Rates of weed spread in spatially heterogeneous environments

Investigated how the spatial distribution of bare ground influences the rate at which offspring of an introduced invader spread through a perennial ryegrass Lolium perenne community. Artificially created gaps of three sizes were positioned along linear transects according to one of two spatial distributions. These six transects (one for each treatment combination) were positioned as spokes on a wheel and groundsel Senecio vulgaris was introduced into the center. After controlling for the total amount of gap area, the authors monitored the number and position of S. vulgaris establishing for two subsequent generations. The rate of spread of S. vulgaris was sensitive to both the gap size and the gap distribution; plants moved a greater distance when the gaps were large and underdispersed. This pattern follows from the way in which gaps sample from seed shadows. -from Authors