Thursday, August 6, 2009: 3:20 PM
Picuris, Albuquerque Convention Center
Background/Question/Methods Theoretical and empirical evidence suggest that herbivory, soil fertility and neighborhood interactions interactively determine rates of species extinctions and immigrations in plant communities. Initial community properties may also exert a profound influence on community responses to external alterations, yet only a few attempts have been made to elucidate their role in assemblage dynamics. I conducted a seed sowing experiment in northern European mountain tundra to investigate the roles of biotic and environmental constraints on plant immigration, and the dependence of these relationships on inherent community properties. I factorially manipulated the presence of mammal herbivores and neighboring adult plant biomass, soil nutrient availability and pH, and replicated these treatments in five acidic and five non-acidic sites that showed contrasting patterns of inherent community properties, i.e. functional community composition, dominance and soil fertility. Seed mixture of 16 species was added to all experimental plots to outweigh dispersal barriers, and the emergence and establishment of seedlings in different treatments were followed for three years.
Results/Conclusions I found that exclusion of mammal herbivores had no significant impact on plant colonization rates nor did it interact with any other treatments. However, colonization rates were negatively influenced by fertilization and positively affected by the removal of neighboring adult vegetation, and the biomass removal counteracted the negative effects of nutrient enrichment. The effects of fertilization and biomass removal on seedling recruitment were both greater in the non-acidic habitats; the among habitat differences were associated with initial nutrient availability and forb:shrub ratio of vegetation, but were independent of community evenness. Fertilization effects on immigrations became increasingly negative in relation to increasing prevalence of forbs which may be explained by the greater biomass increment potential of forbs under conditions of nutrient enrichment. Biomass removal enhanced colonization rates to a smaller extent in high shrub dominance where the overall recruitment was lowest, suggesting that dominant shrubs can create a more stressful environment for seed germination that persists even after the removal of the dominant vegetation itself. My results highlight the role of initial community properties, i.e. the potential for productivity increase of the resident species and the traits of the dominant plant groups as important mediators of biotic and environmental perturbations on plant immigration rates.
Results/Conclusions I found that exclusion of mammal herbivores had no significant impact on plant colonization rates nor did it interact with any other treatments. However, colonization rates were negatively influenced by fertilization and positively affected by the removal of neighboring adult vegetation, and the biomass removal counteracted the negative effects of nutrient enrichment. The effects of fertilization and biomass removal on seedling recruitment were both greater in the non-acidic habitats; the among habitat differences were associated with initial nutrient availability and forb:shrub ratio of vegetation, but were independent of community evenness. Fertilization effects on immigrations became increasingly negative in relation to increasing prevalence of forbs which may be explained by the greater biomass increment potential of forbs under conditions of nutrient enrichment. Biomass removal enhanced colonization rates to a smaller extent in high shrub dominance where the overall recruitment was lowest, suggesting that dominant shrubs can create a more stressful environment for seed germination that persists even after the removal of the dominant vegetation itself. My results highlight the role of initial community properties, i.e. the potential for productivity increase of the resident species and the traits of the dominant plant groups as important mediators of biotic and environmental perturbations on plant immigration rates.
