Brief overview
Dryland species must adapt to an environment known for its variation in climate, both in terms of temperature and water availability. Some areas have been identified as especially important to the survival of these uniquely adapted plants and animals: Centers of Plant Diversity; Endemic Bird Areas; Protected Areas; and Global 200 Ecoregions.
Map description
The IUCN-World Conservation Union and World Wildlife Fund-US (WWF-US) have identified 234 Centers of Plant Diversity (CPDs) worldwide. To qualify as CPDs, mainland centers must contain at least 1,000 vascular plant species and at least 10 percent endemism; island centers must contain at least 50 endemics or at least 10 percent endemic flora. CPDs house important gene pools of plants of value to humans, encompass a diverse range of habitat types, support a significant proportion of species adapted to special soil conditions, and are subject to the threats of large-scale devastation. The size of CPDs ranges from approximately 100 to more than 1 million square kilometers.
The 234 CPDS can be mapped according to aridity zone. At least 42 of the 234 CPDs are found in drylands. These dryland CPDs are more abundant in lower latitudes, especially in South America. However, every region has at least one dryland CPD and thus, each region includes an area where the diversity of dryland plants is high and where conservation practices could safeguard a great variety of species. For example, the Southwest Botanical Province in Western Australia, an area of nearly 310,000 square kilometers of Eucalypt forests and woodlands, has approximately 2,472 vascular plant species restricted entirely to the province.
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Diversity in drylands has been identified in areas with a large number of endemic bird species. Birdlife International has identified 217 endemic bird areas (EBAs) worldwide. An EBA is defined as:
An area which encompasses the overlapping breeding ranges of restricted-range bird species, such that the complete ranges of two or more restricted-range species are entirely included within the boundary of the EBA. This does not necessarily mean that the complete ranges of all of an EBA’s restricted-range species are entirely included within the boundary of that single EBA, as some species may be shared between EBAs.
Birdlife International defines restricted-range species as all landbirds which have had a breeding range of less than 50,000 square kilometers throughout historical times (i.e. post-1800, in the period since ornithological recording began). Some birds that have small ranges today were historically widespread, and are therefore not treated as restricted-range species. Extinct birds that qualify on range size are included.
Approximately 60 EBAs are found in whole or in part within the three dryland aridity zones. These EBAs range from 11 to 100 percent dryland; 42 (or 70 percent) are at least 40 percent dryland. They are most extensive in South America and Australia, and are not present at all in Europe. All other regions, Africa, Middle East, Asia, and North and Central America contain at least one EBA which is at least partially dryland.
Each EBA is assigned a biological importance rank from 1 to 3 (most biologically important) on the basis of its size and the number and taxonomic uniqueness of its restricted-range species. Several dryland EBAs have the highest rank for biological importance. For example, the Central Chile EBA is 160,000 square kilometers of scrub and semi-arid drylands with 8 restricted-range species.
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Protected areas around the globe have been identified by IUCN-The World Conservation Union and mapped by UNEP-World Conservation Monitoring Centre (WCMC). IUCN defines protected area as:
An area of land and/or sea especially dedicated to the protection and maintenance of biological diversity, and of natural and associated cultural resources, and managed through legal or other effective means.
IUCN assigns each protected area to one of six management categories. These categories vary in management purpose from scientific research to sustainable use, and include:
- strict nature reserves and wilderness areas (Category I);
- national parks (Category II);
- national monuments (Category III);
- habitat or species management areas (Category IV);
- protected landscapes (Category V); and
- areas managed mainly for the sustainable use of natural ecosystems (Category VI).
Approximately 1300 protected areas—in Categories I-VI—are located in whole or in part within the three dryland aridity zones. Of these 1300 protected areas, over three-fourths are entirely dryland; nearly 90 percent are at least 40 percent dryland. The dryland protected areas are most extensive in South America and Africa, followed by Asia, Australia, and North America.
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When all three types of biodiversity conservation areas are combined on one map—Centers of Plant Diversity, Endemic Bird Areas, and Protected Areas—several patterns appear that are worthwhile noting in relation to drylands:
- Every continent has some type of conservation area designated within the dryland aridity zones and thus preserving dryland biodiversity;
- Endemic Bird Areas and Centers of Plant Diversity within drylands are generally close to or overlap with each other; both are poorly represented in much of central Asia, the drylands of Africa, and the drylands of Canada and the United States.
- South America and Australia appear to be the regions best represented by all three dryland biodiversity conservation areas: EBAs, CPDs, and protected areas.
Map description
The World Wildlife Fund-US has identified 232 ecoregions worldwide as “outstanding examples of the world’s diverse ecosystems and priority targets for conservation actions.” Of the 138 terrestrial ecoregions within this “Global 200,” 24 can be characterized as dryland ecoregions with at least 40 percent land area within the dryland aridity zones (Table 9: Global 200 Ecoregions in Drylands).
The dryland ecoregions included in the Global 200 were selected on the basis of species richness, species endemism, unique higher taxa, unusual ecological or evolutionary phenomena, and global rarity of major habitat types. For example, the Madagascar Dry Forests along the western coast of Madagascar was selected because it contains some of the world’s richest tropical dry forests with very high island and local endemism. It supports one of the world’s most threatened reptiles (the angonoka tortoise (Geochelone yniphora). These 24 dryland ecoregions contain some of the most important drylands biodiversity in the world today.
Sources
Davis, S.D., V.H. Heywood, and A.C. Hamilton. 1995. Centres of Plant Diversity: A Guide and Strategy for their Conservation, Vol. 2. IUCN-World Conservation Union and World Wildlife Fund.
Davis, S.D., V.H. Heywood, and A.C. Hamilton. 1994. Centres of Plant Diversity: A Guide and Strategy for their Conservation, Vol. 1. IUCN-World Conservation Union and World Wildlife Fund.
Olson, D.M. and E. Dinerstein. 1997. The Global 200: A Representation Approach to Conserving the Earth’s Distinctive Ecoregions. World Wildlife Fund, draft manuscript. 176pp.
Stattersfield, A.J., M.J. Crosby, A.J. Long, and D.C. Wege. 1998. Endemic Bird Areas of the World: Priorities for Biodiversity Conservation. Birdlife Conservation Series No. 7. Cambridge: Birdlife International. 846pp.
UNEP. 1997. United Nations Environment Programme. World Atlas of Desertification, 2nd edition. Edited by N. Middleton and D. Thomas. London: UNEP. 182pp.
UNEP/GRID. 1991. United Nations Environment Program/Global Resource Information Database. Global Digital Datasets for Land Degradation Studies: a GIS Approach. Prepared by U. Diechmann and L. Eklundh. GRID Case Study Series No. 4. UNEP/GEMS and GRID. Nairobi, Kenya.
UNEP-WCMC. 1999. United Nations Environment Programme/World Conservation Monitoring Centre. Protected Areas Database. World Conservation Monitoring Centre; database available online and upon request; http://www.unep-wcmc.org
WWF-US. 1999. World Wildlife Fund. Ecoregions Database. Washington, CD: WWF-US. Unpublished Database.
