Effects of Soil Resources and Interspecific Competition on Patterns of Exotic Grass Invasion in Arid Landscapes

EPA Grant Number: U914957
Title: Effects of Soil Resources and Interspecific Competition on Patterns of Exotic Grass Invasion in Arid Landscapes
Investigators: Miller, Mark Steven
Institution: University of Colorado at Boulder
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1996 through January 1, 1999
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1996) RFA Text |  Recipients Lists
Research Category: Fellowship - Geography , Academic Fellowships , Ecological Indicators/Assessment/Restoration

Objective:

In arid landscapes of the Colorado Plateau, ability of the exotic (nonnative) annual grass Bromus tectorum to invade native plant communities varies widely among communities physically juxtaposed on the landscape. The objectivegoal of this research is to determine how spatiotemporal patterns of soil-resource availability and competition from native grasses interact to generate distinct patterns of B. tectorum invasion in Canyonlands National Park, Utah.

Approach:

Variations in the invasibility of native plant communities have been hypothesized to be caused by physicochemical soil characteristics that mediate: (1) patterns of soil-resource availability; and (2) the strength of competitive interactions between B. tectorum and native species. These hypotheses were tested in field experiments initiated in January 1997 at Canyonlands National Park. Experimental plots were established at 17 grassland sites possessing different soil characteristics and different relative abundances of B. tectorum and the native perennial bunchgrass Stipa hymenoides. At each site, 18 circular plots measuring 1.2 m in diameter were randomly assigned to one of 18 multi-factor treatment combinations. Experimental factors combined in the treatments were: (1) species combination (S. hymenoides alone, B. tectorum alone, or both species together),; (2) soil chemistry (treated with KCl, CaO, MgO, or untreated),; and (3) soil moisture (watered on a biweekly basis, or unwatered). Treatment effects on plant performance were quantified by measuring plant densities, seasonal relative growth rates, and end-of-season biomass. Treatment effects on soil chemistry and soil moisture were measured with buried ion-exchange resin bags and soil samples analyzed for volumetric water content. Mineral contents of plant tissues also were analyzed to assess variations in nutrient uptake attributable to experimental treatments. Results strongly suggest that soil CaCO3 is a master variable responsible for among-site variations in Bromus performance at Canyonlands. Growth-rate measurements, tissue analyses, resin-bag data, and geochemical principles in combination indicate that high levels of soil CaCO3 adversely impact Bromus through effects on P nutrition during winter. Subsequent spring growth is highly dependent on previous winter growth, precipitation levels, and soil traits that govern moisture availability due to a spring shift in resource limitation from P to soil moisture. Clear relationships of plant performance to soil characteristics can be illusive in the absence of data relating seasonal growth dynamics to seasonal dynamics of limiting soil resources.

Results strongly suggest that soil CaCO3 is a master variable responsible for among-site variations in Bromus performance at Canyonlands. Growth-rate measurements, tissue analyses, resin-bag data, and geochemical principles in combination indicate that high levels of soil CaCO3 adversely impact Bromus through effects on P nutrition during winter. Subsequent spring growth is highly dependent on previous winter growth, precipitation levels, and soil traits that govern moisture availability due to a spring shift in resource limitation from P to soil moisture. Clear relationships of plant performance to soil characteristics can be illusive in the absence of data relating seasonal growth dynamics to seasonal dynamics of limiting soil resources.

Supplemental Keywords:

fellowship, spatiotemporal patterns, plant communities, soil, soil-resource availability, soil chemistry, soil moisture, nutrient uptake., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Ecology and Ecosystems, habitat dynamics, landscape context, community composition, invasive plant species, community genetic diversity, bunch grass, ecological consequences, soil chemistry

Progress and Final Reports:

  • 1996
  • 1997
  • Final