Endangered cacti in the Chihuahuan Desert: I. Distribution patterns

We mapped the geographical distribution of 39 endangered species of cacti from the Chihuahuan Desert Region. We divided the region into grids of 30 minutes latitude by 30 minutes longitude and calculated species frequencies for each grid. The grid with the highest species richness values are aggregated in areas of moderate elevation, particularly towards the southeastern and, to a lesser extent, the eastern margins of the Chihuahuan Desert Region in northern San Luis Potosi and the southern portions of Coahuila, Nuevo León, and Tamaulipas. This vast area constitutes the mos important nucleus of cactus species concentration in the continent. Species richness decreases toward the western segment of the Chihuahuan Desert Region and from the Cuatro Ciénegas region to the north and northwest. Another important area is the Queretaroan-Hidalgoan Arid Zone, where several grids containing an important assemblage of endangeren species occur. Climatic factors, such as minimum temperatures and mean annual precipitation, explain the current distribution patterns of these plants, and the recent Pleistocene climatic episodes appear to have played a determinant role in the existence of areas of high species concentration and in the proliferation of narrow endemics. Special actions are urgently needed to conserve the endangered Cactaceae of this region. We propose that a carefully selected network of small areas taken as the sole criterion in the determination of protected areas. Additional criteria, such as degree of endemicity, degree of threat to species and areas, habitat diversity, and biogeographic congruence with other plant and animal group, should be analyzed before these areas are selected. Propagation in botanical gardens using scientific criteria and commercial propagation would be additional methods of conservation