Niche theory and plant growth form

Abstract

Plant growth form diversity (GFD) is high in the vegetation of North American deserts, and increases from north (Great Basin Desert) to south (Sonoran Desert). While abiotic features (annual temperature, precipitation, and seasonality) appear to limit the range of desert plant GFD, biotic features associated with the coexisting plants at a site, and their GF distribution, add further constraints. Climate may constrain the GF options at certain sites and select for some degree of GF convergence there, but within sites other species in the vegetation select for GF segregation that fosters the local coexistence of species. In this paper GF variation is viewed along structural niche axes, and related to classical niche theory; several corollaries of the theory are examined in the light of plant GF patterns. These are: a) regular spacing of species on the structural niche axis, and the concept of limiting similarity; b) niche axis complementarity, such that species dissimilar in position on one axis, e.g. GF, are similar in position on other axes, e.g. habitat or substrate, and vice versa; c) niche shifts in GF within species are expected, and occur, as the suite of coexisting species varies among sites with similar climate; d) in some desert plant guilds species with very similar GF do not coexist at a site, but act as geographical replacements in different sites.