Abiotic Controls on Invasive Species and Biodiversity: Comparison of Forest and Shrubland

EPA Grant Number: R828901
Title: Abiotic Controls on Invasive Species and Biodiversity: Comparison of Forest and Shrubland
Investigators: Meixner, Thomas , Allen, Edith B. , Fenn, Mark , Poth, Mark
Current Investigators: Meixner, Thomas , Allen, Edith B. , Fenn, Mark
Institution: University of California - Riverside
EPA Project Officer: Hiscock, Michael
Project Period: July 15, 2001 through July 14, 2004 (Extended to June 14, 2005)
Project Amount: $448,122
RFA: Exploratory Research to Anticipate Future Environmental Issues (2000) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Water , Ecosystems


Atmospheric nitrogen (N) deposition rates in southern California are among the highest in North America. This same region is the habitat for numerous threatened and endangered species. N deposition may be accelerating the replacement of native vegetation by invasive species even in areas that have been set aside as endangered species preserves. Atmospheric N deposition therefore represents a threat to species preservation plans in southern California and elsewhere in the west. However, different ecosystems in southern California are responding in different ways to increases in N deposition, coastal sage scrub (CSS) is being converted into exotic annual grassland while overstory and understory communities in coniferous forests appear to be more resistant to invasion.

We propose that the reason for this differing response to N deposition is in the hydrologic properties of the two systems. The CSS is a relatively closed system due to low rates of rainfall and runoff. The coniferous forests are open due to high rates of rainfall and runoff. The CSS thus retains a greater fraction of deposition encouraging the growth of invasive weeds while the coniferous zone retains a smaller fraction of deposition and is thus less susceptible to invasion.


We will conduct a number of studies to verify the closed versus open nature of the two systems and determine the effects of N deposition on plant composition along two N deposition gradients. We will conduct irrigation experiments to investigate the effect of increased precipitation in CSS and coniferous systems. We will determine the rates of N cycling within the CSS and coniferous systems as well as the gaseous and hydrologic fluxes of N. We will also conduct vegetation surveys across N deposition gradients in the CSS and coniferous zones to determine the prevalence of invasive species in the two systems and to quantitatively match the degree of invasion to the amount of deposition.

Expected Results:

With our hydrologic N process and vegetation studies, we hope to determine the relationship of N deposition to species loss that could be used to support regulation of the sources of atmospheric N deposition in response to endangered species issues.

Supplemental Keywords:

acid deposition, ecological effects, nitrogen oxides, terrestrial ecosystem, restoration, ecology, hydrology., RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, State, Forestry, Ecological Effects - Environmental Exposure & Risk, Monitoring/Modeling, Biology, Futures, Exp. Research/future, atmospheric nitrogen, emerging environmental problems, extinction risk, ecological exposure, biodiversity, endangered species, forest, biopollution, shrubland, runoff, exploratory research, hydrology, invasive species, irrigation, forests, ecological dynamics, rainfall, California (CA), acid deposition, futures research

Progress and Final Reports:

  • 2002 Progress Report
  • 2003 Progress Report
  • 2004
  • Final Report