Transcript Kirkpatrick, C., C. J. Conway, and P. B. Jones

DISTRIBUTION AND RELATIVE ABUNDANCE OF ARIZONA
FOREST BIRDS IN RELATION TO BURN SEVERITY
Chris Kirkpatrick1, Courtney J. Conway2, and Patricia B. Jones1
1 University of Arizona; 2 USGS Arizona Cooperative Fish and Wildlife Research Unit
Results
• We observed evidence of fire at 406 of 1,513 survey points:
300 survey points had evidence of “less severe fire” and 106
survey points had evidence of “severe fire”.
NEW MEXICO
Virginia’s warbler
ARIZONA
• TUCSON
• Median time since fire was 6 years (range 2-47 years) for 82%
of 406 burned survey points.
• We detected a total of 10,473 individuals of 97 species and
found associations between fire and bird presence/absence for
17% of 65 species analyzed and between fire and bird relative
abundance for 25% of 16 species analyzed (Table 1).
Photo credit: Brian Small
Table 1. Direction and strength of associations between bird presence/absence and
relative abundance and two levels of burn severity using data collected during
montane forest bird surveys in southeastern Arizona, April to July, 2000.
Introduction
• Many montane forest birds in the southwestern U.S. (especially
those inhabiting pine and pine-oak woodlands) evolved in areas
that historically experienced recurrent (≥1 fire every decade),
low- to moderate-severity surface fires.
• During the last century, grazing of surface fuels by introduced
livestock and widespread fire suppression have greatly reduced
the frequency of surface fires in the region.
• Marshall (1957, 1963) speculated that fire suppression and
subsequent fuels accumulation had reduced the distribution and
abundance of many “open-woodland” birds in the “Sky Island”
mountain ranges of southeastern Arizona (Fig. 1).
• Increased fuel loads have resulted in a recent increase in the
frequency of large, often severe wildfires (Fig. 2) and prompted
the use of low-severity 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 fires (especially fires of
different severities) on the unique avian community inhabiting
montane forests of southeastern Arizona.
Fig. 3. Burn severity index (BSI):
Presence/Absence
MEXICO
Species
Objectives
Methods Continued
• To identify effects of recent fires (both severe
and less-severe) on the distribution and relative
abundance of forest birds in mountains of
southeastern Arizona.
• To control for elevation, we included elevation
as a covariate in the regression models and
restricted data for each species to the elevational
range in which we observed the species.
Methods
• From April to July 2000, we conducted 3-min
point count surveys at 1,513 points along 84
routes (located primarily in pine and pine-oak
woodlands) in the Chiricahua, Huachuca, Santa
Catalina, Rincon, Santa Rita, Pinaleno, Galiuro,
and Santa Teresa mountains (Fig. 1).
• We quantified burn severity within 100 m of
each survey point using a burn severity index
(BSI; Fig. 3). Based on available fire history
data, we estimated median time since fire for the
majority of the burned survey points.
• We included route as an independent variable
in the regression models to control for the lack
of independence between survey points along
routes.
• We based our conclusions on the combined
evidence of P-values from hypothesis testing and
magnitudes of differences (odds ratios)
generated from parameter estimation.
1
2
3
4
0) No evidence of fire
1) Evidence of low-severity surface fire (e.g., fire-charring roughly 0-0.3 m above
ground on a few trees)
2) Evidence of moderate-severity surface fire (e.g., fire-charring roughly 0.3-1.5 m
above ground on most trees; a few small oaks or pines killed in understory)
3) Evidence of high-severity surface fire (e.g., fire charring often >1.5 m above
ground on trees; almost all oaks or pines killed in understory)
4) Evidence of high-severity crown fire (e.g., all above-ground vegetation killed)
Less-severe
Fire
Severe
Fire
Less-severe
Fire
Hairy woodpecker
+
+
n/a
n/a
Greater Pewee
+
+
n/a
n/a
Western Wood-Pewee
++
0
++
0
White-breasted Nuthatch
+
+
n/a
n/a
Red-breasted Nuthatch
--
--
n/a
n/a
House Wren
++
+
++
+
Warbling Vireo
--
--
--
0
Yellow-rumped Warbler
0
-
n/a
n/a
Grace’s Warbler
+
+
n/a
n/a
Virginia’s Warbler
+
0
n/a
n/a
Spotted Towhee
0
-
+
-
=
=
=
=
=
Strong, positive association (P ≤ 0.05 and odds ratio ≥3.0)
Positive association (P ≤ 0.10 and odds ratio 1.5-3.0)
Strong, negative association (P ≤ 0.05 and odds ratio ≤0.3)
Negative association (P ≤ 0.10 and odds ratio 0.3-0.6)
No observed association.
Conclusions
• Most (73%) of the species analyzed were positively associated
with recently burned areas and displayed stronger associations
(i.e., more extreme odds ratios) with survey points that had
evidence of severe as opposed to less-severe fire.
• None of the 16 species identified by Marshall (1963) as “openwoodland” birds showed positive associations with burned areas.
1) no evidence of fire (BSI 0)
2) evidence of “less-severe fire” (BSI 1-2)
3) evidence of “severe fire” (BSI 3-4)
• To test for associations between birds and
recent fire, we used: 1) logistic regression to
examine whether bird presence/absence was
associated with burn severity for 65 bird species,
and 2) ordinal logistic regression to examine
whether bird relative abundance was associated
with burn severity for a subset of 16 bird species.
++
+
-0
• Positive associations were particularly strong for western woodpewee and house wren and negative associations were
particularly strong for warbling vireo and red-breasted nuthatch.
• We collapsed BSI values into 3 general
categories to increase power of statistical tests:
0
Severe
Fire
Fig. 1. “Sky Island” mountain ranges of southeastern AZ
Fig. 2. Start of the 34,000-ha Aspen Fire, Catalina Mountains, AZ
Relative Abundance
Red-faced warbler
Photo credit: Brian Small
Literature Cited
Marshall, J. T. Jr. 1957. Birds of pine-oak woodland in southern Arizona and adjacent
Mexico. Pacific Coast Avifauna Number 32.
Marshall, J. T. Jr. 1963. Fire and birds in the mountains of southern Arizona.
Proceedings of the Tall Timbers Fire Ecol. Conf. 2:135-141.
• Our results suggest that recent fires have had a positive effect
on the distribution/relative abundance of several montane forest
bird species in the region. However, these species are not the
“open-woodland” birds we would have expected to have
benefited from fire based on research by Marshall (1967, 1963).
• Because some bird species appear to respond differently to
different levels of burn severity, future studies should examine
how birds respond to fire across a range of burn severities instead
of examining simple responses of birds to “fire” per se.