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An Ecologically Based Decision Support System for Managing Leafy Spurge (Euphorbia esula) Infested Rangeland

 Roger Sheley

Question 1. What major problem or issue is being resolved and how are you resolving it?

arious rangeland weed control techniques have been developed and used with unpredictable outcomes (Hansen 1993). Herbicidal control of most weeds requires continuous and periodic applications. For example, the most effective herbicide for leafy spurge control, picloram (4-amino-3, 5, 6-trichloropicolinic acid) provides only temporary reductions in plant density (Lym and Messersmith 1985, Lym and Messersmith 1994). Performance of biological control organisms is highly dependent upon the specific weed, quantities of agents released, and site conditions (Rees and Spencer 1991). Biological agents may significantly impact populations during some growing seasons, while having little or no effect in other years. Research suggests that sheep and goat grazing can be used effectively to control some weeds, but outcomes vary depending on specific grazing management strategies (Lym et al. 1994). More recently, revegetation of infested rangeland has shown some potential for successful weed management, but environmental and economic considerations associated with this intensive system require its thoughtful use (Lym and Tober 1997, Ferrel et al. 1998, Sheley et al. 1999). Although single weed control methods are rarely effective, developing integrated weed management strategies may provide effective, long-term solutions to noxious weed problems (Andrascik 1994).

Question 2. How serious is the problem? Why does it matter?

Although integrated approaches can have a synergistic effect on weeds, most management tactics are not effective when used in combination (Lym 1992). Rangeland managers need useful models for evaluating alternative integrated strategies (Archer 1989, Schatterer 1989, Laylock 1991). It is imperative that these models are capable of predicting the response of plant communities to management tactics such as herbicides, biological control, grazing, revegetation, and their integration. These models should help land managers determine if proposed management strategies are ecologically sound and cost-effective. Management decisions must be based on a predicted outcome, and these predictions must be based on our scientific understanding of the biology and ecology of the plants in the community (Luken 1990, Sheley et al. 1996). Life-history tables have been used in order to predict the dynamics of weed populations. These tables consist of a series of states (growth stages) and a series of transitions that represents the flow of individuals from one growth stage to the next. Each state represents the number of individuals of a particular growth stage that are present per unit area. The transitions have values that correspond to the proportion of individuals that advance from one state to the next within a generation. The state value is multiplied by the transition value to yield the number of individuals that advance to the next state. A single species life-history table was used to demonstrate the response of leafy spurge populations to picloram (Bowes and Thomas 1978). A second single species life-history table was used to simulate development of leafy spurge populations from the introduction of propagules and the response of leafy spurge populations to the reduction of particular transition values (Watson 1985). The transition values were constant in these earlier models. Density dependent factors were not considered. A later model incorporated intra-specific density dependent transition functions (Maxwell et al. 1988). Sensitivity analysis was run on this model to identify vulnerable areas in the life cycle of leafy spurge. More recently, Sheley and Larson (1994) developed a two species life-history table that was used to compare the population dynamics of two winter annuals, cheatgrass (Bromus tectorum) and yellow starthistle (Centaurea solstitialis). This information was developed into a preliminary computerized tool to assess integrated weed management.

These models have centered on controlling the weed with minimal regard for the original and resulting plant community (Sheley et al. 1996). Management practices based on these models have resulted in re-invasion by the same or different weed species because weeds rapidly occupy the niches opened by control procedures. Integrated approaches that favor desired species over weeds are necessary for the successful management of rangeland weeds, therefore multi-species models must be developed (Andrascik 1994). Although existing models have provided a method for understanding and predicting single-species population dynamics, they have not been useful in developing decision support systems. On rangeland, a useful decision support system must be capable of predicting the responses of interactions among desired species and weeds (Sheley et al. 1996). The life-history parameters of multi-species systems are dependent upon intra- and inter-specific interactions (Pyke 1991). Once multi-species models are developed, the effects of management strategies on the weed and desired species can be predicted. Our overall objective is to develop an ecologically based decision support system for leafy spurge infested rangeland. This decision support system will be user friendly, and it will allow land managers to base management plans on predicted outcomes.

Question 3. How does it relate to the National Program(s) and National Program Component(s)?

TEAM Leafy Spurge is a part of the USDA-ARS Area-Wide Management Program. It is a component of Crop and Commodity Pest Biology, Control and Quarantine (304). TEAM Leafy Spurge complements efforts to develop new and improved pest control technologies and assess component technologies for integrated pest management (IPM) systems.

Question 4. What was your most significant accomplishment this past year?

Integrated weed management approaches can have a synergistic effect on weeds; however, management tactics may not always be effective when used in combination - thus rangeland managers need useful models for evaluating alternative integrated management strategies (Archer 1989, Schatterer 1989, Laylock 1991). We are studying the competitive relationships among these species in order to quantify the transitions among growth stages in this model at Montana State University. We have developed a preliminary version of the computer program that will run the decision support system. This decision support system will be user friendly, and it will allow land managers to base management plans on predicted outcomes.

Question 5. Describe your major accomplishments over the life of the project, including their predicted or actual impact.

We have developed a conceptual life history model for leafy spurge and two grass species. We are studying the competitive relationships among these species in order to quantify the transitions among growth stages in this model. When the competitive relationships are determined, we will use the life history model to predict plant community dynamics over time. We have established two field experiments at the MSU agronomy farm that we are using to study interference among the species. We are also studying competition among grasses and spurge at several other sites across Montana, and information from these sites will allow us to improve and assess the accuracy of the model. Finding appropriate research sites and setting up these experiments was very challenging. Therefore, we consider this one of our major achievements for this project. Large amounts of information are available about the effects of management tools upon leafy spurge. When this information is incorporated into the model, it will enable us to predict effects of leafy spurge management upon infested communities. We have developed a comprehensive database of leafy spurge information and have organized information from this database so that it may be included in the model. This is a very valuable component of this project because research on leafy spurge needs to be synthesized and integrated for it to be valuable to weed managers. We have developed a preliminary version of the computer program in Visual Basic 2000 that will run a decision support system that is based on our life history model. This program allows the user to propose management plans and visualize the results of these plans with various output options including charts and graphs. This program is extremely simple to operate and will eventually enable weed managers to predict the results of weed management actions before implementation. This will allow range managers to base management decisions on predicted outcomes.

Question 6. What do you expect to accomplish year by year, over the next three years?

During 2000 we will develop the final version of the computerized decision support system and begin to incorporate actual research-based information. Many of the growth stage transitions in the life history model have not been estimated from data. In 2001 and 2002 data will be collected and used to quantify these transitions. This data will come from our research projects and various other sources. Data is incorporated into the model in the form of various curvilinear regression equations that describe the data. The curve fitting process is very complex and will require a large amount of work. Data from multiple sites and years will be used to quantify the life history model. This will be used to quantify the probability of various weed management outcomes instead of simply indicating the most likely outcome.

Question 7. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology?

This project will result in a computerized decision support system for leafy spurge infested rangeland. This program will direct the development of weed management plans using our best understanding of ecology and weed science. This project has not resulted in any publications to date. We expect five refereed publications over the next three years. One publication will summarize a competition experiment among leafy spurge and two grass species that was conducted across three moisture regimes in a greenhouse. One paper will describe competition among leafy spurge and two grass species in the field, and another paper will outline our decision support system. We have also begun a paper that will focus on the importance of quantifying uncertainty in decision-making in weed-infested rangeland. To validate our model we have removed grasses or leafy spurge from 2-m2 plots at 50 sites across Montana. Information from these plots will allow us to evaluate the accuracy of the model and quantify the magnitude of site-to-site and year-to-year variation. These plots will also be used to determine the increase in grass production that results from removing leafy spurge under a variety of different site conditions, and we will submit one paper that describes yield response to weed removal at these sites.

Question 8. List your most important publications in the popular press (no abstracts) and presentations to non-scientific organizations, and articles written about your work (NOTE: this does not replace your peer-reviewed publications which are listed below).


Question 9. Scientific publications


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