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Impact of prescribed burning on diffuse knapweed (centaurea diffusa) infestations and floral diversity in Kalamalka Lake Provincial Park Nicholson, Andrew Ross


This study investigated the infestation of Kalamalka Lake Provincial Park, British Columbia by diffuse knapweed (Centaurea diffusa Lam.). Surveys of six different types of grassland ecosystem association/seral stages for species richness and diversity in the spring of 1990 and 1991, and for diffuse knapweed density in the fall of 1990 and 1991 revealed that increasing diffuse knapweed density was not associated with reduced richness or lower diversity. A multiple discriminant analysis on the density of diffuse knapweed showed that the level of accessibility of a site was the most important factor in the spread of knapweed, and that the amount of bare soil may be an important co-factor. A multiple discriminant analysis for species richness revealed that time since the last herbicide treatment was the most important factor affecting species richness of a site. A prescribed burning experiment was conducted on two sites in Kalamalka Lake Provincial Park. One site was infested with diffuse knapweed. Neither spring nor fall burning reduced (p>0.05) any class of knapweed (i.e. seedlings, rosettes, bolted plants, or total knapweed). The other site initially had no knapweed, and neither burning treatment resulted in the establishment of any knapweed up to the end of the first growing season after the burns. Although there were initial differences in the richness and diversity of the two sites, neither burning treatment altered (p>0.05) the seasonal pattern or level of richness or diversity by the end of the study. Both spring and fall burning treatments reduced the amount of available fuel and increased the amount of bare soil. The increase in percent bare soil was strongly correlated (r2=0.792) to fire intensity. Management recommendations include continued monitoring of the burn sites to determine if the burning treatments result in changes in the density of knapweed or species richness over the next few years. A moratorium on the use of herbicides is also recommended in order to maintain species richness and diversity in the park.

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