Multiple-scale invasion patterns of an exotic forage using probability as a function of management and environmental variability

Exotic invasive forages present a major concern for land managers, conservationists, and restoration ecologists worldwide.  The same traits that make these plant species successful forages also allow them to become aggressive invaders once they escape cultivation.  The goal of this study was to map exotic forage invasion under two management regimes at two spatial scales, and quantify environmental variability among sites.  By including management regime and environmental variability into a probability analysis, we hope to identify key factors which influence invasion pattern and rate of spread.  A coordinate grid mapping system was used to monitor Lespedeza cuneata invasion at broad (500 m²; 12.5 m² grain) and fine (5 m²; 0.5 m² grain) spatial scales in rangelands managed with homogeneous or heterogeneous applications of fire and large herbivore grazing.  Ordination and probability analysis were conducted on annual invasion data and environmental data over a four year period.  Initial results indicate that homogeneous grazing management promotes invasion, and heterogeneous management based on the fire-grazing interaction decreases the rate and probability of L. cuneata invasion.  In addition, sites with lower soil organic matter and increased broad scale invasion appear to have higher probabilities of invasion at fine spatial scales.  Understanding these invasion patterns and proximate causes of exotic forage invasion may enable management and restoration to more specifically target problem areas within the management unit.