Estimating Economic Carrying Capacity for an Ungulate Guild in Western Canada

Abstract

Elk Island National Park in western Canada provides an ideal case study for an economic carrying capacity estimate because it supports high density of four species of ungulates (11/km 2 ), lacks large predators, and is enclosed by a 2.1-meter mesh fence. This high density of ungulates has created persistent management challenges by altering vegetation structure and community composition. Using linear programming, we explored optimal allocation of forage resources for bison (Bison bison bison), moose (Alces andersoni), wapiti (Cervus elaphus manitobensis) and deer (Odocoileus virginianus and O. hemionus) to maximize ungulate biomass and numbers, when constrained by use of the major forage classes and minimum viable populations (MVP) of those ungulate species that do not cross the boundary fence (bison and wapiti). Maximum numbers of animals were achieved by a stocking combination dominated by deer and bison, whereas maximum biomass was attained when bison and moose were abundant but deer were absent. Wapiti remained at MVP during all solutions. Optimal solutions consistent with current ungulate densities were associated with 7 to 11% forage removal. This is less than normally assumed for sustainable forage use, and may reflect the need to account for other biotic and abiotic losses to forage in carrying capacity models for which ungulate densities can be constrained by availability of a preferred forage class (e.g., grass) as well as forage quality. This research extends the conventional animal-unit concept to multispecies systems and provides templates based on forage biomass allocation for resource managers facing similar problems of joint stocking in different environments.

Assessing Potential Habitat and Carrying Capacity for Reintroduction of Plains Bison (Bison bison bison) in Banff National Park

“…Our second goal was to estimate bison carrying capacity given the potential habitat available. We focused on winter under the assumption that this was the season that sets the upper limit on bison population size [ 28 , 29 ]. First, we estimated available forage biomass ( Fig 2 ), then we constrained availability based on grazing intensity, HSI, and the three snow-depth scenarios.…”

“…They used field trials to estimate a refuge for plants of 13% of the standing forage biomass, equivalent to a maximum offtake of 87%. At the lower end of published studies, Kuzyk et al [ 29 ] reported results of carrying capacity estimates for 4 ungulates species in Elk Island National Park using 7–15% forage use for graminoids and forbs, and 60% for shrubs, based on empirical observations in that system. Similarly, Sachro et al [ 62 ] used a grazing intensity of 25% to estimate elk nutritional carrying capacity in Banff.…”

“…Coughenour [ 33 ] reported that plains bison diet in Yellowstone National Park during winter constituted 95% graminoids and 5% shrubs. Kuzyk et al [ 29 ] reported 96% graminoids and 4% shrubs for bison (both wood and plains bison) in Elk Island National Park. In the MacKenzie Wood Bison Sanctuary, Northwest Territories, Larter [ 63 ] reported 96.1–98.8% diet composition of graminoids during winter, with the remainder being shrub biomass.…”

“…Despite the recent emphasis of the role of summer vegetation in determining ungulate population dynamics, little is known about summer forage for the nutritional ecology and population dynamics of bison. We focused, therefore on winter, assuming that this was the season that sets the upper limit on bison population size [ 28 , 29 ].…”

Forage yield and cattle carrying capacity differ by understory type in conifer forest gaps

“…Estimates of animal carrying capacity (Baars and Jeanes, 1997;Afzal et al, 2007;Savadogo et al, 2007;Chaudhry et al, 2010;Robinson et al, 2010;Hajno and Tahiri, 2011) have been successfully used in management decisions and planning (Mayer et al, 2006) and help to achieve sustainable utilization of ecosystems (Stoddart et al, 1975;Kuzyk et al, 2009). Animal carrying capacity is defined as the maximum stocking rate that a certain land area can support on a sustainable basis during a defined grazing season (FAO, 1991).…”