Oiii Liviiii; Rcxoiirces — Riparian Ecosyxteins 



291 



Figure. The Rio Grande study area. 



separating saltcedar from other scrub-shrub 

 types would have been desirable. Unfortunately, 

 saltcedar could not be distinguished from other 

 scrub-shrub types on the 1935 photography 

 used to classify the area and was therefore 

 included in the riparian scrub-shrub and wet- 

 land scrub-shrub classes. 



Trends 



Major changes in surface cover occurred on 

 the floodplain of the Rio Grande between 1935 

 and 1989 (Table). Five of eight wetland or 

 riparian types declined by about 17,000 ha 

 (42.000 acres), including 5,453 ha (13,475 

 acres) of river or artificial channel: 4,015 ha 

 (9,921 acres) of wet meadow, marsh, or pond: 

 2,638 ha (6,519 acres) of riparian scrub-shrub: 

 2,507 ha (6,195 acres) of riparian forest: and 

 2,482 ha (6,133 acres) of wetland scrub-shrub. 

 Upland range also declined by 5,2 1 7 ha ( 1 2.89 1 

 acres). 



The largest gains occurred in urban (1 1.389 

 ha: 28,143 acres) and agricultural (5,395 ha; 

 13,331 acres) cover types. Only three wetland 



Table. Suilace cover changes in the Rio Grande Hood- 

 plain. Velarde to Elephant Butte Reservoir, NM. 1935-89. 



or riparian cover types (lake, wetland forest, 

 and dead forest or scrub-shrub) increased. 

 Higher water levels in Elephant Butte Reservoir 

 and construction of Cochiti Reservoir, New 

 Mexico, produced a gain of 2,552 ha (6,306 

 acres) of lake. Wetland forests increased by 

 1,779 ha (4,396 acres). Most of this increase 

 occurred between the levees and the stream 

 channel, which has become narrower and 

 straighter because of levee construction and 

 channel stabilization. Dead forest or scrub- 

 shrub increased by 1,197 ha (2,958 acres). Most 

 of this mortality was at the upper end of 

 Elephant Butte Reservoir because of high water 

 in themid-1980's. 



The total forested area (wetland plus ripari- 

 an) declined only slightly between 1935 (9.861 

 ha: 24.367 acres) an'd 1989 (9.133 ha: 22.568 

 acres), but this does not mean that concern for 

 the long-term future of the woodlands is unwar- 

 ranted. Only about 27% of the area forested in 

 1935 still suppoils forests, indicating that sig- 

 nificant changes have occurred even in cases 

 where the net change in area has been small. As 

 noted before, much of the cottonwood forest is 

 now confined between the levees and the river 

 channel. The flow regime of the Rio Grande, 

 however, has been altered significantly (e.g.. 

 lower peak flows) since most of these stands 

 were established, and conditions favorable for 

 germination and establishment of cottonwood 

 now occur only rarely. Russian olive and 

 saltcedar are likely to continue to replace cot- 

 tonwood. especially under current hydrologic 

 conditions (Howe and Knopf 1991 ). 



References 



Anderson, J.R.. E.E. Hardy. J.T. Roach, and R.E. Witmer. 

 1976. A land use and land cover classification system for 

 use with remote sensor data. U.S. Geological Survey 

 Professional Paper 964. 27 pp. 



Cowardin, L.M., V.C. Caner, F.C. Golet. and E.T. LaRoe. 

 1979. Classification of wetlands and deepwater habitats 

 of the United States. U.S. Fish and Wildlife Service 

 FWS/OBS 79/81. 131 pp. 



Rio Grande floodplain. 



