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Estimating Woody Biofuel Supply
Ademe Woody Biofuel / Glossary & Coefficients / Glossary
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Glossary & Coefficients




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A single or double line of trees planted at regular intervals, at least 25 m in length, with an average crown width of less than 20 m. The regular spacing of the trees (more than 1 m apart) and their similar diametre distinguish alignments from hedgerows.

This is the quantity of wood that can be harvested in the future if sustainable management practices are applied. A given availability corresponds to the harvestable volume as a function of (1) the initial age and diametre class of the stand and (2) the type of silvicultural treatment. The notions of resource and availability are complementary but of a different nature: resource is static (supply) whereas availability is dynamic (flow).

Availability (global)
"Global" availability usually corresponds to a maximum volume since this notion does not include - or rarely includes - the technical, environmental, social and economic constraints that limit harvestability. For example, global availability is independent of the local wood transformation context which may fluctuate for structural and conjectural reasons.

Availability (technical and economic)
This is the remaining availablility once technical constraints (loss during harvest), environmental constraints (maintaining soil fertility) and economic constraints (harvesting costs) have been taken into account.

Availability (additional)
This refers to the available supply that is not currently being marketed. The figure can be positive (in this case, an additional volume of wood is potentially available for harvest) or negative (in this case, harvesting levels are above biological increment for the period under consideration).

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The biomass of a single specimen, a population or an ecosystem is the mass of living matter it contains.
Directive EnR 2001/77/CE relative to the promotion of electricity produced from renewable energy gives the following definition: the biodegradable portion of products, waste and residue originating from agricultural activites (including plant and animal material), silvicultural activities and related industries, and industrial and municipal waste.

Biomass Compartments
The available wood supply has been divided into three general categories (or compartments) of potential use defined by the dimension (diametre) and physical characteristics (quality) of the wood:

1. Potential use - Construction-Quality Wood (CW): This category corresponds to all the woody biomass contained in the stem (sawlogs) with a minimum small-end diametre defined according to species and region (minimum commercial cut size) and of sufficient quality to provide sawn timber or peelers.

2. Potential use - Industrial Roundwood and Woody Biofuel (IRWB): This category is defined as a combination of three componants: (1) all the biomass in other stem logs between the minimum diametre for construction-quality wood and the minimum diametre for roundwood at 7 cm, (2) biomass from stems in the construction wood diametre class but whose low quality precludes its use as construction wood, (3) biomass from large branches of more than 7 cm in diametre at the small end. This category includes wood of more than 7 cm at the small end suitable for industrial transformation (panel products, pallets, fencing) and for energy production (firewood, chips, pellets).

3. Small Branchwood (SBW): This category is defined as all the biomass contained in the stem and branchwood with a large-end diametre of less than 7 cm (crown and small branches). This category could also be termed wood with a large-end diametre of less than 7 cm suitable for energy production (chips, pellets).

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The crown refers to the aerial parts of the tree excluding the main stem and including the tree top, branches and twigs. In this study, foliage is not included in the crown.

Construction Wood (CW)
For the definition retained in this study, see " Biomass Compartments".

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In this study, a forest is defined as an area of more than 0.05 ha with trees capable of reaching a height of more than 5 m at maturity in situ, a forest cover of more than 10% and a width of at least 20 m. The definition here includes small wooded plots or clumps of trees (surface area between 0.05 and 0.5 ha) and excludes poplar plantations. It differs from the FAO definition (a surface area of more than 0.5 ha including poplar plantations) due to the important role played by small wooded plots for firewood production.

Forest (production)
A forest where wood production is either the main or secondary priority - in other words where harvesting wood is feasible (without considering profitability) and compatible with other possible roles (social, environmental, etc.).

Forest (other)
A forest where wood production is non existant or very limited. This category includes forests that are inaccessible, protection forests where felling is prohibited, and/or wooded parks with a landscape, recreational or cultural role.

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Harvesting feasibility
Physical feasability of harvesting for a given stand is evaluated based on four types of IFN field observations: slope, terrain, skidding distance and presence or absence of access tracks. The four difficulty classes used in the study are explained below.

A hedgerow is a line of woody vegetation with a crown width of less than 20 m and a length of at least 25 m which contains at least 3 forest trees big enough to be included in the survey and at least one such tree every 10 m on average. Below these thresholds, the structure would be included in the "isolated tree" category.

Heathland and Scrubland
A heathland is defined as an area of more than 0.05 ha with a width of over 20 m. Heathland is not cultivated and vegetation may or may not be woody. A maximum of 10% of the area may be covered with vegetation; beyond this level, the area is classified as open forest. In this study, heathland includes alpine grasslands, Corsican scrub or maquis, Mediterranean limestone heathlands or garrigues, fallow land and vacant lots.

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Industrial Roundwood and Woody Biofuels (IRWB)
For the definition retained in this study, see " Biomass Compartments".

Isolated tree (or field tree)
This term refers to individual specimens or small groups of forest trees whose crown area is less than 0.05 ha.

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Poplar Plantations
Poplar plantations are wooded areas of more than 0.05 ha where the total canopy cover is more than 10%. The relative percentage of poplars must be more than 75%. In this study, poplar plantations have been treated separately.

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The resource is the quantity of wood that exists in a given zone at a given date. The forest resource is measured by the National Forest Inventory (Inventaire forestier national or IFN).

Roundwood is the woody material produced in the part of the tree (stem and branches) with a small-end diameter of more than 7 cm. In many cases, the roundwood cut corresponds to the maximum amount of wood harvested by logging companies.

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Small Branchwood (SBW)
For the definition retained in this study, see " Biomass Compartments" above.

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A tree is a large woody plant with a naked stem which does not branch at the base, with a height equal to or greater than 5 metres or potential to reach such a height at maturity.

The trunk, which foresters usually call the "stem", includes:
  • A butt length which extends from the base of the tree up to a small-end diametre of around 20 cm for broadleaves and 15 cm for conifers. The butt log is free of branches and is often the highest quality part of the tree with the highest market value;
  • Second and third quality lengths extend beyond the butt length to a small-end diametre of 7 cm called the "roundwood threshold diametre". The volume of the stem from the base of the tree to the roundwood threshold diametre is called the "stem roundwood volume". This is the volume measured by the IFN.

Total above-ground volume
The total above-ground volume corresponds to all the woody parts of the tree above the ground level (from the base of the trunk to twig tips).

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Urban resource
In this study, the "urban" resource refers to woody resources located in urban areas. This includes urban alignment trees and trees found in parks, public and private gardens, city squares and car parks.

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The volume of a tree as defined by the IFN is the geometric overbark volume of the stem below the roundwood cut line at 7 cm in diametre. Most of the crown is excluded from the IFN volume. Mesurements are taken 1.30 cm from the ground on trees with a diametre of at least 7.5 cm.

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