Macro- and Micro–scale Influences on Riparian Vegetation in Western Colorado

The relative importance of macro-and micro-scale processes in the biosphere is controversial, with some researchers emphasizing micro-scale population dynamics and others macro-scale landscape dynamics. I hypothesize that there is spatial variation in the linkage between and importance of macro-and micro-environmental influences on vegetation, and explore this hypothesis in a case study of riparian vegetation in the mountains of western Colorado. I estimate percent cover, by species, in 115-0.1 ha samples of riparian vegetation at relatively undisturbed sites. Environmental variables measured at each site include several channel characteristics, valley characteristics, geographical coordinates, and drainage basin characteristics. I determine major gradients in vegetation variation by Bray-Curtis ordination and interpret the gradients by correlating ordination axis scores with the values of environmental variables measured at each site. The first ordination axis is a complex gradient related to elevation, drainage basin variables, and channel width. The second axis correlates with stream gradient and sinuosity. When the overall data matrix is broken into four parts, by cluster analysis, separate ordinations of each part reveal that the vegetation varies along distinct gradients in each part, with macro-environmental variables important in some parts and micro-environmental variables important in others. The nature of the link between macro- and micro-environments varies spatially, as hypothesized, and may be temporally transient.