The vegetation of central Arizona is a mosaic of four vegetation types: chaparral, chaparral grassland, woodland, and woodland grassland. We analysed ten environmental variables, three disturbance variables, and five disturbance indicators to answer the question: What is the relative importance of environment and disturbance in explaining the vegetation pattern of our study area? We found that chaparral, chaparral grassland, and woodland are differentiated primarily by environmental factors and have high stability in the landscape. In contrast, woodland grassland is differentiated primarily by disturbance and is likely an early-successional stage of woodlands. Although other researchers have indicated that semi-arid vegetation is generally unstable, the vegetation of central Arizona is composed of two systems: those with a more stable landscape position determined primarily by environmental factors and those with a less stable landscape position determined primarily by disturbance factors.

Nomenclature: Kearney & Peebles (1960) and McDougall (1973).

Abbreviations: A = Grazing allotment size and chance corrected within-agreement; C = Number of permitted domestic grazing animals; CCA = Canonical Correspondence Analysis; DCA = Detrended Correspondence Analysis; MRPP = Multi-Response Permutation Procedure; NMS = Non-Metric Multi-dimensional Scaling; S = Fire size class; T = Grazing period; W = Probability that fire burned a stand or a conversion event took place.