The rapid determination of invasion stages and the degree to which an invasive plant (IP) has become established and spread in an ecosystem (“invasiveness”) is essential for developing methods of mitigation and control. We mapped the invasion stages and quantified the invasiveness of a group of IPs of great concern in the Upper Midwest forestlands by using the USDA Forest Service’s Forest Inventory and Analysis (FIA) data. Specifically, we used the product of the estimated presence probability and mean cover rate of an IP from a group of FIA plots in a county to represent its severity or area occupied. We then calculated the empirical cumulative density function (ECDF) of the occupied area and used classification and regression tree (CART) to classify the ECDF into a number of disjoint segments to spatially represent invasion stages of an IP. The invasiveness of an IP in three major forest type groups was then investigated via regression analysis of the change in the estimated mean cover rate with the estimated presence probability across the mapped invasion stages (a proxy for invasion time).
Results/Conclusions
There were four invasion stages for nonnative bush honeysuckles (Lonicera spp.) and multiflora rose (Rosa multiflora), and three for garlic mustard (Alliaria petiolata) and common buckthorn (Rhamnus cathartica). Overall, nonnative bush honeysuckles, common buckthorn, and garlic mustard are more invasive than multiflora rose. At both local and regional scales, plant invasion may increase or decrease biodiversity in terms of the mean values of the calculated biodiversity indices, but plant invasion will always decrease the range of the calculated indices, suggesting that the impacts of plant invasion on biodiversity is scale related. This study demonstrates the feasibility of using data from a single time period for determining invasion stages and invasiveness for IPs. The methodology can be used at any scale and for groups of plants or individual species without the need for time-dependent data and will allow for the rapid deployment of measures aimed at controlling or eradicating invasive plants.