Vegetation of the Santa Catalina Mountains: community types and dynamics

Abstract

This paper interprets plant community dynamics within three major vegetation regions - the Sonoran desert, the Encinal and coniferous forest - which extend from 700 m to the summit (2 766 m) on the south slope of the Santa Catalina Mts., Arizona. On the bajada, Larrea tridentata and disturbed desert scrub communities have been degraded by overgrazing and Carnegiea gigantea reproduction is failing on many sites. In the Spinose, suffrutescent desert scrub on protected lower mountain slopes Carnegiea is reproducing but mature populations are periodically decimated by freezing temperatures. In the desert grassland, graminoids or Agave schottii dominate, the former favored by fire, the latter by fire protection. In the Encinal above 1 220 m an open oak woodland dominated by Quercus oblongifolia is transitional to the pine, oak woodland where fire and drought result in several community segregates. A relict Cupressus arizonica forest is restricted to certain canyons. Above the Encinal (2 100 m) a Pinus ponderosa-Q. hypoleucoides forest is replaced by a less xeric P. ponderosa forest. In the latter a dense pine understory develops with fire protection and savanna-like pine stands are favored by fire. At higher elevations a mature Pseudotsuga menziesii, Abies concolor forest dominates the north-facing slopes where fire plays a significant factor in its perpetuation. An even-aged subalpine Abies lasiocarpa stand on the north slope below the summit suggests post-fire origin. In the Pinaleno Mts. to the northeast, mixed conifer and spruce, fir forests complete the vegetation gradient typical of these southwest mountain ranges. Here fire and windthrows interact in maintaining a mosaic of pure or mixed even or uneven-aged stands.