Predicting old-growth structures in temperate small-scale private forests using landscape data

Abstract Key message Old-growth forest structures in small-scale private forests are strongly shaped by landscape context and can be reliably predicted using freely available spatial data. Remnant forest patches within mixed cultural landscapes act as important reservoirs and connectivity elements for forest biodiversity and should be prioritized in conservation and management planning. Context Many forest species of high conservation concern depend on old-growth structures, which are often rare in contemporary production forests. In small-scale private forests, these structures are fostered by inactive owners and influenced by parcel topography. Aims We attempt to quantify the abundance of old-growth structures in small-scale private forests in Lower Saxony, Germany. Landscape-related predictors are employed to model spatial distribution patterns. Methods The Parcel Index of Conservation Attributes (PICA) was calculated from forest structural data and modeled using a gradient boosting tree model. Independent survey data was used to evaluate its performance externally. The predictions are shown in the form of a spatial distribution map. Results The prediction identified parcels with a high abundance of old-growth structures. These were mostly found outside of large, more intensively managed forest regions and consisted of stands rich in broadleaf trees situated in semi-open, mixed-use cultural landscapes. Conclusion Predictions about the spatial distribution of valuable habitats can be made using freely available landscape-scale data. Verifying these predictions using small samples increases the trustworthiness of the model. Forest patches in fragmented agricultural landscapes can act as islands of old-growth structures. These patches are vital for rare forest species and must be urgently protected.