Forest management intensity measures as alternative to stand properties for quantifying effects on biodiversity

While land use is known to be a major driver of biodiversity loss, it is generally difficult to quantify land-use intensity. As a consequence, studies often use a qualitative approach and contrast different land-use categories, or use structural ecosystem attributes as a proxy for land-use intensity. In this paper we compared these different approaches with two quantitative approaches using forest management as an example. We carried out detailed biodiversity assessments of ten different groups of organisms, ranging from fungi and plants to arthropods and birds; in 12 different forest stands of four forest types in three regions of Southern Germany. We compared the explanatory power of the categorical approach to the explanatory power of (1) stand structural attributes, (2) stand structural complexity indices, (3) measures of forest 'naturalness', and (4) a recently developed quantitative descriptors of land-use intensity in forests, Silvicultural Management Intensity (SMI). The diversities of many taxa differed between the different land-use categories but the explanatory power of the categorical approach strongly decreased when using jackknifing. Single structural attributes explained differences in biodiversity for some taxa which were illustrative for proximate mechanisms underlying biodiversity changes. Stand structural complexity indices i.e., combinations of single structural attributes, showed higher explanatory power than single structural attributes but explained less variation in biodiversity among stands than land-use intensity measures. SMI was negatively correlated with forest 'naturalness', and, for many groups of organisms, increasing SMI decreased biodiversity, but trophic guilds responded differently. Some guilds, such as wood- and bark living fungi, saprophytic arthropods, herbivores, canopy predators and breeding birds showed a clear negative response to increasing land-use intensity, while for others such as plants there was no relationship. Some guilds, such as mosses and ground dwelling predators appeared to even benefit from increased land-use intensity. Using a quantitative measure of land-use intensity can thus help to understand even more subtle relationships between human impact and the diversity of organisms. Measures such as SMI seem to be useful tools for quantifying land-use intensity in forests and may be applied to biodiversity data of different forest ecosystems worldwide.