How to promote spider diversity of heathlands: impact of management intensity

Abstract Heathland health is deteriorating across Northwestern Europe due to various threats which commonly are the result of global change drivers and inadequate management. Varying traditional management practices have been modified to counteract this development, all of which have inevitable trade-offs in terms of promoting associated biodiversity, ecosystem functions and services. These trade-offs are mainly between low (low biomass/soil removal) and high (large biomass/soil removal) intensity management practices. Here we analysed the impacts of low (mowing) versus a newly developed high intensity (scarification, i.e. mowing with subsequent moss removal) management practice on spider diversity, as an excellent bioindicator for habitat quality shifts due to environmental change. We sampled spiders at 15 plots, 5 replicates of the two management practices each, as well as 5 unmanaged controls in the Lüneburg Heath, Northern Germany, one year after the management was implemented. No spider species showed aversion to mowed plots likely due to the increased habitat heterogeneity provided by mowing, while spider abundance and functional richness responded negatively to the increased homogeneity induced by scarification. However, scarification benefited some critically endangered specialists such as Psimmitis sabulosa due to their preference for high bare soil cover. Therefore, managing heathlands with a mosaic of mowed and scarified patches could likely promote spider diversity and protect threatened species while limiting negative effects on functional diversity. Since our results apply to the effect of management on spider biodiversity only one year after the management has been implemented, future research should focus on how these effects change over time.