The Collembola community of pure and mixed stands of beech (Fagus sylvatica) and spruce (Picea abies) of different age

SummaryThe idea of establishing mixed forests that are better adapted to site conditions than spruce monocultures has attracted increasing attention of forest owners and governmental institutions over the last decades. Currently, beech is being replanted and an increasing proportion of German forests are mixed stands. Focusing on the reaction of the soil fauna to forest conversion, this study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce. Stands of different age were investigated in a factorial design with the factors stand type (beech, spruce and mixed stands) and stand age (30 and 120 years). Collembola communities did not differ strongly between stand types and stand age and were dominated by Folsomia quadrioculata and Mesaphorura species (e.g. Mesaphorura macrochaeta). Moreover, neither total abundance of Collembola nor densities of the fungal feeding euedaphic Onychiurinae and Tullbergiinae significantly responded to stand type and stand age. The density of the epedaphic and partly herbivorous groups Symphypleona/Neelipleona and Entomobryidae in the 120-year-old stands significantly exceeded that in the 30-year-old stands; presumably, this was due to the well developed herb layer in the 120-year-old stands with more open canopies. Canonical correspondence analysis (CCA) of the Collembola community of the L/F horizon also indicated that most of the epigeic species were associated with the 120-year-old stands. Moreover, the diversity of Collembola significantly increased with forest age which likely reflects increased amount and diversity of food resources in the 120-year-old stands. The density of the hygrophilous species Fo. quadrioculata was significantly higher in the spruce than in the beech stands; probably this was due to the higher water content in litter of the spruce stands. Moreover, the results of the CCAs indicated that soil pH is an important structuring force for the Collembola communities. Overall, the results suggest that stand type and forest age impact Collembola communities, presumably via changes in the amount and quality of food resources, such as living plant and herb litter materials. The pronounced changes which occurred with forest age likely were related to the development of more dense and diverse herb layer in mature forests which provides additional food resources in particular for epedaphic species. On the other hand, dominant species/functional groups of Collembola, such as hemiedaphic species, appear to depend predominantly on abiotic factors, most importantly soil pH and soil water content.