Great Basin Naturalist Memoirs


Alpine vegetations and floras are compared in two transects across the Intermountain Region. The first extends from the Beartooth Mountains in the central Rocky Mountains to the Sierra Nevada some 1200 Km to the southwest. It includes six mountain ranges. The second transect crosses the Mohave Desert from Olancha Peak in the southern Sierra Nevada to Charleston Peak and thence to San Francisco Peaks in northern Arizona. The largest numbers of arctic-alpine species are in the Beartooth and Ruby mountains, indicating migrations of these species along the Rocky Mountain cordillera. The lowest numbers of arctic-alpine species are in the central western Great Basin and in the Sierra Nevada. Sorensen's Index of Floristic Similarity was calculated for all possible pairs of the nine alpine areas. There is little correlation of floristic similarity with alpine proximity across the Intermountain Region. Rather, any such correlation seems to be in a north-south direction; this is stronger in the eastern part of the region. Insularity and uniqueness of alpine floras seem to increase toward the western part of the basin. This is probably due to evolution of alpine endemics from preadapted lowland taxa.