Terrestrial Ecosystems 



Overview 



Whereas several other 

 sections in this volume 

 cover individual species or locations, the arti- 

 cles in this section address the integration of 

 individual species into communities and 

 ecosystems {see glossary). Terrestrial ecosys- 

 tems include a rich variety of community types 

 and cover a range extending from nearly aquat- 

 ic wetlands along our coasts and myriad rivers, 

 lakes, and streams, to mountain tops and arid, 

 desert locations. The diversity of these ecosys- 

 tems offers both challenge and opportunity. The 

 challenge stems from the sheer number of 

 potential ecosystems to be analyzed. Grossman 

 and Goodin (this section) discuss 371 imperiled 

 and critically imperiled communities, and state 

 that this number represents only 10%- 15% of 

 all terrestrial communities. This implies a mini- 

 mum of 2,500-3,500 individual terrestrial com- 

 munity types. Obviously, a single report cannot 

 hope to address more than a few of these many 

 terrestrial communities and ecosystems. 



Discussions of biological diversity have tra- 

 ditionally revolved around the protection of 

 individual species. More recently, we have 

 begun to realize that protection of community or 

 ecosystem diversity is equally important. 

 Patchwork conversions of natural landscapes for 

 agriculture, silviculture, and development result 



in a fragmentation that leaves small remnant 

 areas of natural ecosystems (Burgess and Sharpe 

 1981). As these natural patches become smaller 

 and more isolated, their ability to maintain 

 healthy populations of many plant and animal 

 species is reduced (Harris 1984). As individual 

 species are lost from each fragment, the com- 

 munity changes and both species and ecosystem 

 diversity are reduced. Thus, large numbers of 

 natural ecosystems are now in danger. 



Kendall (this section) discusses one such 

 imperiled ecosystem. The whitebark pine 

 {Pimis albicaiiUs) ecosystem of the western 

 mountains is endangered because of the com- 

 bined effects of an introduced disease and fire 

 suppression. The effects of introduced diseases 

 on natural species and ecosystems have been 

 well documented. Several species, such as the 

 American chestnut {Castanea dentata). have 

 been virtually eliminated and other species have 

 been greatly reduced by introduced diseases. 

 The effects on ecosystems where these species 

 were previously found have been dramatic 

 (Shugan and West 1977). 



Alteration of natural fire regimes has played 

 a major role in the reshaping of natural ecosys- 

 tems. In many systems a reduction in fire fre- 

 quency can lead to invasion by fire-intolerant 

 species and eventual loss of the original ecosystem. 



Science Editor 



Raymond J. Boyd 



Bureau of Land 



Management 



Service Center 



Denver Federal Center, 



Bldg. 50 



Denver, CO 80225 



Text by 



B.D. Keeland 



National Biological 



Service 



Southern Science Center 



700 Cajundome Blvd. 



Lafayette, LA 70506 



