Document: JOS-3-48-43

The interaction of fire intensity and elk herbivory on aspen regeneration and arthropod biodiversity: An intermediate burn hypothesis.

BAILEY, J.K.* and T.G.WHITHAM

Northern Arizona University, Flagstaff, AZ, 86011 USA. ¹

Abstract:
Fire burn severity has direct effects on aspen regeneration, and indirectly effects elk herbivory and insect diversity. Furthermore, the intensity of elk herbivory also affects insect diversity. In 1996, the Hochderfer crown fire burned approximately 15,000 acres of montane forest in Northern Arizona. This fire presented an opportunity to examine the direct and indirect interactions of fire and herbivory on above-ground aspen productivity, and insect diversity. Using experimental elk exclosures established by the U.S. Forest Service, and manually cutting aspen ramets, we addressed three questions: First, how does burn severity and elk herbivory affect above-ground aspen production? Second, how does burn severity and elk herbivory affect insect diversity on a stand level? Third, what is the relationship between above-ground aspen production and insect diversity? Fire positively affected above-ground aspen productivity where areas of high burn severity had the strongest effect. Elk herbivory negatively affected productivity, and had the strongest effect in zones of high burn severity. Furthermore, fire and elk herbivory had different effects for insect communities, and interacted so that the intermediate severity burn zones, with moderate levels of elk herbivory had the highest insect diversity. Finally, intermediate levels of productivity had the highest levels of insect diversity. These data are important because they demonstrate that abiotic (fire) and biotic (elk herbivory) factors can have complex interactions which impact aspen stand productivity and the biodiversity of associated insects. In the western U.S., because we manage forests for large ungulate herds and we suppress natural fire regimes, we virtually eliminate the regeneration of aspen, a keystone species in montane ecosystems, and effectively decrease montane ecosystem biodiversity on multiple trophic levels.

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This abstract is being presented at: 10:15 AM in session:
Oral Session #22: Multiple Disturbance Effects, Including Fire.