Historical and recent fire ecology on national wildlife refuges: a case study on Aransas National Wildlife Refuge

Abstract

Background
The southeastern United States consists of diverse ecosystems, many of which are fire-dependent. Fires were common during pre-European times, and many were anthropogenic in origin. Understanding how prescribed burning practices in use today compare to historic fire regimes can provide perspective and context on the role of fire in critical ecosystems. On the Aransas National Wildlife Refuge (ANWR), prescribed burning is conducted to prevent live oak ( Quercus fusiformis ) encroachment and preserve the openness of the herbaceous wetlands and grasslands for endangered whooping cranes ( Grus americana ) and Aplomado falcons ( Falco femoralis ). This field note builds a digital fire atlas of recent prescribed burning on the refuge and compares it to the historical fire ecology of ANWR.

Results
Findings indicate that the refuge is maintaining fire-dependent ecosystems with an extensive burn program that includes a fire return interval between 2 and 10 years on a majority of the refuge, with some locations experiencing much longer intervals. These fire return intervals are much shorter than the historic burn regime according to LANDFIRE.

Conclusions
Following the fire return intervals projected by LANDFIRE, which project longer intervals than the prescribed fire program, would likely be detrimental to endangered species management by allowing increased woody plant encroachment and loss of open habitat important to whooping cranes and Aplomado falcons. Since prescribed fire is part of the management objectives on many national wildlife refuges in the United States, quantifying recent and historical fire ecology can provide useful insights into future management efforts, particularly in cases where endangered species are of special concern and management efforts may be counter to historical disturbance regimes.

Full text

Goldenetal. Fire Ecology (2024) 20:46
https://doi.org/10.1186/s42408-024-00273-z
FIELD NOTE
Historical andrecent re ecology onnational
wildlife refuges: acase study onAransas
National Wildlife Refuge
Katherine E. Golden1* , Benjamin L. Hemingway2, Amy E. Frazier3, Wade Harrell4, Samuel D. Fuhlendorf1 and
Craig A. Davis1
Abstract
Background The southeastern United States consists of diverse ecosystems, many of which are fire-dependent. Fires
were common during pre-European times, and many were anthropogenic in origin. Understanding how prescribed
burning practices in use today compare to historic fire regimes can provide perspective and context on the role of fire
in critical ecosystems. On the Aransas National Wildlife Refuge (ANWR), prescribed burning is conducted to prevent
live oak (Quercus fusiformis) encroachment and preserve the openness of the herbaceous wetlands and grasslands
for endangered whooping cranes (Grus americana) and Aplomado falcons (Falco femoralis). This field note builds
a digital fire atlas of recent prescribed burning on the refuge and compares it to the historical fire ecology of ANWR.
Results Findings indicate that the refuge is maintaining fire-dependent ecosystems with an extensive burn program
that includes a fire return interval between 2 and 10 years on a majority of the refuge, with some locations experi-
encing much longer intervals. These fire return intervals are much shorter than the historic burn regime according
to LANDFIRE.
Conclusions Following the fire return intervals projected by LANDFIRE, which project longer intervals than the pre-
scribed fire program, would likely be detrimental to endangered species management by allowing increased woody
plant encroachment and loss of open habitat important to whooping cranes and Aplomado falcons. Since pre-
scribed fire is part of the management objectives on many national wildlife refuges in the United States, quantifying
recent and historical fire ecology can provide useful insights into future management efforts, particularly in cases
where endangered species are of special concern and management efforts may be counter to historical disturbance
regimes.
Keywords Burn regimes, Fire-dependent ecosystem, Mean fire return interval, Landsat, Normalized burn ratio,
Prescribed fire
Resumen
Antecedentes El sudeste de los EEUU consiste en diversos ecosistemas, muchos de ellos fuego-dependientes. Los
fuegos fueron comunes durante la era pre-europea, y muchos de ellos de origen antrópico. El entender cómo las
quemas prescriptas en uso en estos tiempos se comparan con regímenes de fuegos históricos puede proveer de
una perspectiva y el contexto sobre el rol del fuego en ecosistemas críticos. En el Refugio Nacional de Fauna Silvestre
Open Access
© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the
original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or
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licence, visit http://creativecommons.org/licenses/by/4.0/.
Fire Ecology
*Correspondence:
Katherine E. Golden
k8golden@gmail.com
Full list of author information is available at the end of the article

Page 2 of 11
Goldenetal. Fire Ecology (2024) 20:46
Introduction
Fire plays an important role in natural ecosystems, but
fire suppression has become a dominant paradigm of land
management over the past century (Keane et al. 2002;
Dombeck etal. 2004; Bowman etal. 2011). In the United
States, fire suppression throughout most of the 20th-
century has generally resulted in altered fire regimes and
accumulation of fuel, leading to more extreme and severe
wildland fires in many locations (Ryan etal. 2013; Stam-
baugh etal. 2014a). Following World War II, an explicit
focus on fire suppression was enhanced as an increase in
manpower and surplus military equipment allowed addi-
tional resources to be used to fight wildland fires. Since
then, some federal agencies in the United States have
continued to take a reactive approach to fighting fires
rather than proactively addressing fire-dependent eco-
systems by maintaining them through prescribed burns
(Dombeck et al. 2004; Dale 2006). As fire suppression
has proved unsuccessful in preventing large wildland
fires, prescribed burning has re-emerged as a viable tool
to reduce fuel loads. However, individual land manage-
ment agencies must decide if prescribed burning is an
appropriate tool for ecosystem management and whether
programs should aim to match the historic fire regime or
whether a new fire regime should be established based on
agency objectives.
e United States Fish and Wildlife Service (USFWS)
has maintained prescribed fire programs on national
wildlife refuges and provides a compelling case from
which to assess fire management practices and examine
the effects of prescribed fire regimes on the landscape.
e USFWS was given a clear mandate for developing
and implementing management objectives under the
National Wildlife Refuge System Improvement Act of
1997 (Dolin 2003), with each refuge encouraged to man-
age for historical conditions, including the use of fire
when applicable (Schroeder et al. 2004; Meretsky etal.
2006). Since then, the USFWS has expanded its policies
to focus on using prescribed burns to improve wildlife
habitat, reduce fuel loads, and maintain fire-dependent
ecosystems on lands they manage. However, the USFWS
faces a challenging conundrum when reintroducing fire
to the landscape: whether to attempt to return the land-
scape to historic conditions or to manage the landscape
for current objectives resulting in different vegetation
communities compared to the past. A topic of debate
surrounding ecosystem restoration includes whether his-
toric conditions should be used as a reference point for
restoration or if an ecosystem service-based approach
is warranted given that ecosystems are dynamic and
specific management goals that often guide restora-
tion efforts may not follow historic disturbance regimes
(Hiers et al. 2012; Dey and Schweitzer 2014). Under-
standing how a prescribed burn program will alter the
existing vegetation community is important and neces-
sary for implementing management objectives for wild-
life refuges because the complex interactions between
fire and other land management activities may have
unintended consequences for wildlife populations (Fon-
taine and Kennedy 2012). ese considerations are par-
ticularly relevant for wildlife refuges that contain critical
habitat for endangered species where the need to protect
these species often guides and prioritizes management
activities. Aransas National Wildlife Refuge (ANWR) is
a USFWS refuge that has been using prescribed burns
since the 1980s to manage critical habitat for endangered
de Aransas (ANWR), las quemas prescriptas son conducidas para prevenir la invasión de árboles de roble fusiforme
(Quercus fusiformis) y preservar la apertura de claros en humedales herbáceos y pastizales para especies en peligro
como la grulla chillona (Grus americana) y el halcón plomizo (Falco femoralis). Esta nota de campo construye un atlas
digital de incendios de quemas prescriptas recientes en ese refugio y la compara con la historia de la ecología del
fuego del refugio ANWR.
Resultados Los resultados indican que el refugio mantiene los ecosistemas dependientes del fuego mediante un
extensivo programa de quemas prescriptas que incluye un retorno de intervalo del fuego de entre 2 y 10 años en la
mayoría del refugio, con algunos lugares experimentando muchos mayores intervalos. Estos intervalos de retorno del
fuego son muchos más cortos que el régimen de fuegos históricos de acuerdo con el programa LANDFIRE.
Conclusiones Siguiendo los intervalos de retorno del fuego proyectados por LANDFIRE, que proyectan interva-
los más largos que el programa de quemas prescriptas, estos serían detrimentales para el manejo de las especies
en peligro, ya que se incrementarían las especies leñosas y por lo tanto se reducirían los espacios abiertos que son
importantes para la grulla chillona y el halcón plomizo. Dado que las quemas prescriptas son parte de los objetivos
de manejo de muchos refugios de fauna de los EEUU, la cuantificación de la ecología del fuego reciente e histórica
puede proveer de perspectivas útiles en esfuerzos de manejo futuros, particularmente en casos en los que especies
en peligro requieren de una consideración especial y los esfuerzos de manejo pueden ir en contra de los regímenes
de disturbios históricos.

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Goldenetal. Fire Ecology (2024) 20:46
species, specifically whooping cranes (Grus americana)
and Aplomado falcons (Falco femoralis).
Understanding the implications of potential state
changes of vegetation communities resulting from pre-
scribed burn programs is key for quantifying program
impacts on land management activities and allocating
future funding to maintain these programs. is field
note presents a record of fire ecology of ANWR to bet-
ter understand how the current prescribed burn regime
compares to the historical regime. e objectives of
this study were to (1) map the long term (1985–2013)
prescribed burn regime using a remote sensing-based
workflow and the spatial distribution and magnitude of
recent burning and compare it to both historical records
and LANDFIRE, and (2) analyze the impacts of the pre-
scribed burn regime on the vegetation community using
high spatial resolution land cover data to provide guid-
ance on balancing the habitat requirements for federally
threatened and endangered species that utilize the refuge.
Methods
Study site
ANWR is a remnant of a coastal prairie fire-dependent
ecosystem located along the southeastern coast of Texas,
USA (Fig.1). e refuge is composed of five administra-
tive units (Aransas, Tatton, Matagorda Island, Myrtle
Foester-Whitmire, and Lamar) totaling about 47,000ha
and buffered by over 5,200ha of bay area waters under
protection by the USFWS (for a more detailed descrip-
tion, see Aransas National Wildlife Refuge Comprehen-
sive Conservation Plan and Environmental Assessment
[USFWS 2010]). e refuge consists of fire-adapted veg-
etation communities that have historically burned due
to natural ignitions and intentional burning by Native
Americans and early settlers (Lynch 1941; Hanselka
1980; Sparks etal. 2012; Stambaugh etal. 2014b). On the
main portion of the refuge (Aransas/Tatton Unit, called
Aransas from here forward), the most prevalent vegeta-
tion type is the Texas coastal bend live oak (Quercus fusi-
formis) – redbay (Persea borbonia) forest, followed by
the Texas coastal bend interdune swale grassland, which
is adapted to both fire and periodic flooding (USFWS
2010).
Shortly after the refuge was established in the late
1930s, cattlemen noted that burns were needed to reduce
and prevent brush buildup (Halloran 1943). Woody plant
encroachment on coastal grasslands is a problem for con-
servation as both the endangered whooping cranes and
Aplomado falcons prefer open habitat (Saintilan and Rog-
ers 2015). Live oak has spread throughout ANWR, cov-
ering much of the refuge beyond the immediate coastal
areas. In the 1980s, ANWR implemented a prescribed
burning program to maintain woody vegetation at early
successional stages and low canopy heights to foster vis-
ibility for the protected whooping cranes, aid them in
predator detection, and promote foraging and roosting
Fig. 1 Location of the Aransas National Wildlife Refuge, Texas, USA (Aransas/Tatton, Lamar, Matagorda Island, and Myrtle Foester-Whitmire units)
along the Texas Gulf Coast. Administrative burn units delineated by the refuge are outlined in white

Page 4 of 11
Goldenetal. Fire Ecology (2024) 20:46
(Armbruster 1990; Lewis 1995; Chavez-Ramirez 1996;
Chavez-Ramirez etal. 1996; Golden etal. 2022). Studies
have shown that repeated summer burns decrease stem
densities and result in more open thickets (Kelley 1980;
Hays 1999), therefore, summer burns are conducted at
ANWR to prevent woody encroachment (USFWS 2010)
and winter burns are conducted to facilitate foraging
opportunities for whooping cranes (Chavez-Ramirez
1996).
Data preparation andprocessing
Mapping theRecent Fire Regime withLandsat
We used satellite remote sensing to develop a digital
atlas of all fires conducted between 1985 and 2013 as
part of ANWR’s prescribed burn program. Using Land-
sat imagery, we delineated burn perimeters and indexed
fires based on their severity to give land managers a bet-
ter understanding of the spatial and temporal extent of
historical burns on the landscape (Henry and Yool 2002).
When fire destroys the cell structure of plants, chloro-
phyll production decreases, which influences spectral
reflectance in the mid-and near-infrared regions of the
electromagnetic spectrum (Patterson and Yool 1998;
Jensen 2007). e Normalized Burn Ratio (NBR) lever-
ages these wavelength regions based on the theory that
healthy vegetation reflects light strongly in the near-
infrared (NIR) portion, and burned areas have reduced
absorption of shortwave infrared (SWIR) radiation due
to decreased water content (Rogan and Yool 2001; Key
and Benson 2006). Normalizing reflectance values from
the SWIR band with values from the NIR band enhances
burned areas on an image, allowing for more accurate
burn mapping. NBR is computed as:
Differencing NBR values from before and directly after
a fire allows burned areas to be differentiated from non-
burned areas. e differenced normalized burn ratio
(ΔNBR) is defined as:
ΔNBR ranges from -2 to 2, with values near zero sug-
gesting little change over time and thereby indicat-
ing areas that likely did not burn. Positive ΔNBR values
from ~ 0.1 to ~ 1.35 are indicative of areas that have expe-
rienced a burn, whereas values greater than 1.35 are likely
to be clouds (Key and Benson 2005).
We obtained a database from the USFWS of 481 pre-
scribed burns performed at the refuge from 1985 thru
2013, including the ignition date, the mapping unit in
which the burn was conducted (Fig.1; units are specific
NBR
=
Band4
−
Band7
Band4+Band 7
NBR
=
NBRpre
−
fire
−
NBRpost
−
fire
to ANWR), and the estimated acreage of each burn.
Although wildland fires may have occurred on the ref-
uge complex, only one was documented in the database
and was excluded from our analyses. Using the ignition
dates, we obtained cloud-free, Landsat images before
and after each burn from the US Geological Survey Earth
Resources Observation and Science Center (http:// glovis.
usgs. gov). Imagery from both Landsat TM and Landsat
ETM + were considered to increase the pool of available
image dates, but use of ETM + images collected after
30 May 2003 was limited due to the scan line corrector
failure. Due to the sub-tropical climate of south Texas,
images captured more than three months after a fire
are not likely to show evidence of a burn as vegetation
regrows quickly (Lonard etal. 2004). erefore, fires for
which a cloud-free image could not be identified within
three months after the ignition date were not mapped.
Pre-fire images could be captured up to one year prior to
the burn, as it is rare for ANWR to burn the same area
twice in a single year.
NBR was computed for the pre- and post-fire images,
and values were differenced to compute ΔNBR. Following
the threshold guidelines noted above along with visual
validation, ΔNBR pixel values ranging from 0.15 to 1.50
were classified as burned. Contiguous pixels classified as
‘burned’ were vectorized to create a spatial polygon rep-
resenting the burn extent. e accuracy of the mapped
burns was verified by refuge staff (W. Harrell, U.S. Fish
and Wildlife Service, Albuquerque, New Mexico, USA,
personal communication).
A total of 375 burns (~ 78% of the original 481 burns
in the database) were mapped from 1985–2013 (Table1).
One hundred and six burns could not be mapped due to a
lack of cloud free images, which is common in sub-tropi-
cal regions. We were able to account for 58 of the missing
burns through an archive analysis and first-hand knowl-
edge from refuge staff to estimate the administrative unit
where those burns occurred, providing a mean fire return
interval (MFRI; discussed below) that is slightly different
than the map shown in Fig.2. Our mapping rate of 78%
is within the average capture rate dependent on usable
imagery from LANDSAT for the southeastern United
States (Picotte and Robertson 2011).
To quantify the spatial distribution and magnitude of
prescribed burning on the refuge, we computed basic
descriptive statistics using the mapped burn polygons. By
overlaying the polygons, we computed the MFRI for each
pixel as well as each administrative burn unit (see Fig.1)
for the 28-year study period. We then classified the study
period into approximately five-year increments and cat-
egorized each pixel in the study area based on the num-
ber of time periods in which it was burned. We modeled
the spatial and temporal changes in fire patterns over the

Page 5 of 11
Goldenetal. Fire Ecology (2024) 20:46
5-year increments using the StampR package in R (Rob-
ertson etal. 2007; Long and Robertson 2018) in order to
highlight areas the refuge burns regularly.
Contextualizing theHistoric Fire Regime withLANDFIRE
We used the Landscape Fire and Resource Management
Tools Project (LANDFIRE) to build a historical fire ecol-
ogy of ANWR to compare to the recent (1985–2013)
fire regime. LANDFIRE was developed by the US Forest
Service and the Department of the Interior to provide a
nationally complete, comprehensive, and consistent set of
products to support planning, fire, and natural resource
management across the conterminous United States.
ere are more than 20 geospatial layers of vegetation,
fuel, disturbance, and other variables to understand and
contextualize wildland fire management.
We used the MFRI and Fire Regime Group (FRG) lay-
ers to develop an understanding of the historical fire
regime on ANWR as these metrics align most closely
to the variables we mapped for the current fire regime.
e MFRI represents the time between fires based on
the assumed historic fire regime, with 22 classes rang-
ing from 0–5 years (continuous to frequently burned)
up to > 1,000years (USGS 2013). e FRG represents the
historic fire regime for a given area by classifying areas
based on fire return interval and burn severity: Group I
is a ≤ 35-year return interval with low and mixed sever-
ity fire, Group II is a ≤ 35-year return interval with
Table 1 Descriptive statistics of prescribed burns on Aransas National Wildlife Refuge (1985–2013) computed using the digital fire
atlas
Years No. of res
mapped No. of res not
mapped Min. mapped re
size (ha) Max. mapped re
size (ha) Mean of mapped res
(ha) (
±sd)
Sum of mapped
burned area (ha)
1985–1989 24 9 9.3 1,264.7 374.8 (
±310)
8,995.0
1990–1994 50 19 8.2 863.2 156.3 (
±135.5)
7,816.4
1995–1999 98 49 2.0 1,024.8 166.8 (
±172.3)
16,344.0
2000–2004 60 11 5.5 398.4 157.3 (
±110.6)
9,348.0
2005–2009 93 15 7.7 669.7 163.0 (
±126.3)
15,162.0
2010–2013 50 3 5.1 1,356.2 218.2 (
±246.8)
10,907.6
1985–2013 375 106 2.0 1,356.2 183.1 (
±
181) 68,573.0
Fig. 2 Number of times each area was burned during the study period (1985—2013) on Aransas National Wildlife Refuge, Texas, USA

Page 6 of 11
Goldenetal. Fire Ecology (2024) 20:46
replacement severity level fire, Group III is a 35–200year
fire return interval with low and mixed severity fire,
Group IV is a 35–200 year fire return interval with
replacement severity, and Group V is a 200 + year fire
return interval at any level of severity. We computed the
hectares of each MRFI and FRG group on the refuge and
compared these findings to descriptions of the historic
fire regime in the area from Stambaugh et al. (2014b),
Frost (1998), and Guyette etal. (2012).
Vegetation community classication data
To assess how the recent prescribed burn regime relates
to the existing vegetation communities on the refuge, we
used the Terrestrial Ecological Systems classification sys-
tem created by NatureServe and the Missouri Resource
Assessment Partnership (MoRAP) (NatureServe 2009;
Ludeke etal. 2010a, 2010b). e MoRAP data include
a thematic map (10m resolution) of detailed ecological
systems generated using remote sensing, ground-refer-
ence data, soil types, riparian areas, and digital elevation
models (Ludeke etal. 2010a). Vegetation types are based
on the Terrestrial Ecological Systems Classification by
NatureServe. e 32 vegetation classifications present
on ANWR were aggregated into four general classes:
grassland, forest/woodland, wetland/marsh, and shrub-
land. We aggregated these vegetation classifications as
the prescribed fire program is focused on these struc-
tural components of vegetation for managing whooping
crane habitat. Since the data are only available for a single
time point (2004–2005), it is not possible to measure the
impact of prescribed burning on the vegetation commu-
nity directly. However, they can be used to understand
the spatial relationship between the areas in which burn-
ing is performed and the existing vegetation communi-
ties at those sites on the refuge. We overlaid the MoRAP
data with the digital atlas of prescribed burns for 2005
and calculated basic statistics to determine which vegeta-
tion communities have been burned most frequently.
Results
Digital atlas ofprescribed res
On average, the refuge conducted 13 prescribed burns
per year with an average burn size of 183ha (Table1).
About 35% of burns were less than 100ha, about 30%
were between 100 and 200 ha, and about 35% were
greater than 200ha. Large portions of the refuge were
burned multiple times between 1985 and 2013 (Fig. 2),
resulting in high mean fire return intervals (Fig.3). Some
areas were burned ten times or more over the 28-year
study period, whereas areas in the center of the main
Aransas unit and the coastal areas, which are tidal, were
never burned. On Matagorda Island, most areas were
burned between one and five times.
e mean fire return interval for administrative burn
units ranged from 2 to > 28years (Fig.3). While we were
able to account for some of the missing burns, even with
Fig. 3 Mean fire return interval per administrative prescribed burn unit between 1985–2013. Blue units indicate areas where no burns were
detected from 1985–2013. Aransas National Wildlife Refuge, Texas, USA

Page 7 of 11
Goldenetal. Fire Ecology (2024) 20:46
these additional data, our estimate of the MFRI for each
unit is conservative, as 48 burns remain missing. On
Aransas, the mean fire return interval was 7.5years, with
a range of 1.3 to > 28years. Sections of the main unit that
were not burned during the 28-year study period likely
have a much greater fire return interval. On Matagorda
Island, the mean fire return interval was 4.8years, with
a range of 1.8 to 14years (Fig.3). Much of the Myrtle
Foester-Whitmire Unit has been burned in recent years,
however ANWR did not acquire this unit until 1993 and
did not implement prescribed burning until 2004.
Results indicate that the refuge consistently burns
many of the same locations, with the southern coast of
Aransas, the northwestern portion Aransas (Tatton unit),
and the majority of Matagorda Island receiving regu-
lar burn prescriptions (see Supplemental Information).
MoRAP shows that the areas burned (in 2005) were
mostly grassland and shrubland, which together account
for more than 70% of the land area on the unit and more
than 85% of the areas burned (Table2). Established for-
est/woodland accounts for about 11% of the land area of
ANWR, but only about 7% of the area burned. Wetlands,
which account for 18% of the land area on ANWR, were
less than 4% of the area burned. A chi-square test showed
that the areas burned in each habitat type are signifi-
cantly different than what would be expected if fires were
randomly distributed (p < 0.001). ese results provide
support that the refuge is using prescribed fire to actively
manage woody cover in grasslands and shrublands,
which aligns with one of their goals of maintaining open
areas for the benefit of whooping cranes and Aplomado
falcons (CWS and USFWS 2007).
Historic re regime
According to LANDFIRE, 60.9% of the refuge is in Fire
Regime Group III (a historical mean fire return interval
of 35–200years with low and mixed severity fire) (Fig.4).
More than a third of the refuge (37.5%) is classified as
Group II (an MFRI of 35years or less with replacement
severity fire), and less than 1% is classified as Group I
(≤ 35-year MFRI with low and mixed severity fire). e
LANDFIRE results indicate that the refuge histori-
cally burned with an interval between 35 and 200years
with low and mixed severity fire. Most of the refuge
(59.84%) had a LANDFIRE mean fire return interval of
81–90years, while 23.65% had a fire return interval of
26–30years. Just over 10% of the refuge had a fire return
interval of 0–5years (Fig.5). e LANDFIRE results sug-
gest that the recent burn regime on ANWR differs greatly
from the historical regime and burning is much more fre-
quent than it was in the past.
Discussion
e choice by land management agencies to mimic a
historic fire regime or develop a contemporary fire man-
agement plan can have substantial implications for wild-
life management. ANWR is faced with the challenge of
developing a management strategy to restore historic
conditions on the refuge or implementing a much differ-
ent management strategy for endangered and threatened
species with each strategy resulting in different outcomes
(Schroeder et al. 2004). We found that the prescribed
mean fire return interval for many areas of ANWR aligns
with accounts of historic fire frequencies published in the
literature but is much shorter than the interval reported
in the LANDFIRE database.
We triangulated the findings through historical
accounts, which suggest that burning was common
throughout Texas (Lynch 1941; Box etal. 1967; Sparks
et al. 2012), particularly the Southern Coastal Plain
(Hanselka 1980) and that low intensity fires contributed
to the presence of open grasslands and savanna-like eco-
systems in the southeastern United States (Boyd 1999;
Fowler and Konopik 2007). e general consensus is
that southeastern Texas, including the Gulf Coast, had
a very short MFRI between 2 and 12years (Frost 1998;
Guyette et al. 2012; Stambaugh et al 2014b), which is
supported by historical accounts of the use of anthropo-
genically-ignited fire on this landscape. ese historical
accounts align more closely with the findings from our
digital fire atlas than the LANDFIRE data. Low sever-
ity fire was likely more common at ANWR than high
severity stand-replacing fires, based on both landscape
structure and vegetative fuel, supporting the view that
coastal Texas had a short fire return interval indicative of
a fire-dependent ecosystem. While the geographic scales
Table 2 Vegetation types present on Aransas National Wildlife Refuge based on MoRAP vegetation data and the percentage of each
type burned by prescribed fires in 2005
Vegetation type Total hectares on
ANWR Percent of ANWR
land area Total hectares
burned Percent burned of total
hectares on ANWR Percent of total
hectares burned
Grassland 13,031.8 40.0 1,259.9 9.7 44.9
Shrubland 10,062.5 31.0 1,230.4 12.2 43.9
Wetland/Marsh 5,854.5 18.0 108.0 1.8 3.9
Forest/Woodland 3,513.5 11.0 204.6 5.8 7.3

Page 8 of 11
Goldenetal. Fire Ecology (2024) 20:46
represented in the literature vary (e.g., some studies are
regional, others continental, etc.), these archives provide
a useful context to interpret the historic burn regime of
the Texas Gulf Coast region. Additionally, the use of data
including fire scars and evidence of charcoal from sedi-
ment cores, combined with historical records and digital
Fig. 4 LANDFIRE Fire Regime Group (FRG) classification on Aransas National Wildlife Refuge, Texas, USA
Fig. 5 LANDFIRE Mean Fire Return Interval (MRFI) classification on Aransas National Wildlife Refuge, Texas, USA

Page 9 of 11
Goldenetal. Fire Ecology (2024) 20:46
mapping, can provide an in-depth look at the historical
fire regime.
e landscape structure and climate on ANWR sup-
port the need for a frequent fire return interval to slow
the spread of woody species and maintain critical habi-
tat for wildlife. ANWR is susceptible to woody invasion
due to rainfall and overall productivity levels because it
is located in a subtropical climate (Ratajczak etal. 2012;
Archer etal. 2017) and therefore, the refuge must con-
sider encroaching woody species as a potential problem
that prescribed fire can help ameliorate. e encroach-
ment of woody species can increase or decrease the
existing fuel load and create a feedback loop that results
in a changed fire regime, and combined with other natu-
ral disturbances on the refuge, including herbivory and
significant weather events such as hurricanes, can per-
manently change the vegetation communities present,
potentially altering critical habitat for endangered species
(Brooks etal. 2004; Zouhar etal. 2008).
Both the whooping crane and Aplomado falcon have
specific habitat requirements, and fire is used to main-
tain the appropriate extent of oak communities, open
grassland, and wetlands for these federally listed endan-
gered species. e MoRAP data showed that the refuge
is primarily burning grassland and woody shrubland veg-
etation types. Whooping cranes that utilize ANWR tend
to not be observed in areas of dense live oak woodland
and shrubland (Golden et al. 2022). Continuous pre-
scribed burns help set back vegetation to early succes-
sional stages and lower overall plant height as whooping
cranes prefer unobstructed views that allow for preda-
tor detection (Armbruster 1990), roosting, and foraging
(Lewis 1995) as do Aplomado falcons for hunting prey
and breeding, particularly on Matagorda Island (Perez
etal. 1996; Macías-Duarte etal. 2004; Hunt etal. 2013).
Using LANDFIRE intervals to guide prescribed burning
may be detrimental to whooping crane management, and
it is likely that the open habitat critical to both whoop-
ing cranes and Aplomado falcons use of the refuge would
be lost to woody plant encroachment. Prescribed fire can
meet refuge objectives such as maintaining the grass-
lands and prairie habitat as well as the coastal savanna
habitat that benefits not only endangered species but
also other focal species such loggerhead shrikes (Lanius
ludovicianus), seaside sparrows (Ammospiza maritima),
and painted buntings (Passerina ciris) (USFWS 2010).
Lastly, this field note provides evidence of the ability
to use satellite mapping to provide a comprehensive and
accurate account of prescribed burn history. Even with the
very fast regeneration time for vegetation in a sub-trop-
ical climate, Landsat captured nearly 80% of burns that
occurred on the refuge.e long-term archive of Landsat
imagery, going back to the mid-1980s, permits retroactive
assessments to provide a precise record of fire manage-
ment on the refuge. For other agencies looking to use fire
as a management option, digitally mapping fire perimeters
immediately after they are conducted, either via GPS or
imagery, can help improve the accuracy of reporting met-
rics such as area and exact location burned. e recent
availability of very high spatial (< 5m) and temporal (daily
repeat) imagery from companies like Planet and Maxar
has the potential to make burn scar mapping even more
reliable and precise. e technology on Planet cubesats is
evolving rapidly and is responsive to a budding user com-
munity (Frazier and Hemingway 2021), and the recent
addition of short-wave infrared channels on the Planet
cubesats will aid in high precision fire mapping. Another
option for land managers is to use drones to collect their
own imagery post-fire to compute metrics of burn area,
fire severity, and other metrics. While these technologies
cannot be employed retroactively to map past fires, they
can be integrated into monitoring programs in the future.
Conclusions
e ecosystems of ANWR have developed in response
to both the presence of fire (i.e., fire-adapted species
present on the refuge) and the lack of fire on the land-
scape (i.e., the spread of invasive woody plants). e
risk of following the historic burn regime according to
LANDFIRE would likely create a scenario of increased
woody plant encroachment in ANWR. e need to
manage habitat for critically endangered and threat-
ened species here should take precedence over return-
ing the landscape to presumed historic conditions. e
loss of biodiversity is a larger ecological concern if spe-
cies were to go extinct; therefore, maintenance of bio-
diversity should be a more important primary objective
than historic restoration of the fire interval, particularly
on refuges with critical habitat designations.
Abbreviations
ANWR Aransas National Wildlife Refuge
FRG Fire regime group
MoRAP Missouri Resource Assessment Partnership
MFRI Mean fire return interval
NBR Normalized burn ratio
ΔNBR Differenced normalized burn ratio
NIR Near infrared
SWIR Shortwave infrared
USFWS United States Fish and Wildlife Service
Supplementary Information
The online version contains supplementary material available at https:// doi.
org/ 10. 1186/ s42408- 024- 00273-z.
Supplementary material 1.

Page 10 of 11
Goldenetal. Fire Ecology (2024) 20:46
Acknowledgements
This work was supported by the Bollenbach Endowment and the Groendyke
Endowment at Oklahoma State University. The authors thank the United
States Fish and Wildlife Service for providing the prescribed burn data.
Authors’ contributions
The research design was conceptualized by all authors. Methodology and for-
mal analysis were completed by Katherine Golden and Benjamin Hemingway.
Original draft preparation was completed by Katherine Golden, Amy Frazier,
Benjamin Hemingway, Craig Davis, and Sam Fuhlendorf. All authors contrib-
uted to revising the manuscript.
Funding
A.E.F and B.L.H were supported by NSF grant 1,934,759. A.E.F is also sup-
ported by NSF grant 2,225,079. C.A.D is supported, in part, by the Bollenbach
Endowment at Oklahoma State University. S.D.F is supported, in part, by the
Groendyke Endowment at Oklahoma State University.
Availability of data and materials
The data used in the current study are available from the corresponding
author on reasonable request.
Declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors have no conflict of interest or competing interests to declare.
Author details
1 Department of Natural Resource Ecology and Management, Oklahoma State
University, Stillwater, OK 74078, USA. 2 RedCastle Resources, Inc, Salt Lake City,
UT 84111, USA. 3 Department of Geography, University of California, Santa
Barbara, CA 93106, USA. 4 U.S. Fish and Wildlife Service, Albuquerque, NM
87102, USA.
Received: 2 November 2022 Accepted: 7 April 2024
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