EFFECTS OF FIRE ON MONTANE FOREST BIRDS IN SOUTHEASTERN

ARIZONA

Chris Kirkpatrick and Courtney J. ConwayArizona Cooperative Fish and Wildlife Research Unit, University of

Arizona

Summary - The frequency of high-intensity wildfires has increased in mountain ranges of the southwestern U. S. due to more than a century of fire suppression and subsequent fuels accumulation. Montane forest birds in the region evolved in forests that once experienced recurrent, low-intensity ground fires. These species are now faced with the prospect of frequent high-intensity wildfires that can transform or eliminate large portions of montane forest. To assess the effects of recent wild and prescribed fires on this avian community, we surveyed montane forest birds in 8 ‘sky island’ mountain ranges in southeastern Arizona and examined how the presence of 38 bird species correlated with evidence of severe and less-severe fire damage at >1500 survey points. We detected an association between presence and recent fire damage for 19 of 38 bird species analyzed. Of these species, 11 were positively associated with fire (6 with severe fire damage, 3 with less severe fire damage, and 2 with both) and 8 were negatively associated with fire (6 with severe fire damage and 2 with both severe and less severe fire damage). In addition, we found that only 1 of 16 species previously identified as being associated with open-woodlands showed a positive association to areas with evidence of recent fire. Our results suggest that fires, especially severe wildfires, have the potential to affect the distribution of many montane forest birds in southeastern Arizona. However, the current fire regime is unlikely to facilitate restoration of montane forests to pre-fire suppression conditions, and thus, many birds associated with open forests will continue to be excluded from the region.

   

Methods Continued• We used logistic regression and modeled fire severity as a categorical independent variable. To increase the power of our tests, we collapsed fire severity values into three classes: 1) no fire damage (fire severity class 0); 2) less-severe fire damage (fire severity classes 0.5 to 2); and 2) severe fire damage (fire severity classes 2.5 to 4).

• We compared proportion of birds detected at points with severe fire damage and no fire damage and proportion of birds detected at points with less-severe fire damage and no fire damage.

• We included elevation as a continuous independent variable in regression models and restricted data for each species to the elevational range within which we observed the species.

• We based our conclusions on the combined evidence of P-values from hypothesis testing and magnitudes of differences (odds ratios) generated from parameter estimation.

Figure 2. Sky Island mountain ranges of southeastern AZ

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Figure 1. Start of the 34,000-ha Aspen Fire, Catalina Mountains, AZ

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Introduction Montane forest birds in the Southwest U. S. evolved in forests that historically experienced frequent ( 1 fire every decade), low- to moderate-intensity ground fires (Ganey et al. 1996).

• During the last century, grazing of surface fuels by introduced livestock and widespread fire suppression have greatly reduced the frequency of ground fires in these ecosystems (Pyne 1996).

• The subsequent increase in fuel loads has resulted in a recent increase in frequency of large, high-intensity wildfires (Swetnam et al. 1999; Figure 1) and has prompted increased use of low-intensity prescribed fires by land management agencies to reduce fuel loads.

• Despite the increasing frequency of wild and prescribed fires, few studies have examined the effect of fire on the avian community.

Objective - To assess the effects of recent fires on this avian community, we surveyed montane forest birds in southeastern Arizona and examined how presence of 38 bird species correlated with evidence of severe and less-severe fire damage at >1500 survey points.

Figure 3: Index of fire severity (below) and photographs (above) showing representative fire damage for fire index class 0 (left) to fire index class 4 (right).

0. no evidence of recent fire damage 1. evidence of low-intensity ground fire (e.g., fire-scarring roughly 0-0.3 m above

ground on a few trees)2. evidence of moderate-intensity ground fire (fire-scarring roughly 0.3-1.5 m above ground on most trees; a few small oaks and/or pines killed in understory)3. evidence of high-intensity ground fire (e.g., fire scarring often >1.5 m above ground on trees; almost all understory oaks and/or pines killed [some oaks resprouting]; a few large trees killed [burned snags or fallen trunks])4. evidence of high-intensity crown fire (e.g., all above-ground vegetation killed)

Methods• We conducted 3-min point counts along 84 survey routes in the Chiricahua, Huachuca, Santa Catalina, Rincon, Santa Rita, Pinaleno, Galiuro, and Santa Teresa Mountains (Fig. 2).

• We used an of index of fire severity (Fig. 3) to quantify visual evidence of recent (<15 years old) fire damage at each survey point.

Results• We observed evidence of fire damage on 69% (n = 58) of our survey routes and at 27% (n = 406) of survey points.

• Species negatively associated with evidence of severe fire damage, in order of decreasing strength of associations, were Bewick’s Wren, Red-breasted Nuthatch, Mexican Jay, Warbling Vireo, Black-headed Grosbeak, Stellar’s Jay, Dusky-capped Flycatcher, and Hermit Thrush.

• Species negatively associated with evidence of less-severe fire damage, in order of decreasing strength of associations, were Red-breasted Nuthatch and Black-headed Grosbeak.

• Species positively associated with evidence of severe fire damage, in order of decreasing strength of associations, were Western Wood-Pewee, House Wren, Virginia’s Warbler, Hairy Woodpecker, White-breasted Nuthatch, Greater Pewee, Spotted Towhee, and Yellow-eyed Junco.

• Species positively associated with evidence of less-severe fire damage, in order of decreasing strength of associations, were Yellow-rumped Warbler, Greater Pewee, House Wren, Hairy Woodpecker, Black-throated Gray Warbler, and Pygmy Nuthatch.

• Only 1 of 16 species previously identified as being associated with open-woodlands (Marshall 1963) showed a positive association to areas with evidence of recent fire

Discussion and Conclusions• We detected associations between bird presence and recent fire damage for half of the 38 bird species analyzed.

• Most species showed an association to areas with severe fire damage (16) as opposed to less-severe fire damage (8).

• Our results suggest that fires, especially severe wildfires, can affect the distribution of many species of montane forest birds in the southwestern U. S.

• Current fire regime is unlikely to facilitate restoration of montane forests to pre-fire suppression conditions; thus, many birds associated with open forests will continue to be excluded from the region.