|Young, Kurt - OREGON STATE UNIV|
Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 22, 2007
Publication Date: January 1, 2008
Citation: Young, K.R., Mangold, J.M. 2008. Medusahead outperforms squirreltail through interference and growth rate. Journal of Invasive Plant Science and Management. 1:73-81 Interpretive Summary: Understanding the mechanisms and processes fostering invasion and dominance by medusahead is central to its management. We simultaneously conducted two studies that evaluated the effects of nitrogen and phosphorus on interference between the medusahead and squirreltail and compared growth rates of the two species. We grew medusahead and squirreltail in growth tubes in various density combinations. We applied one of four nutrient treatments to each growth tube. Additionally, we grew individual medusahead and squirreltail plants and measured their growth over a 72 day period. We found that medusahead typically imposed a two to seven times stronger influence than squirreltail on plant-plant interactions. Medusahead accumulated biomass, leaf area, and root length twice as fast as squirreltail. Our data suggest medusahead outperformed squirreltail in all aspects of interference and growth rate. We believe that medusahead may be outperforming squirreltail by growing faster and therefore increasingly gaining access to resources. The results from our study suggest that squirreltail cannot effectively compete with medusahead. To restore squirreltail to medusahead-infested rangeland, medusahead densities should be reduced with integrated weed management strategies. On medusahead-free rangeland, prevention and early detection and eradication programs are critical.
Technical Abstract: Understanding the ecological processes fostering invasion and dominance by medusahead is central to its management. The objectives of this study were 1) to quantify and compare interference between medusahead and squirreltail under different concentrations of soil N and P and 2) to compare growth rates of medusahead and squirreltail under normal soil N and P availabilities in an effort to identify mechanisms by which medusahead invades and dominates semi-arid rangeland. We hypothesized that: 1) N and P additions would increase medusahead’s interference ability relative to the native grass in the interference study and 2) medusahead would display higher growth rates and biomass accumulation than squirreltail. We grew medusahead and squirreltail in an addition series in a greenhouse and applied one of four nutrient treatments weekly (high N, low P; high N, high P; low N, high P; and low N, low P (control)). After 70 days density and biomass by species were sampled. We also grew individual medusahead and squirreltail plants in control soil conditions. Biomass, leaf area, and root length were determined for each species at 14 day intervals over 72 days. Regression models for medusahead and squirreltail suggested N appeared to be playing a much larger role than P in interference between the species. The high N treatment did not increase medusahead’s interference ability relative to squirreltail as we had hypothesized. Medusahead typically imposed a two to seven times stronger influence on interference relationships than squirreltail. Medusahead accumulated biomass, leaf area, and root length twice as fast as squirreltail. Results from our study suggest that medusahead seedlings will likely dominate over squirreltail seedlings. To restore squirreltail to medusahead-infested rangeland, medusahead densities should be reduced with integrated weed management strategies. On medusahead-free rangeland, prevention and early detection and eradication programs are critical.