Effects of Plant Community Structure on Invasion by Exotic Plant Species

EPA Grant Number: U915791
Title: Effects of Plant Community Structure on Invasion by Exotic Plant Species
Investigators: Smith, Melinda D.
Institution: Kansas State University
EPA Project Officer: Michaud, Jayne
Project Period: August 1, 2000 through August 1, 2003
Project Amount: $88,902
RFA: STAR Graduate Fellowships (2000) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems


The objective of this research project is to examine the effects of species diversity and abundance in determining invasibility of plant communities. Specific hypotheses to be tested include: (1) invasion by exotic species will increase with increasing native species richness; (2) invasion will decrease with increasing plant species density (dominance); and (3) density of species, in particular of the dominant plant species, will more strongly influence invasibility than the number of species in a community.


Four levels of richness (4-6, 7-9, 10-12, and 13-16 species) and three levels of density (low, medium, high) will be randomly assigned to tallgrass prairie plots established at the Konza Prairie Biological Station (Manhattan, KS). Species richness will be reduced by removing species according to their frequencies of occurrence in tallgrass prairie. Thus, species that occur at a very low frequency will be removed first. Density will be reduced by removing stems of species also according to their relative frequencies, with only individuals of the most abundant species being removed. Richness and densities will be permanently altered using targeted herbicide applications. Treatments applied in this way will mimic natural processes, such as grazing or climatic variability, which often reduce abundance of the most common species but also result in loss or local extinction of the least common species. Seeds of the exotic legume species, Melilotus officinalis, will be added to treatment plots at a constant density. Invasibility of the experimental plots will be quantified by measuring establishment success and growth of Melilotus. Mechanisms for invasion will be quantified by measuring light availability throughout the growing season, biomass production, community composition, and nutrient availability at the end of the growing season.

Expected Results:

To control and manage invasions and predict which ecosystems are most at risk for future invasions, it is critical that the factors that influence invasions by exotic plant species be identified. Therefore, studies are needed that evaluate characteristics of communities, such as richness and abundance of species that may influence invasibility, and the underlying mechanisms of these factors on invasions of plant communities.

Supplemental Keywords:

abundance, community structure, density, diversity, dominant plant species, exotic species, grassland, invasibility, invasion, invasive species, Kansas, KS, Melilotus officinalis, plants, removal, species richness, tallgrass prairie., RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, State, Ecological Effects - Environmental Exposure & Risk, Ecological Risk Assessment, Ecology and Ecosystems, Ecological Indicators, ecological effects, plant indicator, ecosystem integrity, plant density, conservation, plants, plant community structure, ecological assessment, ecological impacts, Kansas (KS), invasive species, changes in species composition, adaptation

Progress and Final Reports:

  • 2001
  • 2002
  • Final