Impacts of ungulates on rangeland dynamics in aspen-boreal ecosystems of Alberta.

摘要

The ability of rangelands to sustain livestock and wild herbivores is primarily a function of amount of forage, forage quality, and the efficiency by which the forage is harvested. A series of studies were conducted to assess the impact of these factors on rangeland dynamics in Aspen-Boreal ecosystems of Alberta.; The effects of defoliation time, frequency, and intensity on herbage yield and quality were determined by clipping trials. Plants were defoliated in early May, June or July; at 2-, 4- or 6-week intervals; and at 15, 10 or 5 cm from the soil surface. Herbage removal was greatest when initially defoliated in May. Greatest accumulated herbage yields were obtained at 10-cm defoliation height. Less frequent defoliation produced the greatest herbage yield. Average crude protein yield for forb and grass ranged from 1.5 to 3 g m−2 , and 6 to 10 g m−2, respectively.; In a greenhouse experiment, aboveground phytomass decreased with increased water stress. Defoliation decreased both aboveground and belowground phytomass compared to a non-defoliated control. Root:shoot ratio increased with increasing water stress, defoliation intensity and frequency.; Seasonal dynamics of ungrazed pastures were determined by clipping and weighing green and dry vegetation and litter pools. Green herbage, standing dead and litter increased from spring to summer and decreased from summer to fall. Average growing conditions resulted in a peak phytomass of 350 g m−2, and varied by year.; Investigation of the effects of intensive short-duration (SDG) and continuous (CG) grazing by wapiti (Cervus elaphus) on soil compaction and herbage yield indicated that the SDG did not show any advantage over CG in improving soil physical characteristics and herbage production.; A preliminary computer simulation model of Bromus-Poa pastures grazed by farmed wildlife (specifically wapiti and bison) indicated that pasture condition benefited slightly from rotational grazing at high stocking densities but animal performance declined compared to continuous grazing. Proper use of the model, when the factors which influence bioeconomic efficiency are well-defined, will hopefully lead to a simple practical pasture simulator that could be used to evaluate continuous or rotational mixed species grazing systems in terms of pasture and animal productivity.