Wet prairies dominated by the perennial bunchgrass Deschampsia cespitosa occurred extensively in the Willamette Valley at the time of Euro-American settlement. Historical evidence and recent habitat changes suggest that late summer fires set by Native Americans suppressed woody vegetation and promoted vegetative growth, seed production and seedling recruitment of herbaceous species. Using prescribed fire for prairie management is challenging; dry season mowing is often the preferred alternative in wet prairies. We initiated a seven year experiment to compare the effects of late summer/fall mowing and burning on native and non-native vascular plants in a remnant Willamette Valley wet prairie. We analyzed change in percent frequency from pre-treatment to the first two post-treatment years (and over all years) with ANOVA for a randomized complete block design. Twenty-five of 61 species or life stages showed treatment effects from burning or mowing. Ordination and MRBP tests indicated small treatment effects on overall species composition. With burning, the response of 15 species was desirable relative to management objectives (the increase of a native herbaceous or decrease of non-native or woody species) and eight showed undesirable effects. With mowing, eight and seven species exhibited desirable and undesirable treatment outcomes, respectively. While both fire and mowing appear to provide short term benefits to native wet prairie plants, more species benefitted from burning than mowing. While prescribed fire may be a preferred management tool where and when it can be implemented, the optimal management treatment will depend upon the suite of introduced species at a given site.
For more articles from the Spring 2011 issue of Northwest Science please refer to the link below: