Fire decreases arthropod abundance but increases diversity: Early and late season prescribed fire effects in a Sierra Nevada mixed-conifer forest

Scott M Ferrenberg,Jon E Keeley,Dylan W Schwilk,Eric Groth,Eric E Knapp

doi:10.4996/fireecology.0202079

Abstract

Prior to fire suppression in the 20th century, the mixed-conifer forests of the Sierra Nevada, California, U.S.A., historically burned in frequent fires that typically occurred during the late summer and early fall. Fire managers have been attempting to restore natural ecosystem processes through prescription burning, and have often favored burning during the fall in order to mimic historical fire regimes. Increasingly, however, prescription burning is also being done during the late spring and early summer in order to expand the window of opportunity for needed fuel reduction burning. The effect of prescribed fires outside of the historical fire season on forest arthropods is not known. The objective of this study was to compare the short-term effects of prescribed fires ignited in the early and late fire season on forest floor arthropods. Arthropod abundance and diversity were assessed using pitfall trapping in replicated burn units in Sequoia National Park, California. Overall, abundance of arthropods was lower in the burn treatments than in the unburned control. However, diversity tended to be greater in the burn treatments. Fire also altered the relative abundances of arthropod feeding guilds. No significant differences in arthropod community structure were found between early and late season burn treatments. Instead, changes in the arthropod community appeared to be driven largely by changes in fuel loading, vegetation, and habitat heterogeneity, all of which differed more between the burned and unburned treatments than between early and late season burn treatments.

Highlights

The responses of forest arthropods to fire has not been extensively investigated and studies that have been done show variable outcomes (Bess et al 2002, Moretti, et al 2004)
Other studies have demonstrated the importance of fire in creating diverse habitat mosaics that benefit various arthropod taxa and feeding guilds (Buddle et al 2000, Gandhi et al 2001, Moretti et al 2004)
The objectives of this study were: 1) to evaluate short-term changes in arthropod abundance and diversity following prescribed fires, 2) to determine the effects of season of fire on the arthropod community structure, and 3) to investigate how environmental changes resulting from the burning season treatments may have influenced the arthropod community

Summary

Introduction

The responses of forest arthropods to fire has not been extensively investigated and studies that have been done show variable outcomes (Bess et al 2002, Moretti, et al 2004). Other studies have demonstrated the importance of fire in creating diverse habitat mosaics that benefit various arthropod taxa and feeding guilds (Buddle et al 2000, Gandhi et al 2001, Moretti et al 2004). A large volume of evidence points toward the influence of vegetation community traits on arthropod distribution and diversity (Root 1973, Mopper and Simberloff 1995, Fernandes and Price 1988, Waring and Cobb 1992, Hunter 1992, Marques et al 2000), as well as to the influence of the structure and composition of the forest floor litter layer (York 1999, Moretti et al 2004, Gibb et al 2006). Litter, and woody surface fuels as a result of fire are likely to influence the abundance and diversity of arthropod taxa and functional feeding guilds. Excluding fire from Sierra Nevada forests has altered forest structure by increasing the abundance of shade tolerant tree species (e.g. white fir) at the expense of shade intolerant but more fire resistant species (e.g. sugar pine and ponderosa pine)

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Conclusion