Herbivory by wild and domestic ungulates in the intermountain west
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Management of wild ungulates is seldom undertaken with a focus on the effects on forest health and productivity but rather focusing on populations of the ungulates and their habitat needs. Consequently, only limited research has examined grazing and browsing by ungulates in coniferous forests as a chronic disturbance factor affecting nutrient turnovers, competitive interactions among plant species, and rates and trajectories of successional pathways. Local effects are quite variable and depend on ecosystem productivity. Grazing can have mixed effects on species richness and the spread of exotic plants at the landscape scale. Grazing also can affect nitrogen fixation and rate of nitrogen mineralization. Ungulate density relative to carrying capacity of the site largely determines the effects of herbivory. High population densities of ungulates have been shown to change plant species composition, growth of trees, and to damage regeneration. Grazing also reduces accumulation of fine fuels on the forest floor, which formerly carried low-intensity, high-frequency ground fires. Effects of wild ungulates can be controlled by hunting regulations, and in some cases, by artificial contraception. Effects of grazing by livestock can be controlled through management actions such as changes in livestock numbers, changes in timing and duration of grazing, altering livestock distribution with fencing and placement of salt and supplemental feed, and specialized rotational grazing systems such as deferred and rest rotation.