Environmental distribution of four Carex species (Cyperaceae) in an old-growth forest.

We conducted an in-depth characterization of the range of micro-environments (1 m) in which four Carex species (C. backii, C. communis, C. plantaginea, and C. platyphylla) grow in the understory of an old-growth, deciduous forest in southern Québec, Canada. All four species occurred in significantly different micro-environments. Carex plantaginea was found at the wet end of a moisture gradient, in soils with high nitrate availability. Carex backii and C. platyphylla were found at the dry end of the moisture gradient, with C. backii occupying soils with higher phosphorus availability than C. platyphylla. Carex communis, the only ant-dispersed species studied, was found in the broadest range of environmental conditions. Our results suggest that environmental heterogeneity and interspecific microhabitat preferences are important for the maintenance of local species diversity in the forest understory, not only for common species as demonstrated in previous studies, but for infrequent species, and those within a functional group (upland Carex species). However, there was some evidence that the distributions of C. backii and C. communis were not in equilibrium with current environmental conditions, indicating that historical factors, such as dispersal and colonization events, may also have important effects on the distributions of these species and the maintenance of species diversity in old-growth forest.