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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
Recommendations for Sustainable Wood Fuel Harvesting
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
Recommendations for Sustainable Wood Fuel Harvesting
3
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.
Recommendations for Sustainable Wood Fuel 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).
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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
Recommendations for Sustainable Wood Fuel Harvesting
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)
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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
Recommendations for Sustainable Wood Fuel Harvesting
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.
Recommendations for Sustainable Wood Fuel Harvesting
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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