WEYDV-02-015

Interaction of Cattle Grazing and Aspen Regeneration
Sponsor: 
Weyerhaeuser Company Limited
Lead Researcher: 
Art Bailey, PhD, University of Alberta, Edmonton
Body: 
Forestry and ranching interests often conflict on Alberta crown lands when cattle graze in regenerated aspen cutblocks. Foresters fear that grazing activity may reduce stocking, growth and injure regenerating aspen thus promoting future stain and decay of the wood. The general objective of this research was to evaluate the effects of livestock grazing, wild ungulate browsing, and tree harvesting on aspen regeneration and incidence of decay.

The study took place north of Nojack, in the Weyerhaeuser’s Edson Forest Management Agreement area. Harvest and grazing studies were carried out in cutblocks logged in summer 1994. All experimental units were established within the Aspen-Balsam poplar/Green alder/Marsh reed grass community type. Cattle grazed the experimental units from June to September. Ungulates in the study area were assumed to utilize the cutblocks as well (especially during winter). The decay study took place in regenerated aspen stands that were approximately 25 years old.

Aspen regeneration and forage production were maximized with light to moderate skidding disturbance regimes, decreased with no-skid and increased with skidding intensity. Decking disturbances significantly reduced aspen regeneration and forage production. Wild ungulate browsing was not found to affect aspen regeneration, however aspen regeneration was found to be most successful in absence of cattle. Grazing of cutblocks by cattle during August-September was not found to impact aspen regeneration. Annual grazing for four or five years reduced aspen stem height within June-July grazed treatments, thus impeding aspen regeneration. Grazing in June increased aspen wounding and mortality rates relative to July grazing. Aspen stems were most susceptible to cattle damage during June. Deferring cattle grazing until July improved aspen regeneration. By July the aspen stems were less likely to be foraged by cattle. There was no correlation between the percentage of sound, stained, or decayed wood in trees and the intensity of grazing. Although future defect volumes cannot be predicted, the low percent values for decay and stain suggest that the presence of cattle did not lead to an increase in defect volume. This is not surprising since the major decay of aspen, Phellinus tremulae, appears to use broken branch stubs as its avenue for entering the bole of trees.