RUI: Fluctuating Resources and Mechanisms of Invasibility Along the Prairie-Forest Border

Macalester College, Saint Paul MN

Investigators

Abstract

0208125 Davis It is widely agreed that invasion ecology theory needs to become more mechanistic, quantitative, and predictive and that field experiments and better models are required to help accomplish this goal. The initial goal of the proposed project is to test a recent mechanistic hypothesis of invasibility and to develop a quantitative empirical model that can be used to predict the changing invasibility of an environment over time. The hypothesis tested proposes that a mechanistic relationship exists between invasibility and resource availability, and that changes in invasibility are often due to changes in the competition intensity from resident vegetation, which in turn result from fluctuations in resource availability. This project will be conducted in a native grass environment located on a Minnesota sand plain. Thus, a second goal of the project is to increase our understanding of the invasion dynamics associated with grasslands and woodland/grassland ecotones in semi-arid environments. These goals will be accomplished in a study consisting of three parts. During the first stage, an empirical model of invasibility will be developed using data from a field experiment in which temporal patterns of resource availability (water) will be manipulated in plots being experimentally invaded. During this stage, data from the field experiments will also be used to directly test predictions of the fluctuating resource availability hypothesis. Water was selected as the resource to be manipulated because previous studies of seedling establishment at Cedar Creek have shown that establishment success of herbaceous and plants was most strongly correlated with soil water conditions. During the second stage, an existing mechanistic soil water model will be used to produce season-long soil water profiles at the study site under a variety of climatological (temperature and rainfall) data sets, including climatological data recorded at the study site during the project, historical climatological data for the region, and various hypothetical temperature and precipitation regimes that might occur in the future if the climate changes. During the third stage, the season-long water profiles produced by the mechanistic model will be used as input for the empirical model of invasibility. The invasibility predictions produced by the integration of the empirical and mechanistic models will compared to invasibility data obtained from a separate field experiment conducted during the study. If the integrated model is successful in its predictions, then it will be used with the historical and hypothetical climatological data to determine the extent of annual variability in invasibility of native grasslands in the past, and the extent to which invasibility may change in the future if temperature and/or precipitation regimes change. The goals of the proposed study are both to advance ecological theory and the ecological understanding of specific environments. In addition to testing a recent mechanistic theory of invasibility, the study will develop a method to model and predict invasibility that is intended to be transferable to other environments. Recent evidence has shown that grasslands and old fields are more responsive to fluctuations in precipitation than other biomes and that water limited environments such as grasslands and savannas are likely to be some of the biomes most affected by future climate change. Thus, by testing a specific mechanistic theory of invasibility in the water limited grassland-forest ecotone at Cedar Creek with an experimental study culminating in the development of a model of invasibility, this study will contribute to the important pool of knowledge that will be necessary to predict and prepare for the possible ecological consequences of global environmental change in these environments.