2002 Progress Report: Predicting the Distribution and Dominance of Exotic Species Across Landscapes of Southern AppalachiaEPA Grant Number: R828897
Title: Predicting the Distribution and Dominance of Exotic Species Across Landscapes of Southern Appalachia
Investigators: Huston, Michael A. , Johnston, J. W. , Pounds, Larry R.
Institution: Interdisciplinary Solutions for Environmental Sustainability Inc.
EPA Project Officer: Hiscock, Michael
Project Period: September 1, 2001 through August 31, 2004 (Extended to January 31, 2006)
Project Period Covered by this Report: September 1, 2001 through August 31, 2002
Project Amount: $448,205
RFA: Exploratory Research to Anticipate Future Environmental Issues (2000) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Water , Ecosystems
Displacement of native species by invasive exotic species is one of the most serious types of "biopollution" and is a major threat to biodiversity worldwide. Over the past few years, several field studies (Stohlgren et al. 1999; Lonsdale 1999) have found results that contradict a central tenet of the classical ecological theory of invasibility, calling into question the conclusion that high species diversity confers resistance to invasion. The primary objective of this research project is to develop a method for predicting spatial patterns of exotic species invasion and dominance across landscapes, as well as the time period over which a particular exotic species is likely to be a problem in a given area. We also will determine the degree to which the physiology and life history traits of invasive species are correlated with the spatial patterns of invasion, specifically with patterns of disturbance and resource availability. This will allow prediction of which environment a particular exotic species is most likely to invade, whether its effect will be severe or minor, and how long it is expected to be a problem in relation to changes in environmental conditions caused by natural successional changes.
The main objectives of this research project are to: (1) test the ecological theory of invasions based on environmental properties; and (2) develop a method for predicting spatial patterns of exotic species invasion and dominance across landscapes, as well as the time period over which a particular exotic species is likely to be a problem in a given area. The approach taken here differs from the traditional approach to understanding plant invasions, which focused on the properties of species, specifically those properties that made them more "weedy" or "invasive." Our approach is based on the dynamic equilibrium model of species diversity, and assumes that both native and exotic species respond similarly to environmental conditions; particularly those related to mortality-causing disturbances and resources necessary for growth. This model predicts that the most favorable conditions for plant establishment and survival (and consequently, high species diversity) should occur where physical conditions allow survival of most species but competitive interactions are weak and competitive exclusion occurs slowly, if at all. These conditions predicted to occur where resource availability (and thus plant growth and productivity) is low and disturbances are infrequent, but also where plant resource availability is high and mortality-causing disturbances are frequent (Huston 1979, 1994).
One corollary is that the diversity of native and exotic species should be positively correlated (see Figure 1a). This prediction is the opposite of classical competition theory, which predicts that the correlation should be negative, because communities with a high diversity of native species should be more resistant to invasion than communities with low diversity. In addition, the model predicts that plant dominance should be highest, and thus the potential impact of invasive species greatest, under productive conditions where competitive exclusion occurs more rapidly (see Figure 1b). Our model of invasions thus predicts the probability and intensity (impact) of plant invasions, as well as the probable duration of the survival of a population of exotic species, based on the rate of competitive exclusion. This research project will test these predictions using a combination of field surveys and experiments.
Figure 1. Predicted Community Susceptibility to Establishment and Dominance of Invading Species in Environments Classified According to Disturbance and Productivity. ( a) Predicted susceptibility of communities to invasion. Darker shading indicates higher susceptibility. Ellipses indicate the predicted contours of species diversity, with the highest diversity within the smallest ellipse in the lower left. Note that communities with low diversity are least likely to be invaded successfully, and communities with high diversity are most likely have invaders establish successfully. (b) Predicted dominance and life histories of successful invaders under various combinations of productivity and disturbance. Shading indicates expected dominance of a community by a successful invader.
The first year's activities focused on the spatial patterns of exotic and native plant species distributions on the landscape of the Oak Ridge National Environmental Research Park, near Knoxville, Tennessee. This landscape has a unique history because of its role in the Manhattan Project during World War II. Prior to the war, this area was rural and isolated, with much of the population engaged in subsistence agriculture and living in log cabins. Most of the landscape was in cultivated fields and pasture, with a relatively small proportion in forest. In 1942, the entire population was evicted and relocated, and the area was secured for the top-secret activities of the Manhattan Project. The entire landscape, with the exception of three isolated areas dedicated to nuclear research and production, was abandoned and natural succession allowed to occur. Most of the landscape is now forested, and relatively undisturbed outside of the roads, powerline rights-of-way and the three Manhattan Project facilities.
The distribution of vegetation sampling plots was designed to sample topographic variability on three major ridge-forming geological formations on the Oak Ridge National Environmental Research Park, located Ridge and Valley physiographic province near Oak Ridge, Tennessee. Two transects, 1 km in length, one initiated at the base of the north-facing slope, and one at the base of the south-facing slope were established on Black Oak Ridge, East Fork Ridge, Pine Ridge, Chestnut Ridge, Haw Ridge, and Copper Ridge, with sample plots every 50 m. Each multi-scale sample plot was composed of three 1 x 1-m plots for species-cover estimates, nested within a 5 x 5-m and a 10 x 10-m plot, in which all species were identified. With sample plots every 50 m, the 12 transects contained 240 10 x 10-m sample plots, with 720 1 x 1-m plots with cover and height measurements for all species. Sampling focused on understory vegetation, both herbaceous and woody, native and exotic. Ancillary data include forest basal area by species, canopy openness, litter mass, and soil pH, and carbon and nitrogen in the 0-10 cm layer. All plots were visited at least three times during the growing season to identify species differing in phenology and to determine the identities of all species present. Field data were quality checked and entered into Excel spreadsheets, and the global positioning system (GPS) locations of all plots entered into a MapInfo geographic information system (GIS). Vegetation sampling was completed by mid-October, 2002. Preliminary analysis indicates that our sample plots encountered approximately 480 out of the total of 1,100 plant species recorded on the Oak Ridge Reservation. Of these, 37 species were nonnative, out of the total of 167 nonnative species recorded on the reservation. Most of the 37 exotic species occurred at very low frequencies, with only three species present in more than 10 percent of the 240 10 x 10-m plots (see Figure 2). Thus, after 60 years of recovery, the formerly agricultural landscape is now covered by forest with a relatively low incidence of exotic species. Other patterns of interest from the preliminary analyses include a negative correlation of forest basal area with the cover and species richness of both native and exotic species, with a more rapid decline of exotic species richness than of native species richness. We also found a positive correlation between the number of native and the number of exotic species per plot, which also has been reported in several larger scale surveys published over the past several years. This positive correlation is consistent with our model of invasibility, but contradicts the predictions of classical invasion theory.
Figure 2. Ranked Frequencies of Exotic Plant Species Encountered During Systematic Sampling of Landforms and Geological Formations of the Oak Ridge Reservation in Eastern Tennessee. Most of the landscape is forested. Frequencies are based on presence in 240 completely censused 10 x 10-m plots, distributed as 12 transects 1-km in length, with 10 x 10-m sample plots every 50 m. Note that only 3 out of 37 species were present in more than 10 percent of the plots. These species were Lonicera japonica, Microstegium viminium, and Ligustrum sinense.
Plans are being developed with the research and resource management staff from the Great Smoky Mountain National Park to examine radial patterns of native and exotic species abundance in relation to back-country campgrounds. Some campgrounds, particularly those that have been used by horses, have a high incidence of exotic species, while campsites used by hikers only have very few exotic species. We will use a transect approach similar to that used on the Oak Ridge Reservation to sample patterns of native and exotic species richness around campsites in different major vegetation types within the park. In addition, we will conduct resource manipulation experiments (light, water, soil nutrients, and leaf litter) on the Oak Ridge Reservation to test hypotheses related to environmental constraints on the spatial distribution of common exotic species.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 14 publications||1 publications in selected types||All 1 journal articles|
||Huston MA. Management strategies for plant invasions: manipulating productivity, disturbance, and competition. Diversity and Distributions 2004;10(3):167-178.||