Safe sites for tree regeneration in wooded pastures: A case of associational resistance?

Question: Are tree saplings in wooded pastures spatially associated with specific nurse structures or plants that facilitate tree sapling survival? Location: Wooded pastures in the Jura Mountains, Switzerland. Methods: In two sites, 73 kin apart, we sampled 294 plots of 4 m(2), systematically distributed on I ha. We recorded number and height of all established Picea abies saplings (> I a of age and up to 40 cm in height), and visually estimatec cover of rocks, shrubs, tree stumps, overhanging tree branches and unpalatable plant species. Results: Despite differences in site characteristics, we found overall positive effects of cover of unpalatable plants, rocky outcrops and tree stumps on the density of Picea saplings. Plots with tree stumps and higher cover of rocky outcrops and unpalatable plants were more likely to contain Picea saplings. Conclusions: Unpalatable plants, rocky outcrops and tree stumps seem to form safe sites for Picea saplings in this grazed system, improving their establishment and survival. Our findings support the idea that associational resistance drives the dynamics of wooded pastures, but experimental evidence for this hypothesis is still required.