| |
about woodfuel
General Comments
This study covers all ownerships, i.e. public forest managed by the Forestry
Commission on behalf of the government; forest managed by other government
departments, such as the Department of Defence, and non-governmental organisations;
and privately owned woodland.
Estimates of current resource are based on the most recent information.
In addition the potential resource from forests and woodlands is forecast
into the future using well established procedures to estimate production
based on knowledge of the existing types of forests, their growth rates,
and expected felling age. The available resource is not forecast into
the future for sawmill co-products, arboricultural arisings or SRC.
This study estimates operationally available resource, i.e. the quantity
that it would be possible to make available at roadside. It does not take
economic feasibility into account, for example it does not exclude resource
on the basis that it might be too expensive. Judgements about economic
feasibility are the potential developers’ responsibility. Moreover
the decision is likely to change through time depending on a host of factors,
in particular financial support structures and incentives, transportation
costs, harvesting costs, timber prices, and prices of competing co-product
markets. The effect of recycling is especially difficult to predict. Our
approach has been to provide a sound and consistent basis for estimates
of the resource available at roadside in a way that facilitates decisions
on woodfuel developments.
The scope of this study included the following sources of woodfuel:
Forests and woodlands.
This includes:
- harvesting brash. In this study we define these as the tops of
the stems and side branches, often called ‘lop and top’.
In forestry the term ‘harvesting brash’ has a slightly
wider meaning, i.e. all the parts of the tree left after the saleable,
better quality stem material has been removed; it would include forked
stems and ‘butt reducings’
- precommercial thinnings, i.e whole trees that are too small to justify
the cost of extraction for existing markets
- small roundwood, i.e. small stems cleaned of side branches with a
top diameter greater than 7cm
- poor quality final crops. Though large enough to be used for timber
these are of such poor form that they are normally left on site or they
may currently be cut for firewood
- traditional coppice. Certain species, in particular hazel and sweet
chestnut, can regenerate new stems from the base following harvesting
of the previous stems. These are occasionally grown on their own but
are traditionally grown along with single stemmed trees of high timber
value.
- This study did not include an estimate for standing deadwood (or
harvesting residuals), i.e. trees that have died due to excessive shading
by their neighbouring trees, drought, or disease. A few standing dead
trees may be left to provide wildlife habitats but most are normally
felled along with the living trees. They are currently not extracted
since the timber is not suitable for present markets but standing deadwood
does represent a potential woodfuel resource especially as the moisture
content is lower than for living trees. Although the number and volume
of trees that have died in any previous 5 year period can be estimated,
it was not possible in the time available to estimate the accumulated
mass over the crop’s life any the decrease in mass and energy
content through degradation and decomposition.
Back to top
Primary processing co-products
from, for example, sawmills.
Approximately 50% of the volume of stem wood that is sold to sawmills
can be converted into timber in the form of planks, batons etc, and the
remainder (co-product), which can include bark, chips, and sawdust, is
normally sold for a variety of different purposes such as paper and panelboards.
This study did not include co-products from secondary processing, nor
did it include post-consumer waste. This study does not include any form
of recycled or waste wood. Parallel studies are attempting to quantify
these resources.
Back to top
Arboricultural arisings.
Urban areas and transport corridors such as roads and railways. The products
of fellings, thinnings and prunings of trees in these areas (‘arboricultural
arisings’), are generally left on site in the form of chippings
or removed to land fill sites. A small proportion is currently used for
energy end markets.
Back to top
Short rotation coppice.
In these systems, cuttings are planted at close spacing, normally on good
quality ground, cut back after one year to encourage the generation of
multiple stems form the base. These new stems are cut in 2-4years depending
on growth rate; this cycle can be repeated many times until the base and
root system being to loose vigour or more productive varieties justify
replacement.
Back to top |
|
