Prescribed burn and cattle grazing in ponderosa pine forests: Implications for the herbaceous understory.
Kerns, Becky *,1, Thies, Walter 1, Niwa, Chris 1, 1 USDA Forest Service, Corvallis, Oregon
ABSTRACT- The concept that native biodiversity is likely to benefit from restoration of natural processes is a central tenet of ecological restoration and ecological management frameworks. Fire has functioned historically as a key disturbance agent in forest ecosystems, and there is broad consensus that controlled fire reintroduction is urgently needed in western dry forests. Much of this forest type is also used for livestock grazing. A critical question is how prescribed fire and grazing impact understory plant communities and exotic species. To address this issue, we built grazing exclosures in 4 eastern Oregon ponderosa pine stands scheduled for 5-year interval prescribed fire reburns. Our objectives were to examine herbaceous response to the reburns with and without cattle grazing. Vegetation and environmental data were sampled from 0.03 ha exclosures prior to and for 2 years after the reburns from the following randomly applied treatments: no burn no grazing, no burn grazing, spring reburn no grazing, spring reburn grazing, fall reburn no grazing, fall reburn grazing. Three grazing exclosures that excluded cattle but were accessible to other grazers were built in each treatment. Preliminary findings indicated that prior to reburning, there was no difference in total species richness and cover between grazing and no grazing treatments. Two growing seasons after treatments, there was no difference in species richness between grazed and ungrazed areas for any of the burn treatments. For fall burned areas, understory cover was 34% in exclosures, significantly higher (p = 0.07) than areas open to cattle grazing (23% cover). No difference was detected for spring burn and no burn units. The exclusion of cattle did not impact exotic species cover, including cheatgrass. Our results suggest that post-fire grazing can reduce herbaceous understory abundance, but this impact interacts with fire regime and fire severity.
Key words: prescribed fire, forest understory, cattle grazing, season of burn
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