| Summary: | 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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