Invasion of North Temperate Forest Soils by Exotic Earthworms
Principal investigators
Peter M. Groffman, Institute of Ecosystem Studies
Patrick J. Bohlen, Archbold Biological Station
Timothy J. Fahey, Cornell University
Ruth Yanai, Syracuse University
Graduate student:
Esteban Suarez, Cornell University
student research
In this project, we are testing the global hypothesis that earthworm invasion of north temperate forests will have large consequences for nutrient retention and uptake in these ecosystems. Furthermore, we suggest that invasion of new forest habitats by non-native earthworms will be an important component of change in ecosystem processes in many northeastern forests in the coming decades. Previous research has shown that invasion of forests by exotic earthworms dramatically alters forest floor structure and potentially affects key nutrient cycling processes, such as nitrification. However, it is not clear how the dramatic physical changes in forest soil caused by earthworm invasion relate to overall system-level nutrient retention. Virtually nothing is known about the effect of earthworm invasion on plant nutrient uptake, fine-root production or foliar chemistry. We are testing three main hypotheses to increase our understanding of this potentially important process in forest ecosystems. Our predictions are that earthworm invasion will, 1) increase hydrologic and gaseous losses of N and decrease retention of exogenous N, 2) alter soil nutrient-supplying (N and P) capacity with consequences for plant nutrient demand and foliar nutrient contents and 3) change the vertical distribution, production and functioning of fine roots.
We are addressing these hypotheses with a two-pronged approach. The first approach involves controlled introductions of earthworms into experimental forest plots. These plots will provide insight into the transition that occurs immediately following earthworm invasion. The second approach involves comparing forest stands already invaded by earthworms with adjacent stands lacking earthworms, viewing these stands as endpoints along a gradient of earthworm invasion. We are conducting our experiments in forests at two different geographic locations, one in eastern and the other in central New York.
There are numerous opportunities for quantitative analysis and modeling in this project. Earthworm effects on ecosystems are complex, with alterations of both biotic (roots, microbial biomass) and abiotic (soil profile, structure, hydrology) components. A quantitatively-oriented graduate student could greatly improve our assessment of the effects of earthworm invasion on ecosystem processes and advance the start-of-the-art in interdisciplinary environmental modeling as well.
For more information on this project, go to: http://www.ecostudies.org/research/reports/grofrep2.html
Student Research:
Invasion of North Temperate Forest Soils by Exotic Earthworms
Esteban Suárez
This project contributes to our understanding of the distribution of exotic earthworms and their effect on nutrient cycling in northern hardwood forests. Over the last three years I have been monitoring earthworm community dynamics along invasion fronts in the Arnot Forest in central New York. I am also conducting decomposition experiments to determine the effects of earthworms on litter disappearance. In particular, I am examining effects of earthworms belonging to different functional groups. In addition to descriptive and experimental approaches, I will use modeling techniques in two phases of my research. First, I am planning to develop a frame-based spatial model to simulate the invasion of exotic earthworms in the Arnot Forest as a function of interactions among topography (which affects soil moisture), temporal rainfall patterns, and land use history. Ideally, this could help me to i) ascertain if the three variables described are sufficient to explain the current extent of earthworm invasion in the Arnot Forest, and ii) predict the future extent of earthworm invasion under different scenarios of climate change predicted for the northeast. I will also use modeling to explore the potential long-term effect of exotic earthworm activity on the storage of soil organic matter in northeastern hardwood forests. I will use an extensive data set collected in earthworm-invaded and control sites at the Arnot Forest to parameterize the CENTURY model. I will then use CENTURY to assess the net effect of earthworm invasion on long-term soil organic matter accumulation and nutrient cycling.
top
Overview