Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2003
Publication Date: 6/20/2005
Citation: Rinella, M.J., Sheley, R.L. 2005. Influence of soil water availability on competition among leafy spurge (euphorbia esula) and grasses. Western North American Naturalist. 65(2):233-241. Interpretive Summary: Understanding the competitive relationships among leafy spurge and associated desired grasses is helpful in predicting their response to management. We studied their relative competitive abilities under various moisture regimes. Competition became less intense as the number of water applications increased, however the importance of competition was not influenced by frequency of watering. This suggests that predictions of leafy spurge and grass biomass will have equal accuracy in years with few or many precipitation events.
Technical Abstract: Some perturbations differentially influence invasive plant and grass production. For example, growth regulator herbicides and biological control agents can dramatically reduce leafy spurge production while having little or no influence on grass production, and overgrazing can reduce grass production while not substantially influencing leafy spurge production because cattle typically ingest little or no leafy spurge. To predict how grass production will respond to a perturbation that only influences leafy spurge and to predict how leafy spurge production will respond to a perturbation that only affects grasses, competitive relationships must be understood. Seeding mixtures of leafy spurge and two grasses were planted in experiments and grow for 127 d to determine if different water application regimes influenced competition among these three species. Competition became less intense as the number of water applications increased. If this finding holds true under field conditions, then it indicates that competition is less intense in years and locations with numerous precipitation events. Competitive interactions (i.e. competition coefficients) were less variable when water was applied more frequently, but the ability of models to account for variation in plant weight (i.e. r2) was not influenced by the frequency of water application. This suggests that models will predict invasive plant and grass biomass with equal accuracy in years with few or many precipitation events. Competitive effects were similar regardless of grass species, which suggests that grasses might be considered collectively in predicting response to perturbations in the field.