Jan Helbach¹, Julian Frey2,*, Christian Messier3 & Michael Scherer-Lorenzen¹
Contact person: Jan Helbach (jan.helbach@biologie.uni-freiburg.de), University of Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany
1. Geobotany, Faculty of Biology, University of Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany
2. Chair of Remote Sensing and Landscape Information Systems, Faculty of Environment and Natural Resources, University of Freiburg, Tennenbacherstr. 4, 79106 Freiburg, Germany
3. CEF, ISFORT, Université du Québec en Outaouais et à Montréal, Montréal, Canada
*Current address: Chair of Forest Growth, Faculty of Environment and Natural Resources, University of Freiburg, Tennenbacherstr. 4, 79106 Freiburg, Germany
Keywords: understory diversity, environmental heterogeneity, stand structural diversity, coexistence, community ecology, ConFoBi
Abstract One of the most important drivers of the coexistence of species is the resource heterogeneity of a certain environment. Thus, many studies in different ecosystems have been carried out to test whether species richness is affected by resource heterogeneity. To date, only few studies have measured light and soil resources heterogeneity in forests to investigate its influence on plant diversity. In this study, the aim was to determine (1) which resources have major influences on forest understory plant diversity; (2) the influence of the forest canopy on the heterogeneous distribution of light and soil resources; (3) whether heterogeneity of resources increases understory plant species richness; and (4) if stand structural complexity is an indicator for understory plant species richness. Measures of stand structural complexity were obtained through inventories and remote sensing techniques in 135 study plots of temperate forests, established along a gradient of forest structural complexity. We surveyed vegetation, measured light conditions and soil properties six times in each of all plots. We calculated the standard deviations of these parameters to receive a measure of heterogeneity. Results showed that heterogeneity of light and soil C:N ratio increases with increasing stand structural complexity, increasing light heterogeneity leads to increased understory plant species richness, and finally, an increase of stand structural diversity predicts an increase in understory plant diversity. The study clearly shows that resource heterogeneity theory plays a major role in the coexistence of understory plant species and hence its diversity. These results suggest that understory plant diversity could be increased in forests managed by single tree harvesting by spatially varying the quantities of trees to be logged to create a more heterogeneous understory light environment. Introduction