2003 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 , 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 Period Covered by this Report: July 15, 2002 through July 14, 2003
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 (CSS) and conifer forest ecosystems of southern California. Specifically, we have focused on the controls on mineral nitrogen (N) availability, and on the impacts of this availability on the presence, absence, and dominance of invasive plant species. Our starting hypothesis was that CSS ecosystems would be more susceptible to increases in atmospheric N deposition because of the relatively closed N cycle in these ecosystems compared to the more open N cycle of conifer forests in southern California.
Our work has been focused on two main areas. The first details the movement of water and N vertically in the CSS 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 involves understanding the influence the invasive grasses and soil N concentrations have on biogeochemical turnover in the CSS. This biogeochemical work has a direct impact on how this ecosystem is influenced by plant invasion. The 2 years of results for soil fate and transport cover the soil system with depth under extreme drought and relatively wet conditions and provide a good comparison with each other. At the forest sites, steep mountainous terrain and subsurface geomorphology controls solute transport through soils during precipitation and snowmelt events. At the CSS sites, conversion to grasses decreases infiltration depths and increases N and water availability to invasive grasses. Several studies currently are investigating the biogeochemistry of the invasive grass 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, indicating a positive feedback between increased deposition and plant invasion.
We will focus on analyzing vegetation survey data and spatial remote sensing of the subsurface to determine if the results at our specific sampling points can be extended over the broader landscape. Work also will shift to simulate this system under different climate, vegetative, and hydrologic conditions using the detailed field data that we have collected.