harts efforts in Shropshire (UK) over the last 30 years.

A major limiting factor for temperate forest gardens in the amount ofsunlight available to the lower layers of the garden: in tropical regions, the

strong light conditions allow even understorey layers to receivesubstantial light, whereas in temperate regions this is not usually thecase. To compensate for this, understorey layers in temperate forestgardens must be chosen very carefully - there are plenty of plant cropswhich tolerate shady conditions, but many are not well known. Many ofthe more common shrub or perennial crops need bright conditions, and itmay be necessary to design in more open clearings or glades for suchspecies.

Temperate forest gardens are also usually small in area, from tiny back

garden areas up to a hectare (2.5 acres) in size. While food productionand land use remain the concern of a minority of landowners andbusinesses, their use is likely to be limited to alternative and organicgardeners and land users.

The key features which contribute to the stability and self-sustainingnature of this system are:

the large number of species used, giving great diversity the careful inclusion of plants which increase fertility, such as

nitrogen fixers (eg. Alders [Alnus spp], Broom [Cytisus scoparius],Elaeagnus spp, and shrub lupins [Lupinus arboreus]).

the use of dynamic accumulators - deep rooting plants which cantap mineral sources deep in the subsoil and raise them into thetopsoil layer where they become available to other plants, eg.Coltsfoot [Petasites spp], Comfreys [Symphytum spp], Liquorice[Glycyrrhiza spp], Sorrel (and docks!) [Rumexspp].


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the use of plants specially chosen for their ability to attractpredators of common pests, eg umbellifers like tansy.

the use, where possible, of pest and disease resistant varieties, eg.apples.

the increasing role of tree cover and leaf litter which improve

nutrient cycling and drought resistance.

A forest garden is organised in up to seven layers . Within these, thepositioning of species depends on many variables, including theirrequirements for shelter, light, moisture, good/bad companions, mineralrequirements, pollination, pest-protection, etc. The layers consist of:

Canopy trees - the highest layer of trees. May include species such

as Chestnuts [Castanea spp], Persimmons [Diospyros virginiana],honey locusts [Gleditsia triacanthos], Strawberry trees [Arbutusspp], Siberian pea trees [Caragana arborescens] Cornelian cherries[Cornus mas], Azeroles and other hawthorn family fruits [Crataegusspp], Quinces [Cydonia oblonga], Apples [Malus spp], Medlars[Mespilus germanica], Mulberries [Morus spp], Plums [Prunus


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domestica], Pears [Pyrus communis], highbush cranberries[Viburnum trilobum].

Small trees and large shrubs, mostly planted between and belowthe canopy trees. May includes some of the canopy species ondwarfing rootstocks, and others such as various bamboos,

Serviceberries [Amelanchierspp], Plum yews [Cephalotaxus spp],Chinkapins [Castanea pumila], Elaeagnus spp, and Japanesepeppers [Zanthoxylum spp]. Others may be trees which will becoppiced to keep them shrubby, like medicinal Eucalyptus spp, andbeech [Fagus sylvatica] and limes [Tilia spp] with edible leaves.

Shrubs, mostly quite shade tolerant. May include common specieslike currants [Ribes spp] and berries [Rubus spp], plus others likechokeberries [Aronia spp], barberries [Berberis spp], Chinesedogwood [Cornus kousa chinensis], Oregon grapes [Mahonia spp],New Zealand flax [Phormium tenax] and Japanese bitter oranges[Poncirus trifoliata].

Herbaceous perennials, several of which are herbs and will alsocontribute to the ground cover layer by self-seeding or spreading.These may include Bellflowers with edible leaves [Campanula spp],Comfreys [Symphytum spp], Balm [Melissa officinalis], Mints[Mentha spp], Sage [Salvia officinalis], and Tansy [Tanacetumvulgare].

Ground covers, mostly creeping carpeting plants which will form aliving mulch for the forest floor. Some may be herbaceous

perennials (see above), others include wild gingers [Asarum spp],cornels [Cornus canadensis], Gaultheria spp, and carpetingbrambles (eg. Rubus calycinoides & R.tricolor).

Climbers and vines. These are generally late additions to thegarden, since they obviously need sturdy trees to climb up. Theymay include hardy kiwis [Actinidia spp], and grapes [Vitis spp].

The final layer is the root zone or rhizosphere. Any design shouldtake account of different rooting habits and requirements of differentspecies, even if root crops are not grown much. Some perennialswith useful roots include liquorice [Glycyrrhiza spp] and the

barberries [Berberis spp] whose roots furnish a good dye andmedicinal products. Various beneficial fungi can also be introducedinto this layer.


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BENEFITS: A long-term biologically sustainable system for growing food &

other products for a household Once established, little work is needed to maintain

DRAWBACKS: Planting out and establishment usually requires large numbers of

plants and substantial work


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Other agroforestry types Riparian buffer strips are natural or re-established streamside

forests made up of tree, shrub and grass plantings; they buffer

pollution of waterways from adjacent land, reduce bank erosion,protect aquatic environments and enhance wildlife value.

Contourbufferstripsarebasicallyrows oftrees(andsometimesshrubs)in rowsalongcontours,withalleys between for forage or alley cropping. The aim is to reducesoil erosion on slopes and give some wind protection.

Fertility plantings are plantings of trees and/or shrubs with themain aim of improving nutrient input and/or cycling for a forage oralley crop. Nitrogen-fixing trees and shrubs are usually used, forexample Italian alder, Elaeagnus, Sea buckthorn, and Black locust.Nitrogen fixed by bacteria in association with their roots is madeavailable to other crops via leaf fall, rain drip, root-root contact andbeneficial fungi. The amounts made available are in the same orderas from perennial legumes.

Field windbreaks protect a variety of wind-sensitive row, cereal,vegetable, orchard and vine crops, resulting in up to 25% increases

in production; and also control wind erosion, and increase beepollination. Livestock windbreaks help reduce animal stress andmortality, and reduce feed consumption; weight gains of up to 10%and milk production increases of 8-20% can result. Farm homes inwindy areas protected by windbreaks can expect heating costs tobe cut by as much as 30%.


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Windbreak spacing depends on windbreak height (H), soilerodibility, crop sensitivity & rotation, and climate.

texto agroforestería martin crawford

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