290 



Riparian Ecosystems — Our Liviitt; Resources 



For further information: 



David E. Busch 



South Florida Natural Resources 



Center 



National Park Service 



Everglades National Park 



4001 State Rd. 9}}b 



Homestead, FL 33034 



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Surface Cover 

 Changes in the 

 Rio Grande 

 Floodplain, 

 1935-89 



by 



James E. Roelle 



National Biological Service 



Warren W. Hagenbiick 

 U.S. Fish and Wildlife Service 



Riparian (streaniside) vegetation communi- 

 ties piovidc valuable habitat for wildlife, 

 pailicularly in the arid and semi-arid Southwest, 

 where such communities make up less than 1% 

 of the landscape (Knopf et al, 1988). 

 Agricultural conversion, urban and suburban 

 expansion, water development, recreation, and 

 invasion by non-native species such as Russian 

 olive (Elaeaguiis augustifolia) and saltcedar 

 (Tamaiix spp.) have severely reduced the extent 

 and quality of these habitats. Despite such 

 impacts, the tloodplain of the Rio Grande in 

 central New Mexico supports one of the most 

 extensive cottonwood (Populus fremontii) 

 gallery forests (bosque) remaining in the 

 Southwest (Howe and Knopf 1991). and inter- 

 est in ensuring the long-term health and viabili- 

 ty of native communities along the Rio Grande 

 has been steadily increasing (Crawford et al. 

 1993). This article documents changes between 

 1935 and 1989 in cover types of the tloodplain 

 of the Rio Grande in central New Mexico. 



Study Area 



The study area covers the historical tlood- 

 plain of the Rio Grande from Velarde. New 



Mexico, to the narrows at Elephant Butte 

 Reservoir. New Mexico, a distance of nearly 

 250 river mi (402 km; Figure). The historical 

 tloodplain in this reach encompasses more than 

 95.000 ha (nearly 236,000 acres); about 9.650 

 ha (24,000 acres) were omitted from the analy- 

 sis because 1989 photography was unavailable. 



Classification 



Wetlands were classified according to the 

 system used by the U.S. Fish and Wildlife 

 Service's (USFWS) National Wetlands 

 Inventory (Cowardin et al, 1979). Wooded 

 riparian (nonwetland) areas were classified 

 according to an unpublished system developed 

 by the USFWS and the Arizona Riparian 

 Council, The remaining uplands were classified 

 according to a system developed by the U.S. 

 Geological Survey (Anderson et al. 1976). 



These classification systems provided more 

 than 160 cover classes, an unmanageable num- 

 ber for an analysis of change. Thus, we aggre- 

 gated the original classes in our geographic 

 information system (GIS) into 1 1 broader types. 



Expansion of saltcedar is of great concern in 

 the Rio Grande valley in New Mexico, and 



