Human Modification for the Canada-US Transboundary Study Area

Measures of ecological integrity are increasingly being used to monitor and evaluate the status and condition of their landscapes, and numerous methods have been developed to map the pattern of human activities. The ‘Human Modification – Transboundary (HMT)’ model is designed to provide a comprehensive, but parsimonious approach, that uses several stressor/threats datasets to estimate level of human modification. There are three important elements that define the HM approach: (a) the human modification stressors and their data sources (b) the measurement unit used for each stressor, and (c) the method used to combine the effects of multiple stressors into an overall score of human modification. The way in which these various data layers are combined into a single index is quite important. The method used here minimizes bias associated with non-independence among several stressor/threats layers (Theobald 2013). The HMT model assumes the contribution of a given threat decreases as values from other threats overlap. Locations with multiple threats will have a higher human modification value that locations with just a single threat (assuming the same value), but the cumulative human modification score converges to 1.0 as multiple human impact data layers are added. Individual factors were combined across multiple data layers using a fuzzy sum “increasive” function (Theobald 2013). This approach generates an internally valid model that has a direct, empirical, and physical basis to estimate the degree of human modification.