An Evaluation of the Use of Mechanical Clearings by Ungulates in Northwest Alberta
Removal of forest and shrub cover through mechanical clearing has historically been used to increase the quantity and quality of browse for ungulates in northwest Alberta. The purpose of this report is to quantify differences in browse density and use by ungulates at six clearings (established between 1988 and 2003) located among three different sites in northwest Alberta. I defined successful clearings, created by reductions in forest and shrub cover communities, as those where the densities of available browse (stems/ha) and use by ungulates (measured as both number of stems browsed [number/ha] and density of faecal pellet groups [number/ha]) exceeded that in adjacent control (i.e., reference) sites. The abundance of browse and pellets were estimated by establishing replicate plots (circular plot size = 3.57 m in diameter = 10 m2) within clearings. In each plot, I counted and measured the number of stems, stem density (number of stems/ha) and browse height for different cover type (i.e., different species of plants browsed by ungulates). Using these data I calculated: i) mean browse density (number/ha), ii) mean browse height (cm) and, iii) mean pellet density (number/ha) as a measure of use by ungulates. Because the morphology of faecal pellets differs among ungulates species, I used pellet counts to identify the main species of ungulate that was consuming browse.
Analyses showed marked differences in browse density and browse use but not density of pellet groups between the mechanical clearings and the reference sites in the Bear Creek site. Browse production (density of stems/ha) on the hand-cut willow in Bear Creek was significantly higher than that observed in the mechanical clearings or the control area.
At the Nitehawk site, there were marked differences in browse density, browse use and density of pellet groups between the mechanical clearings and the reference sites. Nitehawk Clearings C and D had much higher levels of moose usage (pellet groups/ha) than Clearing B or control areas.
North Smoky clearings did not have significantly greater browse production or utilization than the control area. Similarly, there was little difference evident in the number of moose pellets groups in clearings and control areas.
These results suggest that there are benefits to developing predictors of successful clearing techniques and prospective sites should be assessed for their potential to provide browse for ungulates prior to the completion of clearing. For example, the effectiveness of clearing sites dominated by willow may be increased if a portion of the willow stem is retained to facilitate re-growth. Within a broader context, it may also be beneficial to develop standards for the completion of mechanical clearings and to evaluate their effectiveness to provide browse for ungulates.