THE TOPOGRAPHIC RELATIVE MOISTURE INDEX: AN APPROACH TO SOIL-MOISTURE ASSESSMENT IN MOUNTAIN TERRAIN

The Topographic Relative Moisture Index (TRMI), designed to indicate the relative soil moisture availability among sites in mountain terrain, is described. The TRMI is a summed scalar index of four slope parameters: topographic position, slope aspect, steepness, and slope configuration. A review of other methods of characterizing site moisture relations, including direct monitoring, water-balance climatology, site index, and other inferential topographic/edaphic indices, reveals that the simple, straightforward application of the TRMI is rapid, inexpensive, and effective in field research. The ability of the TRMI to portray significant patterns of plant response to environment is demonstrated from empirical studies at both the species-level (the ecology of Arizona cypress) and community-level (forest patterns in Yosemite National Park).

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