Changes in soil mesofauna communities with increasing proportions of Douglas-fir and silver fir in European beech forests

Temperate forests are challenged by increasing temperature and drought events due to climate change. In order to enhance forest resilience, mixed forest stands are increasingly promoted. However, little is known on how different mixture proportions affect soil animal communities as drivers of litter decomposition and other ecosystem functions. We investigated major soil mesofauna groups, including oribatid mites (Oribatida, Acari) and collembolans (Collembola, Insecta) as detritivores and mesostigmatid mites (Mesostigmata, Acari) as predators, in mixed stands of European beech (Fagus sylvatica) with two conifer species of different proportions including non-native Douglas-fir (Pseudotsuga menziesii) and native silver fir (Abies alba) in southern Germany. Oribatid mites were most abundant and diverse, and responded sensitively to changes in forest type with an altered community composition at species- as well as family-level. Collembolans were less abundant and featured lower diversity, which was higher in Douglas-fir - beech compared to silver fir - beech mixtures. Mesostigmatid mites were least abundant, while reaching an intermediate species richness, and did not significantly respond to forest mixtures. However, only species composition of oribatid mites at both family- and species-level responded to differences in forest types pointing to similar effects of low and high conifer proportions in mixed beech stands on soil mesofauna communities, indicating that in particular oribatid mites may serve as indicator for consequences of planting different mixed forest types. Overall, the results indicate that the consequences of planting non-native and native conifers, such as Douglas-fir and silver fir, in mixed stands with beech are similar with the mesofauna community in both overlapping in large with that in pure beech stands.