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Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/28/2006 Publication Date: 7/1/2006 Citation: Rinella, M.J., Sheley, R.L. 2006. Using light attenuation to estimate leafy spurge impacts on forage production. Rangeland Ecology and Management 59(4):431-437. Interpretive Summary: Rangeland managers often focus management efforts on suppressing weed populations in hopes that forage production will increase. The magnitude of grass response to rangeland weed suppression helps determine if these management efforts are warranted. Unfortunately, techniques for predicting grass response to weed suppression are not widely available. This is partly because data on weed abundances per unit area are needed to predict grass response, and gathering these data with currently available techniques is extremely time-consuming. In this paper, we explore a rapidly measured index (< 2 minutes per sample location) that is highly correlated with weed (i.e. leafy spurge) abundance per unit area. The index is based on the shading leafy spurge caused when it was grown in combination with grasses in 2 field experiments. We used the shading index to develop an equation that predicts grass response to leafy spurge suppression. Model evaluations led us to believe that the equation is an accurate predictor of grass response to leafy spurge suppression. Light attenuation could prove useful for quantifying some weed impacts. Technical Abstract: Rangeland managers often focus management efforts on suppressing weed populations in hopes that forage production will increase. The magnitude of grass response to rangeland weed suppression helps determine if these management efforts are warranted. Unfortunately, techniques for predicting grass response to weed suppression are not widely available. This is partly because data on weed abundances per unit area are needed to predict grass response, and gathering these data with currently available techniques is extremely time-consuming. In this paper, we explore a rapidly measured index (< 2 minutes per sample location) that is highly correlated with weed (i.e. leafy spurge Euphorbia esula L.) abundance per unit area. The index is based on the light attenuation leafy spurge caused when it was grown in combination with perennial grasses in 2 field experiments. We used the light attenuation index to develop a probabilistic model that predicts grass response to leafy spurge suppression. Predictive ability of the model was assessed by comparing model predictions to data from 3 published experiments where herbicides suppressed leafy spurge. The herbicide experiment data fell within the range of values (i.e. credibility interval) the model predicted even though the model development site and the herbicide experiment sites were separated by several hundred kilometers and were measured during different years. Therefore, we conclude that the model’s predictive capability is not compromised dramatically by spatial and temporal variation. Light attenuation could prove useful for quantifying some weed impacts. |
