Abstract. 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.
Summary
Data about the relative densities of raptors are analysed in comparison to landscape patterns in southern Africa. The impact of man on the environment reduces the diversity of raptor communities. Different raptor groups are influenced differently by man, with habitat destruction as the outstanding negative factor, especially on eagles. Black‐shouldered kite (Elanus caeruleus) and black kite (Milvus migrans) are enhanced by human activities, the former by habitat, the latter by diet. A comparison of data from the literature indicates a decline of raptors (black‐shouldered kite excluded) during the last 30 years in Transvaal and Orange Free State.
Résumé
Des données concernant les densités relatives de certains rapaces sont analysés en fonction des types d'habitats en Afrique australe. L'impact de l'homme sur l'environment réduit la diversité des communautés de rapaces. Des groupes différents de rapaces sont influencés différemment par I'homme, la destruction de l'habitat étant le facteur négatif majeur, spécialement chez les aigles. L'élanion blanc (Elanus caeruleus) et le milan noir (Milvus migrans) sont favorisés par les activités humaines, le premier par l'habitat, le second par la nourriture. Une comparaison des données de la littérature indique un déclin des rapaces (excepté l'éelanion blanc) durant les 30 dernières années au Transvaal et dans l'Etat Libre d'Orange.
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