Ashe Juniper Research Articles

Seasonal Patterns and Drivers of Ashe Juniper Foliar Live Fuel Moisture and Relevance to Fire Planning

Foliar live fuel moisture (LFM)—the weight of water in living plant foliage expressed as a percentage of dry weight—typically affects fire behavior in live wildland fuels. In juniper communities, juniper LFM is important for planning prescribed burns and wildfire response but can be time consuming to obtain regularly. Also, there has been little analysis of the ways in which juniper LFM varies seasonally or is affected by weather conditions, soil moisture, or other variables such as drought index. Using an eight-year dataset of Ashe juniper (Juniperus ashei J. Buchholz) LFM observations from four sites in central Texas, USA, we found that the interannual variability of Ashe juniper LFM differs among seasons. Throughout the eight-year sample period, winter LFM fluctuated within a narrow range between about 80% and 120% and was weakly related to Keetch-Byram Drought Index (KBDI). During summer, LFM fluctuated widely and was more strongly related to KBDI. KBDI below 315 was positively related to LFM, while KBDI above 526 was strongly negatively related to LFM. For this region, we offer a KBDI of about 500 as a threshold for fire planning, above which the potential for critically low Ashe juniper LFM becomes more likely.

Characterizing the encroachment of juniper forests into sub-humid and semi-arid prairies from 1984 to 2010 using PALSAR and Landsat data

Over the past few decades, wide encroachment of eastern redcedar (Juniperus virginiana) and Ashe juniper (Juniperus ashei) into the prairies of the U.S. Great Plains has affected wildlife habitats, forage and livestock production, and biogeochemical cycles. This study investigates the spatio-temporal dynamics of juniper forest encroachment into tallgrass prairies by generating juniper forest encroachment maps from 1984 to 2010 at 30m spatial resolution. A pixel and phenology-based mapping algorithm was used to produce the time series maps of juniper forest encroachment using a combination of Phased Array type L-band Synthetic Aperture Radar (PALSAR) mosaic data from 2010 and Landsat 5 and 7 data (10,871 images from 1984 to 2010). We analyzed the resultant maps to understand the dynamics of juniper forest encroachment at state and county spatial scales and examined juniper occurrence by geographic region and soil type. The juniper forest maps were generated over five multi-year periods: the late 1980s (1984–1989), early 1990s (1990–1994), late 1990s (1995–1999), early 2000s (2000–2004), and late 2000s (2005–2010). We also produced a map of time since stand detection of juniper forests in 2010. Our major findings include: (1) juniper forests have expanded linearly in time at an annual rate of ~40km2/year since 1984; (2) juniper forests had notable spatial clusters in its expansion process; (3) ~65% of juniper forests in 2010 were <15years after stands have been detected; and (4) juniper forests in 2010 were mainly distributed in sandy and loamy soils with relatively low available water storage in the top soils. This study demonstrates the potential of combining a cloud computing platform (Google Earth Engine), time series optical images (Landsat), and microwave images to document the spatial-temporal dynamics of juniper forest encroachment into prairies since the 1980s at the regional scale. The results can be used to study the causes, consequences, and potential future distribution of juniper encroachment, which are relevant to the sustainable management of prairie ecosystems.

Effect of bio-char on methane generation from glucose and aqueous phase of algae liquefaction using mixed anaerobic cultures

Activated carbon is known to enhance methane formation in anaerobic reactors via interspecies electron transfer between fermentative bacteria and methanogenic archaea. Biochar, a by-product of biomass pyrolysis process, could also perform similar functions due to its conductive properties and the presence of redox active moieties. Hence, this study was conducted to evaluate the effectiveness of different types of activated carbons and biochars on anaerobic digestion. Biochars obtained from canola meal, switchgrass and Ashe juniper were tested for methane production from both glucose and aqueous phase of bio-oil generated via hydrothermal liquefaction of algae. The results suggested that absorbents enhanced methane production. Furthermore, biochars synthesized at intermediate temperatures significantly increased methane yield and reduced the lag time required for methane formation. In addition, the results suggested that the redox active moieties such as quinones and phenazines in biochars are responsible for electron transport, which ultimately enhanced methane production.

Tuning the physicochemical properties of biochar derived from Ashe juniper by vacuum pressure and temperature

Ashe juniper is a problematic plant in central Texas due to rapid expansion causing the alteration of rangeland plant communities and hydrological landscapes. The thermochemical conversion of Ashe juniper into biochar with specific properties is a promising option for valorization of Ashe juniper. This study presents the effects of temperature (350, 450 and 520°C) and vacuum pressure (0.09, 0.7 and 3kPa) on physical and chemical properties of biochar produced by vacuum pyrolysis from Ashe juniper. We found that temperature had a major effect on the degree of carbonization and surface functionality, as well as the O/C and H/C ratios regardless of vacuum pressure. It was determined that the effect of vacuum pressure severity on product properties depends on pyrolysis temperature. In addition, the vacuum pressure was a crucial factor for controlling the surface area and porosity at each constant pyrolysis temperature. This work also demonstrated that the biochar from Ashe juniper under vacuum pyrolysis showed improved aromaticity and surface area compared to the biochar derived from other biomass. Biochar produced at 450 and 520°C showed potential application as an adsorbent, a catalyst support and a carbon sequestration agent. Methylene blue (MB) adsorption test confirmed that biochar produced at 450°C and 0.7kPa showed potential as an adsorbent.

Measuring canopy loss and climatic thresholds from an extreme drought along a fivefold precipitation gradient across Texas.

Globally, trees are increasingly dying from extreme drought, a trend that is expected to increase with climate change. Loss of trees has significant ecological, biophysical, and biogeochemical consequences. In 2011, a record drought caused widespread tree mortality in Texas. Using remotely sensed imagery, we quantified canopy loss during and after the drought across the state at 30-m spatial resolution, from the eastern pine/hardwood forests to the western shrublands, a region that includes the boundaries of many species ranges. Canopy loss observations in ~200multitemporal fine-scale orthophotos (1-m) were used to train coarser Landsat imagery (30-m) to create 30-m binary statewide canopy loss maps. We found that canopy loss occurred across all major ecoregions of Texas, with an average loss of 9.5%. The drought had the highest impact in post oak woodlands, pinyon-juniper shrublands and Ashe juniper woodlands. Focusing on a 100-km by ~1,000-km transect spanning the State's fivefold east-west precipitation gradient (~1,500 to ~300mm), we compared spatially explicit 2011 climatic anomalies to our canopy loss maps. Much of the canopy loss occurred in areas that passed specific climatic thresholds: warm season anomalies in mean temperature (+1.6°C) and vapor pressure deficit (VPD, +0.66kPa), annual percent deviation in precipitation (-38%), and 2011 difference between precipitation and potential evapotranspiration (-1,206mm). Although similarly low precipitation occurred during the landmark 1950s drought, the VPD and temperature anomalies observed in 2011 were even greater. Furthermore, future climate data under the representative concentration pathway 8.5 trajectory project that average values will surpass the 2011 VPD anomaly during the 2070-2099 period and the temperature anomaly during the 2040-2099 period. Identifying vulnerable ecological systems to drought stress and climate thresholds associated with canopy loss will aid in predicting how forests will respond to a changing climate and how ecological landscapes will change in the near term.

Responses of an Endangered Songbird to an Extreme Drought Event

Abstract Given natural variation in weather conditions and increased risk of drought associated with climate change, understanding how birds respond to fluctuations in precipitation is a necessary step toward development of more-effective, long-term management strategies for species of conservation concern. We compared behaviors and reproductive output of the federally endangered Vireo atricapilla (Black-capped Vireo, hereafter Vireo) during an extreme drought event and a year with moderate rainfall. During the drought, Vireos had lower pairing and territory success, delayed nest initiation, fewer re-nesting attempts, and lower nest-success. Brood parasitism by Molothrus ater (Brown-headed Cowbirds), which is one of the main threats to Vireo population persistence, was also greater during the drought year. Nest placement varied between years, with Vireos using the evergreen Juniperus asheii (Ashe Juniper) as a nest substrate more often when conditions were dry and the deciduous Diospyros texana (Texas Per...

Effects of juniper removal and rainfall variation on tree transpiration in a semi-arid karst: evidence of complex water storage dynamics

Brush removal is widely practiced as a tool for increasing groundwater recharge, but its efficacy depends greatly on the way in which the removed species interact with the hydrological system relative to the vegetation replacing it. We examined the effects of Ashe juniper removal in the recharge zone of the Edwards Aquifer, Texas, USA, a karst aquifer. The study was conducted in an Ashe juniper (Juniperus ashei)–live oak (Quercus fusiformis) woodland on a hill slope composed of rocky, shallow soils over fractured limestone bedrock. Ashe juniper is a native species that has been encroaching grasslands and savannas over the past century. In September 2008, a plot was cleared of 90% of its juniper trees. Tree transpiration, predawn water potentials and vegetation cover across the cleared plot and an adjacent reference site were measured from May 2009 to December 2011. Stand-level tree transpiration from May 2009 to March 2010 was diminished by a severe summer drought in 2009, from which trees were slow to recover. Subsequently, tree transpiration was 5–10× higher in the woodland compared to the clearing. For all of 2011, also a drought year, tree transpiration in the woodland exceeded precipitation inputs, indicating a high capacity for water storage at the study site. However, site differences for oak trees were generally larger than for juniper trees. While juniper removal accounted for a 431 mm year−1 difference in tree transpiration between sites, vegetation cover in the clearing increased from 42% to 90% over two years, suggesting that understory growth was increasingly compensating for the loss of juniper transpiration. We conclude that the removal of a relatively shallow-rooted tree, when replaced with herbaceous vegetation and low shrubs, has little effect on deep recharge. By contrast, successive years of precipitation extremes may be more effective increasing recharge by lowering the water transport capacity of trees in the aftermath of severe drought. Copyright © 2016 John Wiley & Sons, Ltd.

Canopy foliation and area as predictors of mortality risk from episodic drought for individual trees of Ashe juniper

Drought is killing an increasing number of trees globally, yet mortality risk remains difficult to predict at fine spatial scales. We sought to identify metrics of living individuals that could be used to estimate mortality risk of Ashe juniper (Juniperus ashei) trees and eventually to estimate the fraction of juniper populations at risk from drought. Ashe juniper is a keystone species in the Edwards Plateau region in central Texas, USA. We analyzed tree rings from both living and dead trees to determine growth rate prior to an historic drought in 2011 and measured morphological, physiological, and stand-level variables hypothesized to link growth rate and mortality risk. Slowly growing trees were disproportionately vulnerable to mortality. Fractional mortality of sampled trees was correlated to the difference between the mean predrought basal area increment (BAI) per tree and the predrought BAI of minimally stressed trees growing on deep soil (=BAI90 − BAI). Slowly growing trees had sparsely foliated canopies. BAI90 − BAI was positively correlated to the difference between: (1) leaf area per unit of projected canopy area per tree (LA) and the LA of minimally stressed trees and (2) projected canopy area (CA) and the CA of comparably sized trees. By contrast, there was no correlation between growth of living trees and light interception by neighboring trees, soil depth, or two functional metrics, the stem–leaf Ψ gradient and leaf light use efficiency. Mortality risk in Ashe juniper populations can be estimated from nondestructive measurements of leaf and canopy area of individual trees using relationships among risk, growth, and leaf and canopy area.

Golden-cheeked Warbler Behavior in Relation to Vegetation Characteristics across their Breeding Range

Abstract We examined golden-cheeked warbler (Setophaga chrysoparia; hereafter warbler) behavior by age, sex, and habitat characteristics across their breeding range in central Texas (1995–1997). This federally endangered songbird foraged more on oak (Quercus spp.) substrates early in the breeding season and more on Ashe juniper (Juniperus ashei) late in the breeding season. We observed no overall difference in tree species use by warbler sex and age; however, we detected female and juvenile warblers in the low and middle canopy more often for all behaviors than males. Also, female warblers rested less and foraged twice as much as male warblers, who instead vocalized more than females and juveniles. In the southernmost study location, male warblers foraged more and vocalized less. More specifically, they foraged more on oaks when compared to other tree species, suggesting vegetation may influence warbler behavior in some locations. As the breeding season progressed, warblers increased their use of lower tr...

Airborne laser altimetry and multispectral imagery for modeling Golden‐cheeked Warbler (Setophaga chrysoparia) density

AbstractRobust models of wildlife population size, spatial distribution, and habitat relationships are needed to more effectively monitor endangered species and prioritize habitat conservation efforts. Remotely sensed data such as airborne laser altimetry (LiDAR) and digital color infrared (CIR) aerial photography combined with well‐designed field studies can help fill these information voids. We used point count‐based distance sampling survey data and LiDAR‐fused CIR aerial photography to model density of the Golden‐cheeked Warbler (Setophaga chrysoparia), an endangered songbird, on the 10 000‐ha Balcones Canyonlands National Wildlife Refuge (BCNWR). We developed a novel set of candidate models to explain Golden‐cheeked Warbler detection probability and density using habitat covariates characterizing vegetation structure, composition, and complexity as well as habitat fragmentation, topography, and human infrastructure. We had the most model support for covariates calculated using focal means representing a 3.2 ha territory size (100 m radius) vs. 1.8 and 7.0 ha territory sizes. Detection probability decreased with canopy cover and increased with topographic roughness. Golden‐cheeked Warbler density increased with canopy cover, was highest at a 7:3 ratio of Ashe juniper (Juniperus ashei) to broadleaf tree canopy cover, and decreased with global solar radiation. Predicted warbler densities using 3 min point counts were similar to six estimates from independently collected warbler territory mapping on BCNWR with a mean difference of 6% and a Root Mean Squared Error of 1.88 males/40 ha. The total population size for BCNWR was estimated at 884 Golden‐cheeked Warbler males (95% CI 662, 1206) and predicted densities across the refuge ranged from 0.0 to 0.50 male warblers per ha. On the basis of observed habitat relationships, we defined high quality habitat as having at least 60% canopy cover with Ashe juniper comprising 50–90% of the canopy. We estimated 48% of the area at BCNWR managed for Golden‐cheeked Warblers was in high quality habitat conditions and identified patches within the lower habitat quality areas (14% of warbler management areas) that had the greatest potential to become high quality habitat with management. Our approach combined robust wildlife surveys with highly scalable remotely sensed data to examine habitat relationships, estimate population size, and identify existing areas of high quality habitat. This method can be applied to other species of conservation interest and can be used with multiple years of remotely sensed data to assess changes in habitat at local to regional scales.

Characteristics of Vegetation Used by Golden-Cheeked Warblers in Central Texas

Abstract Setophaga chrysoparia (Golden-cheeked Warbler; hereafter Warbler) breeds in oak—juniper woodland across central Texas. Our knowledge of Warbler-habitat associations remains limited to a small number of long-term study sites. However, ecological conditions within Warbler habitat may vary by geographic location. We estimated vegetation characteristics at 24 sites occupied by Warblers and at 80 Warbler nests and compared site and nest vegetation across natural regions. We found differences in vegetation volume at sites and nests across regions. We also found differences across regions in canopy height at sites, but no differences in canopy height at nests. Tree species richness and diversity and the proportion of Juniperus ashei (Ashe Juniper) used by Warblers at sites and nests varied across regions. Our study identifies geographic variation in Warbler habitat characteristics across the species' breeding range.

Density influences accuracy of model-based estimates for a forest songbird

Golden-cheeked Warblers (Setophaga chrysoparia) are endangered songbirds that breed exclusively in the Ashe juniper (Juniperus ashei )a nd oak (Quercus spp.) woodlands of central Texas. Despite being the focus of numerous studies, we still know little about the size of the range-wide breeding population and how density varies across the spectrum of juniper co-dominated woodlands. Models that have been tested and shown to be accurate are needed to help develop management and conservation guidelines. We evaluated the accuracy and bias of density estimates from binomial mixture models, the dependent double-observer method, and distance sampling by comparing them to actual densities determined by intensive territory monitoring on plots in the Balcones Canyonlands Preserve, Austin, Texas. We found that the binomial mixture models consistently overestimated density by 1.1-3.2 times (actual density = 0.07-0.46 males/ha), and the other two models overestimated by 1.1- 29.8 times at low density and underestimated by 0.5-0.9 times at high density plots (actual density = 0.01-0.46 males/ha). The magnitude of error for all models was greatest at sites with few or no birds (<0.15 males/ha), with model performance improving as actual density increased. These non-linear relationships indicate a lack of sensitivity with respect to true changes in density. Until systematic evaluation demonstrates that models such as those we tested provide accurate and unbiased density estimates for a given species over space and time, we recommend additional field tests to validate model-based estimates. Continued model validation and refinement of point-count methods are needed until accurate estimates are obtained across the density spectrum for Golden-cheeked Warblers and other songbird species. RESUMEN. La densidad influencia la precisi´

Landscape and local effects on occupancy and densities of an endangered wood-warbler in an urbanizing landscape

Golden-cheeked warblers (Setophaga chrysoparia), an endangered wood-warbler, breed exclusively in woodlands co-dominated by Ashe juniper (Juniperus ashei) in central Texas. Their breeding range is becoming increasingly urbanized and habitat loss and fragmentation are a main threat to the species’ viability. We investigated the effects of remotely sensed local habitat and landscape attributes on point occupancy and density of warblers in an urban preserve and produced a spatially explicit density map for the preserve using model-supported relationships. We conducted 1507 point-count surveys during spring 2011–2014 across Balcones Canyonlands Preserve (BCP) to evaluate warbler habitat associations and predict density of males. We used hierarchical Bayesian models to estimate multiple components of detection probability and evaluate covariate effects on detection probability, point occupancy, and density. Point occupancy was positively related to landscape forest cover and local canopy cover; mean occupancy was 0.83. Density was influenced more by local than landscape factors. Density increased with greater amounts of juniper and mixed forest and decreased with more open edge. There was a weak negative relationship between density and landscape urban land cover. Landscape composition and habitat structure were important determinants of warbler occupancy and density, and the large intact patches of juniper and mixed forest on BCP (>2100 ha) supported a high density of warblers. Increasing urbanization and fragmentation in the surrounding landscape will likely result in lower breeding density due to loss of juniper and mixed forest and increasing urban land cover and edge.

The Use of Commercial Bacterial Soil Inoculant Regime in an Urban Prairie Restoration

ABSTRACT: For successful grassland restoration, commercial soil inoculants are often recommended to increase establishment success. In spring 2009, a 0.94-ha tract was targeted for restoration at Phil Hardberger Park, a 126-ha park in the heart of San Antonio, Texas. Woody species, mainly Texas persimmon (Diospyros texana Scheele), and Ashe juniper (Juniperus asheii Buchholz), were removed and the area was divided into 10 subplots measuring 911 m2 on average. In September 2009, over 40,000 plugs of seven native grass species were planted. In addition, native prairie seed mixes, including various grass and forb seeds, were sown into the site at a rate of 11.26 kg/ha. Half of the native grass plants were treated with a soil bacteria inoculant plus additional nutrients (IN) (BioGensis IIITM DS Tainio Technology and Technique Inc.), and half were left as controls (C). Soil samples from the plots were taken in February 2010 and 2011 and analyzed for soil nutrients, bacteria, protozoa, and fungi. Vegetation dat...

Restoring Early-Successional Shrubland Habitat for Black-Capped Vireos using Mechanical Mastication

Disturbance-dependent shrublands and the birds that nest in them are declining due to factors that include fire suppression and tree encroachment. Mechanical treatments are often used to decrease the threat of wildfire in sensitive areas, such as the wildland-urban interface, and could be used for restoration. We evaluated the use of mechanical mastication (also called mulching or chipping) to restore early-successional structure to oak-dominated shrublands in Texas, which provide nesting habitat for the endangered black-capped vireo (Vireo atricapilla Woodhouse). After mastication, overall vegetation height remained low for at least four growing seasons (pretreatment: 2.9 ± 0.1 m, mean ± SE; year 4: 1.1 ± 0.1 m). Canopy-sized Ashe juniper (Juniperus ashei Buchholz) was eliminated by mastication for the duration of the study, but other woody species remained abundant, maintaining vegetation density below 1 m. Black-capped vireos foraged in the masticated areas during the first and second breeding seasons after treatment, and started nesting in them during the third breeding season. By the fourth breeding season, breeding pairs were more than twice as abundant as before mastication (mean of 8.7 vs. 3.7 territories) and nests were farther from existing trails (mean ± SE of 39.9 ± 8.2 m vs. 18.4 ± 3.5 m), indicating that the birds were using more of the available space for breeding. We did not find a difference in the probability of nests in masticated areas surviving over the 28-day period from egg laying to fledging compared to nests from other areas (95% CI 0.28–0.62 and 0.18–0.47, respectively). Mastication is an effective substitute for prescribed fire to restore early-successional structure in shrublands dominated by resprouting woody plants and can also provide short-term control of nonsprouting species.

The joint effects of fire and herbivory on hardwood regeneration in central Texas woodlands

Oaks (Quercus spp.) are not regenerating in forests and woodlands in central Texas and elsewhere. This has been attributed to fire suppression. However, overabundant white-tailed deer (Odocoileus virginianus) can also limit oak regeneration. We hypothesized that both fire re-introduction and protection from deer would increase the number and growth of hardwood seedlings, saplings, and sprouts in a central Texas woodland co-dominated by Texas red oak (Quercus buckleyi) and Ashe juniper (Juniperus ashei). We measured the separate and joint effects of prescribed fire and deer herbivory on the number, size, and growth of Ashe juniper and hardwoods, tree mortality, and canopy cover. We collected data one year before and three years after deer-fence construction and a prescribed fire. Fire stimulated re-sprouting in oak and other hardwoods, but had no detectable effect on their seedlings or saplings, even three years later. Deer exclusion increased the number of seedlings transitioning to the sapling size class. Both fire and deer exclusion together were required to increase average sprout height above the browseline. The apparent adaptations of native hardwoods to fire are the strongest evidence we have for an important role for fire pre-settlement. Our results also indicate that fire suppression in central Texas and other parts of the south-central US is causing a shift, not to more mesic-adapted species as observed in the eastern US, but to juniper (Juniperus spp.), which is at least as xeric-adapted as oak. Therefore, thinking about the “oak regeneration problem” needs to be expanded beyond “mesophication” to incorporate the shift to juniper in drier regions. It is likely that deer control is necessary to allow fire to have positive effects on the regeneration of oaks and other hardwoods in this region and wherever deer are over-abundant. Moreover, the negative effects of deer herbivory on oak growth may partially account for reported failures of single fires alone to promote hardwood regeneration elsewhere.

Small-scale variability in water storage and plant available water in shallow, rocky soils

Background and aims We quantified spatial variability in water storage and plant access to water in the rocky soils of a karst savanna dominated by Ashe juniper (Juniperus ashei) and honey mesquite (Prosopis glandulosa).

Mapping Potential Groundwater‐Dependent Ecosystems for Sustainable Management

Ecosystems which rely on either the surface expression or subsurface presence of groundwater are known as groundwater-dependent ecosystems (GDEs). A comprehensive inventory of GDE locations at an appropriate management scale is a necessary first-step for sustainable management of supporting aquifers; however, this information is unavailable for most areas of concern. To address this gap, this study created a two-step algorithm which analyzed existing geospatial and remote sensing data to identify potential GDEs at both state/province and aquifer/basin scales. At the state/province scale, a geospatial information system (GIS) database was constructed for Texas, including climate, topography, hydrology, and ecology data. From these data, a GDE index was calculated, which combined vegetative and hydrological indicators. The results indicated that central Texas, particularly the Edwards Aquifer region, had highest potential to host GDEs. Next, an aquifer/basin scale remote sensing-based algorithm was created to provide more detailed maps of GDEs in the Edwards Aquifer region. This algorithm used Landsat ETM+ and MODIS images to track the changes of NDVI for each vegetation pixel. The NDVI dynamics were used to identify the vegetation with high potential to use groundwater--such plants remain high NDVI during extended dry periods and also exhibit low seasonal and inter-annual NDVI changes between dry and wet seasons/years. The results indicated that 8% of natural vegetation was very likely using groundwater. Of the potential GDEs identified, 75% were located on shallow soil averaging 45 cm in depth. The dominant GDE species were live oak, ashe juniper, and mesquite.

Spatial and temporal distribution of oak wilt in golden‐cheeked warbler habitat

ABSTRACTResearch suggests the presence of oak wilt in Ashe juniper–oak (Juniperus ashei–Quercus spp.) woodland has a negative effect on habitat selection and quality for the federally endangered golden‐cheeked warbler (Setophaga chrysoparia). We used aerial imagery and an occupancy model to estimate the amount of golden‐cheeked warbler habitat within our study region in Texas, USA, that was affected by oak wilt over a 10‐year timeframe, 2008–2018, and to assess the current probability of warbler occupancy in areas affected by oak wilt prior to 1983. We also quantified vegetation characteristics to assess regeneration in areas affected by the disease. Our results indicate that oak wilt frequently occurs in golden‐cheeked warbler habitat and will continue to spread into warbler habitat in the coming years. We estimated that 6.9% of golden‐cheeked warbler habitat within our study region in the southwestern portion of the warbler's range was affected by oak wilt in 2008. By 2018, we predict that 13.3% of golden‐cheeked warbler habitat will be affected by the disease. Areas affected by oak wilt prior to 1983 were less likely to be classified as current potential warbler habitat than were unaffected areas. We found no differences between the understory vegetation of affected and unaffected areas but, in general, oaks were more common in the overstory than in the understory, suggesting that species composition in affected areas may shift following an outbreak of oak wilt. Future management efforts should address the threat oak wilt poses to golden‐cheeked warblers by incorporating applicable preventative measures. © 2014 The Wildlife Society.

Effects of a forest pathogen on habitat selection and quality for the endangered golden‐cheeked warbler

ABSTRACTOak wilt is a fatal forest disease caused by the fungus Ceratocystis fagacearum. Loss or degradation of habitat caused by oak wilt may negatively affect forest songbirds, including the federally endangered golden‐cheeked warbler (Setophaga chrysoparia), a species that breeds exclusively in the Ashe juniper–oak woodlands (Juniperus ashei–Quercus spp.) of central Texas, USA. During 2010 and 2011, we investigated the influence of oak wilt on golden‐cheeked warbler habitat selection and quality at 25 study sites that each contained forest affected by oak wilt and unaffected forest. We assessed habitat selection in terms of use versus availability at 2 scales: within the patch and within the territory. We also assessed post‐breeding use of affected forest by comparing detection densities in affected and unaffected forest. To assess the influence of oak wilt on habitat quality, we compared the reproductive outcome of territories in unaffected and affected areas. We assessed within‐patch habitat selection for 67 territories and found that golden‐cheeked warblers used affected forest significantly less than its availability. We found use of affected forest to be variable within the 14 territories that contained affected forest in &gt;10% of their area. Post‐breeding use of affected forest was also variable. Pairing success was 27% lower for males whose territories contained &gt;10% affected forest but fledging success was not affected. Our results suggest that the presence of oak wilt negatively influences habitat selection and quality for golden‐cheeked warblers, likely due to reduced canopy cover in susceptible oak species. © 2013 The Wildlife Society.