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Methodology and definitions



General remarks

Within, the work of the forest resources assessment is currently being shared between the former FAO/ECE Agriculture and Timber Division, Geneva, which covers the developed countries; and the Forest Resources Division at FAO headquarters, Rome, which is responsible for the developing countries.

Terms and definitions for the Forest Resource Assessment 1990 ,

Developed countries

Forest Land: with tree crown cover (stand density) of more than about 20% of the area. Continuous forest with trees usually growing more than about 7m in height and able to produce wood. This includes both closed forest formulations where trees of various storeys and undergrowth cover a high proportion of the ground and open forest formulations with a continuous grass layer in which tree synusia cover at least 10% of the ground.

Other wooded land: Land which has some forestry characteristics but is not forest as defined above. It includes: open woodland and scrub, shrub and brushland (see below), whether or not used for pasture or range. It excludes land occupied by “Trees outside the forest” (see below).

Exploitable: Forest on which there are no legal, economic or technical restrictions on wood production. It includes areas where, although there are no such restrictions, harvesting is not currently taking place, for example, areas included in long-term utilization plans or intentions.

Unexploitable: Forest and other wooded land on which there are legal, economic or technical restrictions on wood production. It includes (a) forest and other wooded land with severe legal restrictions on wood production, e.g. national parks, nature reserves and other protected area such as those of special scientific, historical or cultural interest; (b) forest and other wooded land where physical productivity is too low or harvesting and transportation costs to the nearest market are too high to warrant wood harvesting, apart from occasional possible cuttings for auto-consumption.

Stocked (forest): Forest with existing tree crown cover (stand density) of more than about 20% of the area; also forest nurseries and seed orchards.

Unstocked (forest): Forest on which tree crown cover (stand density) has been reduced to less than 20% or has been removed as a result of human intervention or natural causes, e.g. by felling or burning, but which is expected to revert to stocked forest.

Scrub, shrub and brushland: Land with scrub, shrub or stunted trees where the main woody elements are shrubs (usually more than 50 cm and less than 7 m in height), covering more than about 20% of the area, not primarily used for agricultural or other non-forestry purposes, such as grazing of domestic animals. “Trees outside the forest” are excluded.

Under active management: Forest and other wooded land that is managed according to a professionally prepared plan or is otherwise under a recognized form of management applied regularly over a long period (five years or more).

Net change: The net difference over given period between increase in area of forest and other wooded land from afforestation and natural extension and loss of such land to other uses.

Growing stock: The living part of the standing volume.

Forest Resources Assessment 1990 of the developing countries

Forests are ecological systems with a minimum crown coverage of land surface (here assumed as 10 percent) and generally associated with wild flora, fauna and natural soil conditions; and not subject to agronomic practices. For the present assessments, a tree is defined as a woody perennial with a single main stem (except in coppice crops where multiple stems replace a single stem), a more or less definite crown and a minimum height of more than 5 meters on maturity. Only forest areas more than 100 ha (minimum area) are considered.

Forests are further subdivided according to their origin into two categories:

i) Natural forests are a subset of forests composed of tree species known to be indigenous to the area.

ii) Plantation forests refer to:

a) Forests established artificially by afforestation on lands which previously did not carry forest within living memory.

b) Forests established artificially by reforestation of land which carried forest before and involving the replacement of the indigenous species by a new and essentially different species or genetic variety.

Other wooded land includes the following two categories:

i) Forest fallow refers to all complexes of woody vegetation deriving from the clearing of natural forest for shifting agriculture. It consists of a mosaic of various succession phases and includes patches of uncleared forests and agriculture fields which cannot be realistically segregated and accounted for areawise, especially from satellite imagery. Forest fallow is an intermediate class between forest and nonforest land uses. Part of the area which is not under cultivation may have appearance of a secondary forest. Even the part currently under cultivation sometimes has appearance of forest, due to presence of tree cover. Accurate separation between forest and forest fallow may not always be possible.

ii) Shrubs refer to vegetation types where the dominant woody elements are shrubs with more than 50 cm and less than 5 meters height on maturity. The height limits for trees and shrubs should be interpreted with flexibility, particularly where the minimum tree and maximum shrub heights, which may vary between 5 and 7 meters approximately.

Other Land Use account for the balance of the land area. Since total land will, to the degree possible, be reported by the main land use classes from the FAO Production Yearbook, agricultural and other land classes need to be accounted for, giving a total class set as follows:

i) Arable land

ii) Land under permanent crops

iii) Permanent meadows and pastures

iv) Forests and wooded lands

v) Other land

The ecological regions are defined with the help of ecological parameters: climate, physiography, and soils. The climatic parameters include mean annual rainfall, rainfall regime, length of the dry season, relative humidity and temperature.

Ecofloristic zones are further sub-division of ecological regions based on the dominant or characteristic woody species of the flora, with attention given to their successional position and the leaf-retining characteristics of the forest canopy (i.e. phenology). For each ecofloristic zone it is possible to define the corresponding climax vegetation formation.

The classification of vegetation formations is based mainly on physiognomic criteria which can be seen in field and remote sensing documents, such as density, continuity of plant cover, height, etc. The denomination of the formations (e.g. dense forests, secondary forests, woodlands, thickets, savannas, etc.) is derived from the classification of Yangambi (1956) and of UNESCO (1973). The vegetation formations are further subdivided on the basis of density, ranging from the woody types that are the most closed, to the types that are the most open. This reflects the different stages of the regressive series or, in very rare cases, the evolutionary tendency of the vegetation within a zone. Dominant forest formations by ecological zone are distinguished as follows.

Volumes are defined using one of the following specifications:

VOB Gross “Volume Over Bark” of free bole (from stump or buttresses to crown point or first main branch) of all living trees of all species more than 10 cm diameter at breast height (or above buttresses if these are higher). “Volume over bark” is generally used in the tropics as opposed to “Volume inside bark” because there are no volume tables that account for bark thickness.

Biomass is the oven dry weight of all species of trees to a minimum dbh of 10 cm, above ground only, and includes main stems, branches, twigs, leaves and fruits. Different procedures in estimating biomass will be followed for the different vegetation types.

Deforestation is defined in the strict sense of complete clearing of tree formations (closed or open) and their replacement by nonforest land uses (alienation).

Deforestation refers to “change of land use from forest to other land use or depletion of forest crown cover to less than 10 per cent”. Changes within the forest class which negatively affect the stand or site and, in particular, lower the production capacity, are termed forest degradation. Thus degradation is not reflected in the estimates of deforestation. In the case of degradation of forests in developed countries, information on forest damage and threats to the forest ecosystems of the industrialized countries are collected regularly under other programmes of the Joint FAO/ECE Agriculture and Timber Division (e.g. forest fire statistics, monitoring of forest dieback).

Forest Degradation takes different forms, particularly in open formations, derived mainly from human activities such as overgrazing, overexploitation (for fuelwood in particular), repeated fires, or due to attacks by insects, diseases, plant parasites or other natural sources such as cyclones. In most cases forest degradation does not show up so much as a decrease in the area of woody vegetation but rather as a gradual reduction of biomass, changes in species composition and soil degradation. The logging of forests for sawlogs and veneer logs without a proper management plan can contribute to forest degradation if the extraction of mature trees is not accompanied with their regeneration or if the use of heavy machinery causes soil compaction or loss of productive forest area.

Definitions used in relation to protected areas

All protected areas combine natural areas in five World Conservation Union, formerly the International Union for Conservation of Nature and Natural Resources (IUCN), management categories (areas at least 1 000 hectares).

Totally protected areas are maintained in a natural state and are closed to extractive uses. They encompass the following three management categories:

Category I. Scientific reserves and strict nature reserves possess outstanding, representative ecosystems. Public access is generally limited, with only scientific research and educational use permitted.

Category II. National parks and provincial parks are relatively large areas of national or international significance not materially altered by humans. Visitors may use them for recreation and study.

Category III. Natural monuments and natural landmarks contain unique geological formations, special animals or plants, or unusual habitats.

Partially protected areas are areas that may be managed for specific uses, such as recreation or tourism, or areas that provide optimum conditions for certain species or communities of wildlife.

Some extractive use within these areas is allowed. They encompass two management categories:

Category IV. Managed nature reserves and wildlife sanctuaries are protected for specific purposes, such as conservation of a significant plant or animal species.

Category V. Protected landscapes and sea-scapes may be entirely natural or may include cultural landscapes (e.g. scenically attractive agricultural areas).

Definitions used in relation to wood production

Fuelwood and charcoal

Wood in the rough (from trunks, and branches of trees) to be used as fuel for purposes such as cooking, heating or power production. Wood for charcoal, pit kilns and portable ovens is included. The figure for trade in charcoal are given in weight.

Industrial roundwood

The commodities included are sawlogs and veneer logs, pulpwood, other industrial roundwood and, in the case of trade, chips and particles and wood residues.Definitions used in

remote sensing survey

Brief definition of the land cover classes used in the pan-tropical survey of forest resources based on high resolution satellite data.

Other specifications:

Scale: the scale of the interpreted satellite images is 1 : 250 000.

Minimum mapping unit = 3 x 3 mm, approximately 50 ha, or 2mm width for linear features.

A forest class is considered continuous or non fragmented when the non-forest elements (below minimum mapping unit) present in it are less than 30 % of the class.

A forest class is considered fragmented when the non-forest elements (below minimum mapping unit) present in it are more than 30 % of the class and the forest fraction is between 10 and 70 %.

The composite classes (Fragmented Forest, Long Fallow, Short Fallow) are used where individual elements are below minimum mapping unit (< 3 x 3 mm).