Providing evidence to improve practice

Individual study: Impacts of fire, cutting and raking, and weeding on controlling dominant invasive grasses and increasing native flora in Cowichan Garry Oak Reserve, British Columbia, Canada

Published source details

MacDougall A.S. & Turkington R. (2007) Does the type of disturbance matter when restoring disturbance-dependent grasslands? Restoration Ecology, 15, 263-272

Summary

Garry oak Quercus garryana savanna (wooded prairie) occurs from southwest British Columbia (Canada) to California (USA). Fire suppression (fire being a natural process in shaping the community) over 150 years has led to increased tree cover and litter accumulation. In many areas non-native grasses have invaded. In British Columbia, reinstatement of burning extant fragments may adversely affect now rare fauna and flora, and is impractical near built-up areas. This study within Cowichan Garry Oak Reserve (48°48′N, 123°38′W), assessed alternative methods to restore native flora at two grasslandsites invaded by non-native smooth meadow-grass Poa pratensis and cock’s-foot Dactylis glomerata.

In May 2000 at each site, 10, 4 x 10 m blocks were established and 1 m² plots within each randomly assigned one of three treatments applied annually (2000 to 2004) in July or early October: selective manual removal of Poa and Dactylis, cutting and raking, or burning, plus a control. One site had shallow soil (8 cm deep) the other deep soil (43 cm).

In May 2000, prior to treatment application, plots were assessed (using 1m² quadrats) for: species richness; species cover; evenness, and reproductive output (number of flowering heads) of common perennial grasses and forbs. Other parameters recorded were: light at ground level, soil moisture, bare soil, available soil nitrogen and soil organic matter. Most variables were remeasured in May 2001-2004.

 

After 4 years, all treatments significantly increased light availability and bare soil compared to controls; soil nitrogen, organic matter and moisture were unaffected. Treatments were similarly effective at suppressing non-natives and increasing native plants. Effectiveness depended more on season and site rather than treatment type.
 
Treatment in summer reduced average cover of the two dominant grasses (Poa and Dactylis) each to less than 2.5% (controls: deep soil site around 50% Poa cover, Dactylis 16%; shallow soil site Poa 25%; Dactylis 26%). Number of flowering heads of both also declined significantly. A morphologically similar, native cool-season grass Bromus carinatus responded similarly.
 
Autumn cutting and burning did not significantly reduce Dactylis, whilst Poa decreased from 65 to 10% cover at the deep soil site and 25 to 11% in the shallow soil site.
 
Positive responses by native species were significantly greater on the shallow soil site, but could simply be attributed to there being a higher native diversity to start with.
 
 
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://onlinelibrary.wiley.com/doi/10.1111/j.1526-100X.2007.00209.x/full