Monoculture and mixture-planting of non-native Douglas fir alters species composition, but promotes the diversity of ground beetles in a temperate forest system

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Planting non-native tree species, like Douglas fir in temperate European forest systems, is encouraged to mitigate effects of climate change. However, Douglas fir monocultures often revealed negative effects on forest biota, while effects of mixtures with native tree species on forest ecosystems are less well understood. We investigated effects of three tree species (Douglas fir, Norway spruce, native European beech), on ground beetles in temperate forests of Germany. Beetles were sampled in monocultures of each tree species and broadleaf-conifer mixtures with pitfall traps, and environmental variables were assessed around each trap. We used linear mixed models in a two-step procedure to disentangle effects of environment and tree species identity on ground beetle abundance, species richness, functional diversity and species assemblage structure. Contradictory to our expectations, ground beetle abundance and functional diversity was highest in pure Douglas fir stands, while tree mixtures showed intermediate values between pure coniferous and pure beech stands. The main drivers of these patterns were only partially dependent on tree species identity, which highlights the importance of structural features in forest stands. However, our study revealed distinct shifts in assemblage structure between pure beech and pure Douglas fir stands, which were only partially eased through mixture planting. Our findings suggest that effects of planting non-native trees on associated biodiversity can be actively modified by promoting beneficial forest structures. Nevertheless, integrating non-native tree species, even in mixtures with native trees, will invariably alter assemblage structures of associated biota, which can compromise conservation efforts targeted at typical species composition.

Original languageEnglish
JournalBiodiversity and Conservation
Issue number5
Pages (from-to)1479-1499
Number of pages21
Publication statusPublished - 04.2021
Externally publishedYes

Bibliographical note

Funding Information:
Open Access funding enabled and organized by Projekt DEAL. This work was funded by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 316045089/GRK2300.

Funding Information:
We thank Christian Ammer, Serena Müller, Jonas Glatthorn, all members of the RTG 2300 consortium and the local foresters who coordinated and helped with the establishment and maintenance of the project. This work was supported by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—316045089/GRK2300.

Publisher Copyright:
© 2021, The Author(s).

    Research areas

  • Exotic species, Functional diversity, Insects, Microhabitats, Mixed-species forestry, Pseudotsuga menziesii
  • Biology