Isolating the role of soil resources, defoliation, and interspecific competition on early establishment of the late successional bunchgrass Festuca campestris

Abstract

Native grasslands are valued for biodiversity and supporting dormant season grazing, but are prone to invasion. In western Canada, revegetation of Festuca campestris grasslands may be hindered by Poa pratensis, an invasive grass. To determine the competitive interaction of these species during establishment, two greenhouse experiments were conducted where F. campestris seedlings were planted in monocultures or mixtures with P. pratensis. The first experiment used equal‐aged (3‐month old) seedlings of both species, while the second experiment used unequal‐aged seedlings (4‐month‐old F. campestris and 2‐month‐old P. pratensis). Seedling performance was measured in response to manipulations of water and nitrogen, defoliation, and plant neighbor. While water and nitrogen reduced the biomass and vegetative reproduction (tillering) of F. campestris, exposure to P. pratensis most strongly limited the growth of F. campestris seedlings regardless of other treatments. More frequent and consistent decreases in F. campestris due to P. pratensis were observed in older F. campestris seedlings than younger seedlings. Defoliation also reduced the growth of F. campestris, and the added presence of P. pratensis during defoliation further enhanced these reductions in younger, equal‐aged bunchgrass seedlings. Overall, these results suggest that when restoring native F. campestris grasslands, early establishment may be improved by reducing the negative impacts of P. pratensis, and avoiding severe defoliation.