Subproject 11: Invasibility
Invasion - diversity interactions in subtropical forests: the interplay of herbaceous and woody species richness
PI: Alexandra Erfmeier, Dr. (University of Halle)
Co-PI: Helge Bruelheide, Prof. Dr. (University of Halle)
Summary
This subproject will study effects of tree and shrub species richness and composition on herb layer species richness, composition and invasion in subtropical China. We regard herb layer community composition (1) as response variable to in the Main Experiment and (2) as a predictor variable for invasion resistance towards exotic plant species. We will record herb layer species composition before and after clearing of the existing vegetation for tree and shrub planting and subsequently in the newly planted plots of the Main Experiment to study relationships between herbaceous and woody species diversity. After tree and shrub planting, we will analyze the influence of woody species diversity on the invasion of exotic herbs into the plots. The analysis of diversity-invasibility relationships will be complemented by seed and seedling addition experiments using both native and exotic herbs in the Main Experiment and in the glasshouse. In the Main Experiment, the influence of propagule pressure on the invasion success will be studied by manipulating seed rain intensities for selected herbaceous species. In the glasshouse, we will assess the influence of resource availability and disturbance on the invasion success of exotic herb species.
The monitoring in the field will be done in close collaboration with the Chinese partner project. While the present project focuses on effects of woody species richness and environmental factors on herb layer responses, the Chinese partner will focus on relationships between native and exotic herbaceous plant assemblages.
Objectives
Monitoring studies on herb layer communities as part of the baseline studies in the research group aim at assessing to what extent tree layer and/or structural diversity can act as predictor of overall diversity through a positive effect of complementarity. Additionally, it is meant to determine the relative proportion of exotic species already present in the plots. Experimental approaches aim at quantifying factors covarying with species richness.
The specific aims and methods of this subproject are:
1. Analysis of tree species richness effects, field monitoring: The occurrence of resident native species and invasive exotic plants in the herb layer will serve as ecosystem functioning variable of the Main Experiment.
2. Analysis of native-exotic relationships (NER) in herb layers: field experiment Artificial herb layer communities with different species diversity levels will encounter different levels of exotic diversity in a complete design.
3. Identification of covariates of diversity effects: field experiment: This approach is meant to test for the effects of propagule pressure, disturbance intensities and resource availability on exotic species invasion by seed and seedling addition treatments with different seed rain intensities.
4. Analysis of covariates under controlled conditions, glasshouse experiment: This approachs intends to manipulate genotypic diversity of exotic species across different experimental environments to disentangle chance effects of propagule establishment and genotype effects.