Middle Rio Grande Biological Survey [Final Report]

Hink, Valerie; Ohmart, Robert

A biological survey of riparian habitats of the Middle Rio Grande Valley between Española and San Acacia, New Mexico was carried out by a study team from the Center for Environmental Studies at Arizona State University. The study was a multiple agency effort by the Corps of Engineers, the Bureau of Reclamation, the Fish and Wildlife Service, and the New Mexico Department of Game and Fish. The objectives of the study were to identify the major types of riparian habitat within the study reach, and to characterize the vegetation and terrestrial vertebrate communities of each type. Two consecutive years were spent in field data collection. The study focused on the area within and including the drains and levees that parallel the river. The major communities were cottonwood/Russian olive, cottonwood/coyote willow, cottonwood/juniper, Russian olive, cattail marsh, salt cedar, and sandbar/river channel; drains and the vegetation at the edges of the bosque along the levees were also treated as distinct communities. Six vegetation structure types were defined within the communities, based on the overall height of the vegetation and the amount of vegetation in the lower layers. The riparian community as a whole supported a rich assemblage of vertebrate species, particularly birds, and population densities were comparable to those observed in other Southwestern riparian systems. The highest densities and diversities of vertebrate wildlife were found in mature cottonwood/Russian olive stands and in dense, intermediate-aged cottonwood/coyote willow stands, especially along the edges of the levees. Cattail marshes supported high population densities but fewer numbers of species, although a relatively large proportion of the species occurring in cattail marsh habitats were unique to them. Open areas, early growth stands, salt cedar habitats, and the river channel supported lower densities and numbers of vertebrate species. Detailed vegetation maps of the study area were prepared and are included with the report. General recommendations for management of the riparian/riverine resource were presented, and specific recommendations were made regarding the biological impacts of a proposed Corps of Engineers levee rehabilitation project.

Middle Rio Grande Biological Survey [Final Report]

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