The influence of environmental factors on the distribution and density of invasive Centaurea stoebe across Northeastern USA

Centaurea stoebe is an emerging invader in northeast US, and is a major invasive plant in the northern Midwest and western USA. Although it has been present in New York State (NYS) for over 100years, its apparent recent population increases and spread provide a rare opportunity to study a plant in the early stages of invasion. Using occurrence, density and change in density in species distribution models, we assessed the potential influence of environmental factors on the invasion of spotted knapweed in northeast US. Within different parts of C. stoebes range, different factors explained its occurrence, density and change in density over 2years. Across northeast US, climate and soil factors were the most influential predictors explaining C. stoebes distribution, while within Long Island in southeastern NYS and the Adirondack Mountains in northern NYS, precipitation and disturbance respectively were the most important. Using density and change in density, we found that for both Long Island and the Adirondacks, tree cover, precipitation, and temperature were the most influential determinants. The comparatively minor influence of disturbance on C. stoebe density is likely because C. stoebe in the northeastern US is almost exclusively found in open disturbed sites, so this factor does not discriminate among densities. Our study is valuable for both basic ecological understanding and decision making, as control efforts may depend on whether management goals are to decrease the risk of spread to other locations, or decrease the density in locations in which invaders already occur.