Vegetation of the Santa Catalina Mountains, Arizona: A Gradient Analysis of the South Slope

• Published in: Ecology (Durham) 1965-07, Vol.46 (4), p.429-452
• Main Authors: Whittaker, R. H., Niering, W. A.
• Format: Article
• Language: English
• Subjects: Abies concolor; Abies lasiocarpa; Agave; altitude; Ambrosia; Arctostaphylos; Bajadas; canyons; climate; Coniferous forests; Deserts; flora; Forest ecology; gneiss; granite; grasses; grasslands; Haplopappus; hemicryptophytes; Juniperus; Larrea tridentata; mountains; Parkinsonia microphyllum; phanerophytes; Pinus ponderosa; plateaus; Pseudotsuga menziesii; Quercus; shrublands; Shrubs; Sloping terrain; Species; subalpine forests; topographic slope; Topographical elevation; trees; Vauquelinia; Vegetation; volcanic soils; Woodlands
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1934875

Vegetation of the southwest slope of the Santa Catalina Mountains of southeastern Arizona was sampled and transects prepared for 1,000—ft (305 m) elevation belts on granite and gneiss soils from the summit forests (2,440—2,750 m) to the base of the mountains (900 m). Transects also represented subalpine forests above 2,750 m in the Pinaleno Mts. and vegetation of the valley plain or bajada below the mountains, and samples were taken from volcanic soils below 900 m in the Tucson Mts. Principal community—types from high elevations to low are: subalpine forest (Picca engelmanni in the Pinaleno Mts. and Abies lasiocarpa), montane fir forest (Abies concolor, Pseudotsuga menziesii), pine forests (Pinus ponderosa, P. strobiformis), pine—oak forests (P. ponderosa, Quercus hypoleucoides), pine—oak woodlands (P. ponderosa, P. chihuahuana, Q. hypoleucoides, Q. arizonica), pygmy conifer—oak scrub (Pinus cembroides, Juniperus deppeana, Q. arizonica, Q. emoryi, Arctostaphylos pringlei, A. pungens, monocot shrubs), open oak woodland (Q. emoryi, Q. oblongifolia, Vauquelinia californica, monocot shrubs, and grasses), desert—grassland (Agave schottii, Haplopappus laricifolius, and grasses), Sonora desert of mountain slopes (north—slope shrub phase, and south—slope spinose—suffrutescent phase), upper bajada desert (Cercidium microphyllum, Franseria deltoidea), and lower bajada desert (Larrea tridentata). Forests of canyons and arroyos are also described. Relations of communities to elevation and topograhic moisture gradients are represented in a mosaic chart. Physiognomic relations of communities are represented in charts of growth—form coverage in relation to elevation and topographic moisture gradients. Growth—form diversity increases from high—elevation forests strongly dominated by evergreen—needleleaf trees to desert of lower mountain slopes in which pinnate leguminous trees, spinose shrubs, suffrutescent semi—shrubs, and stem—succulents share dominance. Among Raunkiaer life—forms hemicryptophyte species are most numerous at middle and higher elevations, phanerophyte species at lower elevations. In open oak woodlands and desert grasslands phanerophytes, hemicryptophytes, and suffrutescent chamaephytes each make up about one—third of the perennial flora. Desert floras of mountain slopes are characterized by predominance of suffrutescent chamaephytes over both phanerophytes and hemicryptophytes, and large numbers of therophyte species. Analysis in terms of geographic area