sustainable woodfuel harvesting – finnish practical ...€¦ · sustainable woodfuel harvesting...

Activating Private Forest Owners to Increase Forest Fuel Supply

IEE/08/435/SI2.529239

Task 4.2.1 Deliverable 12

Sustainable Woodfuel Harvesting –

Finnish Practical Applications

Martti Kuusinen

Forestry Development Centre Tapio

Recommendations for Sustainable Wood Fuel Harvesting

1

Contents

1 PREFACE .................................................................................................................................................................... 2

2. PRINCIPLES AND ACTIONS IN SUSTAINABLE WOODFUEL HARVESTING......................... 3

PRINCIPLE 1: WOODFUEL SHOULD BE HARVESTED ONLY ON SUITABLE SITES. ...................................................... 3

Action 1.1. Woodfuel should not be harvested in places where it constitutes a substantial threat to profitable silviculture, biodiversity, water protection or recreation. ............................ 3

PRINCIPLE 2: WOODFUEL HARVESTING SHOULD NOT SUBSTANTIALLY DIMINISH GROWTH POTENTIAL OR

SILVICULTURAL QUALITY OF THE HARVESTING SITES. ............................................................................................... 4

Action 2.1. A portion of the biomass is always left on the harvesting sites................................ 4

Action 2.2. Thinnings should maintain proper stand density and structure ................................ 5

Action 2.3. Damage to remaining trees and soil surface should be avoided .............................. 5

Action 2.4. Harvesting operations should not increase fungal or insect damages in the stands. .................................................................................................................................................................... 6

PRINCIPLE 3: WOODFUEL HARVESTING SHOULD NOT DIMINISH THE BIODIVERSITY OF FOREST ECOSYSTEMS... 7

Action 3.1. Woodfuel harvesting should not reduce the amount of coarse woody debris in the forests............................................................................................................................................................. 7

Action 3.2. Tree species’ diversity and natural stand structure should be maintained. ......... 7

PRINCIPLE 4: WOODFUEL HARVESTING SHOULD NOT CAUSE EROSION NOR REDUCE THE ECOLOGICAL VALUE OF

WATER SYSTEMS............................................................................................................................................................ 7

Action 4.1. The risk of erosion should be recognised and managed. ............................................. 7

Action 4.2. Buffer zones are applied beside all water courses. ........................................................ 8

Action 4.3. Unnecessary disturbance of soil surface should be avoided. ..................................... 9

PRINCIPLE 5: RECREATIONAL, CULTURAL AND LANDSCAPE VALUES SHOULD BE TAKEN INTO ACCOUNT IN

WOODFUEL HARVESTING. ............................................................................................................................................. 9

Action 5.1. Objects valuable to cultural heritage are taken into account in woodfuel harvesting. ............................................................................................................................................................ 9

Action 5.2. Harvesting sites with special recreational values or landscape values are felled with specific instructions and planning. ................................................................................................... 10

PRINCIPLE 6: CLIMATE CHANGE MITIGATION SHOULD BE A PRIME CONSIDERATION IN ALL WOODFUEL HARVESTING OPERATIONS.......................................................................................................................................... 10

Action 6.1. Woodfuel harvesting should not reduce the carbon sinks of the harvested stands. .................................................................................................................................................................. 10

Action 6.2. The carbon storage in the forest soils should be preserved..................................... 10

Action 6.3. Carbon efficiency is maximized throughout the whole procurement chain. ....... 11

Action 6.4. The energy content of the woodfuel should be maximized throughout the whole procurement chain.............................................................................................................................. 12

PRINCIPLE 7: QUALITY AND ENERGY CONTENT OF WOODFUEL SHOULD BE MAXIMIZED THROUGHOUT THE

WHOLE PROCUREMENT CHAIN. ................................................................................................................................... 12

Action 7.1. Woodfuel is seasoned and stored properly...................................................................... 12

Action 7.2 Impurities amongst woodfuel are minimized ................................................................... 14

3. REFERENCES .................................................................................................................................................... 15


2

1 Preface

This publication is a part of the AFO-project (Activating Private forest Owners to Increase forest

Fuel Supply - IEE/08/435/SI2.529239, www.afo.eu.com) funded by the European Union’s

Intelligent Energy Programme. The AFO-project is coordinated by VTT, Technical Research Centre

of Finland. The other partners are Forestry Development Centre Tapio (Finland), Technical Center

of Forest, Wood Products and Furniture (France), Institute for Forestry Development IDF-CNPPF

(France), Forestry Commission (UK), South Yorkshire Forest Partnership (UK), Energy Restructuring

Agency (Slovenia), BIOENERGY 2020+ GmbH (Austria) and Environmental Projects State Ltd

(Latvia).

AFO's main objective is to increase woodfuel supply from privately owned European forests. In

terms of EU-level bioenergy promotion, private forest owners (PFO's) form a conclusive forest

owner group, as they possess most of the European wood energy potential. AFO carries out

various activation procedures to initiate woodfuel supply clusters among PFO's. These clusters are

brought together with the potential energy wood users, focusing on local small- and medium scale

heat plants. The project operates during 2009-12 in six countries and five specific target areas.

Finland and Austria are countries of high woodfuel utilization level and strong experience of

bioenergy harvesting and procurement systems. Best practices are transferred from these

countries to less experienced partner countries with vast private forests ownership (France,

Slovenia, Latvia and UK). Results and best practices acquired in the project will be disseminated

throughout all EU member states.

Currently there are few EU countries that have considered woodfuel production in their

legislation, forest certification criteria or other forestry guidelines. The aim of this publication is to

present basic principles and practical guidelines on how to ensure the sustainability of woodfuel

harvesting operations in boreal forests. The guidelines are described on a relatively general level,

so that they are more or less straightforwardly applicable to other European conditions. Since the

EU 27 consists of such a diverse range of forest ecosystems, more detailed instructions suitable to

particular circumstances should be established by national or regional institutions.

These recommendations are based on projects conducted by Forestry Development Centre Tapio

to create guidance for sustainable woodfuel production in Finland (Äijälä et al 2010). In the

process of adaptation and translation, many guidelines have been compressed and generalized so

that the original Finnish formulation has unsharpened.

It should also be noted that there is only limited research information available regarding many

issues related to woodfuel harvesting and its environmental impacts. Therefore several of the

following guidelines have been established on the grounds of ‘precautionary principle’.

The sustainability of woodfuel harvesting is executed on two levels, described later in the form of

seven principles: i) only suitable sites with no-risks or low-risks are selected for woodfuel

harvesting; and ii) a necessary set of actions is carried out to preserve the sustainability on sites

chosen for woodfuel harvesting.

Martti Kuusinen

Helsinki, December 2010


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2. Principles and actions in sustainable woodfuel harvesting

Adapting the following guidelines, one should bare in mind that there are fundamental differences

at a national level in the existing harvesting practices and bureaucracy in Europe. For example,

stump harvesting is strictly restricted in Great Britain and Germany and the following

recommendations are not to be followed in this aspect.

Unlike in many European countries, in Finland “wood fuel” is primarily referred to as branches, top

and the stump i.e. residues of round wood logging. In addition, small-diameter trees from early

thinnings are commonly considered as a woodfuel fraction. Therefore, the following guidelines

focus on harvesting other woody fractions than stem wood.

It is important to be aware that most negative impacts of woodfuel harvesting relate to

accumulation of nutrient rich components such as branches, needles in particular, and fine roots

(see image 2). Woodfuel harvesting of just stem wood harvesting, means many risks are avoided.

Thus, whenever only stemwood is harvested for woodfuel production, traditional guidelines for

round wood harvesting should be applied.

Principle 1: Woodfuel should be harvested only on suitable sites.

Action 1.1. Woodfuel should not be harvested in places where it constitutes a substantial

threat to profitable silviculture, biodiversity, water protection or recreation.

Branches, needles, leaves, bark and roots possess varying amounts of nutrients that are essential

for photosynthesis and tree growth. The recession in the yield caused by biomass accumulation is,

however, very irregular depending on the vegetation zone and site characteristics. The most

harmful case in the perspective of silviculture would be to worsen an existing chemical imbalance

in the soil. Therefore areas with signs of chemical imbalance are not recommended for whole tree

harvesting, stump harvesting or logging residue harvesting. The greatest risks in yield effects

resulting from logging residue harvesting have shown to occur on sites where tree biomass

possesses vast nitrogen storage and on the most infertile sites with very slim humus layers and

low carbon storage in the soil.

Harvesting logging residues or stumps increases tremendously the volume of biomass from the

site. For example, on a mature mesic spruce stand in Southern Finland, logging residues possess

approximately 25 percent of the total biomass volume and stumps 15 percent respectively. In case

round wood is harvested from nature conservation areas or other sites valuable in terms of

biodiversity, woodfuel harvesting operations in conjunction should be considered carefully. In

certain conditions it is, however, recommendable to accumulate nutrient rich woodfuel fractions

from biodiversity hot spots. Such circumstances could be e.g. most infertile sites that are

eutrophicating or herb rich woodlands where logging residues would hinder the ground

vegetation.

Stump lifting should not be applied on areas with special importance to ground water utilization,

because it may damage the natural filtration mechanism of the top layers of the soil. At least areas

that are currently used for groundwater accumulation and areas that are estimated to be utilised

for this purpose are not recommended for stump harvesting.


4

Principle 2: Woodfuel harvesting should not substantially diminish growth

potential or silvicultural quality of the harvesting sites.

Action 2.1. A portion of the biomass is always left on the harvesting sites.

As described in Action 1.1, green biomass and roots possess remarkable amounts of nutrients

essential to the growth of the trees (see figure 2). As they also have a significant role in

biodiversity preservation, a proportion of all biomass fractions are recommended to be left on the

site. There is a general objective to sustain approximately 30 percent of the biomass of the

branches on the harvesting sites.

Image 1. Within few spring or summer weeks

the colour of the logging residues turns

brown. Consequently, nutrient rich needles

fall down on the ground during the

harvesting. Photo by Martti Kuusinen.

Seasoning logging residues on the stand for a few spring or summer weeks before processing is

the primary method to dry the material. This makes the nutrient rich needles and leaves fall off

leaving them on the site (image 1). Furthermore, the quality of the fuel improves as the chlorine

found in needles does not corrode the boiler. This seasoning method works fine with spruce and

birch, but there are some species like pine and oak that do not drop their leaves so rapidly.

0

100

200

300

400

500

600

700

800

35 yrs 58 m3/ha 100 yrs 258 m3/ha 30 yrs 192 m3/ha 62 yrs 342 m3/ha

Pine stand (dryish) Spruce stand (fertile)

Nitrogen, kg/ha

Needles

Branches

Stem

Stump

Thick roots

Thin roots

Image 2. Amounts (kg/ha) of Nitrogen in tree’s biomass on two Pine and two Spruce dominated

stands in Southern Finland. The lack of nitrogen is the most common factor hindering the growth in

boreal upland forests. Most of the nitrogen accumulated into the biomass is allocated to needles

and branches. (Helmisaari et al 2008).


5

Stumps do not include as much nutrients as branches, but retention stumps act as stocks of

carbon and spots of undisturbed soil surface. At least 25 stumps are recommended to be left on

every operated hectare of stump harvesting, which corresponds approximately 5 percent of the

total stump number. In addition, all stumps in conjunction to valuable habitats, buffer zones and

other corresponding sites with special features should be left untouched. All stumps from previous

harvesting operations and stumps with diameters less than 15 cm should also be left on the stand.

Action 2.2. Thinnings should maintain proper stand density and structure

Woodfuel harvesting on young and intermediate stands should maintain the stem density on a

level suitable to the conditions. Suitable thinning intensity can be determined to maintain enough

growing trees to avoid growth losses and to be intensive enough to produce profitable quantities

of woodfuel (image 3).

An important factor is proper tree selection for thinning, which is carried out primarily on the basis

of stems’ quality as future saw log. Trees of lowest quality are cut for woodfuel. In addition, tree

species most valuable in terms of monetary value are preferred as remaining, although there

should always be diversity as monocultures are not recommended.

Image 3. Proper treatment of growing

stands enables profitable thinning

operations and good harvesting

conditions with high levels of light

penetration and adequate mean stem

size later in intermediate phase. In

addition, the remaining stand is

regularly distributed and the quality of

the stems is good. Photo by Martti

Kuusinen.

Action 2.3. Damage to remaining trees and soil surface should be avoided

Woodfuel harvesting is often a competitive alternative for round wood harvesting in young stands

with poor previous management. High stem densities and correspondingly low mean stem sizes

are typical symptoms of lack of young stand management. The fact that there are lots of stems

close to each other makes it very challenging to cut some of them away and to leave the rest

standing untouched. Damages in stems or roots decrease the growth of the tree, weaken the

quality of the valuable saw logs and expose the whole stand to diseases. In addition, damages in

the roots weaken significantly the wind stability of the stand.


6

Thus, to create good harvesting conditions (maximise light penetration and mean stem volume),

proper care of young stands’ treatment is essential. A stand can also be prepared for harvesting by

cutting the smallest stems with a cleaning saw beforehand.

To avoid damages in soil surface, branches should be used for soil protection under harvesting

machinery, a ‘brash mat’, even in whole tree harvesting or logging residue harvesting. It is also

important to choose the season for harvesting so that the softest terrains are frozen or as dry as

possible when harvested.

There has been a basic requirement for maintaining at least 96 percent of the remaining trees

undamaged. Respectively, at least 96 percent of the hauling tracks should remain undamaged

provided that the quality of the harvesting is considered to be satisfactory.

Image 4. Damages in remaining trees and hauling tracks

may lead to fungal diseases and losses in yield. Photo by

Martti Kuusinen.

Action 2.4. Harvesting operations should not increase fungal or insect damages in the

stands.

As described in the previous section, damages in roots or stems expose the trees to fungal

diseases and as their state weakens, they are more vulnerable to insect and abiotic damages also.

Woodfuel storage may in some conditions form a threat of fungal and insect damages to the

surrounding woodlands. In Finnish conditions, harmful beetles like the European spruce bark

beetle (Ips typographus) and Lesser pine shoot beetle (Tomicus minor) benefit greatly if lots of

fresh timber is available for them to lay eggs on. On the other hand, the most common fungal

threat, Annosum root rot (Heterobasidion ssp.) begins forming fruiting bodies in no more than two

years, when infected stems are stored. Storage should be located and, if necessary, transported

away so that these damages are avoided.


7

Principle 3: Woodfuel harvesting should not diminish the biodiversity of forest

ecosystems.

Action 3.1. Woodfuel harvesting should not reduce the amount of coarse woody debris in

the forests.

The lack of Coarse Woody Debris (CWD) is one of the main challenges to ecologically sustainable

forestry on all European forest vegetation zones. In Finland there are 419 endangered saproxylic

species, which is 43 per cent of all red-listed species living in forests. Therefore, all existing stocks

of CWD should be maintained untouched where they are present (image 5). Some saproxylic

species are able to exist on stumps and therefore a portion of the stumps is recommended to be

left on the harvesting site (see Action 2.1) also.

Image 5. Clusters of coarse woody

debris are, in the long run, true

biodiversity hot spots in commercial

forests. Photo by Martti Kuusinen.

To avoid the situation where intensive woodfuel harvesting decreases significantly populations of

common forest species dependant on thinnings timber, whether of stumps or roots, a portion of

the harvestable woodfuel fraction should be left unharvested at sites (see Action 2.1).

Action 3.2. Tree species’ diversity and natural stand structure should be maintained.

Although woodfuel thinnings most often lead to the removal of the smallest and shortest trees of

the stand, for those of poorest form there should always be some variation in the stand structure.

For instance, a few patches of non-thinned woodland should be maintained on each harvesting

site to create hiding and nesting places for fauna. Respectively, there should exist variation in

terms of tree species also if possible. There are numerous endangered or otherwise species that

are dependant on a singular tree species.

Principle 4: Woodfuel harvesting should not cause erosion nor reduce the

ecological value of water systems

Action 4.1. The risk of erosion should be recognised and managed.

Grain size of the mineral soil particles, terrain slope and surface vegetation are the main factors

influencing the risk of erosion. Due to the massive disturbance that stump harvesting causes to the

soil surface, there is an evident risk of erosion and nutrient leakage to water bodies and ground

water. Areas with steep slopes and areas adjacent to water courses are high risk sites in terms of


8

erosion. Stump harvesting should always be considered thoroughly on such sites and special

measures (e.g. sufficient buffer zones) should be carried out to avoid soil particles ending up in

water systems. Whole tree or slash harvesting increase greatly the amount of nutrients taken

away from the site, which decreases the risk of nutrient pollution.

0

0,5

1

1,5

2

2,5

< 0,002 < 0,006 < 0,02 < 0,06 < 0,2 < 0,6 < 2 < 6 < 20 < 60

Soil particle diameter, mm

Req

uir

ed w

ater

flo

w s

pee

d, m

/s

Image 6. Erosion risks of mineral soils upon grain size, based on the water flow speed required for

mobilising singular soil particles. Soils with coarse silt and/or fine sand fractions are most likely to

be eroded (National Board of Waters, Finland 1986).

Action 4.2. Buffer zones are applied beside all water courses.

Buffer zones are belts of untouched soil around water courses. The harvesting operations,

especially stump lifting, should be confined so that there are always at least 5 to 10 metres of

untouched soil boardering the water system. To achieve the best possible efficiency in terms of

nutrient capture, living trees should be continuously maintained on the buffer zones. The more

trees there are and the bigger the trees are, the better is the impact on water protection.

Continuous cover forestry is also an option, whenever the circumstances are favourable.

Since the riparian forests along water courses are typically rich with tree species, they can also be

considered to be valuable for biodiversity and also for landscape aesthetic.

Image 7. Living trees improve the filtering effect

of the buffer zones. However, maintaining the

soil surface untouched is most essential. The red

lines demonstrate the recommended minimum

widths of the buffer zones beside a lake, a rivulet

and a ditch, attached to a stump lifting area.

(Image by Juha Varhi)


9

Action 4.3. Unnecessary disturbance of soil surface should be avoided.

Soil disturbances are the most challenging environmental effect of stump lifting. Studies show that

stump lifting uncovers 1,5 times more soil than traditional soil preparation on average, depending

on the site characteristics. This leads to increased risks in nutrient leakage and soil erosion.

Therefore, any unnecessary scarification should be avoided. It is also important to shake the

stump pieces clean above the stump hole and not to spread the loose soil material across the site,

at processing or haulage.

Images 8 and 9. Minimizing the amount of bare soil surface is the most essential environmental

objective of stump lifting and hauling operations. Photos by Martti Kuusinen.

Principle 5: Recreational, cultural and landscape values should be taken into

account in woodfuel harvesting.

Action 5.1. Objects valuable to cultural heritage are taken into account in woodfuel

harvesting.

Forests can be ‘treasure chest’ of objects relation to history of mankind. There are prehistoric

graves, monuments of ancient living dwellings and war historic structures (image 10) to name but

a few examples. Unfortunately, these objects are often difficult to locate and identify since humus

and moss have covered and camouflaged them in the course of decades and even centuries.

Image 10. A World War II tank barrier in

Eastern Finland. All trees have been

removed from the object in conjunction

to final felling, to preserve the historic

values of the site. Soil preparation or

stump lifting is not recommended. Photo

by Martti Kuusinen.


10

Basic instruction for these sites:

- Soil preparation or stump lifting should not be carried out on or close to objects valuable to

cultural heritage. In the case of an object is identified as a result of a harvesting operation, it

should be excluded from the harvesting site.

- Sites should not be crossed with machinery.

- To maintain the historical values of the sites, it is in some cases justifiable to remove all

growing trees. Often roots of trees in the long run cause the most harm to sites below the

surface.

Action 5.2. Harvesting sites with special recreational values or landscape values are felled

with specific instructions and planning.

Thinning is a good way to preserve recreational values of overgrown woodlands with high stand

densities. The conditions for wild berry and mushroom picking, mountain biking and horse riding,

hiking and hunting are improved significantly.

Clear felling is often a dramatic change in the landscape. Stump lifting operations and woodfuel

stacks are a minor inconvenience by comparision, but they should however be considered and

planned carefully in locations where recreational use is previalent.

Principle 6: Climate change mitigation should be a prime consideration in all

woodfuel harvesting operations

Action 6.1. Woodfuel harvesting should not reduce the carbon sinks of the harvested

stands.

Efficient regeneration is one of the main measures to maintain and enhance carbon sinks in

forests. Woodfuel harvesting should not cause delays in the regeneration on the harvesting sites.

Logging residues and stumps should be harvested as quickly as possible after the timber

harvesting, allow for seasoning on the site of harvestable residues.

Principle 2 (Woodfuel harvesting should not substantially diminish growth potential of harvesting

sites) can respectively be seen as an objective to avoid reductions in carbon accumulation to the

stand (see Action 2.1).

Action 6.2. The carbon storage in the forest soils should be preserved.

Harvesting round wood or woodfuel causes a reduction in the carbon storage of the site, if

compared to the the biomass is being left on the site and it decomposes gradually. This however,

is temporary since most of the carbon accumulated by the wood would be released to the

atmosphere in the long run. Nevertheless, it is possible to minimize the negative impact with the

following measures:

- Harvesting woodfuel with small diameter (branches, coppice) causes a short term reduction to

the carbon stock of the site. Therefore, they should be preferred harvested material.

- A proportion of the biomass is recommended to be left on the site, with coarse woody

particles (such as stumps and stem wood logs) are preferential since they form a long lasting

carbon storage on the site.


11

- Disturbances in the soil enhance carbon emissions. Soil preparation methods should be chosen

deliberately and any unnecessary disturbances in the soil should be avoided (Action 4.3).

- Soils with massive carbon storages, such as peatlands, should be operated with special

caution. Different types of soils react to measures such as drainage and harvesting in different

ways in relation to green house gas emissions, and management planning needs to consider

this.

Years after harvesting

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60 70 80 90 100

Car

bo

n d

ioxi

de

emis

sio

ns

[kg

CO

2/M

Wh

]

Coal

Natural gas

Heating oil

Spruce stump(diameter 26 cm)

Spruce branch(diameter 2 cm)

Image 11. Retained in the forest, decomposing branches and stumps form a gradually diminishing

stock of carbon in the soil. As a result of woodfuel harvesting and combustion, this carbon stock is

rapidly returned to the atmosphere. Woodfuel can thus be determined to create CO2 emission in

the soil. Since the decomposing of a stump is a much longer lasting process compared to that of

branches, the carbon stock that branches form is not as long lasting and consequently the CO2

emission rate of stumps is higher. The graph describes the emissions throughout the entire life

cycles of different energy sources (Repo et al. 2010)

Action 6.3. Carbon efficiency is maximized throughout the whole procurement chain.

Woodfuel harvesting chains normally emit relatively small amounts of green house gases

compared to the energy content of the fuel they produce. It has been estimated that in Northern

European circumstances the usage of fossil fuels throughout the whole logging residue

procurement chain corresponds to no more than 2-3 percent of the energy content of the wood

chips produced.

Carbon efficiency can be maximized in the harvesting process by using efficient harvesting

practices and modern technology. For example:

- Sites with high harvesting productivity (MWh/h) are preferred.

- Transportation of water is minimized i.e. woodfuel is seasoned prior to road transportation.

- Harvesting sites close to the plants are preferred.

- Old and worn-out machines are replaced with up-to-date ones.


12

Protracted storage of wood chips with high moisture content has in some studies caused massive

outputs of methane, which is a 20 times more effective green house gas as carbon dioxide. Thus,

woodfuel storages of high moisture content should be reduced primarily and chipping as required

for combustion.

Action 6.4. The energy content of the woodfuel should be maximized throughout the

whole procurement chain.

The optimisation of fuel quality is critical question not only for the pricing and competitiveness of

the fuel, but also from the tackling of climate change. The quality of the woodfuel is poor, the

operating efficiency of the whole chain in terms of GHG balance can turn to negative. Woodfuel

quality optimisation and storage practices are described in detail under Principle 7.

Principle 7: Quality and energy content of woodfuel should be maximized

throughout the whole procurement chain.

Action 7.1. Woodfuel is seasoned and stored properly

Unlike pulpwood and saw timber, the quality of woodfuel improves through seasoning. It is

recommendable to leave the cut woodfuel drying on the site for a few spring or summer weeks

before hauling to the road side storage. Overall, it is recommended that woodfuel is seasoned at

least for four months before combustion, except for hard wood, which requires at least six

months’ seasoning period. The time of the year and the humidity are the most essential factors

influencing required length of the seasoning. As the moisture content has decreased to proper

level ( 20-25 percent), the challenge is to maintain it until the heating season.

There are some basic principles for choosing the optimal place for a woodfuel storage in road

sides, mostly to maximize the drying of the fuel:

- The site is windy and open to sunshine.

- There are no overhead lines hindering the loading/unloading.

- The woodfuel is easily loaded to a truck or fed into a chipper with a vehicle crane. Roading,

infrastructure, weight limits and access are all taken into account.

- There should not be any loose rocks or other objects harmful to chipping operations

underneath the stored / processed fuel.

- Storage consisting of nutrient rich particles, such as needles, should not be placed close to

waterfronts or on top of ditches, in order to avoid nutrient contamination.


13

Image 12. A proper wood fuel storage has

1) a cover made of fibre or plastic; 2) base

construction to create an airspace between

the storage and the ground; 3) a peak to

avoid rain pouring in from the front side,

and 4) adequate height (4-5 metres).

(Photo by Tanja Lepistö)

A good storage possesses the following characteristics:

- The top of any storage is covered. However, only dried woodfuel should be covered. Covering

wet, fresh woodfuel traps moisture and hinders drying, usless using a one-way porous

membrane.

- The bottom of the storage is separated from the ground with a base construction (e.g. stems)

to prevent the soil moisture shifting to the storage. There should be an airspace between the

ground and the bottom of the storage.

- The storage is as high as possible, yet steady. The higher it is, the less it gathers rain water.

For the safety, the height should not exceed 5 metres.

- The cut end or ‘feet’ of the stems are oriented southward for maximum sun radiation

absorption.

Image 13. Covering reduces the moisture content of the logging residue pile during the heating

season significantly, even if it is done with a fibre cover with the width of four metres placed in

the middle of the pile (as in image 12). (Hillebrand&Nurmi 2001)

0

10

20

30

40

50

60

May June July August October January

Mo

istu

re c

on

ten

t, %

Uncovered

Covered

Felling

Hauling


14

Action 7.2 Impurities amongst woodfuel are minimized

Impurities, such as metal objects, rocks or frozen soil blocks may cause severe damages to the

chipping machinery and thus reduce the competitiveness of woodfuel as an energy source.

Experience shows that most often these objects get into a woodfuel pile as a result of careless

storage place selection. Hence, storage sites should always be empty of rocks and waste materials

and there should be some sort of base construction separating woodfuel from the ground (see

image x).

Soil particles are a challenge especially in stump harvesting, although crushing machinery is not as

vulnerable to rough substances as chippers . Excessive soil contamination causes problems in the

combustion process. The smaller the particle size of the soil is, the more difficult it is to separate it

from the stump and root particles. The stump blocks should be shaken well during the lifting. In

addition, the stumps should be left on the harvesting site for a few weeks so that environmental

conditions can remove as much soil as possible.

Images 14 and 15. The overall target of woodfuel harvesting is to produce high-quality raw

material for further processing. Rocks and other impurities cause damages and delays in the later

phases of the production chain and reduce the efficiency in general. Crushers (image 14) are not as

vulnerable as chippers (image 15). Photos by Martti Kuusinen.


15

1. References

Helmisaari, H.-S., Finér, L., Kukkola, M., Lindroos, A.-J., Luiro, J., Piirainen, S., Saarsalmi, A.,

Smolander, A. & Tamminen, P. 2008. Energiapuun korjuu ja metsän ravinnetase. Julkaisussa:

Kuusinen, M. & Ilvesniemi, H. (toim.). Energiapuun korjun ympäristövaikutukset, tutkimusraportti.

Tapion ja Metlan julkaisuja (Available at www.metsavastaa.net/energiapuu/raportti). s. 18-29.

Äijälä, O., Kuusinen, M. & Koistinen, A. (toim.) 2010. Hyvän metsänhoidon suositukset

energiapuun korjuuseen ja kasvatukseen. Metsätalouden kehittämiskeskus Tapion julkaisuja.

National Board of Waters, Finland, 1986. Planning of land drainage, Part 1. Report 278.

Repo, A., Tuomi, M. and Liski, J. 2010. Indirect carbon dioxide emissions from producing bioenergy

from forest harvest residues. GCB Bioenergy, doi:10.1111/j.1757-1707.2010.01065.

Hillebrand, K. & Nurmi, J. 2001. Hakkuutähteen laadunhallinta. Julkaisussa: Alakangas, E. (toim.).

Puuenergian teknologiaohjelman vuosikirja 2001. Puuenergian teknologiaohjelman

vuosiseminaari, Jyväskylä, 5.-6.9.2001. VTT Symposium 216: 285-295

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