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SYNTHESIS & INTEGRATION
Spotted Owls and forest fire: a systematic review and meta-analysis
of the evidence
DEREK E. LEE
1,2,
1
Wild Nature Institute, 15 North Main Street #208, Concord, New Hampshire 03302 USA
Citation: Lee, D. E. 2018. Spotted Owls and forest fire: a systematic review and meta-analysis of the evidence. Ecosphere
9(7):e02354. 10.1002/ecs2.2354
Abstract. Forest and Spotted Owl management documents often state that severe wildfire is a cause of
recent declines in populations of Spotted Owls and that mixed-severity fires (5–70% of burned area in high-
severity patches with >75% mortality of dominant vegetation) pose a primary threat to Spotted Owl popula-
tion viability. This systematic review and meta-analysis summarize all available scientific literature on the
effects of wildfire on Spotted Owl demography and ecology from studies using empirical data to answer the
question: How does fire, especially recent mixed-severity fires with representative patches of high-severity
burn within their home ranges, affect Spotted Owl foraging habitat selection, demography, and site occupancy
parameters? Fifteen papers reported 50 effects from fire that could be differentiated from post-fire logging.
Meta-analysis of mean standardized effects (Hedge’sd) found only one parameter was significantly different
from zero, a significant positive foraging habitat selection for low-severity burned forest. Multi-level mixed-
effects meta-regressions (hierarchical models) of Hedge’sdagainst percent of study area burned at high sever-
ity and time since fire found the following: a negative correlation of occupancy with time since fire; a positive
effect on recruitment immediately after the fire, with the effect diminishing with time since fire; reproduction
was positively correlated with the percent of high-severity fire in owl territories; and positive selection for for-
aging in low- and moderate-severity burned forest, with high-severity burned forest used in proportion to its
availability, but not avoided. Meta-analysis of variation found significantly greater variation in parameters
from burned sites relative to unburned, with specifically higher variation in estimates of occupancy, demogra-
phy, and survival, and lower variation in estimates of selection probability for foraging habitat in low-severity
burned forest. Spotted Owls were usually not significantly affected by mixed-severity fire, as 83% of all stud-
ies and 60% of all effects found no significant impact of fire on mean owl parameters. Contrary to current per-
ceptions and recovery efforts for the Spotted Owl, mixed-severity fire does not appear to be a serious threat to
owl populations; rather, wildfire has arguably more benefits than costs for Spotted Owls.
Key words: adaptive management; evidence-based decision making; meta-analysis; mixed-severity fire; Spotted Owls;
Strix occidentalis; systematic review; wildfire.
Received 22 April 2018; revised 1 June 2018; accepted 11 June 2018. Corresponding Editor: Joseph A. LaManna.
Copyright: ©2018 The Author. This is an open access article under the terms of the Creative Commons Attribution
License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
2
Present address: Pennsylvania State University, State College, Pennsylvania 16801 USA.
E-mail: derek@wildnatureinstitute.org
INTRODUCTION
Wildfires are major natural disturbances in for-
ests of the western United States, and native
plants and animals in this region have been
coexisting with fire for thousands of years of
their evolutionary history (Pierce et al. 2004,
Power et al. 2008, Marlon et al. 2012). Western
forest fires typically burn as mixed-severity fires
with each fire resulting in a mosaic of different
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vegetation burn severities, including substantial
patches (range, 5–70% of burned area; mean,
22%) of high-severity fire (Beaty and Taylor 2001,
Hessburg et al. 2007, Whitlock et al. 2008, Wil-
liams and Baker 2012, Odion et al. 2014a, Baker
2015a). High-severity fire (high vegetation burn
severity) kills most or all of the dominant vegeta-
tion in a stand (>75% mortality; Hanson et al.
2009, Baker 2015a,b) and creates complex early
seral forests, where standing dead trees, fallen
logs, shrubs, tree seedlings, and herbaceous
plants comprise the structure (Swanson et al.
2011, DellaSala et al. 2014). Post-fire vegetation
processes (i.e., succession) then commence
according to the pre-fire vegetation, local wild-
fire processes, propagules from outside the dis-
turbance, and the dynamic biotic and abiotic
conditions at the site (Gutsell and Johnson 2006,
Johnson and Miyanishi 2006, Mori 2011).
Spotted Owls (Strix occidentalis) occur in west-
ern U.S. forests and have been intensively stud-
ied since the 1970s (Fig. 1). The species is
strongly associated with mature and old-growth
(i.e., late-successional) conifer and mixed
conifer–hardwood forests with thick overhead
canopy and many large live and dead trees and
fallen logs (Guti
errez et al. 1995). Its association
with older forests has made the Spotted Owl an
important umbrella indicator species for public
lands management (Noon and Franklin 2002).
The scientific literature has established that the
optimal habitat for Spotted Owl nesting, roost-
ing, and foraging is provided by conifer and
mixed conifer–hardwood forests dominated by
medium (30–60 cm) and large (>61 cm) trees
with medium (50–70%) to high (>70%) canopy
cover (Guti
errez et al. 1995). The populations of
all three subspecies have declined due to wide-
spread historical and ongoing habitat loss, pri-
marily from logging mature and old-growth
forests favored by the owls for nesting and roost-
ing (Seamans et al. 2002, Forsman et al. 2011,
USFWS 2011, 2012, Conner et al. 2013, Tempel
and Guti
errez 2013, Dugger et al. 2016).
Research on Spotted Owl in fire-affected land-
scapes did not begin until the early 2000s, and
much of what scientists previously understood
about habitat associations of Spotted Owl was
derived from studies in forests that had generally
not experienced recent fire, and where the non-
suitable owl habitat was a result of logging
(Guti
errez et al. 1992, Franklin et al. 2000, Sea-
mans et al. 2002, Blakesley et al. 2005, Seamans
and Guti
errez 2007, Forsman et al. 2011, Tempel
et al. 2014). Because Spotted Owls are associated
with dense, late-successional forests, it has often
been assumed that fires that burn at high severity
are analogous to clear-cut logging and have a
negative effect on population viability. It has
become widely believed among wildlife manage-
ment professionals that severe wildfire is a con-
tributing cause of recent Spotted Owl population
declines (USFWS 2011, 2012, 2017), and many
land managers believe that forest fires currently
pose the greatest risk to owl habitat and are a pri-
mary threat to population viability (Davis et al.
2016, Guti
errez et al. 2017). These beliefs result in
fuel-reduction logging projects in Spotted Owl
habitat (USDA 2012, 2018) which the USDA
Forest Service and US Fish and Wildlife Service
state are actions consistent with Spotted Owl
recovery (USDA 2012, 2018, Guti
errez et al. 2017,
USFWS 2017). Narrative literature reviews
have attempted to summarize the effects of fire
on Spotted Owl (Bond 2016, Guti
errez et al.
2017), but evidence-based conservation decisions
should be based upon systematic, transparent
reviews of primary literature with quantitative
meta-analysis of effects (Sutherland et al. 2004,
Pullin and Stewart 2006, Pullin and Knight 2009,
Koricheva et al. 2013).
The following systematic review and meta-ana-
lysis summarize all available published scientific
literature on the effects of wildfire on aspects of
Spotted Owl demography (survival, recruitment,
and reproduction), site occupancy, and habitat
selection, from studies using empirical data to
answer the question: How does fire, especially
mixed-severity fire with substantial patches of
high-severity fire within their home ranges, affect
Spotted Owl demography, site occupancy, and
habitat selection in the first few post-fire years?
METHODS
Literature search
I conducted a systematic review of the primary
scientific literature and used meta-analyses and
meta-regression to examine the evidence for the
direct effects of wildfire on Spotted Owl demo-
graphy, site occupancy, and habitat selection. My
subject was Spotted Owls; the intervention was
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SYNTHESIS & INTEGRATION LEE
wildfire; the outcomes were change or difference
in estimates of demography, site occupancy, and
habitat selection probabilities; and the compara-
tor was pre-fire estimates or control estimates
from unburned areas (Pullin and Stewart 2006). I
searched the following electronic databases on 1
April 2018: Agricola, BIOSIS Previews, ISI Web
of Science, and Google Scholar. Search terms
Fig. 1. Range map for the three subspecies of the Spotted Owl (Strix occidentalis).
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SYNTHESIS & INTEGRATION LEE
were as follows: spotted AND owl AND fire,
Strix AND occidentalis AND fire. My search
included papers published in any year.
I used a threefold filtering process for accepting
studies into the final systematic review. Initially, I
filtered all articles by title and removed any obvi-
ously irrelevant material from the list of articles
found in the search. Subsequently, I examined the
abstracts of the remaining studies with regard to
possible relevance to the systematic review ques-
tion, using inclusion criteria based on the subject
matter and the presentation of empirical data. I
accepted articles for viewing at full text if I deter-
mined that they may contain information perti-
nent to the review question or if the abstract was
ambiguous and did not allow inferences to be
drawn about the content of the article. Finally, I
read all remaining studies at full text and either
rejected or accepted into the final review based
upon subject matter (Pullin and Stewart 2006,
Koricheva et al. 2013). Studies that only modeled
effects of simulated fires on Spotted Owl habitat
and demography were not considered here.
Because post-fire logging often occurred, I also
recorded effects of this disturbance where they
were reported. I believe all studies in the final
review were generally comparable because time
since fire and percent of high-severity burn were
similar among studies (Tables 1, 2), and the high
number of non-significant results reported indi-
cates little to no publication bias exists in this
topic (Tables 1, 2; Appendix S1: Fig. S1). I consid-
ered the basic sampling unit of all studies to be
the central core of the owl breeding-season terri-
tory (~400 ha, or a circle with radius 1.1 km cen-
tered on the nest or roost stand) because this is
the spatial and temporal scale for sampling used
in almost all Spotted Owl studies. In contrast,
Spotted Owl year-round home ranges vary
according to latitude and dominant vegetation,
but range from 300 to 11,000 ha, or circles with
radius 1.0–5.9 km (Zabel et al. 1992). I consid-
ered forest fires to affect the landscape scale
(~10,000 ha/decade), but that fires would affect
numerous individual owl breeding-season terri-
tories (1200 ha) and year-round home ranges
(300–19,000 ha) in various ways.
Meta-analyses and meta-regression
I evaluated all final review papers and
included all papers where effects of fire were
reported and could be differentiated from other
disturbances such as post-fire logging. I extracted
evidence by reading every paper and tabulating
all quantified results from text, tables, and fig-
ures (Table 1). I noted the mean (
x) and variation
(SD) of burned and unburned groups for all sig-
nificant and non-significant parameters, the
parameters being estimated, sample sizes
(n=number of owl breeding sites in burned and
unburned groups), amount of high-severity fire
in the total fire perimeter and/or within the owl
territory core areas examined, time since fire
(years), amount of post-fire logging that
occurred, subspecies (California =Strix occiden-
talis occidentalis, Mexican =Strix occidentalis
lucida, or northern =Strix occidentalis caurina),
and whether the result was statistically signifi-
cant (as defined in each paper).
I conducted all analyses in R 3.3.1 (www.r-pro
ject.org). For meta-analysis, I noted or calculated
the mean, variance (SD), and sample size for
burned (treatment) and unburned (control)
groups. I calculated raw effect sizes as mean
differences (
xburned
xcontrol) and signs (positive
or negative) for all reported effects, regardless
of their statistical significance. Most papers
reported effect sizes as probabilities (occupancy,
survival, and foraging habitat selection) so raw
effect sizes were scaled between negative and
positive one with a mean of zero, making com-
parison among studies easy. When papers
reported multiple effects (e.g., occupancy and
reproduction, or survival and recruitment), I
recorded each effect individually. Where papers
did not report any effect size for a parameter
determined to have no significant effects from
fire, I included a zero to represent the presence of
no significant effect and to avoid a significance
bias in the meta-analysis. I stratified data by sub-
species (California, Mexican, or northern) and
parameter type according to whether the study
estimated site occupancy, foraging habitat selec-
tion (substratified into selection for low-, moder-
ate-, and high-severity burned forest), and
demographic rates (substratified into survival,
reproduction, and recruitment). I performed
meta-analyses on parameters for which ≥4 esti-
mates existed from ≥4 different fires.
I used three quantitative methods for evaluat-
ing the evidence (Koricheva et al. 2013): a ran-
dom-effects meta-analysis of mean effect sizes as
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SYNTHESIS & INTEGRATION LEE
Table 1. Summary of systematic review of studies examining effects of fire on Spotted Owls.
No. Ref. Sample size HOD Time since fire Context
Fire effects
(=statistically
significant,
NS =non-
significant) Fire
Any
effect
Signif.
effect
Post-fire
logging
1 Bond et al.
(2002)
21 owls in 11
burned sites
OD 1 yr post-fire No effect on
survival, site
fidelity, mate
fidelity, or
reproduction. 50%
of territories
burned 36–88%
high severity, 50%
burned mostly low
–moderate severity,
unknown amount
of post-fire logging
No significant
effects. (3% higher
survival NS, 1%
lower site fidelity
[occupancy] NS,
26% higher repro
NS)
0/+/+0.032
0.013
+0.259
na na
2 Jenness
et al.
(2004)
33 burned and
31 unburned
breeding
sites
OD 1-yr study,
1–4yr
post-fire
No effect on
occupancy from
fire or amount of
high-severity fire.
No effect on
reproduction. 55%
of burned
territories area
burned, 18% at
high severity,
unknown amount
of post-fire logging
No significant
effects from fire.
(14% lower
occupancy NS,
7% lower repro in
burn NS)
0/0.14
0.07
na na
3 Bond et al.
(2009)
Seven radioed
owls from
four burned
sites
H 1-yr study, 4 yr
post-fire
Owls preferred
burned forest for
foraging, especially
high-severity
burned forest.
Owls preferred
roost sites burned
at low severity and
avoided unburned
sites and sites
burned at
moderate and high
severity. 69% of
foraging area
burned, 13% at
high severity, <3%
post-fire logging
Positive effect from
fire on foraging
habitat selection
(+42%, +42%
+33%), negative
and positive effect
of fire on roosting
nesting habitat
selection (+29%,
13%, 28%)
+/+0.33
+0.42
+0.42
+0.29
0.13
0.28
+0.33
+0.42
+0.42
+0.29
0.13
0.28
na
4 Bond et al.
(2010)
Five radioed
owls in
occupied
burned sites
H 1-yr study, 4 yr
post-fire
Three of five owls
occupied burned
forest over winter
No significant
effects, perhaps
some positive
effect
0/+na na na
5 Clark et al.
(2011)
11 radioed
owls in
burned and
post-fire
logged sites,
12 in
unburned
sites
D 2-yr study,
3–4yr
post logging
No effects on
survival. Reduced
survival in salvage-
logged areas
relative to owls in
unburned forest.
14% high severity,
21% post-fire
logged
Negative survival
effect from
combined effects
of fire and
post-fire logging
(0.07 NS)
?nana0.07
6 Roberts
et al.
(2011)
16 burned and
16 unburned
survey areas
O 1-yr study,
2–14 yr
post-fire
No effect of fire on
survey area
occupancy. 14% of
survey area burned
at high severity,
little to no post-fire
logging
No significant
effect from fire.
Possible negative
effect from basal
area and canopy
cover model
(26% lower
occupancy in
burned survey
area NS)
0/0.260 na na
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SYNTHESIS & INTEGRATION LEE
(Table 1. Continued)
No. Ref. Sample size HOD Time since fire Context
Fire effects
(=statistically
significant,
NS =non-
significant) Fire
Any
effect
Signif.
effect
Post-fire
logging
7 Lee et al.
(2012)
41 burned and
145
unburned
breeding
sites
O 11-yr study,
1–7yr
post-fire from
six large fires
No effect on
occupancy
probability. 32%
high severity.
Unknown amount
of post-fire logging
No significant
effect from fire,
perhaps a slightly
positive effect (4%
higher occupancy
in burned sites
NS)
0/++0.041 na na
8 Bond et al.
(2013)
Seven radioed
owls
H 1-yr study, 4 yr
post-fire
Owls in burned
forest have same
size or smaller
home ranges than
owls in unburned
forest. 69% of
foraging area
burned, 13% at
high severity, 3%
post-fire logging
No significant
effect from fire,
possible positive
effect (HR size
12% smaller in
burned area NS)
0/++0.12 na na
9 Clark et al.
(2013)
40 burned and
salvage-
logged sites
and 103
unburned
sites
O 13-yr study,
1–4yr
post-fire
Lower site
occupancy on
salvage-logged
sites relative to
unburned sites.
11% high severity,
13% post-fire
logged
Negative effect on
occupancy from
combined fire and
post-fire logging
(0.39)
?nana0.39
10 Lee et al.
(2013)
71 burned and
97 unburned
breeding
sites, post-
fire logging
on 21 of the
burned sites
O 8-yr study,
1–8yr
post-fire
No effects from fire
or logging. Burned
site occupancy 17%
(10% for pairs)
lower than
unburned sites.
Post-fire logged
sites occupancy 5%
lower than
unlogged burned
sites. 23% high
severity in burned
sites, 59% logged
in post-fire logged
sites
No significant
effect from fire,
negative effect
(17% lower any
occupancy, 10%
lower pair
occupancy in
burn NS)
Same data as ref.
no. 14
0/0.171
0.107
na 0.05
11 Ganey
et al.
(2014)
Four radioed
owls
H 1-yr study,
4–6yr
post-fire
Owls moved to
burned forest over
winter. Burned
wintering sites had
2–6 times more
prey biomass
relative to
unburned core
areas. 21% high
severity, unknown
amount of post-fire
logged
Positive effect from
fire
+na na na
12 Tempel
et al.
(2014)
12 burned, 62
unburned
sites
DO 20-yr study of
survival and
reproduction,
6-yr study of
occupancy.
No effect on
survival,
reproduction, or
site extinction.
Reported a
negative effect of
fire on colonization
rate, but
colonization
parameter was
faulty due to low
sample size and
zero colonization
events. Unknown
amount of high-
severity fire,
unknown amount
of post-fire logging
No significant
effect from fire.
Possible negative
effect from fire
(6% lower
occupancy when
fire frequency
doubled in
simulations that
assumed zero
post-fire
colonizations)
0/0
0
0.060
0.060 na
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SYNTHESIS & INTEGRATION LEE
(Table 1. Continued)
No. Ref. Sample size HOD Time since fire Context
Fire effects
(=statistically
significant,
NS =non-
significant) Fire
Any
effect
Signif.
effect
Post-fire
logging
13 Lee and
Bond
(2015a)
45 burned
breeding
sites
O Rim Fire, 1-yr
study, 1 yr
post-fire
Higher burned-site
occupancy rates
than any published
unburned area.
100% high-severity
fire in territory
surrounding nest
and roost sites
reduced single owl
occupancy
probability 5%
relative to sites
with 0% high
severity. Amount
of high-severity
fire did not affect
occupancy by pairs
of owls. In fire
perimeter: 37%
high severity, no
post-fire logging
Positive (17%
higher occupancy
rates). Small
negative effect on
site occupancy
(3% lower
occupancy in
burn). No
significant effect
on pair
occupancy
+/0 +0.175
0.04
0
+0.175 na
14 Lee and
Bond
(2015b)
71 burned and
97 unburned
breeding
sites, post-
fire logging
on 21 of the
burned sites
OD 8-yr study,
1–8yr
post-fire
Occupancy of high-
quality sites
(previously
reproductive) that
burned was 2%
lower than
unburned sites.
Occupancy of
high-quality sites
that were post-fire
logged was 3%
lower. Occupancy
of low-quality sites
(previously non-
reproductive) was
19% lower in
burned vs.
unburned sites and
26% lower after
post-fire logging.
Fire did not affect
reproduction. 23%
high severity in
burned sites, 59%
logged in post-fire
logged sites
Negative effect on
site occupancy
(2% and 19%
lower), No
significant effect
on reproduction
/0 0.02
0.19
0
0.02
0.19
0.03
0.26
15 Bond et al.
(2016)
Eight radioed
owls in five
sites
H 2-yr study,
3–4yr
post-fire
Owls used forests
burned at all
severities in
proportion to their
availability, with
the exception of
significant
selection for
moderately burned
forest farther from
core areas. 23%
high severity, <5%
post-fire logging
No significant
effect from fire
(3% lower
probability of use
in high-severity
burn NS), some
positive effect
(15% higher
probability of use
of low-severity
burn NS, 10%
higher probability
of use in
moderate-severity
burned forest NS,
3% higher
probability of use
of moderate
severity away
from the core)
0/+0.03
+0.15
+0.10
+0.033 na
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SYNTHESIS & INTEGRATION LEE
(Table 1. Continued)
No. Ref. Sample size HOD Time since fire Context
Fire effects
(=statistically
significant,
NS =non-
significant) Fire
Any
effect
Signif.
effect
Post-fire
logging
16 Comfort
et al.
(2016)
23 radioed
owls in
post-fire
logged area
H 2-yr study,
3–4yr
post logging
Scale-dependent
effects of logging
(+/). Owls
selected a
moderate amount
of hard edges
around logged
stands. 14% high
severity, 21%
post-fire logged
Positive and
negative effect
from post-fire
logging created
edges
?nana+/
17 Jones et al.
(2016)
30 burned
sites, 15
unburned
sites, nine
radioed owls
in seven sites
OH 23-yr study,
1 yr post-fire
Negative effects
from high-severity
fire. Positive effect
of low- to
moderate-severity
fire. 64% high-
severity burn, 2%
post-fire logging
>50% high-severity
burned sites had
lower occupancy
(0.49), <50%
high-severity
burned sites had
higher occupancy
(+0.07 NS). High-
severity burned
habitat was
avoided
(0.307), low-
tomoderate-
severity burn was
preferred (+0.04
NS)
+/+0.070
0.490
0.307
+0.04
0.490
0.307
+0.04
na
18 Tempel
et al.
(2016)
43 burned
sites and 232
unburned
sites in four
study areas
O 19-yr study,
examined 3-yr
post-fire
effects
No effects of fire.
One study area
had positive effect
of fire. Lower site
extinction
probability
correlated with
proportion of site
where wildfire
reduced canopy
>10%. 1% of all
territories burned,
unknown amount
of post-fire logging
No significant
effect from fire,
some positive
effect (1% lower
extinction rate in
burned sites NS)
0/++0.003
0
0
0
na na
19 Eyes et al.
(2017)
13 radioed
owls in eight
sites (14 owl-
year data
sets)
H 3-yr study,
1–14 yr
post-fire
No effect of fire on
foraging habitat
selection, owls
foraged in all burn
severities in
proportion to their
availability. 6%
high severity, little
to no post-fire
logging
No significant
effect from fire.
Possibly negative
effect (6% lower
probability of use
for highest burn
severity NS; 3%
lower use of
moderate severity
NS)
0/0.06
0.03
na na
20 Rockweit
et al.
(2017)
193 burned
and 386
unburned
encounter
histories
from 28
burned (8, 2,
4, 14) and 70
unburned
sites
D 26-yr study,
4–26 yr
post-fire
Four fires had
different effects.
Generally, fires
reduced survival
and increased
recruitment. 10%,
12%, 16%, and 48%
high severity, no
post-fire logging
reported
Two fires had no
significant effects
on survival or
recruitment. Two
fires had reduced
survival (0.17
and 0.30), one
had increased
recruitment
(+0.22)
0/+/0.03
0.10
0.17
0.30
+0.01
+0.02
+0.04
+0.22
0.17
0.30
+0.22
na
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SYNTHESIS & INTEGRATION LEE
the standardized difference in means (Hedge’sd;
Hedges and Olkin 1985); multi-level linear mixed-
effects models (hierarchical models) meta-regres-
sion of time since fire and percent of high-severity
fire in the study area as covariates to explain
heterogeneity in mean effect sizes (Hedges and
Vevea 1998, Nakagawa and Santos 2012); and a
random-effects meta-analysis of variation to
examine differences in parameter variances due to
fire with effect sizes as the natural logarithm of
the ratio between the coefficients of variation
(lnCVR; Nakagawa et al. 2015). For analyses, I
used the metafor package of R (Viechtbauer 2010)
and used function metacont for random-effects
meta-analyses, function rma.mv for multi-level
linear mixed-effects model meta-regression, and
function rma for random-effects meta-analysis
of variation (Viechtbauer 2010). Study within
geographic area was included as multi-level
random effects to properly estimate study site-
and region-specific variation and to account
for repeated measurements (pseudo-replication)
within a study or region. Regions were defined as
Sierra Nevada, southern California, national
parks, not California, and the Eldorado density
study area (because several studies used data
from there).
I used all three methods at three levels: on all
parameters, on three main groups of parameters
(occupancy, foraging habitat selection, and
demography), and on subgroups of habitat selec-
tion (for low-, moderate-, and high-severity
burned forest) and demography (survival, repro-
duction, and recruitment). In meta-analyses, I
used ztests to determine if effects were signifi-
cantly different from zero (95% confidence inter-
val excluded zero). In meta-regression, ztests
determined whether intercepts or slope coeffi-
cients were significantly different from zero. I
quantified heterogeneity among effects as
Cochran’sQ(Hedges and Olkin 1985) and I
2
(Higgins and Thompson 2002). I used a funnel
plot and the rank correlation test (Kendall’ss)to
assess publication bias (Begg and Mazumdar
1994).
RESULTS
Literature search
I found 21 papers reporting empirical evidence
relevant to direct fire effects on owls (Table 1).
Three papers presented data from a study area
which was extensively logged post-fire and
results did not discriminate between effects of
fire and post-fire logging (Clark et al. 2011, 2013,
Comfort et al. 2016), so these three papers were
not included in meta-analyses with the meta-
analysis set of papers that were not confounded
(Table 1. Continued)
No. Ref. Sample size HOD Time since fire Context
Fire effects
(=statistically
significant,
NS =non-
significant) Fire
Any
effect
Signif.
effect
Post-fire
logging
21 Hanson
et al.
(2018)
54 burned
sites in eight
fires that
were
occupied
immediately
before fire,
before–after
comparison
O 14-yr study,
1 yr post-fire
Eight large fires (4
included in Tempel
et al. 2016). Four
groups: 20–49%
and 50–80% high-
severity fire; and
<5% and ≥5%
post-fire logging
within 1500 m of
site center. Mean
63% high severity
in core areas, mean
17% logged if ≥5%
of core was
post-fire logged
Compared burned
site occupancy
with unburned
occupancy from
Tempel et al.
(2016)
No significant
effect from fire,
significant
negative effect of
post-fire logging
(3% reduction in
occupancy if 50–
80% of core
burned high-
severity fire NS,
52% reduction in
occupancy from
≥5% post-fire
logging)
0/- 0.017
0.013
na 0.52
Notes: HOD indicates habitat selection (H), occupancy (O), or demographic (D) parameters were estimated. A question
mark (?) indicates confounded fire and post-fire logging effects, so fire effects could not be estimated.
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SYNTHESIS & INTEGRATION LEE
Table 2. Summary statistics for published effects of mixed-severity fire on Spotted Owls (Strix occidentalis) 1987–
2018 used in meta-analysis.
Ref
no. Study Subspecies Region Parameter
n
burned
n
unburned
Raw effect
size (mean
difference)
Significant
(in study)
Time
since
fire
(yr)
Percentage of
high-severity fire in
burned territories
1 Bond
(2002)
CNM NotCal Occupancy 18 100 0.013 na 1 30
1 Bond
(2002)
CNM NotCal Reproduction 7 100 0.259 na 1 30
1 Bond
(2002)
CNM NotCal Survival 21 100 0.032 na 1 30
2 Jenness
(2004)
M NotCal Occupancy 33 31 0.14 na 2.5 16
2 Jenness
(2004)
M NotCal Reproduction 33 31 0.07 na 2.5 16
3 Bond
(2009)
C SN Foraging High 7 7†0.42 0.42 4 13
3 Bond
(2009)
C SN Foraging Low 7 7†0.33 0.33 4 13
3 Bond
(2009)
C SN Foraging Mod 7 7†0.42 0.42 4 13
6 Roberts
(2011)
C NP Occupancy 16 16 0.26 na 8 12
7 Lee
(2012)
C SN Occupancy 41 145 0.041 na 4 32
10 Lee
(2013)
C SoCal Occupancy 71 97 0.171 na 4.5 23
10 Lee
(2013)
C SoCal Occupancy 71 97 0.107 na 4.5 23
12 Tempel
(2014)
C Eldorado Occupancy 12 62 0.06 0.06 3 23‡
12 Tempel
(2014)
C Eldorado Reproduction 12 62 0 na 3 23‡
12 Tempel
(2014)
C Eldorado Survival 12 62 0 na 3 23‡
13 Lee
(2015a)
C SN Occupancy 45 45 0.04 na 1 37
13 Lee
(2015a)
C SN Occupancy 45 45 0 na 1 37
13 Lee
(2015a)
C SN Occupancy 45 145 0.175 0.175 1 37
14 Lee
(2015b)
C SoCal Occupancy 71 97 0.19 0.19 4.5 23
14 Lee
(2015b)
C SoCal Occupancy 71 97 0.02 0.02 4.5 23
14 Lee
(2015b)
C SoCal Reproduction 71 97 0 na 4.5 23
15 Bond
(2016)
C SoCal Foraging High 8 8†0.093 na 3.5 15
15 Bond
(2016)
C SoCal Foraging High 8 8†0.035 na 3.5 16
15 Bond
(2016)
C SoCal Foraging High 8 8†0.092 na 3.5 9
15 Bond
(2016)
C SoCal Foraging Low 8 8†0.115 na 3.5 15
15 Bond
(2016)
C SoCal Foraging Low 8 8†0.167 na 3.5 9
15 Bond
(2016)
C SoCal Foraging Low 8 8†0.169 na 3.5 16
15 Bond
(2016)
C SoCal Foraging Mod 8 8†0.042 na 3.5 15
15 Bond
(2016)
C SoCal Foraging Mod 8 8†0.033 0.033 3.5 16
15 Bond
(2016)
C SoCal Foraging Mod 8 8†0.102 na 3.5 9
17 Jones
(2016)
C Eldorado Foraging High 9 9†0.307 0.307 1 19
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SYNTHESIS & INTEGRATION LEE
by extensive post-fire logging (Table 2). All 21
papers are summarized in Appendix S1.
Fifteen of the 18 papers in the meta-analysis
set reported evidence explicitly pertaining to
mixed-severity wildfires that burned during the
past few decades and which included propor-
tions of high-severity burn characteristic of this
fire regime, while three reported evidence from
an undifferentiated mix of wildfire and
prescribed fires. The studies reported varying
amounts of high-severity fire, a defining feature
of mixed-severity fires, and the burn severity
type that is most responsible for vegetation
changes in wildfires, with an overall mean per-
cent of high-severity fire of 26% (standard error
[SE] =3.6, range 6–64) within the study area.
Because almost all the studies in this review
reported on effects from recent wildfires (all
(Table 2. Continued)
Ref
no. Study Subspecies Region Parameter
n
burned
n
unburned
Raw effect
size (mean
difference)
Significant
(in study)
Time
since
fire
(yr)
Percentage of
high-severity fire in
burned territories
17 Jones
(2016)
C Eldorado Foraging Mod 9 9†0.04 +0.04 1 19
17 Jones
(2016)
C Eldorado Occupancy 14 15 0.490 0.490 1 64
17 Jones
(2016)
C Eldorado Occupancy 16 15 0.07 na 1 19
18 Tempel
(2016)
C SN Occupancy 12 78 0 na 4 23‡
18 Tempel
(2016)
C Eldorado Occupancy 14 60 0 na 4 23‡
18 Tempel
(2016)
C SN Occupancy 3 63 0 na 4 23‡
18 Tempel
(2016)
C NP Occupancy 14 31 0.003 0.003 4 23‡
19 Eyes
(2017)
C SN Foraging High 13 13†0.06 0.06 7 6
19 Eyes
(2017)
C SN Foraging Mod 13 13†0.03 0.03 7 6
20 Rockweit
(2017)
N NotCal Recruitment 8 8 0.01 na 12.5 10
20 Rockweit
(2017)
N NotCal Recruitment 2 2 0.02 na 6.5 16
20 Rockweit
(2017)
N NotCal Recruitment 4 4 0.04 na 4 48
20 Rockweit
(2017)
N NotCal Recruitment 14 14 0.22 0.22 2 12
20 Rockweit
(2017)
N NotCal Survival 4 4 0.30 0.3 4 48
20 Rockweit
(2017)
N NotCal Survival 14 14 0.17 0.17 2 12
20 Rockweit
(2017)
N NotCal Survival 2 2 0.10 na 6.5 16
20 Rockweit
(2017)
N NotCal Survival 8 8 0.03 na 12.5 10
21 Hanson
(2018)
C SN Occupancy 13 201 0.017 0.017 1 63
21 Hanson
(2018)
C SN Occupancy 15 201 0.013 0.013 1 35
Notes: Study indicates first author and year. Subspecies are C, California (Strix occidentalis occidentalis); N, northern (Strix
occidentalis caurina); M, Mexican (Strix occidentalis lucida); CNM, study included all subspecies. Regions are SN, Sierra Nevada,
California (except El Dorado study area and national parks); SoCal, southern California; Eldorado, El Dorado study area in
Sierra Nevada, California; NotCal, not California Spotted Owl subspecies; NP, national parks. Parameters: habitat selection (for-
aging or roosting) in low-, moderate-, (mod) or high-severity burned forest; occupancy, recruitment, reproduction, and survival.
Sample sizes (n) are number of breeding site territories burned and unburned. Raw mean effect size is
xburned
xcontrol, signifi-
cant repeats effects that the individual study determined was statistically significant. Time since fire is the median number of
years between the fire and the parameter estimate(s). Percent high-severity fire in burned study territories is the mean relevant
to the estimate, or the grand mean if percentage of high severity was not reported (see ‡).
†Habitat selection occurred within territories that contained a mosaic of burn severities and unburned forest.
‡Percent high-severity fire was not reported for burned territories only for all territories burned and unburned, so the grand
mean of reported percentages was used.
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SYNTHESIS & INTEGRATION LEE
fires burned in the past 30 yr, mean time since
fire =4yr, SE=1.1, range 1–26), the reported
effects are representative of natural mixed-
severity fires as they burned through currently
existing forest structure, fire regime, and climate
conditions. Papers reported effects of fire on site
occupancy (11), foraging habitat selection (4),
reproduction (4), apparent survival (3), overwin-
ter roosting habitat selection (2), site fidelity (1),
mate fidelity (1), breeding-season nesting and
roosting habitat selection (1), home-range size
(1), and recruitment (1). Sample sizes mea-
sured as number of burned sites were variable
among studies (demography CV =122%, site
occupancy CV =56%, and habitat selection
CV =24%).
Meta-analyses
Meta-analysis of 50 reported effects on occu-
pancy, foraging habitat selection, and demo-
graphic rates found effect sizes and signs were
variable (Table 2 and Fig. 2), with high hetero-
geneity among effects (Q=1091, df =51,
P<0.0001; I
2
=95.3%). Funnel plot (Appen-
dix S1: Fig. S1) and rank correlation test (Ken-
dall’ss=0.108, P=0.27) showed no publication
bias or unusual heterogeneity. Sample sizes
(n=number of reported effects) were variable
among parameter types (Fig. 3). The number of
reported effects were occupancy =20; demogra-
phy =14; and foraging habitat selection =16.
The number of reported effects by demography
subtype were survival =6; reproduction =4;
and recruitment =4. The number of reported
effects by habitat selection subtype were low-
severity burned forest =4; moderate-severity
burned forest =6; and high-severity burned
forest =6.
The mixed-effects model meta-analysis of fire
effects on Spotted Owl parameters grouped by
type (occupancy, demography, and foraging
habitat selection), and subtypes of demography
(survival, reproduction, and recruitment) or for-
aging habitat selection (selection for low-, moder-
ate-, and high-severity burned forest), found
mixed-severity fire has generally no significant
effect on Spotted Owls (Fig. 3a). Mean overall
raw effect size was positive (+0.001), but
weighted mean Hedge’sdfrom the random-
effects model was not significantly different from
zero (Fig. 3a, 95% confidence interval included
zero). Mean raw effect sizes were negative for
occupancy (0.060), demography (0.006), and
survival (0.095), but no Hedge’sdvalue for
these three negative effects was significantly dif-
ferent from zero (Fig. 3a). Mean raw effect sizes
were positive for reproduction (+0.047), recruit-
ment (+0.073), foraging habitat selection (+0.083),
selection of high-severity (+0.004), moderate-
severity (+0.087), and low-severity burned forest
(+0.195), but Hedge’sdvalues were not signifi-
cantly different from zero for any of these posi-
tive effects, except for significant selection of
low-severity burned forest (Fig. 3a).
Variation was generally higher among
parameter estimates from burned areas com-
pared to estimates from unburned areas (mean
CV
burned
CV
unburned
=23%; range 4–57%).
The mixed-effects meta-analysis of variation in
fire effects on Spotted Owl parameters (lnCVR)
found mixed-severity fire resulted in signifi-
cantly higher variation in parameter estimates
in all parameters and in occupancy, demogra-
phy, and survival (Fig. 3b). There was signifi-
cantly lower variation in estimates of foraging
habitat selection probability for low-severity
burned forest (Fig. 3b).
Meta-regression
Meta-regression of all standardized mean
effects found significant effect of time since fire
(Table 3), and a nearly significant effect of per-
cent high-severity burn in territory cores
(Table 3), so those effects were included in
parameter-specific meta-regressions. Subspecies
was not a significant factor (Table 3), so effects
from different subspecies were pooled in subse-
quent parameter-specific analyses.
Meta-regression of occupancy probability
found no significant immediate effect of fire on
occupancy (intercept not significantly different
from zero; Table 4). There was a significant nega-
tive effect of time since fire (Fig. 4, Table 4), but
no effect of percent high-severity fire in study ter-
ritories (Table 4). The negative effect of time
since fire was sensitive to one study (Roberts
et al. 2011), and when that study was omitted,
the effect disappeared.
Meta-regression of demographic parameters
found a significant positive effect on recruitment
immediately after the fire (intercept significantly
different from zero), but the effect diminished
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Fig. 2. Forest plot of effect sizes for 50 Spotted Owl (Strix occidentalis) parameters (grouped into occupancy,
demography, and foraging habitat selection) affected by mixed-severity wildfire as standardized mean difference
(Hedge’sd) between burned and unburned samples. Studies and parameters are listed in Table 2.
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with time since fire (Fig. 5, Table 4). Reproduc-
tion intercept was not significantly different from
recruitment (Table 4), and not significantly dif-
ferent from zero (z=0.218, P=0.86), but
reproduction was significantly positively corre-
lated with the percent of high-severity fire in owl
territories (Fig. 5, Table 4). Survival was signifi-
cantly lower than recruitment (Table 4), but sur-
vival intercept was not significantly different
from zero (z=0.052, P=0.97). There were no
significant survival effects of time since fire or
percent of high-severity fire (Table 4).
Meta-regression of foraging habitat selection
parameters found a significant positive selection
for low- and moderate-severity burned forest,
with high-severity burned forest used in propor-
tion to its availability, but not avoided (Fig. 5,
Table 4). Time since fire did not affect foraging
habitat selection during the period covered by
the studies I examined (up to 7 yr), and the
Fig. 3. Results of mixed-effects meta-analyses of mixed-severity fire effects (n=50 effects from 21 studies) on
Spotted Owl (Strix occidentalis) parameters grouped by type (occupancy, demography, and foraging habitat selec-
tion) and subtype of demography (survival, reproduction, and recruitment), or habitat selection (selection for
low-, moderate-, and high-severity burned forest). (a) Hedge’sdis standardized mean effect size, and error bars
are 95% confidence intervals. The only significant effect (95% confidence intervals excluded zero) was a positive
effect of habitat selection for low-severity burned forest. (b) lnCVR is the natural logarithm of the ratio between
the coefficients of variation, a measure of differences in variation of parameter estimates between burned and
unburned areas. Mixed-severity fire resulted in significantly higher variation in parameter estimates in all param-
eters, occupancy, demography, and survival, and significantly lower variation in habitat selection for low-sever-
ity burned forest.
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SYNTHESIS & INTEGRATION LEE
amount of high-severity fire did not affect habitat
selection overall (Table 4).
Post-fire logging had negative effects on Spot-
ted Owls in 100% of the papers that examined
this disturbance and where effects from fire and
post-fire logging could be differentiated, with
large effect sizes (0.18 occupancy, 0.07
survival).
DISCUSSION
This systematic review and summary of effects
from the primary literature indicated Spotted
Owls are usually not significantly affected by
mixed-severity fire as 83% of all studies and 60%
of all effects found no significant impact of fire
on owl parameters. Meta-analysis of mean effects
found no significant effects of fire on owls, except
a positive effect on foraging habitat selection
for low-severity burned forest. Meta-regression
indicated significant positive effects in recruit-
ment, reproduction, and foraging habitat selec-
tion for low- and moderate-severity burned
forest. Meta-regression found a significant
negative effect of time since fire on occupancy
probability. Meta-analysis of variation found
mixed-severity fire resulted in greater parameter
variation overall, and specifically in occupancy,
demography, and survival, and significantly less
variation in foraging habitat selection for low-
severity burned forest.
These results represent Spotted Owl responses
to mixed-severity wildfires that burned within the
past 30 yr with representative proportions of
high-severity fire in a landscape mosaic. Addi-
tionally, because most of the studies in this review
reported on effects from wildfire, rather than pre-
scribed fire, the fires and their effects are represen-
tative of wildfires as they burned through
currently existing forest structure, fire regime, and
climate conditions. Several studies have reported
that fires during the past few decades have been
larger and more severe than the historical mean
(Miller and Safford 2012, 2017, Mallek et al. 2013,
Steel et al. 2015), but others have disputed this
Table 3. Results from multivariate mixed-effects meta-
regression model of mixed-severity fire effects
(n=50 effects from 21 studies) on Spotted Owl
(Strix occidentalis) parameters related to occupancy,
demography, and foraging habitat selection.
Covariates bSE zP
Intercept (California
subspecies)
1.601 1.070 1.497 0.134
Time since fire 0.199 0.099 2.017 0.044
Percentage of area
high-severity fire in
study territories
0.044 0.023 1.866 0.062
Mix of California,
northern, Mexican
subspecies
0.467 1.592 0.294 0.769
Mexican subspecies 1.947 1.608 1.211 0.226
Northern subspecies 0.360 1.571 0.229 0.819
Notes: SE, standard error. Time since fire was significant, and
percent high-severity burn in territory cores was nearly signifi-
cant, so those effects were included in parameter-specificmeta-
regressions. Subspecies was not a significant factor, so effects
from different subspecies were pooled in subsequent parameter-
specific analyses. Bold values are significant at alpha =0.05.
Table 4. Table of model coefficients from multi-level
linear mixed-effects model meta-regression for effects
of mixed-severity fire on Spotted Owls 1987–2018.
Coefficient bSE zP
Occupancy
Intercept 1.854 1.115 1.662 0.096
Time since fire 0.512 0.216 2.375 0.018
Percentage of area
high-severity fire in
study territories
0.036 0.022 1.645 0.100
Demography
Intercept
(Recruitment)
2.328 1.152 2.021 0.043
Time since fire
(Recruitment)
0.153 0.065 2.347 0.019
Percentage of area
high-severity fire in
study territories
0.032 0.022 1.466 0.143
Reproduction 6.479 3.337 1.942 0.052
Survival 2.558 1.206 2.121 0.034
Time since fire
(reproduction)
0.034 0.422 0.081 0.936
Time since fire (survival) 0.101 0.112 0.900 0.368
Percentage of area
high-severity fire
(reproduction)
0.234 0.109 2.142 0.032
Percentage of area
high-severity fire
(survival)
0.031 0.033 0.924 0.356
Foraging habitat selection
Intercept (High severity) 1.167 2.926 0.399 0.690
Time since fire 0.061 0.529 0.115 0.908
Percentage of area
high-severity fire in
study territories
0.084 0.068 1.236 0.216
Low severity 1.936 0.732 2.644 0.008
Moderate severity 0.777 0.321 2.416 0.016
Note: SE, standard error. Bold values are significant at
alpha =0.05.
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SYNTHESIS & INTEGRATION LEE
point (Odion and Hanson 2006, Hanson et al.
2009, Odion et al. 2014a, Baker 2015a). Regardless
of what is correct about trends in fire severity,
Spotted Owls appear fairly resistant and/or resili-
ent to effects from recent hot, large fires, wherever
these fires fall in the long-term range of variability
for size and amount of high-severity burn. This is
corroborated by the meta-regressions that explic-
itly quantified the relationship between amount
of high-severity fire and Spotted Owl parameters
and found only a positive significant correlation
(reproduction). My finding of no significant
negative relationships between amount of high-
severity fire and Spotted Owl parameters demon-
strates that large high-severity fire patches,
including territories that burn 100% at high sever-
ity as was seen in sites within several of the stud-
ies in this review, do not have unequivocally
negative outcomes for Spotted Owls.
Contrary to current perceptions, recovery efforts,
and forest management projects for the Spotted
Owl (USFWS 2011, 2012, 2017, USDA 2012, 2018,
Guti
errez et al. 2017) mixed-severity fire as it
has been burning in recent decades does not
appear to be an immediate, dire threat to owl pop-
ulations that require landscape-level fuel-reduction
Fig. 4. Results of multi-level linear mixed-effects models (hierarchical models) meta-regression of time since
fire and percent of high-severity fire in the study area as covariates to explain heterogeneity in effect sizes from
mixed-severity fire on Spotted Owl (Strix occidentalis) parameters of breeding site occupancy and survival. The
only significant effect was a reduction in occupancy with increasing time since fire, but the effect was sensitive to
one study. Symbols indicate subspecies: filled black circles, California; white circles with black outline, Mexican;
light gray circles with black outline, northern; and dark gray circles, all three subspecies.
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Fig. 5. Results of multi-level linear mixed-effects models (hierarchical models) meta-regression of time since
fire and percent of high-severity fire in the study area as covariates to explain heterogeneity in effect sizes from
mixed-severity fire on Spotted Owl (Strix occidentalis) parameters of foraging habitat selection, recruitment, and
reproduction. Significant effects included positive selection for low- and moderate-severity burned forest for for-
aging, increased recruitment immediately post-fire that diminished with increasing time since fire, and increased
reproduction with a positive correlation with amount of high-severity fire. In top two panels, all studies were
California subspecies, and colors indicate forest in different burn severity categories: green, low severity; orange,
moderate severity; red, high severity. In bottom four panels, symbols indicate subspecies: filled black circles, Cal-
ifornia; white circles with black outline, Mexican; light gray circles with black outline, northern; and dark gray
circles, all three subspecies.
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treatments to mitigate fire severity. Empirical stud-
ies reviewed here demonstrated that wildfires can
generally have no significant effect, but effects can
include improved foraging habitat, reduced site
occupancy, and improved demographic rates. Most
territories occupied by reproductive Spotted Owl
pairs that burn remain occupied and reproductive
at the same rates as sites that did not experience
recent fire, regardless of the amount of high-sever-
ity fire in core nesting and roosting areas.
To place my results into perspective, mixed-
severity fire typically affects (≥50% vegetation
basal area mortality) a very small portion (0.02–
0.50%) of Spotted Owl nesting and roosting
habitat per year (Odion et al. 2014b, Baker 2015b,
Stephens et al. 2016). Breeding sites that experi-
enced a typical mixed-severity burn mosaic can
be expected to have occupancy probability
reduced by 0.06 on average. A 0.06 decline in
occupancy is less than typical annual declines in
occupancy rates observed in the Sierra Nevada in
the absence of large fires (Jones et al. 2016:
Fig. 3f). In comparison, post-fire logging caused a
mean occupancy probability reduction of 0.18.
Post-fire logging is likely to be partially
responsible for some of the negative effects
attributed to high-severity fire in the studies
reviewed here (Tempel et al. 2014, Jones et al.
2016, Rockweit et al. 2017, Hanson et al. 2018).
Because Spotted Owl studies typically character-
ize territory vegetation only in the breeding core
area within 1.1 km of the nest, these studies
ignore habitat changes and alterations in the
year-round home-range area that can extend up
to 5.9 km from the nest (Zabel et al. 1992). Spot-
ted Owl habitat protections have generally not
included areas beyond 1 km from the nest, a
management policy that has not contributed to
population recovery.
Complex early seral forests created by fire differ
from post-fire salvage-logged forests in that dead
trees remain on-site, providing perching sites for
hunting owls as well as food sources and shelter
for numerous wildlife species (Hutto 2006, Swan-
son et al. 2011, DellaSala et al. 2014). Longitudi-
nal studies also indicated that burned breeding
sites where owls were not detected immediately
after fire were often recolonized later (Lee et al.
2012, 2013, Tempel et al. 2016), and this review
shows burned forest habitat is used for foraging,
demonstrating the mistake of concluding severely
burned sites or habitats are lost to Spotted Owls
or require restoration (Davis et al. 2016). A recent
global meta-analysis found post-fire logging is
generally not consistent with ecological manage-
ment objectives (Thorn et al. 2018).
This review on fire and Spotted Owls forms
one portion of the evidence base for data-driven
forest management. A recent systematic review
of thinning and fire found 56 studies addressing
fuel treatment effectiveness in real (not simu-
lated) wildfires from eight states in the western
United States (Kalies and Kent 2016). There was
general agreement that thin +burn treatments
(thinning immediately followed by burning) had
some positive effects in terms of reducing fire
severity, while treatments by burning or thinning
alone were less effective or ineffective (Kalies
and Kent 2016). There is also evidence that doing
nothing can achieve many forest restoration
goals related to age structure and fuels’density
(Zachmann et al. 2018). Additional systematic
reviews are needed to examine (1) the quantifi-
able risk of fire to Spotted Owl habitat, as there
are disparate lines of evidence regarding
whether fire is impeding the recovery of late-
seral-stage forests; and (2) the impacts of fuel
treatments on Spotted Owl demography and site
occupancy. Thinning immediately followed by
burning to reduce wildfire risk may or may not
have adverse effects on Spotted Owls (Franklin
et al. 2000, Dugger et al. 2005, Tempel et al.
2014, 2016, Odion et al. 2014b), but the evidence
presented here indicates fire itself has arguably
more benefits than costs to the species and thus
suggests thinning is not necessary.
The results presented here should serve to
guide management decisions, but also should be
understood as limited by the available data. The
sample sizes of number of estimated effects
from mixed-severity fire on survival and
recruitment were small and limited mainly to the
northern subspecies. There were also very few
studies from the Mexican subspecies. A few
studies presented effect sizes that were influen-
tial on results, especially meta-regression results
(Roberts et al. 2011), so studies examining longer
times since fire are needed. We encourage future
studies to increase sample sizes of each parame-
ter and to provide a more balanced sample of
studies from all subspecies, and over longer time
frames.
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SYNTHESIS & INTEGRATION LEE
MANAGEMENT IMPLICATIONS
The preponderance of evidence presented here
shows mixed-severity forest fires, as they have
burned through Spotted Owl habitat in recent
decades under current forest structural, fire
regime, and climate conditions, have no signifi-
cant negative effects on Spotted Owl foraging
habitat selection, or demography, and have signif-
icant positive effects on foraging habitat selection,
recruitment, and reproduction. Forest fire does
not appear to be a serious threat to owl popula-
tions and likely imparts more benefits than costs
for Spotted Owls; therefore, fuel-reduction treat-
ments intended to mitigate fire severity in Spotted
Owl habitat are unnecessary. These findings
should inform revisions to planning documents to
consider burned forest, including large patches of
high-severity burned forest, as useful habitat that
imparts significant benefits to Spotted Owls. For-
est and wildlife planning documents promote a
diverse mosaic of heterogeneous tree densities
and ages (USFWS 2017, USDA 2018), the very
conditions created by mixed-severity wildfire,
and it follows that heterogeneous post-fire struc-
ture would lead to greater variation in some
Spotted Owl parameters, as was observed in the
meta-analysis of variation. Planning documents
(USFWS 2011, 2012, 2017, Guti
errez et al. 2017,
USDA 2018) claiming that forest fires currently
pose the greatest risk to owl habitat and are a
primary threat to population viability appear
outdated in light of this review.
ACKNOWLEDGMENTS
I thank the many Spotted Owl researchers and field
technicians who are responsible for the collection and
analyses of the data reviewed here. I also thank Mon-
ica Bond and Justin Augustine for thoughtful com-
ments on the manuscript. I have no conflict of interest.
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SUPPORTING INFORMATION
Additional Supporting Information may be found online at: http://onlinelibrary.wiley.com/doi/10.1002/ecs2.
2354/full
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Lee Supporting Information: Spotted Owls and forest fire pg. 1
Spotted Owls and forest fire: A systematic review and meta-analysis of the evidence
DEREK E. LEE,
1
Wild Nature Institute, 15 North Main Street, Concord, NH 03302, USA
Appendix S1
Figure S1. Funnel plot of all reported effects of mixed-severity fire on Spotted Owl (Strix occidentalis)
parameters illustrating no publication bias or unusual heterogeneity exists.
Descriptions of papers
1. Bond et al. (2002) was an examination of survival, reproduction, and site and mate fidelity of northern
(S. o. caurina), California (S. o. occidentalis), and Mexican Spotted Owls (S. o. lucida) 1 year after fire.
Short-term (1-year) postfire survival of 21 color-banded Spotted Owls was reported from four separate
study areas encompassing all subspecies: in northwestern California, southern California, New Mexico,
and Arizona. All nest and roost areas were burned, and no post-fire logging had occurred before owls
were surveyed the year after fire. Vegetation burn severity maps were available for 8 of the 11 breeding
sites, with each breeding site defined as a circle approximately 150–400 ha, depending on study area.
Half of the breeding sites where fire severities were mapped burned at low to moderate severity, and
the other half burned 36–88% at high severity. The authors found that 18 of 21 (86%) individual owls
were resighted after fire. These survival rates are higher (+0.03) than the mean from unburned sites.
Sixteen of 18 (89%) surviving owls (of all subspecies) were in the same breeding sites after fire (-0.01),
1
Email: derek@wildnatureinstitute.org
Ecosphere
Lee Supporting Information: Spotted Owls and forest fire pg. 2
and all pairs were faithful to their pre-fire breeding site and mate. Productivity of burned Spotted Owl
sites was higher (+0.26) than mean annual rates of reproduction for long-unburned sites.
2. Jenness et al. (2004) reported pre- and post-fire occupancy of 64 Mexican Spotted Owl sites in four
national forests in New Mexico and Arizona. The authors selected owl breeding sites in fires that burned
from 1993 to 1996 and compared levels of occupancy (single, pair, failed reproduction, and successful
reproduction) in 1997 in 33 burned and 31 unburned sites, including 29 paired burned and long-
unburned sites within 12 km of each other. Post-fire logging was minor in most of the fires. Post-fire
occupancy rates were not significantly different between burned and unburned sites and did not
statistically differ with time since fire. The percent of high-severity fire in a burned site had no significant
influence on whether the site was occupied. The number of successfully reproducing Mexican Spotted
Owl sites did not differ between burned and unburned forests. Non-significant effects included lower
occupancy (-0.14) and lower reproduction (-0.07) in burned sites.
3. Bond et al. (2009) quantified roosting and foraging habitat selection by Spotted Owls in a burned
landscape. The authors banded and radiomarked 7 California Spotted Owls occupying the McNally Fire
in the southern Sierra Nevada, California 4 years after fire. Effects of high-severity fire were not
confounded with post-fire logging because <3% of the foraging ranges of these owls had been post-fire
logged. The probability of an owl using a site for foraging was significantly greater in low- (+0.33),
moderate- (+0.42), and high-severity (+0.42) burned forests than unburned forest. In this study,
California Spotted Owls roosted in all fire intensity classes. Owls selected roost sites burned at low
severity (+0.29) and avoided unburned sites and sites burned at moderate (-0.13) and high severity (-
0.28).
4. Bond et al. (2010) documented 3 of 5 radiomarked California Spotted Owls that occupied the McNally
Fire in the southern Sierra Nevada during the breeding season 4 years post-fire, roosted within the
burned landscape during the following winter.
5. Clark et al. (2011) examined the survival rates of northern Spotted Owls 3–4 years after fire and
postfire logging in two fire areas in southwestern Oregon. Twelve (12) owls were radiomarked in
unburned forest and 11 owls were radiomarked inside the burn perimeter where much of the forest
(20–23%) had been post-fire logged. The authors found no significant effect of fire severity or quantity
of forested habitat on Spotted Owl survival. Six of the owls monitored in unburned forest were known
to have moved outside the fire perimeter after fire and salvage logging, but before survival monitoring
took place. In the original paper, the authors considered the owls that moved similar to the owls inside
the fire perimeter. I combined all outside-the-burn owls to compare with inside-the-burn owls. Non-
significant effects: owls that resided within the post-fire logged landscape had lower survival rates (-
0.07) than those residing in unburned unlogged forest.
6. Roberts et al. (2011) compared effects of wildfire and prescribed burns on occupancy of California
Spotted Owls residing in burned (1 to 15 years since fire) and long-unburned forests in Yosemite
National Park, central Sierra Nevada, California. This study compared occupancy in 16 randomly selected
burned and 16 unburned ‘owl survey areas,’ each 3.75 km2. A total of 19 owl pairs were monitored for a
single year, and vegetation at owl sites was compared with sites that yielded no owl response to build
detectability and occupancy models. The mean ‘owl survey area’ that burned at high severity was 14%,
with the greatest amount of high-severity burn in a survey area being 52%. Because this study was
conducted in a national park, no post-fire or recent pre-fire logging had occurred to confound results.
Lee Supporting Information: Spotted Owls and forest fire pg. 3
The authors found no support for a model of occupancy rates that distinguished between burned and
unburned sites. Non-significant effects: occupancy from model based on canopy cover and basal area
was lower at burned versus unburned sites (-0.26).
7. Lee et al. (2012) published an 11-year longitudinal study of California Spotted Owl occupancy on
national forest lands in the Sierra Nevada, California. The authors used data collected by the U.S. Forest
Service to compile occupancy survey histories at 41 breeding sites within six large mixed-severity fires
that occurred from 2000 to 2007 throughout the Sierra Nevada and at 145 long-unburned control sites.
Fires had no significant effect on occupancy probability. Non-significant effects: occupancy probability
was higher in burned sites (+0.041) relative to unburned. Post-fire logging occurred in an unknown
number of territories.
8. Bond et al. (2013) found Spotted Owls in the McNally Fire area, southern Sierra Nevada, California fed
primarily on pocket gophers (Thomomys spp., 40.3% by biomass) and northern flying squirrels
(Glaucomys sabrinus, 25.9% by biomass), whereas owls fed primarily on flying squirrel and woodrats
(Neotoma spp.) in long-unburned study areas. The mean home-range sizes of the McNally Fire owls
were 12% smaller than those recorded in unburned forests using similar time periods and methodology.
9. Clark et al. (2013) investigated the occupancy dynamics of northern Spotted Owls in burned and
salvage-logged landscapes in three fire areas and an adjacent long-unburned demographic study area in
the southern Oregon Cascade Mountains. The three fires all burned within 1 year of each other.
Modeled occupancy rates of 103 Spotted Owl sites in the long-unburned area were compared with 40
burned sites before and after fire and post-fire logging occurred. Post-fire logging was prevalent, thus it
was not possible to quantify the influence of fire alone on occupancy dynamics and survival. Occupancy
probability declined more steeply after post-fire logging than in the unburned area (-0.39).
10. Lee et al. (2013) used Spotted Owl survey data from 97 long-unburned and 71 burned breeding sites
over 8 years to examine the influence of fire and post-fire logging on local rates of extinction,
colonization, and occupancy probability. Post-fire logging occurred on 21 of the burned sites. None of
the fire and logging coefficients were statistically significant. Non-significant effects: model-averaged
effect sizes suggested that high-severity fire that burned >50% of forest in the 203-ha core area was
correlated with lower occupancy relative to unburned sites. Post-fire logging further increased
extinction probability. The majority (75%) of sites burned below the 50% threshold. Non-significant
effects: burned site occupancy -0.062 lower than unburned sites. Post-fire-logged sites occupancy -0.05
lower than unlogged burned sites.
11. Ganey et al. (2014) reported a sample of 4 radiomarked Mexican Spotted Owls in the Sacramento
Mountains, New Mexico, moved to wintering areas that had burned 4–6 years earlier and that had 2–6
times greater abundance and biomass of small mammal prey than nest core areas associated with those
owls.
12. Tempel et al. (2014) used data from a long-term (>20 years) demographic study of California Spotted
Owls in the Eldorado and Tahoe national forests of the central Sierra Nevada, California to examine the
influence of timber harvest and wildfire on reproduction, survival, and occupancy over a 6-year
timescale using data from 74 breeding sites. Twelve (12) breeding sites experienced fire during the
course of the study. Fire did not significantly affect survival, reproduction, or site extinction. The
coefficient for the effect of fire on site colonization was negative, but the standard error of the
Lee Supporting Information: Spotted Owls and forest fire pg. 4
coefficient could not be estimated making this parameter estimate of low quality. The authors reported
lower occupancy (-0.06) when fire frequency was doubled in simulations that assumed zero post-fire
colonization. Post-fire logging occurred on public and private lands in the study territories, but was not
reported.
13. Lee and Bond (2015a) examined California Spotted Owl site occupancy in the 2013 Rim Fire near
Yosemite National Park, which was the largest fire in recent recorded Sierra Nevada history, burning
more than 100,000 ha. The fires burned through 45 known Spotted Owl breeding sites in the Stanislaus
National Forest and all sites were surveyed by U.S. Forest Service personnel the following year. For all
detections, 100% severe fire surrounding nest and roost sites decreased occupancy probability (-0.04),
but did not affect occupancy by pairs of owls. Single-season modeled occupancy rates 1 year after the
Rim Fire were significantly higher (+0.175) than other previously published occupancy rates in long-
unburned forests.
14. Lee and Bond (2015b) examined how the quality of a site influenced California Spotted Owl
occupancy and reproduction after fire in southern California (using the same dataset as Lee et al. 2013).
Site quality was measured by whether the site supported a single owl, pair of owls, or pair of owls with
offspring the previous year. Amount of severe fire in a core use area was not a significant variable
influencing reproduction. The influence of severe fire on occupancy was minor in sites that had been
occupied and reproductive the previous year (high quality), and if a site remained occupied, severe fire
did not affect the probability of reproduction compared with unburned sites. Occupancy of high-quality
sites (previously reproductive) that burned was -0.02 lower than unburned sites. Occupancy of high-
quality sites that were post-fire logged was -0.03 lower. Occupancy of low-quality sites (previously non-
reproductive) was -0.19 lower in burned versus unburned sites, and -0.26 lower after post-fire logging.
15. Bond et al. (2016) analyzed foraging habitat selection by 8 radiomarked California Spotted Owls in
the Slide Fire in the San Bernardino National Forest of southern California 3 and 4 years after fire.
Habitat selection with sensitivity analysis at three spatial extents of available habitat showed owls used
forests burned at all severities in proportion to their availability (no significant effects), with the
exception of significant selection for moderately burned forest (+0.03) farther from core areas.
16. Comfort et al. (2016) examined foraging habitat selection by 23 radiomarked Northern Spotted Owls
in the Timbered Rock Fire in southwest Oregon in relation to edges created by fire and post-fire logging.
Because post-fire logging occurred immediately following fire on extensive private lands in the study
area, and their remote-sensing methodology could not distinguish between fire and post-fire logged
areas, the authors created a combined burned–logged variable called the ‘disturbance severity.’ The
edges between forested habitats and burned–logged areas were defined as ‘hard’ edges. At smaller
spatial scales (3.2 and 51.8 ha surrounding telemetry locations), increases in disturbance severity
decreased the probability of use, but at larger spatial scales (829 ha), the opposite was true. The use of a
location for foraging was maximized when about 20% of a 3.2-ha area surrounding the location was
composed of hard edge. Owls avoided areas with larger amounts of hard edge, but selected smaller
amounts of edge. Larger, more contiguous hard edges were described as intensively managed edges
created by post-fire logging.
17. Jones et al. (2016) reported on breeding site occupancy dynamics from 15 unburned and 30 burned
sites (14 of which burned >50% high severity), and foraging habitat selection for 9 owls, in the Eldorado
National Forest, central Sierra Nevada, California after the King Fire of 2014. Occupancy declined in
Lee Supporting Information: Spotted Owls and forest fire pg. 5
burned sites relative to unburned, and >50% high-severity burn further reduced occupancy. Foraging
habitat selection showed owls significantly avoided high-severity burn and a non-significant preference
for low-severity burn.
I included the results from this paper in my review, however methodological difficulties in this study
make their results unreliable. First, the Eldorado owl population that provided the data for Jones et al.
(2016) has documented long-term trends of decreasing site colonization and increasing site extinction
probabilities, as reported before the King Fire (Tempel and Gutiérrez 2013). However, Jones et al. did
not account for these pre-fire trends in their site occupancy analyses. This omission of temporal trends
means their results for 2015 could be due to the fact that this single year of post-fire data was the last
year in the dataset, and should not be attributed unequivocally to the King Fire. Fig. 3f shows that the
2015 post-fire year of decrease in occupancy was not significantly different from the 10 previous
instances of documented declines that occurred in the absence of fire. Second, Jones et al. (2016) used
compositional analysis of foraging habitat selection, a method that is inappropriate for central place
foragers like Spotted Owls (Rosenberg and McKelvey 1999). Compositional analysis relies upon an
assumption of no spatial correlation among foraging locations (Rosenberg and McKelvey 1999, Manly et
al. 2002). Central place foraging behaviour results in a clustered distribution of foraging points near the
center of a territory which violates the assumption of no spatial correlation among foraging locations, a
pattern that was apparent for most of the Spotted Owls in Web Figure 3 of Jones et al. (2016). The
appropriate habitat selection analysis is a ‘resource selection function’, a mathematical function that
accounts for the fact that Spotted Owls, as central place foragers, will return to their nest or roost trees
many times during the night, so their probability of using habitats near the nest or roost core is much
higher than the probability of using habitats farther away (Bond et al. 2009, Bond et al. 2016, Eyes et al.
2017). Third, Jones et al. (2016) reported extinction for a territory in WebFigure 4 when the owls shifted
their location by a distance that was less than the diameter of a territory as defined by the authors, and
less than mean foraging distance reported by the authors. This decision inflated their ‘burned site’
extinction probability by classifying a normal within-territory movement as site extinction. These
methodological difficulties in their data analyses limit the utility of Jones et al. (2016) for guiding forest
management, particularly when weighing the risks from management actions relative to risks from fire.
18. Tempel et al. (2016) examined occupancy dynamics in 43 burned breeding sites and 232 unburned
sites in four study areas across the Sierra Nevada using 19 years of data. The authors found no
significant effects of fire on occupancy, but their top ranked model for one study area (Sequoia Kings
Canyon) included a covariate for proportion of the core area where canopy cover was reduced by >10%
by wildfire. This covariate was negatively correlated with territory extinction probability, meaning more
area burned reduced the site extinction probability, thereby increasing occupancy probability (+0.01).
19. Eyes et al. (2017) radiotracked 13 California Spotted Owls over 3 years and collected data on
foraging habitat selection in Yosemite National Park, Sierra Nevada, California. The authors analyzed
foraging by a sample of owls nesting in and near forest burned 1–14 years previously from a mix of
wildfires and prescribed burns. Eyes et al. (2017) found no significant effect of burn severity on foraging
habitat selection, but non-significant effects were reported that showed a decrease in probability of use
for the most severely burned locations (-0.06), and moderately burned locations (-0.03), relative to
unburned locations.
Lee Supporting Information: Spotted Owls and forest fire pg. 6
20. Rockweit et al. (2017) examined survival and recruitment rates of northern Spotted Owls in 70
unburned sites and 28 sites burned in four fires. The authors reported wildfires with different mixtures
of burn severity resulted in different effects on survival and recruitment. Ten owl territory cores that
were burned at mostly low severity (1987 and 1999 fires) were associated with no significant effects on
survival or recruitment. When 14 territory cores burned with moderate amounts of high- and low-
severity fire (2008 fire), the result was a significant reduction in survival (-0.17) and a significant increase
in recruitment (+0.22). When 4 territory cores burned at predominantly high severity (2004 fire), there
was a significant reduction in survival (-0.30). The burned territories were partially post-fire logged,
although that was not reported by the authors (C. Hanson, pers. comm.).
21. Hanson et al. (2018) examined naïve site occupancy of California Spotted Owls in 54 sites that
burned in one of 8 large fires between 2002 and 2015. All sites were occupied in the year immediately
prior to the site burning, and comparisons were before-after fire and logging. Sites were classified into 4
groups based on amount of high-severity burn (20-49% or 50-80%) and amount of post-fire logging (<5%
and ≥5%) in a 1500m-radius circle around the nesting roosting core area. Hanson et al. (2018) found no
significant effect of fire severity on occupancy, but significant effects of post-fire logging. Mean amount
of core areas burned at high severity was 63%. Results were: 80% occupancy in sites with 20–49% high-
severity fire and <5% post-fire logging, 33% occupancy in sites with 20–49% high-severity fire and ≥5%
post-fire logging; and 77% occupancy in sites with 50–80% high-severity fire and <5% post-fire logging,
20% occupancy in sites with 50–80% high-severity fire and ≥5% post-fire logging. Amongst the sites with
≥5% post-fire logging, the mean amount of such logging of the area within a 1500 m radius of site
centers was 16.7% (SD = 8.7%).
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