Vegetation and Pollen Rain in the Cuatro Cienegas Basin, Coahuila, Mexico

Abstract

The Cuatro Cienegas Basin is a desert valley in central Coahuila, Mexico. The basin floor bears many aquatic habitats and supports a complex mosaic of edaphically-controlled vegetation communities. Spatial distribution and species composition of the communities are controlled by available soil moisture and soil salinity. Riparian sites support dense stands of sedges and cattails. Drier locations peripheral to riparian habitats support an extensive grassland community. Playas, stabilized dunes and other extremely dry areas bear a xerophytic community char- acterized by certain halophytic chenopods. Control by local vegetation over compo- sition of pollen rain in the basin floor is extreme, and local pollen rain is dominated by grass, Chenopodiaceae-Amaranthus and aquatic pollen types. Fluctuations of proportions of those pollen types characterize pollen rains on the edaphic communities. This paper presents a vegetational and palynological description of the floor of the Cuatro Cienegas Basin, a small desert valley in north- eastern Mexico. This survey was designed to provide modern control information on which to base interpretations of several late-Quater- nary fossil pollen chronologies that have been developed for the area. The fossil sequences are from sediment cores collected from springs located on the valley floor. Those records, together with descriptions of vegetation and pollen rain on mountains and bajadas surrounding the basin floor, are available elsewhere (Meyer 1973). Gilmore (1947) and Miiller (1947) presented preliminary botanical descriptions of the Cuatro Cienegas area, and Minckley (1969) pro- vided a geological description of the basin that includes a summary of the current status of biological research from the area. The valley is located at ca. 270 N, 1020 W, in the Chihuahuan Desert in central Coahuila, Mexico, roughly 240 km SSE from the Big Bend of the Rio Grande. The floor, or barrial (West 1964), of the basin averages 740 m above mean sea level and is surrounded by mountains rising to 1 Present address: National Commission on Water Quality, 1111 18th St., N.W.,