Weed control as a rationale for restoration: The example of tallgrass prairie

The potential weed control benefits of ecological restoration are rarely cited and largely unstudied. Nevertheless, the nature of many restoration target communities, i.e., diverse, late-successional communities, suggests that restoration may control weeds and that the invasibility of plant communities may decrease with both diversity and successional age. Given the high cost of weed control in nonagricultural land, weed control benefits could be a strong incentive for restoration efforts. We examined the cumulative effects of restoration on weed populations 7 yr after tallgrass prairie restoration on a Minnesota sand plain. The numbers and biomass of volunteer weeds were compared among randomized plots with (1) no restoration, (2) prairie seed addition, and (3) site preparation plus prairie seed addition. After 7 yr, comparison with unrestored sites showed that site preparation plus prairie seed addition had reduced weed biomass by 94%, total weed stem number by 76%, and the stem numbers of four individual weed species. Prairie seed addition alone had no significant effect on weed biomass but reduced weed stem number by 45%. Restoration also reduced available light, which is consistent with the hypothesis that restoration may limit weed invasion by decreasing resource availability.