Exclusion of large herbivores affects understorey shrub vegetation more than herb vegetation across 147 forest sites in three German regions.

Deborah Schäfer,Daniel Prati,Markus Fischer,Peter Schall,Christian Ammer

doi:10.1371/journal.pone.0218741

Deborah Schäfer, Daniel Prati + Show 3 more

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https://doi.org/10.1371/journal.pone.0218741

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Journal: PloS one	Publication Date: Jul 10, 2019
Citations: 10	License type: CC BY 4.0

Affiliation: University of Bern, University of Göttingen

Abstract

BackgroundMany studies have analysed the effect of browsing by large herbivores on tree species but far fewer studies have studied their effect on understorey shrubs and herbs. Moreover, while many studies have shown that forest features and management intensity strongly influence understorey vegetation, the influence of such variation on the effect of large-herbivore exclusion is not known.This studyIn this study, we analysed changes of species richness, Shannon diversity, evenness and cover of understorey herbs and shrubs after excluding large herbivores for seven years on 147 forest sites, differing in management intensity and forest features, in three regions of Germany (Schwäbische Alb, Hainich-Dün, Schorfheide-Chorin). Further, we studied how the effect of large-herbivore exclusion on understorey vegetation was influenced by forest management intensity and several forest features.ResultsAs expected, exclusion of large herbivores resulted in highly variable results. Nevertheless, we found that large-herbivore exclusion significantly increased cover and Shannon diversity of shrub communities, while it did not affect herb communities. Forest management intensity did not influence the effect of large-herbivore exclusion while some forest features, most often relative conifer cover, did. In forests with high relative conifer cover, large-herbivore exclusion decreased species richness and cover of herbs and increased Shannon diversity of herbs and shrubs, while in forests with low relative conifer cover large-herbivore exclusion increased species richness and cover of herbs, and decreased Shannon diversity of herbs and shrubs.ConclusionWe suggest that browsing by large herbivores should be included when studying understorey shrub communities, however when studying understorey herb communities the effects of browsing are less general and depend on forest features.

Highlights

The influence of herbivores on the diversity and composition of Central European forest communities is subject to a long and controversial debate (e.g. [1,2])
Exclusion of large herbivores resulted in highly variable results
We suggest that browsing by large herbivores should be included when studying understorey shrub communities, when studying understorey herb communities the effects of browsing are less general and depend on forest features

Summary

Introduction

The influence of herbivores on the diversity and composition of Central European forest communities is subject to a long and controversial debate (e.g. [1,2]). Together with the reduction of natural predators and partly low hunting intensity, an increase in forage quality through agricultural and silvicultural activities (i.e. overall higher nutrient input) and landscape fragmentation has led to a higher number of large herbivores during the last decades [5,6,7]. These large herbivores, in Central Europe mostly red deer, roe deer, fallow dear and wild boars, can severely damage forest plants by consuming herbs, buds of shrubs and trees, and plant roots. For a comprehensive assessment of the role of herbivory in Central European forests, more multi-site and large-scale studies across different forest types are needed that include shrub and herb species in understorey vegetation

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