Mountain Vegetation - Mountain Geography: Physical and Human Dimensions - page 329

individual plant scales (Gosz 1993). This requires that we recognize that local differ-
ences in species composition and the positioning of vegetation communities are the
result of steep environmental gradients (changing in abiotic conditions over space) su-
perimposed upon the discontinuous geologic substrates, soil types, geomorphic sur-
faces, topo- and microclimatic patterns, and other environmental factors (e.g., Whit-
taker 1953; Peterson et al. 1997; Ferreyra et al. 1998; Löffler and Pape 2008).
Second, we recognize that zonal vegetation patterns are dynamic and are continually
shifting their locations, composition, and structure in response to environmental
change. Third, we need to acknowledge that our current level of understanding is in-
complete with regard to zonal transitions ( ecotones ) (van der Maarel, 1990), the diver-
gent effects of climate on zonal boundaries in subtropical versus higher-latitude envir-
onments (e.g., Morales et al. 2004), and the role of human influences on the spatial or-
ganization of vegetation in transition zones (e.g., Sarmiento and Frolich 2002; Young
and León 2007). Evolution, dispersal, and biotic interactions, such as competition, co-
existence, predation, and mutualism, must further be accounted for in order to more
thoroughly understand the characteristics of mountain vegetation (e.g., Callaway et al.
2002; Pierce et al. 2007; Young and León 2007).