Dynamics of ungulate-plant grazing systems

Grazing stability is determined by three main factors: (i) plant response to grazing, (ii) functional response (intake rate) of herbivores, and (iii) numerical response (population) of herbivores. This stability is investigated with 'predator-prey' graphs or simulation models. This thesis applies the 'predator-prey' approach to wapiti (Cervus elaphus nelsoni) grazing Poa/Bromus grassland openings in boreal mixedwood forests of central Alberta.; Forage dynamics of ungrazed and continuously grazed (irrigated, unirrigated and manured) pastures were determined by clipping and weighing green, dry and litter pools. Manured pasture had the highest green biomass (g/m{dollar}sp2){dollar} (261.1 {dollar}pm{dollar} 25.5, r = 0.47, K = 227, where r is rate of increase and K is maximum green biomass), followed in order by irrigated (197.7 {dollar}pm{dollar} 6.2, r = 0.48, K = 198), unirrigated (164.8 {dollar}pm{dollar} 6.9, r = 0.69, K = 161) and protected (123.5 {dollar}pm{dollar} 6.7, r = 0.85, K = 123). The response of forage to defoliation was determined using clipped plots. Forage compensated for defoliation if moderate and early in the growing season, otherwise cumulative productivity declined. Using movable cages on moderately stocked pasture, defoliation by wapiti was similar to hand-clipping in its impact on forage production. Daily forage removal by wapiti averaged 7.0 {dollar}pm{dollar} 0.6 kg/head/day. Removal depended on available biomass and grazing pressure. On winter pasture, snow cover influenced the efficiency of feeding but interactions between snow characteristics and forage biomass were complex.; Experiments with habituated wapiti grazing hand-constructed swards provided details of the functional response. Intake rate, bite size and cropping rate depended on sward type (forbs, lush green, lawn or senescent). Bite size increased with fiber content and plant height. Cropping rate increased with protein and moisture content, but declined with bite size, plant height and fiber content. Intake rate (g/min) ranged from 21.48 {dollar}pm{dollar} 1.33 to 35.46 {dollar}pm{dollar} 1.99. Bite size (g/bite) ranged from 0.59 {dollar}pm{dollar} 0.03 to 1.34 {dollar}pm{dollar} 0.04. Cropping rate (bites/min) ranged from 15.90 {dollar}pm{dollar} 0.73 to 41.08 {dollar}pm{dollar} 1.55.; 'Predator-prey' graphs predicted that the grazing system to be relatively stable with a single stable point at most stocking densities. However, enrichment through irrigation and nutrient enrichment appeared to have a destabilizing influence. This may have implications for prescribed burning and other range management programs in Elk Island National Park.