- PART A -
Land Cover Classification System:
A Dichotomous, Modular-Hierarchical Approach
Classification is easy:
it is something you just do.
A fool sees not the same tree
that a wise man sees.
W. Blake, Marriage of Heaven and Hell
The main resource controlling primary productivity for terrestrial ecosystems can be defined in terms of land: the area of land available, land quality and the soil moisture characteristics. Despite successful substitution of land-based resources with fossil fuels and mineral resources, land remains of prime importance (Darwin et al., 1996). Land cover and land use represent the integrating elements of the resource base. Changes in land cover and land use affect the global systems (e.g., atmosphere, climate and sea level) or they occur in a localized fashion in enough places to add up to a significant total (Meyer and Turner, 1992). Land cover is the expression of human activities and as such changes with alterations in these. Hence, land cover is a geographical feature which may form a reference base for applications ranging from forest and rangeland monitoring, production of statistics, planning, investment, biodiversity, climate change, to desertification control.
People have reshaped the earth continually but the present magnitude and rate are unprecedented. Nowadays it is realized that it is very important to know how land cover has changed over time, in order to make assessments of the changes one could expect in the (near) future and the impact these changes will have on peoples' lives. As people are the main users of the land, it is important for any system to be oriented towards them.
Due to the lack of appropriate land cover data, many assessments have used models to delimit potential land cover (e.g., Alexandratos, 1995). Although the use of potential land cover is important in modelling simulated future scenarios, there are major limitations. Information describing current land cover is an important input for planning and modelling, but the quality of such data defines the reliability of the simulation outputs (Townshend, 1992; Belward, 1996).
In addition to a high demand for improved land cover data sets because of an increasing need to be able to precisely describe and classify land cover in order to develop sustainable land use systems, there is also a growing need for standardization and compatibility between data sets and for the possibility to map, evaluate and monitor wide areas (Di Gregorio, 1991, Reichert and Di Gregorio, 1995; Thompson, 1996; FAO, 1995 and 1997). Technical advances, such as the vast amount of remote sensing data that has become available from earth observation satellites, makes this increasingly possible (Di Gregorio, 1995).
In 1993, UNEP and FAO organized a meeting to catalyse co-ordinated action towards harmonization of data collection and management and to take a first step towards an internationally agreed reference base for land cover and land use (UNEP/FAO, 1994). The Africover Programme of the Environment and Natural Resources Service (SDRN), which intends to map land cover for the whole of Africa, needed a land cover reference system for operational use.
The objectives of the Africover Programme are to:
The main objective of the initiative for definition of a reference classification is to respond to the need for standardization (or harmonized collection of data, as mentioned in UNCED's Agenda 21 Chapter 10, for which FAO is Task Manager within the UN system) and to develop a common integrated approach to all aspects of land cover. This implies a methodology that is applicable at any scale, and which is comprehensive in the sense that any land cover identified anywhere in the world can be readily accommodated.
Existing published classifications and legends, as well as nomenclatures, were analysed (Danserau, 1961; Fosberg, 1961; Eiten, 1968; UNESCO, 1973; Mueller-Dombois and Ellenberg, 1974; Anderson et al., 1976; Kuechler and Zonneveld, 1988; CEC, 1993; UNEP/FAO, 1994; Duhamel, 1995; Beek, De Bie and Driessen, 1997), together with relevant FAO documents (Nègre, 1995; Barisano, 1996; Wyatt et al., unpubl.).
The initial concepts of the classification were discussed by the international Africover Working Group on Classification and Legend (Senegal, July 1996) (Di Gregorio and Jansen, 1996c; FAO, 1997). While fully developing the system, links with other international ongoing activities on classification of land cover were developed, such as the U.S. Federal Geographic Data Committee (FGDC) - Vegetation Subcommittee and Earth Cover Working Group (ECWG); the South African National Land Cover Database Project (Thompson, 1996); and the International Geosphere-Biosphere Programme (IGBP) - Data and Information System (DIS) Land Cover Working Group and Land Use and Land Cover Change (LUCC) Core Project. The first full operational version of the classification and software application has been developed by the GCP/RAF/287/ITA Africover - East Africa project.
The approach developed for land cover could serve as the basis for a reference classification system with links to specific expertise, because it describes and allows correlation of land cover with a set of independent diagnostic criteria, the so-called classifiers, rather than being nomenclature based. Also, existing classifications and legends can be "translated" into the reference system, thus facilitating the use of existing historical materials. Re-arrangement of the classes, based on re-grouping of the used classifiers, facilitates the extensive use of the outputs by a wide variety of end-users.