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