University of Alberta
The Impacts of Horse Grazing on Conifer Regeneration in West-Central Alberta
By
Barry David Irving
A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Plant Science
Department of Agricultural, Food and Nutritional Sciences
Edmonton, Alberta Spring 2001
ABSTRACT Historical studies of the interaction of livestock and conifer seedling regeneration on timber cutblocks have concentrated on establishing safe livestock stocking rates on areas of uniform vegetation and topography. Forestry cutblocks typically encompass a variety of forest sites that produce a variety of forages for domestic livestock and elicit a complex grazing pattern determined by grazing behaviour. Traditional grazing management using set stocking rate theories often results in variable grazing effects on regenerating conifer seedlings. The purpose of this study was to determine horse grazing behaviour on forestry cutblocks with heterogeneous vegetation and topography under different confinement strategies. Grazing behaviour and conifer seedling damage were studies under free-ranging, semi-confined, and confined strategies for managing horses in Upper Boreal Cordilleran forests south of Hinton, Alberta (400 km west of Edmonton). Horses exhibited selective grazing behaviour. Preferred habitats for winter grazing free-ranging horses were hygric meadows, a non-commercial forest type that is common in west-central Alberta. Diagnostic species for preferred foraging sites were straight horsetail (Equisetum variagatum) and dwarf birch (Betula glandulosa). Winter free-ranging horses avoided grazing recent forestry cutblocks, suggesting hygric meadows provide an alternative preferred habitat that reduces the probability of horse-caused conifer seedling damage. Horses grazing in the summer selected disturbed sites (spur roads, landings, and power lines), hygric meadows and dry pine sites but avoided moist pine and pine/black spruce transition sites. The existence of disturbed sites and hygric meadows attracted horses away from cutblock sites with regenerating conifer seedlings. Disturbed sites and hygric meadows are important alternative preferred habitats for summer grazing horses. Conifer seedling damage and mortality was elevated by horses confined to cutblocks in the summer. Horses damaged conifer seedlings by trampling (vertical displacement and/or basal scarring); there was no evidence of browsing damage in this study. Although conifer seedlings were damaged at rates as high as 37 percent, seedling mortality increased only 2 percent during 2 years of horse grazing. Conifer seedlings were more susceptible to horse damage when they were less than 50 cm tall, were growing on moist sites, or were exposed to early summer horse grazing. The preferred alternative habitat concept can be used to minimize damage to regenerating conifer seedlings coincidental with horse grazing. Horses are a minor damage threat to forestry cutblocks if they are selectively grazing areas that have no conifer seedlings.