Impact of Invasive Plants on Detrital Food Webs

EPA Grant Number: F6F21394
Title: Impact of Invasive Plants on Detrital Food Webs
Investigators: Wolkovich, Elizabeth
Institution: Dartmouth College
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $111,172
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Academic Fellowships , Fellowship - Ecology


Systems undergoing conversion from one dominant plant type to another experience a number of alterations, including changes in physical structure, nutrient availability, and spatial and temporal patterning of resources. These changes are produced by both the living plant and its litter, which can comprise the major portion of a system’s detritus, the pathway through which over 90% of all system energy flows. Studies on invasive plants have often found their litter to be of generally better quality than native plants’ and important a posteriori, but little work has explicitly examined both the community and ecosystem impacts of non-native litter. I am asking a number of questions, including: How do changes in detritus associated with landscape conversion from one functional type to another alter detritus-based food webs and related ecosystem functioning? How do dramatic shifts in detrital quality and quantity alter higher trophic levels of the detrital (“brown”) and grazing (“green”) webs?


The invasion of annual European grasses into semi-arid coastal sage scrub provides an excellent opportunity to examine the effects of drastic changes in detrital composition, as the system shifts from being shrub to grass dominated. Abundant labile grass litter is hypothesized to cause altered soil communities, which are reduced in arthropod abundance but increased in bacteria. Changes are also expected in ecosystem functioning: more abundant labile litter is hypothesized to lead to greater soil organic matter and more rapid soil nitrogen mineralization. These hypotheses are being tested using observations, experiments and modeling. An observational study was conducted in spring 2004 and 2005 which found reduced arthropod abundance and increased soil carbon and nitrogen with increased non-native grass. These results are currently being tested by a litter addition and removal experiment; ecosystem and community parameters are being measured to quantify predicted changes in the soil community and in ecosystem functioning. Finally, modeling studies will test more generally how changes in litter quality and quantity affect upper trophic levels. Using a Lotka-Volterra based model including both the brown and green webs, simulations will be used to examine whether changes in litter quantity and quality leads to predicted increases in top trophic levels.

Expected Results:

Using the invasion of coastal sage scrub by common non-native grasses will provide a start to understanding how plant invasions involving conversion of a landscape from one functional type to another, with the requisite changes in a system’s detritus, contribute to food web shifts and to predict whether observed patterns may be consistent across other systems. This work also has benefits for conservation and restoration of coastal sage scrub, an ecosystem highly threatened by urbanization that provides habitat to a number of federally endangered species.

Supplemental Keywords:

Invasive species, arthropods, food webs, bottom-up, top-down, detritus, coastal sage scrub, Mediterranean grasses,, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Environmental Monitoring, Ecology and Ecosystems, dynamic landscapes, habitat dynamics, detritus based food web, Lotka Volterra model, habitat disturbance, invasive plant species, habitat fragmentation, soil chemistry, exotic grass species

Progress and Final Reports:

  • 2007
  • 2008
  • Final