Abstract

Using spatial statistics to map invasive species populations over time
Track: Parks, Natural Reserves, Fisheries, and Wildlife Management
Authors: Rachel Hutchinson, Joshua Viers

Species invasions are often difficult to quantify because of their high growth rates and large geographic range. Understanding how populations develop can be crucial to effectively manage species for conservation purposes. In a restored riparian floodplain along the Cosumnes River patches of the invasive perennial pepperweed (Lepidium latifolium L.) expanded in dry years and declined in wet years based on annual inventory data collected between 2002 and 2007. To determine if there was a spatial relationship between perennial pepperweed growth and decline and floodplain position, we used a univariate Moran's I with stem count rate of change as the predictor variable. The Moran's I indicated positive and significant correlation in wet years, but not in dry. We also quantified and mapped the areas most affected by using spatially explicit regression analysis and found that population change was a function of floodplain position, with areas of highest change near levee breaches.