SUMMARY
Grasslands of BC are among the most endangered ecosystems in Canada. Although they occupy only 1% of BC’s land base they provide critical habitat for a variety of plants, mammals, birds, reptiles and insects. In northwest BC, mild wet summers, fire suppression and changes in grazing and browsing pressure have reduced grassland area and range quality or condition through shrub and tree encroachment. The goal of this report is to outline the condition of some northwest BC grasslands and to report on the impacts and effectiveness of restoration treatments on their vegetation communities.
Six grassland sites in the southern Skeena region between Smithers and Burns Lake were selected to compare and monitor the effects of three restoration procedures. Grassland monitoring was carried out over a six-year time period starting in 2001 and continuing to 2007. One site was broadcast burned, one was manually brushed, and one site received combinations of burning and brushing. Three sites remained untreated in 2007. Woody plant % cover, herbaceous plant % cover, graminoid (grasses & sedges) % cover, non-native plant % cover and Shannon’s diversity index were used as indicators to monitor grassland condition. In spring 2008, we also counted cervid (deer, moose, elk) pellet groups at all sites shortly after snowmelt.
Woody cover did not increase significantly region-wide from 2001 to 2007, while herbs, graminoids and species diversity were more abundant on untreated grasslands in 2007 than in 2001. Non-native species were more abundant in 2007 (3% cover) than in 2001 (1% cover; p = 0.04). Relative to total herbaceous cover, however, the increase was not statistically significant (p = 0.38), and appears to reflect a greater overall lushness of herbaceous vegetation in 2007 than in 2001 rather than deteriorating grassland condition. Timothy, dandelion, Kentucky bluegrass and smooth brome were the dominant non-native species on the monitoring plots – which do not include roads or other severely compacted and disturbed
soils prone to weed invasion.
Burning and manual brushing, at two sites each, decreased woody cover by 30-40% but there was no corresponding increase in herb or graminoid cover or in species diversity, beyond that observed on untreated grasslands. There was no evidence, at our single site, that combination treatments increased plant response over burning or manual brushing alone. None of the restoration treatments caused a significant increase in non-native plant cover.
All sites were well-used by deer (160 – 1357 pellet groups per hectare). Three sites were well-used by moose (216 – 332/ha in 2007) and one elk pellet group was found. To date, we were not able to detect any preferential use of treated grasslands.
We recommend that field-based monitoring continue over a longer period and larger number of sites to differentiate local and short-term variability from larger trends. Field monitoring should also be complemented by aerial photo inventory to assess changes in grassland area and habitat fragmentation. Manual cutting and spreading of brush prior to burning should be tested as a means to increase burn severity and allow more frequent burns on the same site. Brushing should be discontinued on some treatment plots to determine whether annual brushing has any lasting effect on grassland condition.
