2002 Progress Report: Abiotic Controls on Invasive Species and Biodiversity: Comparison of Forest and ShrublandEPA Grant Number: R828901
Title: Abiotic Controls on Invasive Species and Biodiversity: Comparison of Forest and Shrubland
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 Period Covered by this Report: July 15, 2001 through July 14, 2002
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
Plant invasion is subject to biotic as well as abiotic controls. The objective of this research project is to investigate the abiotic controls on plant invasion in coastal sage scrub and conifer forest ecosystems of southern California. Specifically, we have focused on the controls on mineral nitrogen availability and the impacts of this availability on the presence, absence, and dominance of invasive plant species. Our starting hypothesis was that coastal sage scrub ecosystems would be more susceptible to increases in atmospheric nitrogen deposition because of the relatively closed nitrogen cycle in these ecosystems compared to the more open nitrogen cycle of conifer forests in southern California.
During the past year of the project, our work has focused on two main areas. The first area details the vertical movement of water and nitrogen in the coastal sage scrub and forest ecosystems of southern California. This work is meant to determine how closed or open the system is to atmospheric deposition inputs. The second area involves understanding the influence of the invasive grasses and soil nitrogen concentrations on biogeochemical turnover in the coastal sage scrub. This biogeochemical work has a direct impact on how this ecosystem is influenced by plant invasion. The first year results for soil fate and transport cover the soil system with depth under extreme drought conditions and provide a base for comparing the movement of the measured anions, chloride, and nitrate in wetter years. At the forest sites, steep mountainous terrain and subsurface geomorphology are expected to control solute transport through soils during precipitation and snowmelt events. Several studies currently are investigating the biogeochemistry of the invasive grasses communities in the semi-arid sites in Riverside County. In particular, the results of a decomposition study indicate that litter N is the key to decomposition rates.
One particular road-block this past year was that the 2002 water year was among the driest (at several of our sites the driest) years on record. Therefore, there was almost no plant response (most annuals did not germinate or failed to thrive upon germination), and our fate studies found little change in subsurface conditions. With the wetter conditions this winter, we expect to be able to conduct successful surveys this upcoming spring.