The Role of Space in Plant Population Dynamics: Annual Weeds as an Example

The dynamics and spatial pattern of a weed population are analysed with a model that takes explicit account of the spatial position of individual weeds. In this model weeds are held at a low density in an environment with homogeneous abiotic conditions. Maintaining low weed densities requires a weed removal rate close to the critical removal rate that marks the transition from possible survival to certain extinction of the population. At these low densities, the spatial pattern of weeds and the local population dynamics obey scaling laws. These scaling laws and the value of the scaling exponents are robust to changes in the model. Based on this analysis, weeds are expected to occur in scale-invariant spatial patterns. In a field observation, the spatial distribution of the weed Galium aparine is found to be scale-invariant.