Fire has well established effects on plant community composition, but far less is known about how these effects extend to higher trophic levels. In temperate forests, fire is often expected to improve the nutritional resources available to herbivores by opening the canopy and facilitating growth of understory vegetation. Herbivores are expected to reap long-term benefits as growth of forage peaks and gradually diminishes through time while trees reestablish. This prediction, however, has remained difficult to test, in part because herbivores responses may span multiple temporal scales. Consequently, we further hypothesized that herbivores use burned stands more in spring than summer and that use of these stands corresponds to times of day associated with peak foraging behavior. We tested these hypotheses using a long-term telemetry dataset on an ungulate (elk; Cervus elaphus) collected 1997-2012 from Starkey Experimental Forest and Range (599 animal-years of locations from 274 unique females). Between 2001 and 2003, 26 stands of fir (Abies spp.) and Douglas-fir (Pseudotsuga menziesii) were thinned and burned, while 27 similar stands were held as experimental controls. We used discrete choice models to test for temporal structure in elk response to burned stands and to quantify the magnitude and duration of this response.
Results/Conclusions
After accounting for seasonal and daily differences in elk selection for burned stands, we found evidence for a long-term effect (>10yrs) of fire history on elk behavior. Elk response to burned stands varied as a function of years-since-burn, season (spring/summer) and time of day (night/day). Across years, the effect of fire peaked quickly (<5yrs) and then gradually declined. As hypothesized, elk showed stronger selection for burned stands in spring than in summer, when moisture often limits early seral growth and herbaceous plants senesce. We did not, however, find support for the hypothesized relationship between burned stands and the times of day associated with peak foraging behavior. Instead, we found sharp transition between nocturnal and diurnal behavior, with elk frequently avoiding burned stands during daylight hours. Our results confirm broad theoretical expectations regarding the influence of fire on herbivore behavior and emphasize the importance of tailoring resource selection methods to specific animal behaviors (e.g. foraging). Finally, the strategies of resource selection we observed are only possible within a landscape with a heterogeneous fire history, suggesting that elk benefit from the opportunity to choose between a range of conditions with different attendant risks and rewards.