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Tolerance of understory plants subject to herbivory by roe deer

Authors

  • Barbara Moser,

  • Martin Schütz


B. Moser and M. Schütz, Swiss Federal Research Inst. WSL, CH-8903 Birmensdorf, Switzerland (martin.schuetz@wsl.ch). BM also at: Dept of Environmental Sciences, Swiss Federal Institute of Technology Zurich, CH-8092 Zürich, Switzerland.

Abstract

Current understanding of plant–herbivore interactions postulates that forest understory species are less tolerant to herbivory by large mammals than grassland species. As yet, research on forest species has focused on extensive biomass loss. However, forest dwelling ungulates are often selective browsers, hence biomass loss experienced by forage species is mostly limited to specific plant modules. We investigated the impact of herbivory on common forage species of roe deer Capreolus capreolus by simulating browsing on wild transplants of the two herbs Geum urbanum and Prenanthes purpurea, and the two graminoids Carex sylvatica and Luzula luzuloides. Two clipping regimes simulated different browsing frequencies, whereas shading and full day light represented light conditions in closed forests and gaps, respectively. Single clipping did not affect above ground biomass production of any species, independent of light conditions. Repeated biomass loss led to undercompensation in L. luzuloides, marginal compensation in C. sylvatica, and full compensation in G. urbanum and P. purpurea measured as above ground biomass production. The change in root biomass after clipping was positively correlated with the change in above ground biomass production in all four species. In contrast, nitrogen concentration was negatively correlated with above ground biomass in the graminoids, whereas no relationship between nitrogen and biomass was found in the herbs. Although light conditions and plant provenance affected biomass production, we found no effect of light conditions on plant reactions to herbivory. These results suggest that forest understory species, graminoids as well as herbs, are tolerant to herbivory by selective browsers such as roe deer. As in grassland ecosystems, the degree of compensatory growth depends on amount and frequency of biomass loss.

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