Herbivory by wild and domestic ungulates is a chronic disturbance that can have dramatic effects on vegetation dynamics. Herbivory effects, however, are not easily predicted under different combinations of episodic disturbance such as fire, timber harvest, drought, and insect defoliation. This lack of predictability poses a substantial obstacle to effective management of ungulate herbivory. Traditional models of vegetation transition in forested ecosystems have ignored the influences of ungulate herbivory, while research on effects of herbivory have typically excluded other disturbances. Of the 82 contemporary studies on ungulate herbivory we examined, only 15 (18%) considered the interactions of herbivory with episodic disturbances. Moreover, only 26 (32%) evaluated vegetation response to ungulate herbivory beyond the simplistic treatment levels of herbivory versus no herbivory. Only 31 (38%) used a repeated-measures design of sampling responses over 3 or more time periods. Finally, just 7 (9%) explicitly made inferences to large landscapes such as watersheds, which are often used for management planning. We contend that useful landscape research on herbivory must examine the interactions of ungulate grazing with other disturbance regimes at spatial extents of interest to forest and rangeland managers and under varying ungulate densities and species. We identify herbivory models that could accommodate such information for forested landscapes in western North America. Such models are essential for identifying knowledge gaps, designing future studies, and validating relations of ungulate herbivory on landscapes where episodic disturbances are common, such as those of western North America.
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