Plant species diversity and soil quality in harvested and grazed boreal aspen stands of northeastern British Columbia

Abstract

Understory vegetation in aspen ( Populus tremuloides Michx.) stands produces up to 50% of all forage on Crown land for domestic livestock grazing in the Peace River area of British Columbia (BC), Canada. The objective of this study was to determine the effects of clearcut harvesting and long-term cattle grazing on plant species diversity and soil quality in aspen cutblocks located about 5 km south of Dawson Creek in the Peace River region of BC. The site was winter harvested from November 1988 to March 1989. Cattle grazing was done for one month per year (early June to early July) to achieve 75% utilization of forage vegetation. The experiment was laid out as a split-plot randomized complete block design with three replications and four transects per plot. Sample collection and vegetation assessments were completed during the summer 2001. Timber harvesting of these aspen stands increased the cover of plant species such as bluejoint reedgrass ( Calamagrostis canadensis), northern bedstraw ( Galium boreale), tall bluebells ( Mertensia paniculata), and sweet coltsfoot ( Petasites frigidus) probably as a result of greater light transmission. The cover of young aspen was increased by timber harvesting by over 15 times, while the cover of young balsam poplar ( Populus balsamifera) increased by over 200 times. Ten years of cattle grazing did not significantly affect the canopy cover of aspen, but increased the total number of plant species relative to the ungrazed treatments because of enhanced colonization of endemic species. The measured soil properties were not significantly affected by either the timber harvest or the long-term cattle grazing. Soil penetration resistance showed that harvesting and cattle grazing did not result in soil compaction. Results showed that with appropriate management the timber and ranching industries are compatible on regenerating aspen stands in the Peace River region.