104 • Technologies To Maintain Biological Diversity 



Photo credit- SAF/US Forest Service 



The Society of American Foresters Cover Type IVIap, an example of an ecosystem classification system, aggregates 

 similar stands of forest trees on the basis of the l<ind, number, and distribution of plant species 



and the dominance by tree species. 



for conservation of azonal ecosystems are based 

 on surveys that cut across the biogeographic 

 zones. 



Biogeographic classification systems also 

 need to be supplemented with information on 

 endemism. Patterns of endemism vary among 

 taxa and among regions. Some species with re- 

 stricted distribution are quite common locally, 

 whereas others are extremely rare (26). On the 

 broadest scale, taxa may be endemic to a con- 

 tinent or subcontinent; on a narrow scale, many 

 plant species seem to be restricted naturally to 

 areas as small as a few square kilometers. 



Identifying centers of endemism has been an 

 ongoing effort of conservationists, especially 

 tropical ecologists. An area such as an island 



or a mountain forest may not have an unusually 

 high number of species present, but it may have 

 a high proportion of species not found else- 

 where (i.e., high endemism). Such areas are con- 

 sidered valuable for maintaining biological 

 diversity, because they contribute substantially 

 to diversity on a global scale. 



In sum, a variety of ecosystem classification 

 systems are currently being used by many orga- 

 nizations with different objectives. Although 

 these maps do not indicate the extent of exist- 

 ing ecosystems (e.g., how much forest actually 

 remains), they do correspond roughly to the 

 boundaries of species distributions. Thus, they 

 can be compared with maps of natural areas 

 already protected, and planners can then choose 

 which sites to focus on for more detailed assess- 



