Abstract
Browsing of tree saplings by deer hampers forest regeneration in mixed forests across Europe and North America. It is well known that tree species are differentially affected by deer browsing, but little is known about how different facets of diversity, such as species richness, identity, and composition, affect browsing intensity at different spatial scales. Using forest inventory data from the Hainich National Park, a mixed deciduous forest in central Germany, we applied a hierarchical approach to model the browsing probability of patches (regional scale) as well as the species‐specific proportion of saplings browsed within patches (patch scale). We found that, at the regional scale, the probability that a patch was browsed increased with certain species composition, namely with low abundance of European beech (Fagus sylvatica L.) and high abundance of European ash (Fraxinus excelsior L.), whereas at the patch scale, the proportion of saplings browsed per species was mainly determined by the species’ identity, providing a “preference ranking” of the 11 tree species under study. Interestingly, at the regional scale, species‐rich patches were more likely to be browsed; however, at the patch scale, species‐rich patches showed a lower proportion of saplings per species browsed. Presumably, diverse patches attract deer, but satisfy nutritional needs faster, such that fewer saplings need to be browsed. Some forest stand parameters, such as more open canopies, increased the browsing intensity at either scale. By showing the effects that various facets of diversity, as well as environmental parameters, exerted on browsing intensity at the regional as well as patch scale, our study advances the understanding of mammalian herbivore–plant interactions across scales. Our results also indicate which regeneration patches and species are (least) prone to browsing and show the importance of different facets of diversity for the prediction and management of browsing intensity and regeneration dynamics.
Highlights
Deer browsing on tree saplings severely hampers regeneration in temperate forests of Europe and North America (Ammer, Vor, Knoke, & Wagner, 2010; Kittredge & Ashton, 1995; Putman, 1996; Rooney & Waller, 2003)
At the patch scale a) Species identity and species composition are the main drivers of selection of individual species. b) the identity of the species will be more important than species composition, forage quantity, or species richness. c) we assume rare species in a patch to be browsed proportionally more than abundant species, irrespective of their identity
Mainly species composition and sapling quantity determined browsing probability, whereas at the patch scale, species identity was the most important factor determining the proportion of browsed saplings
Summary
Deer browsing on tree saplings severely hampers regeneration in temperate forests of Europe and North America (Ammer, Vor, Knoke, & Wagner, 2010; Kittredge & Ashton, 1995; Putman, 1996; Rooney & Waller, 2003). As plant species differ in their overall palatability, browsing mammals likely prefer high-q uality over low-quality plant species Such species identity effects on forage selection of deer have been shown in a variety of studies (Boulanger et al, 2009; Kuijper et al, 2010; Maillard & Picard, 1987; Modrý, Hubený, & Rejsek, 2004). We assessed the importance of species richness, species identity, and species composition relative to effects of forage quantity on browsing intensity at two spatial scales: regionally between patches and locally within patches. 1. At the regional scale a) The number of saplings (forage quantity) is the most important driver of patch selection probability, followed by species composition (forage quality), and species richness. At the patch scale a) Species identity and species composition (i.e., the quality of individual saplings and of the surrounding matrix of neighboring saplings) are the main drivers of selection of individual species. b) the identity of the species will be more important than species composition, forage quantity, or species richness. c) we assume rare species in a patch to be browsed proportionally more than abundant species, irrespective of their identity
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