Spatio-temporal analyses of local biodiversity hotspots reveal the importance of historical land-use dynamics

Woodland key habitats (WKHs) form a network of local biodiversity hotspots in human-dominated landscapes of northern Europe. They have been designated based on the presence of old-growth species and structures, and are considered to indicate long-term forest cover. To test whether WKHs do particularly occur in continuous forest land and to explore the scale dependence of relationships between WKH presence and their historical and environmental properties, we analysed them at five spatial scales (from stand to landscape: 80-2500 m) and referring to four reference years (1790, 1860, 1910, and 2010) using univariate and multivariate analyses. We upscaled the georeferenced data using a moving window approach. The study area encompassed 94,886 contiguous forest stands in a boreo-nemoral region of southern Latvia (5178 km(2)) with a relatively short history of intensive land use. At the scale of stands, the presence of WKHs, ranging from 0.1 to 59 ha in size, best corresponded to highly variable land-use histories 100-220 years ago such as natural succession on abandoned land, drained bogs and wetlands, and only partly to continuous forest cover for more than 220 years. We identified short-term (50-70 years) and small-scale (up to 250 m) gaps in past forest cover as significant positive predictors of WKH presence, which resemble patterns caused by natural disturbances. At broader scales (800-2500 m), best explanatory variables were the presence of old forest fragments throughout the landscape, at least 100 years of continuous forest cover, changes in forest cover, i.e., afforestation, between 1790 and 1860, and the proximity to bogs and rivers. We also found that correlations between WKH presence and forest patch density converted from negative coefficients at small spatio-temporal scales to positive ones at broader spatio-temporal scales. Our results highlight the importance of using multi-scale information on land-use history to improve both the understanding and the management of biodiversity in cultural landscapes. In brief, instead of long-term continuous forest cover, we found a surprisingly diverse and dynamic land-use history in places that have been designated as WKHs.