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Title: Linaria dalmatica invades south-facing slopes and less grazed areas in grazing-tolerant mixed-grass prairie

Author
item Blumenthal, Dana
item NORTON, ANDREW - Colorado State University
item Cox, Samuel
item Hardy, Erik
item LISTON, GLEN - Colorado State University
item KENNAWAY, LISA - Animal And Plant Health Inspection Service (APHIS)
item Booth, D
item Derner, Justin

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2011
Publication Date: 8/11/2011
Citation: Blumenthal, D.M., Norton, A.P., Cox, S.E., Hardy, E.M., Liston, G.E., Kennaway, L., Booth, D.T., Derner, J.D. 2011. Linaria dalmatica invades south-facing slopes and less grazed areas in grazing-tolerant mixed-grass prairie. Biological Invasions. 14:395-404.

Interpretive Summary: Identifying environments where invasive plants are most invasive is key to understanding causes of invasion and developing effective management strategies. Dalmatian toadflax, a common invader of mixed-grass prairie, can also be favored by high water and nitrogen availability, but is thought to be unpalatable to cattle, and therefore favored by grazing. We used novel statistical methods to quantify relationships between toadflax cover (measured using very high resolution aerial imagery), and relative snow deposition (estimated with a blowing snow model), slope, aspect, soil texture, and grazing intensity (estimated by proximity to water tanks). Toadflax was common throughout the 400 ha study site, occurring in 742 of 1,861 images. Toadflax cover was high on steeper slopes, particularly those with southern aspects. These two topographic variables were more effective in explaining toadflax distribution than modeled snow deposition, suggesting that factors other than snow deposition cause toadflax invasion on south-facing slopes. Toadflax cover was also high in areas further from water tanks, indicating that grazing may inhibit toadflax invasion. More broadly, this result suggests that grazing can reduce invasion of even unpalatable species in ecosystems with long evolutionary histories of grazing.

Technical Abstract: Identifying environments where invasive plants are most invasive is key to understanding causes of invasion and developing effective management strategies. In mixed-grass prairie, invasive plants are often successful in relatively wet, nitrogen-rich areas, and areas protected from grazing. Dalmatian toadflax, a common invader of mixed-grass prairie, can also be favored by high water and nitrogen availability, but is thought to be unpalatable to cattle, and therefore favored by grazing. We used spatially-adjusted model selection techniques to quantify relationships between toadflax cover (measured using very high-resolution aerial imagery), and relative snow deposition (estimated with a blowing snow model), slope, aspect, soil texture, and grazing intensity (estimated by proximity to water tanks). Toadflax was common throughout the 400 ha study site, occurring in 742 of 1,861 images. Toadflax cover was high on steeper slopes, particularly those with southern aspects. These two topographic variables were more effective in explaining toadflax distribution than modeled snow deposition, suggesting that factors other than snow deposition cause toadflax invasion on south-facing slopes. Toadflax cover was also high in areas further from water tanks, indicating that grazing may inhibit toadflax invasion. More broadly, this result suggests that grazing can reduce invasion of even unpalatable species in ecosystems with long evolutionary histories of grazing.