Vegetation

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Before wolves were extirpated from the Southwest, their distribution and density were correlated to the existence of pinon-juniper woodlands and grassland vegetation. We know this through the historic accounts of 19th century settlers, and because we know that wolves' prey inhabit these areas in greater densities because it is here that there food is more plentiful..

I found two different types of vegetation information pertaining to the Big Bend Area. On TNRIS's web site I was able to locate and download Texas Parks and Wildlife's "The Vegetation Types of Texas." This information was not as helpful as I had hoped. First, the data is at a scale of 1:1,000,000 which is too small to use for detailed analysis. The USGS is developing a state-wide, 1:100,000-scale digital vegetation map for its GAP Analysis Project for Texas, but these files will not be available for a couple more years. Another problem with "The Vegetation Types of Texas" file is that the data gives no indication of vegetative biomass. As a result, we might know from the dataset that grama grass is the dominant vegetation cover within a given polygon, for example, but we cannot make assumptions about the vigor and density of the grass throughout the polygon. This information, however, is necessary to determine a region's suitability for wolves because vegetative biomass influences the region's ungulate carrying capacity.

I have also been exploring how Landsat Thematic Mapper (TM) imagery can be used for vegetation analysis and classification. Fortunately, I was able to acquire some of this data and perform some very basic analysis functions using ENVI, an image processing software package.