. A vegetation index of biotic integrity for small-order streams in southwest Montana and a floristic quality assessment for western Montana wetlands . Wetlands; Plant indicators; Wetland management; Wetlands; Biotic communities; Riparian ecology. Results Human Disturbance Gradient The composite disturbance gradient was calculated from a PC A of four variables: AUM, amount bare ground, bank stability, and browse intensity. The first principal component explained of the variation in the data. It was considered interpretable as it explained more variation in the data than expected by chanc
. A vegetation index of biotic integrity for small-order streams in southwest Montana and a floristic quality assessment for western Montana wetlands . Wetlands; Plant indicators; Wetland management; Wetlands; Biotic communities; Riparian ecology. Results Human Disturbance Gradient The composite disturbance gradient was calculated from a PC A of four variables: AUM, amount bare ground, bank stability, and browse intensity. The first principal component explained of the variation in the data. It was considered interpretable as it explained more variation in the data than expected by chance. Subsequent principal components did not meet this criterion. The component was rescaled so that it ranged between [0, 1], with the least disturbed site scoring 0 and the most disturbed site scoring 1, and was used to represent a composite human disturbance gradient for metric development. Table 3 shows the contributions of the original variables to the composite disturbance index. A PCA including road density was also run. It was rejected in favor of the four variable model because the addition of road density weakened the interpretability of the first principal component (component explained of the variation, not much more than that expected by chance) while road density explained less than 1% of the variation of the component. Table 3. Contribution of individual disturbance factors to a composite disturbance measure extracted by principal components analysis. Variance Explained Factor (R') AUM bare ground bank stability browse intensity Measures of pug and hummock density were not included in the composite human disturbance gradient. The relationship of these measures to grazing intensity appeared to be confounded by physical characteristics of the site, as the extent of pugging and hummocking is controlled to some extent by soil texture and geomorphology. Sites with finer texture soils and depositional surfaces at lower elevations relative to
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