Juniper Woodlands Research Articles

Distribution of Western Juniper Seeds Across an Ecotone and Implications for Dispersal

Abstract. Western juniper woodlands have been the focus of extensive research and management due to range expansion and infilling that began over a century ago. Understanding juniper seed dispersal is vital to identifying processes behind this expansion. Dispersal of Juniperus seeds has generally been attributed to consumption of female juniper cones (“berries”) by frugivorous birds and mammals, which then defecate seeds after gut passage. However, recent studies have found that scatter-hoarding rodents harvest and cache juniper seeds. Rodents caching and failing to recover juniper seeds that have been removed from feces may constitute a secondary mode of dispersal that accounts for more seedling recruitment than primary dispersal by frugivores. We considered implications of juniper seed dispersal by frugivorous birds and subsequent removal of bird-passed seeds and secondary dispersal by scatter-hoarding rodents by examining the distribution of western juniper seeds after dispersal by birds along transect...

Effects of conifer treatments on soil nutrient availability and plant composition in sagebrush steppe

Piñon-juniper woodlands of the western United States have expanded 2 to 10-fold since the late 1800’s. Tree control measures using chainsaws, heavy equipment and prescribed fire have been used to reduce woodlands and restore big sagebrush steppe and decrease woody fuel loading. We evaluated nutrient availability and herbaceous recovery following various cutting and prescribed fire treatments in late succession western juniper woodlands on two sites in southeast Oregon from 2007 to 2012. Sites were a cool, wet big sagebrush-Idaho fescue association (FESCUE), highly resistant to exotic annual grasses and a warm dry big sagebrush-bluebunch wheatgrass association (BLUEBUNCH), moderately resistant to annual grass invasion. Treatments were untreated controls, partial cutting followed by fall broadcast burning (SEP), cut and leave (CUT), and cut and burn in winter (JAN) and spring (APR). Soil inorganic N (NO3−, NH4+), phosphorus (H2PO4−), potassium (K+), and cover of herbaceous species were measured in three zones; interspace, litter mats around the tree canopy (canopy), and beneath felled trees (debris). Following woodland cutting, the results of the various slash treatments measured significant differences through time in the availability of inorganic N, P, and K and vegetation composition. Peak nutrient availability tended to occur within the first two years after treatment. The increases in N, P, and K were greatest in severely burned debris and canopy zones of the SEP and APR treatments. Invasive annual grass cover was positively correlated to soil inorganic N concentrations. Herbaceous composition at the FESCUE site was generally resistant to annual grasses after juniper treatments and native plants dominating post-treatment even in highly impacted debris and canopy zones of the SEP treatment. The BLUEBUNCH site was less resistance and resilient, thus, exotic annual grasses were a major component of the understory especially when tree and slash burning was of high fire severity. To lessen these impacts requires slash burning be applied from late fall to early spring, when fuel moisture and relative humidity are higher, to maintain an adequate perennial herbaceous composition for recovery.

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.

Response of bird community structure to habitat management in piñon-juniper woodland-sagebrush ecotones

Piñon (Pinus spp.) and juniper (Juniperus spp.) woodlands have been expanding their range across the intermountain western United States into landscapes dominated by sagebrush (Artemisia spp.) shrublands. Management actions using prescribed fire and mechanical cutting to reduce woodland cover and control expansion provided opportunities to understand how environmental structure and changes due to these treatments influence bird communities in piñon-juniper systems. We surveyed 43 species of birds and measured vegetation for 1–3years prior to treatment and 6–7years post-treatment at 13 locations across Oregon, California, Idaho, Nevada, and Utah. We used structural equation modeling to develop and statistically test our conceptual model that the current bird assembly at a site is structured primarily by the previous bird community with additional drivers from current and surrounding habitat conditions as well as external regional bird dynamics. Treatment reduced woodland cover by >5% at 80 of 378 survey sites. However, habitat change achieved by treatment was highly variable because actual disturbance differed widely in extent and intensity. Biological inertia in the bird community was the strongest single driver; 72% of the variation in the bird assemblage was explained by the community that existed seven years earlier. Greater net reduction in woodlands resulted in slight shifts in the bird community to one having ecotone or shrubland affinities. However, the overall influence of woodland changes from treatment were relatively small and were buffered by other extrinsic factors. Regional bird dynamics did not significantly influence the structure of local bird communities at our sites. Our results suggest that bird communities in piñon-juniper woodlands can be highly stable when management treatments are conducted in areas with more advanced woodland development and at the level of disturbance measured in our study.

Postfire soil water repellency in piñon-juniper woodlands: Extent, severity, and thickness relative to ecological site characteristics and climate.

Wildfires can create or intensify water repellency in soil, limiting the soil's capacity to wet and retain water. The objective of this research was to quantify soil water repellency characteristics within burned piñon–juniper woodlands and relate this information to ecological site characteristics. We sampled soil water repellency across forty‐one 1,000 m2 study plots within three major wildfires that burned in piñon–juniper woodlands. Water repellency was found to be extensive—present at 37% of the total points sampled—and strongly related to piñon–juniper canopy cover. Models developed for predicting SWR extent and severity had R 2 adj values of 0.67 and 0.61, respectively; both models included piñon–juniper canopy cover and relative humidity the month before the fire as coefficient terms. These results are important as they suggest that postfire water repellency will increase in the coming years as infilling processes enhance piñon–juniper canopy cover. Furthermore, reductions in relative humidity brought about by a changing climate have the potential to link additively with infilling processes to increase the frequency and intensity of wildfires and produce stronger water repellency over a greater spatial extent. In working through these challenges, land managers can apply the predictive models developed in this study to prioritize fuel control and postfire restoration treatments.

A Demographic Structure of Populations of Salvia Lilacinocoerulea Nevski, a Rare Species Endemic to the Western Pamir-Alay (Uzbekistan, Turkmenistan)

Salvia lilacinocoerulea Nevski (Lamiaceae) is an endemic to the Western Pamir-Alay mountain range. Usually it grows on eroded clay soils among sparse juniper forests in the middle mountain belt. Studied coenopopulations of S. lilacinocoerulea are normal, but are not complete. Coenopopulations self-maintenance is carried out by the seed of renewal. The characteristic spectrum of S. lilacinocoerulea coenopopulation is centered, with a peak in the middle-generative individuals. In most cases, specific developmental spectrum of coenopopulation does not coincide with the characteristic ones. The demography structure of mostly investigated coenopopulations is satisfactory. The population growing on the grey clay soil, on strongly eroded slope among sparse juniper woodland was evaluated as critical due to absence in ontogenetic spectrum young individuals and small percentage of generative plant as well.

Vegetation Controls on the Spatio-Temporal Heterogeneity of Deep Moisture in the Unsaturated Zone: A Hydrogeophysical Evaluation

Information on the spatio-temporal variability of soil moisture in the vadose zone is important to assess groundwater recharge and solute transport in unconsolidated substrate as influenced by biological processes. Time-lapse electrical resistivity imaging (ERI) was used to monitor soil moisture dynamics to a depth of 9 m in a grassland, a grassland encroached by a juniper species (eastern redcedar, Juniperus virginiana), a juniper woodland and an oak forest in the south-central Great Plains, Oklahoma, USA. A site-specific relationship between moisture content and electrical conductivity data was developed for the soil zone, and a perched water zone was monitored at two of the sites. Results showed that (a) change in soil moisture content was linearly correlated to change in electric conductivity in the soil zone; (b) vegetation cover type induced differences in vertical bulk electrical resistivity (ER) profiles and influenced the temporal evolution of soil moisture profiles; and (c) juniper encroachment lowered the water level in the perched groundwater aquifer. Our results suggest land use and vegetation cover type, as opposed to rock properties, controls deep water drainage for the vegetation transition zone. Methods used to measure hydrogeophysical changes, such as ERI, can be used for broader understanding of geological, physical, and biological processes and their links in Earth’s critical zones.

Meteorological, snow, streamflow, topographic, and vegetation height data from four western juniper-dominated experimental catchments in southwestern Idaho, USA

Abstract. Meteorological, snow, streamflow, topographic, and vegetation height data are presented from the South Mountain experimental catchments. This study site was established in 2007 as a collaborative, long-term research laboratory to address the impacts of western juniper encroachment and woodland treatments in the interior Great Basin region of the western USA. The data provide detailed information on the weather and hydrologic response from four highly instrumented catchments in the late stages of woodland encroachment in a sagebrush steppe landscape. Hourly data from six meteorologic stations and four weirs have been carefully processed, quality-checked, and are serially complete. These data are ideal for hydrologic, ecosystem, and biogeochemical modeling. Data presented are publicly available from the USDA National Agricultural Library administered by the Agricultural Research Service (https://data.nal.usda.gov/dataset/data-weather-snow-and-streamflow-data-four-western-juniper-dominated-experimental-catchments, doi:10.15482/USDA.ADC/1254010).

Relative habitat- and browse-use of native desert mule deer and exotic oryx in the greater San Andres Mountains, New Mexico

Introduced oryx (Oryx gazella gazella) have expanded into the San Andres Mountains of south-central New Mexico, but little is known of concurrent habitat used by oryx and desert mule deer (Odocoileus hemionus crooki); the latter in New Mexico is a species of special concern that has declined signifi cantly since the introduction of oryx. We used fecal-pellet and browse surveys in combination with presence modeling to identify differences in relative use of habitat types, distribution, and browsing of highly palatable, highly preferred (hereafter, key) plant species during 2004 to 2006 to assess the potential for direct competition in use of resources in the San Andres Mountains. Numbers of pellet groups per transect (hereafter referred to as relative use) of oryx was greatest in sandsage (Artemisia fi lifolia) shrublands and alkali sacaton (Sporobolus airoides) grasslands, whereas mule deer-use was greatest in oak- (Quercus spp.) mountain mahogany (Cercocarpus montanus) shrublands, and pinyon- (Pinus edulis) juniper (Juniperus spp.) woodlands. Use of key mule deer browse species was low (<4.0% of current annual growth browsed) in all habitat types. Relative use of oryx accounted for 42% of the variation in browse percentages in pinyon-juniper woodlands and 58% of the variation in mesquite (Prosopis glandulosa) shrublands, whereas mule deer-use accounted for 79% of the variation in oak-mountain mahogany shrublands and 27% in pinyon-juniper woodlands. Presence models similarly indicated that deer distribution was most positively associated with oak-mountain mahogany shrublands and pinyon-juniper woodlands, while oryx distribution was most positively associated with alkali sacaton grasslands, mixed lowland scrub, and sandsage shrublands. Presence models also indicated that areas closer to roads were positively associated with presence of mule deer and oryx, as were southern aspects for oryx and higher elevations for mule deer. Relationships with roads were likely driven by other attributes (e.g., water sources, arroyos, and canyons) associated with these areas in the San Andres Mountains. Current management strategies aimed at limiting oryx numbers in woodland and shrubland habitat types located in mountainous areas of the San Andres Mountains that show highest use by mule deer should continue to aide in recovery of mule deer populations.

A comparison of change detection measurements using object-based and pixel-based classification methods on western juniper dominated woodlands in eastern Oregon

Encroachment of pinyon (Pinus spp) and juniper (Juniperus spp.) woodlands in western North America is considered detrimental due to its effects on ecohydrology, plant community structure, and soil stability. Management plans at the federal, state, and private level often include juniper removal for improving habitat of sensitive species and maintaining sustainable ecosystem processes. Remote sensing has become a useful tool in determining changes in juniper woodland structure because of its uses in comparing archived historic imagery with newly available multispectral images to provide information on changes that are no longer detectable by field measurements. Change in western juniper (J. occidentalis) cover was detected following juniper removal treatments between 1995 and 2011 using panchromatic 1-meter NAIP and 4-band 1-meter NAIP imagery, respectively. Image classification was conducted using remotely sensed images taken at the Roaring Springs Ranch in southeastern Oregon. Feature Analyst for ArcGIS (object-based extraction) and a supervised classification with ENVI 5.2 (pixel-based extraction) were used to delineate juniper canopy cover. Image classification accuracy was calculated using an Accuracy Assessment and Kappa Statistic. Both methods showed approximately a 76% decrease in western juniper cover, although differing in total canopy cover area, with object-based classification being more accurate. Classification results for the 2011 imagery were much more accurate (0.99 Kappa statistic) because of its low juniper density and the presence of an infrared band. The development of methods for detecting change in juniper cover can lead to more accurate and efficient data acquisition and subsequently improved land management and monitoring practices. These data can subsequently be used to assess and quantify juniper invasion and succession, potential ecological impacts, and plant community resilience.

Changes in Habitat Use of Montezuma Quail in Response to Tree Canopy Reduction in the Capitan Mountains of New Mexico

Montezuma quail (Cyrtonyx montezumae) are unique among quail with respect to clutch size, diet, covey dynamics, and habitat use. With the exception of a few notable early studies, there is relatively little information on the ecology of Montezuma quail. Pervious research has indicated that one of the primary habitats utilized by Montezuma quail is pinyon–juniper (Pinus spp.–Juniperus spp.) woodlands. Throughout many areas of the southwestern United States, pinyon–juniper woodlands are often targeted for thinning projects. Many studies have been conducted on the amount of canopy cover needed by other quail species. However, data on characteristics of their preferred habitat in many of the mountains they inhabit is limited in the literature and no data are currently published on their response to thinning projects. Therefore, studies are warranted to fill in these missing data, which will increase our knowledge about the habitat requirements of Montezuma quail and allow us to make informed decisions about thinning projects in areas occupied by Montezuma quail. The goal of this research was to evaluate Montezuma quail responses to common silvicultural practices, specifically pinyon–juniper thinning in the Capitan Mountains of New Mexico. Results of our project indicated that Montezuma quail selected for sites that had been thinned to reduce canopy cover to a 30–40% mosaic. Selection for this habitat was much higher than selection for the surrounding area, which consisted of ≥70% canopy cover (Manly–Chesson Selectivity Index = 1.68). Overall, this study yields vital information for managers considering implanting thinning projects in Montezuma quail habitat.

La influencia de los factores topoclimáticos en la organización geográfica de los sabinares de Anaga (Tenerife, Islas Canarias)

Se estudian los efectos de los factores topoclimáticos sobre las dos muestras mejor conservadas de la vegetación termófila de la isla de Tenerife: el sabinar de Afur y el de la Punta de Anaga. El análisis se realiza a dos escalas espaciales: comarcal y local. La primera permite mostrar las diferencias entre los dos emplazamientos; mientras que a través de la segunda se ponen de manifiesto las variaciones internas en cada uno de ellos. Las variaciones locales de altitud y orientación dan lugar a cambios florísticos y fisionómicos que aparecen reflejados en los inventarios de campo realizados. Por la mayor diversidad de combinaciones de factores ambientales, en Afur se localiza la muestra de sabinar más rica y compleja. Los análisis a escala local demuestran que los contrastes de orientación pueden llegar a ser más importantes que los provocados por los gradientes climáticos verticales.

Plant Community Dynamics 25 Years After Juniper Control

The expansion of piñon-juniper woodlands over the past 100−150 yr in the western United States has resulted in large-scale efforts to kill trees and recover sagebrush steppe rangelands. Western juniper (Juniperus occidentalis spp. occidentalis Hook.) expansion in the northern Great Basin has reduced sagebrush-steppe productivity and habitat. Chainsaw cutting of western juniper woodlands is a commonly applied practice to kill trees and restore shrub-understory composition. Studies reporting vegetation response following juniper cutting have been limited to early successional stages. This study assessed successional dynamics spanning 25 yr following tree cutting on Steens Mountain, southeast Oregon. Herbaceous standing crop and yield and plant densities were compared between chainsaw cut (Cut) and uncut woodland (Control) treatments. Cut plots were treated in 1991. In the Cut, total standing crop and yield have remained fairly consistent since 1996 and on average were 8 times greater than the Control. Perennial grass yield was 2- to 20-fold greater in the Cut than the Control across measurement years and peaked 14 yr (2005) after treatment. Perennial bunchgrass yield declined to 30−40% of its peak value, and bunchgrass density declined from about 11 plants m−2 in 2005 to 7 plants m−2 between 2005 and 2016. Invasive annual grasses increased in yield and as a percentage of total yield from 3% to 20%, between 2005 and 2016. Juniper and shrub cover and density increases and greater annual grass yields in the Cut have likely contributed to declines in perennial bunchgrass density and yields. Juniper control will be necessary within 5 yr to maintain progression to sagebrush steppe, indicating a treatment longevity of about 25−30 yr. To lengthen the life expectancy of cutting and other mechanical control of piñon-juniper woodlands requires that all age classes of trees be controlled in the initial treatment.

Woodland reduction and long‐term change in breeding bird communities

ABSTRACTForested ecosystems in the western United States have been the focus of tree reduction efforts for decades, with the intent of improving forage for livestock and wildlife. Yet, the long‐term consequences of tree removal for biodiversity are virtually unknown. We conducted bird and vegetation surveys in northwestern Colorado where trees were mechanically removed over 40 years ago. We evaluated differences in avian species richness and community composition, and used a Bayesian hierarchical approach to determine if tree removal had long‐term effects on bird density. We found that tree reduction initiates a long‐term change from dense pinyon (Pinus edulis)‐juniper (Juniperus osteosperma) woodlands to sagebrush scrub, fundamentally altering bird community composition. Disturbed sites were used by fewer species and largely dominated by shrubland‐obligate birds. Further, bird densities were markedly different between historically disturbed sites and reference sites. Densities of many species were correlated with specific vegetative characteristics (e.g., mean tree diameter) that could be factored into management decisions to better sustain diverse natural communities. © 2016 The Wildlife Society.

Spatial dynamics of expanding fragmented thermophilous forests on a Macaronesian island

The increasing availability of aerial photographs and remote sensing images allows the forecasting of forest dynamics in response to land-use changes, such as the abandonment of rural activities. The cessation of these activities launches natural regeneration and demographic expansion of formerly fragmented and isolated forests. By tracking these changes over decades, we were able to identify the environmental factors that promote or hamper natural regeneration of forestlands disturbed for centuries. Here, we tracked the demographic expansion of Juniperus turbinata ssp. canariensis over a study period spanning six decades based on aerial pictures. We applied Local Indicators of Spatial Association (LISA) analyses to identify hotspots and coldspots of regeneration and we further quantified the role of ecological and anthropogenic factors in driving natural regeneration by applying a generalized lineal model. Aerial photos showed a clear demographic forest expansion during the approximately 60years spanned by this study. LISA revealed that this regeneration was not homogeneous across the landscape; rather it was highly aggregated around an increasing number of hotspots of natural regeneration during the study period. The initial density of juniper individuals was the most important variable underpinning the demographic expansion followed by aspect, elevation, and distance to anthropic areas. According to our results, island juniper woodlands regenerate steadily in areas affected by moderate levels of anthropogenic disturbances. Our results provide highly valuable information to implement forest management plans. On-going and future conservation plans to recover the thermophilous Macaronesian forest will particularly benefit from this type of study.

The ecological status of juniper woodlands in Al Jabal Al Akhdar, northern mountains of Oman

There are changes in the local distribution of the juniper, Juniperus seravschanica woodlands as a result of conflicts between biodiversity conservation and human activities in Al Jabal Al Akhdar, Sultanate of Oman. Woodland degradation and poor regeneration of juniper trees are attributed to many factors. Four zones, each with 10 plots and each plot with an area of 10,000 sq m were studied in detail at different altitudes to evaluate the status of the juniper woodlands. Tree density, distribution, health status and seed germination were assessed. The stock density of J. seravschanica in the study localities was less when compared to the previous studies. Juniper appeared as continuous woodlands from Al Hajmata reservoir in Shanut at an altitude of 2168 m a.s.l. and continued with the increase in altitude. The population structures of J. seravschanica in the four zones were evaluated. The heights of trees were normally distributed in the four zones. There were significant differences in the heights of trees among the four zones. Trees in zone 1 were shorter than those in the in the other three zones. J. seravschanica trees are in good health condition in all four zones. Most produced a moderate amount of female and male cones. Regeneration is low as indicated by 65 seedlings (9%) recorded during the survey and 26 small young trees (14%). Seed germination was low with a maximum of 31%.

Remote sensing of the decrease of juniper woodlands in the mountains of Southwestern Saudi Arabia—reasons and consequences

Urban sprawl is a typical land use change in developed countries, which converts agricultural land or vegetated areas to built-up areas or other consolidated land cover types, like roads. In southwestern Saudi Arabia, urban sprawl and establishment of recreation areas decreases the area of juniper woodlands, which are important for carbon sequestration, biodiversity maintenance, erosion control, and atmospheric moisture harvest and water storage. The change detection study applying land cover classification for Landsat TM and ETM+ data from 1984, 1999, and 2014 in the Al Bahah governorate demonstrated a 10 % loss of juniper woodlands from 1984 to 2014, mainly caused by establishment of recreation sites in the mountains. At the same time, built-up area expanded 24 % mostly on the cost of barren lands, but also on the cost of woodlands. The juniper woodlands are also declining in quality as throughout the southwestern mountains a dieback is reported and visible also in the study area. Knowing the scarcity of woodlands in the Arabian Peninsula and the importance of the unique woodlands for water resources, it is of utmost importance to use the results for raising awareness and protecting the juniper woodlands. Further research is required to study the loss of the juniper forests and rate of dieback in the whole study area.

Reduced reproductive fitness of an endemic insular juniper population: An eco-genetic mediation hypothesis

The mutual reinforcement of multiple drivers of global change erodes ecosystem services and accelerates plant population decline worldwide. This is particularly the case for island ecosystems where anthropogenic activity has imperilled insular floras for centuries. Different hypotheses have put forward the combined effects of environmental shifts and genetic factors in driving fecundity decline in threatened populations. In this study, we combined population genetic tools and structural equation models to test the eco-genetic mediation hypothesis, that the environmental conditions influence genetic variation, which in turn affects plant fitness. Our study species is Juniperus cedrus, an endangered juniper species endemic to the Canary Islands. Juniper woodlands have been depleted since the arrival of human inhabitants confined extant populations to marginal lands. More recently, long-distance dispersers have been extirpated from the study area, potentially eliminating connectivity among fragmented populations. We expected strong intrapopulation subdivision and high levels of inbreeding and kinship that should negatively affect individual fitness. We found evidence of population subdivision into several mating neighbourhoods (K=13), some of them highly inbred. However, contrary to our expectations, neither inbreeding nor mean kinship mediated a population response to environmental factors. Our results suggest three remedial actions to reverse the declining demographic trends: (i) re-establish native vegetation to ameliorate local environmental conditions; (ii) restore dispersal services to increase connectivity; and (iii) monitor fitness decline to identify lagged effects associated with deforestation. Overall, this study shows that structural equation models combined with population genetic techniques are suitable tools to identify high-order effects among multiple drivers of global change that underlie forest decline.

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.

Climate change drives decline of Juniperus seravschanica in Oman

The southernmost population of Zeravschan juniper (Juniperus seravschanica) is found in Oman's Hajar Mountains. This is an iconic tree, important to wildlife and local people. However, Oman's juniper population is in decline: many trees have sparse, unhealthy foliage and few saplings can be found. Climate change, over-grazing, and over-harvesting have been suggested as possible causes. In this study, Zeravschan juniper were surveyed across the Jebel Akhdar-Shams range, Oman's largest juniper woodland. Generalised linear models were used to explore tree foliage status and relative abundance of saplings in relation to habitat characteristics, grazing and harvesting. Habitat characteristics associated with temperature and moisture explained patterns in percent living foliage and sapling abundance, but grazing and harvest data did not, suggesting climate change as the main cause of decline. Records of recent local temperature rises and reduced precipitation support this conclusion. Optimal habitat for juniper is now limited to areas near the summit of Oman's tallest mountain, and at lower elevations juniper with healthy foliage are only found in shallow depressions and on shaded north-facing slopes. These areas may offer climatic refugia, and protecting these habitats from other threats will be key to conserving Oman's junipers in the face of climate change.