Effects of spatial scale on estimating the relationship between vegetation and topography in a mountainous environment

Bian, Ling

Research systematically studied the effects of spatial scale on estimating the relationship between vegetation and topography in Glacier National Park, MT. The effects of spatial scale are inherently involved in landscape studies. Little research, however, has focused on the effects of scale dependencies on the relationships between landscape and environment from a systematic perspective. Such a study is important since it relates both to ecological and spatial analyses in a manner that focuses on landscape pattern, process, and scale. This research systematically studied the effects of spatial scale on estimating the relationship between vegetation and topography in Glacier National Park, Montana. The vegetation index, Reflectance/Absorption, derived from the Landsat TM data were chosen to represent vegetative landscape to relate three topographic variables, elevation, slope angle, and slope aspect, derived from the Digital Elevation Models. The effective ranges of spatial scales within which the two sets of variables were spatially dependent, and the degree of the spatial dependences were characterized through semivariogram and fractal analyses. The correlations between the vegetation index and the topographic variables were obtained through regression analysis at a series of aggregated spatial scales. Most topographic variables and the vegetation index were spatially dependent within a scale range representing the ridge-valley distance in the study area. Elevation was the most spatially dependent topographic variable. The vegetation index was less spatially dependent than all the topographic variables because it represented the collective results of many processes and factors functioning at various scales. The correlations between vegetation index and topographic variables were low at fine scales but increased with data aggregation levels; high at the characteristic scales; and slightly depressed at coarser scales for all correlations except for slope angle. The maximum correlations occurred at a scale of the ridge-valley distance. Variables aggregated at this level represented the most basic spatial structures in the study area. At finer or coarser scales, factors other than topography were more effective in affecting the variation in vegetation. The relative importance of the topographic variables varied with scale in a similar manner as that of correlations. The elevation was the most important at all scales.

Effects of spatial scale on estimating the relationship between vegetation and topography in a mountainous environment

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