In this project, I partition forest diversity into structural components by studying the pattern and emergence of herb layer diversity in response to the tree layer diversity and to tree identity as well as to the Ecoscape.
By testing for Janzen-Connell effects, I study effects of biotic components of the Ecoscape on tree layer responses As explanation for the maintenance of biodiversity, I test whether and to what extent regular weeding, phosphorus fertilization and canopy closure can alter herb layer diversity.
Thereby, one focus is to quantify herb layer characteristics and their feedback effects on the trees along an experimental tree biodiversity gradient.
Preliminary tests for Janzen-Connell effects have been conducted to a smaller extent (5 species) in order to detect potential risks in advance.
To quantify the natural seed levels near and far from parent trees, seed traps and adjacent small-scale plots, have been installed in 58 plots.
As major objectives, we test 1.1.) for increasing effects of tree diversity with diminishing influence of the Ecoscape on the herb layer with the time, 1.2.) for changes in tree diversity effects on the herb layer in different nutrient and competition environments (as mediated by phosphate fertilization and no weeding treatments) 2.) for Janzen-Connell effects by studying woody recruitment, and 3.) for important quantitative contributions of the herb layer to the whole CNP balance of the ecosystem.
Accordingly, I assume, that productivity and diversity of the herb layer will be increasingly modified by tree layer diversity and identity with the time, while signals of the Ecoscape will diminish.
In particular, the interactions between biodiversity and ecosystem functions must be much better understood in more complex systems as being provided in forests with their multiple structural layers, each of them contributing separately to the overall diversity.
New insights must be obtained to grasp this multicomplexity of diversity.
As consequences for ecosystem functioning, I also investigate the degree as to which Ecoscape as well as tree layer diversity and identity can alter herb layer productivity and composition.
At last we analyze the role of the herb layer diversity for the nutrient balance, and thus its overall contribution of ecosystem functioning.
Nonetheless, most forest biodiversity studies, just as discussions of threats to biodiversity often ignore the functional role of herb layer.
In my Ph D project, integrated within the “BEF-China” Experiment (FOR 891), a large tree diversity experiment in the subtropics, I address the mechanisms behind tree layer x herb layer interactions by taking profound knowledge of environmental covariation (quantified as the Ecoscape) into account.
The experimental set up of “BEF-China” is designed to separate tree species richness effects from identity effects since all species are equally represented at each diversity level “broken-stick” design.