Open-grown trees as key habitats for arthropods in temperate woodlands: The diversity, composition, and conservation value of associated communities
Abstrakt
Temperate open woodlands are recognized as biodiversity hotspots. They are characterised by the presence of scattered, open-grown, often old and large trees (hereafter referred to as "solitary trees").
Such trees are considered keystone ecological features for biodiversity. However, the ecological role of solitary trees and their importance for woodland communities are still not fully understood.
Communities of arthropods in temperate forests are often structured not only by the horizontal openness of the stand, but also by vertical stratification. Thus there is a need for comparisons among communities associated with solitary trees and different forest strata.
In this study, we analysed the diversity, conservation value, and nestedness of four taxonomic groups (beetles (Coleoptera), bees and wasps (aculeate Hymenoptera), ants (Formicidae), and spiders (Araneae)) on (i) solitary trees in open woodlands, and four habitat types in adjacent closed-canopy forests: (ii) edge-canopy, (iii) edge-understorey, (iv) interior-canopy, and (v) interior-understorey. Across the focal insect groups, solitary trees harboured the greatest number of species, whilst spider communities were also equally rich in forest edge canopies.
The conservation value of communities was highest in solitary trees for beetles, and in solitary trees and edge-canopy habitats for bees and wasps. For spiders, the conservation value was similar across all habitat types, but ordination analysis revealed general preferences for solitary trees among threatened species.
We also found that communities from the forest interior were mostly only nested subsets of the communities found on solitary trees. Our results show an important and irreplaceable role that open-grown trees have in maintaining temperate woodland biodiversity.
Therefore, preservation and maintenance of open-grown trees should be a primary concern in biological conservation.