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Background to Forest Mapping & Data Harmonisation

© 1999 Topham Picturepoint / UNEP / Michael SchneiderUNEP-WCMC has been gathering and compiling spatial data on the extent and conservation status of forests since 1987. Until 1995, WCMC's work focused on tropical moist forests because of their high species diversity. GIS data were first assembled for closed moist tropical forests and used to publish the three volumes of the Conservation Atlas of Tropical Forests, covering Asia (1991), Africa (1992) and the Americas (1996). Because digital data were rare at this time, the process of assembling the forest cover data sets involved digitising manually many paper maps.

Continuing on from the tropical moist forest mapping, the next major initiative was to create the first 'World Forest Map'. This was produced in 1996 and was the first digital global forest map showing actual forest extent and protected areas with forested land. Since this achievement, significant work has been carried out to improve data sources and fill in gaps which occurred in this first attempt. This led to the production of the Global Overview of Forest Conservation CD-ROM in 1997.


Analysis and modelling
The forest programme uses GIS for high level analysis and modelling of related datasets, adding value to existing datasets and creating new ones. For example, UNEP-WCMC is the first to attempt to define and map global mountains and mountain forests. The forest programme also produces a regular update of global forest protection, whereby digital information for forests and protected areas are used to estimate the amount of each major forest type in the world under protection.

Data harmonisation
UNEP-WCMC acts as a custodian of many datasets. For forests, this means gathering in datasets either in digital form from other organisations, or digitizing from paper maps in-house. Datasets are usually from national or regional sources and are subsequently combined to form the global UNEP-WCMC forest map. This involves the complex issue of harmonising the different classifications of the original source data into UNEP-WCMC's global classification. The data vary in scale, from 1:50,000 to 1:1,000,000 or from satellite data from 250m to 1km resolutions. UNEP-WCMC tries to incorporate the most accurate and up-to-date data as possible. The advantage of using this methodology is that it enables a more detailed analysis and comparison of biodiversity related data at sub-national, national, regional and global levels. This is often not possible with other global datasets that are created, for example, from satellite imagery, which generally are at a lower resolution e.g. 1km.

© 1999 Topham Picturepoint / UNEP1UNEP-WCMC's forest category classification system is a simplification of other more complex systems (e.g. UNESCO's forest and woodland 'subformations'), which still retains a certain amount of basic information on forest physiognomy and phenology. This system divides the world's forest into 26 major types, which reflect climatic zones as well as the principal types of trees. Of course each of these major types comprises a great range of forests. These 26 major types can be reclassified into 6 broader categories.



Temperate and Boreal / Tropical Forests

The split between "tropical" and "temperate and boreal " forests can most simply be made by including all those forests that are located between the tropics of cancer and capricorn in the tropical category, and assigning all other forests as "temperate and boreal".



Temperate needleleaf forests cover a larger area of the world than any other forest types. They mostly occupy the higher latitude regions of the northern hemisphere, as well as high altitude zones and some warm temperate areas, especially on nutrient-poor or otherwise unfavourable soils. These forests are composed entirely, or nearly so, of coniferous species (Coniferophyta). In the Northern Hemisphere pines Pinus, spruces Picea, larches Larix, silver firs Abies, Douglas firs Pseudotsuga and hemlocks Tsuga, make up the canopy, but other taxa are also important. In the southern hemisphere most coniferous trees, members of the Araucariaceae and Podocarpaceae, occur in mixtures with broadleaf species that are classed as broadleaf and mixed forests.

Temperate broadleaf and mixed forests, which include a substantial component of trees in the Anthophyta, cover over 6.5 million km2 of the Earth's surface. They are generally characteristic of the warmer temperate latitudes, but extend to cool temperate ones, particularly in the southern hemisphere. They include such forest types as the mixed deciduous forests of the USA and their counterparts in China and Japan, the broadleaf evergreen rain forests of Japan, Chile and Tasmania, the sclerophyllous forests of Australia, the Mediterranean and California, and the southern beech Nothofagus forests of Chile and New Zealand.

Tropical moist forests cover more than 11 million km2 of the humid tropics and include many different forest types. The best known and most extensive are the lowland evergreen broadleaf rainforests, which make up over half this area and include, for example: the seasonally inundated varzea and igap� forests and the terra firme forests of the Amazon Basin; the peat forests and moist dipterocarp forests of Southeast Asia; and the high forests of the Congo Basin. The forests of tropical mountains are also included in this broad category, generally divided into upper and lower montane formations on the basis of their physiognomy, which varies with altitude. The montane forests include cloud forest, those forests at middle to high altitude, which derive a significant part of their water budget from cloud, and support a rich abundance of vascular and nonvascular epiphytes. Mangrove forests also fall within this broad category, as do most of the tropical coniferous forests of Central America.

Tropical dry forests are characteristic of areas in the tropics affected by seasonal drought. Such seasonal climates characterise much of the tropics, but less than 4 million km2 of tropical dry forests remain. The seasonality of rainfall is usually reflected in the deciduousness of the forest canopy, with most trees being leafless for several months of the year. However, under some conditions, e.g. less fertile soils or less predictable drought regimes, the proportion of evergreen species increases and the forests are characterised as "sclerophyllous". Thorn forest, a dense forest of low stature with a high frequency of thorny or spiny species, is found where drought is prolonged, and especially where grazing animals are plentiful. On very poor soils, and especially where fire is a recurrent phenomenon, woody savannas develop (see 'sparse trees and parkland').

Sparse trees and parkland are forests with open canopies of 10-30% crown cover. They occur principally in areas of transition from forested to non-forested landscapes. The two major zones in which these ecosystems occur are in the boreal region and in the seasonally dry tropics. At high latitudes, north of the main zone of boreal forest or taiga, growing conditions are not adequate to maintain a continuous closed forest cover, so tree cover is both sparse and discontinuous. This vegetation is variously called open taiga, open lichen woodland, and forest tundra. It is species-poor, has high bryophyte cover, and is frequently affected by fire.

Forest plantations, generally intended for the production of timber and pulpwood increase the total area of forest worldwide. In 1999 FAO has estimated that total plantation area in developed countries is about 600,000 km2 and in developing countries it is about 550,000 km2. Commonly mono-specific and/or composed of introduced tree species, these ecosystems are not generally important as habitat for native biodiversity. However, they can be managed in ways that enhance their biodiversity protection functions and they are important providers of ecosystem services such as maintaining nutrient capital, protecting watersheds and soil structure as well as storing carbon. They may also play an important role in alleviating pressure on natural forests for timber and fuelwood production.


UNEP-WCMC's harmonised general forest classification consists of 15 different tropical forest types and 11 temperate and boreal forest types. This classification reflects characteristics of forests that can be of conservation importance. For example, whether the forest is tropical, temperate or boreal, whether it is a plantation of exotic species, or whether it is a degraded natural forest type. Not wishing to exclude much of the important areas that support trees which are sparsely distributed, a category for sparse trees and parkland was included. This agrees with the definition of "forest" used by FAO in their Forest Resources Assessments. Apart from this criterion for the limits of tree cover for "forest" (canopy cover between 10-30%) there was no particular height limit used, just that the trees had to be mainly phanerophytes (single-trunked individuals, as most trees) and not chamaephytes (multi-stemmed individuals, as most shrubs).

These 26 forest categories (defined below) are used to enable the translation of forest types from national and regional classification systems to a harmonised global one. (Please note that categories 12 and 13 have been created as a result of data holdings which do not specify the forest type, hence 26 categories are quoted, not 28).

Temperate and boreal forest types


Natural forest with > 30% canopy cover, in which the canopy is predominantly (> 75%) needleleaf and evergreen.
Natural forests with > 30% canopy cover, in which the canopy is predominantly (> 75%) needleleaf and deciduous.
Natural forest with > 30% canopy cover, in which the canopy is composed of a more or less even mixture of needleleaf and broadleaf crowns (between 50:50% and 25:75%).
Natural forests with > 30% canopy cover, the canopy being > 75% evergreen and broadleaf.
Natural forests with > 30% canopy cover, in which > 75% of the canopy is deciduous and broadleaves predominate (> 75% of canopy cover).
Natural forests with > 30% canopy cover, composed of trees with any mixture of leaf type and seasonality, but in which the predominant environmental characteristic is a waterlogged soil.
Natural forest with > 30% canopy cover, in which the canopy is mainly composed of sclerophyllous broadleaves and is > 75% evergreen.
Any forest type above that has in its interior significant areas of disturbance by people, including clearing, felling for wood extraction, anthropogenic fires, road construction, etc.
Natural forests in which the tree canopy cover is between 10-30%, such as in the steppe regions of the world. Trees of any type (e.g., needleleaf, broadleaf, palms).
Intensively managed forests with > 30% canopy cover, which have been planted by people with species not naturally occurring in that country.
Intensively managed forests with > 30% canopy cover, which have been planted by people with species that occur naturally in that country.
Forest plantations showing extent only with no further information about their type, This data currently only refers to the Ukraine.
Forest data showing forest extent only with no further information about their type.


Tropical forest types

Natural forests with > 30% canopy cover, below 1200m altitude that display little or no seasonality, the canopy being >75% evergreen broadleaf.
Natural forests with > 30% canopy cover, between 1200-1800m altitude, with any seasonality regime and leaf type mixture.
Natural forests with > 30% canopy cover, above 1800m altitude, with any seasonality regime and leaf type mixture.
Natural forests with > 30% canopy cover, below 1200m altitude, composed of trees with any mixture of leaf type and seasonality, but in which the predominant environmental characteristic is a waterlogged soil.
Natural forests with > 30% canopy cover, below 1200m altitude in which between 50-75% of the canopy is evergreen, > 75% are broadleaves, and the trees display seasonality of flowering and fruiting.
Natural forests with > 30% canopy cover, below 1200m altitude, in which the canopy is composed of a more or less even mixture of needleleaf and broadleaf crowns (between 50:50% and 25:75%).
Natural forest with > 30% canopy cover, below 1200m altitude, in which the canopy is predominantly (> 75%) needleleaf.
Natural forests with > 30% canopy cover, composed of species of mangrove tree, generally along coasts in or near brackish or salt water.
Any forest type above that has in its interior significant areas of disturbance by people, including clearing, felling for wood extraction, anthropogenic fires, road construction, etc.
Natural forests with > 30% canopy cover, below 1200m altitude in which between 50-100% of the canopy is deciduous and broadleaves predominate (> 75% of canopy cover).
Natural forests with > 30% canopy cover, below 1200m altitude, in which the canopy is mainly composed of sclerophyllous broadleaves and is > 75% evergreen.
Natural forests with > 30% canopy cover, below 1200m altitude, in which the canopy is mainly composed of deciduous trees with thorns and succulent phanerophytes with thorns may be frequent.
Natural forests in which the tree canopy cover is between 10-30%, such as in the savannah regions of the world. Trees of any type (e.g., needleleaf, broadleaf, palms).
Intensively managed forests with > 30% canopy cover, which have been planted by people with species not naturally occurring in that country.
Intensively managed forests with > 30% canopy cover, which have been planted by people with species that occur naturally in that country.



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