Pinyon-juniper Ecosystem Research Articles

Managing for ecological resilience of pinyon–juniper ecosystems during an era of woodland contraction

AbstractDryland woodland ecosystems worldwide have experienced widespread drought‐ and heat‐related tree mortality events coupled with extreme wildfire behavior. In contrast to other forest types where the emphasis has been on the silvicultural enhancement of ecosystem resilience and restoration of structural heterogeneity, limited frameworks are available for management to improve drought resilience in semiarid woodlands. This challenge is especially acute in pinyon–juniper woodlands, a dominant vegetation type across western North America that has experienced extensive tree die‐off over the past several decades while simultaneously undergoing expansion in portions of its range. In this paper, we describe the critical and urgent need to manage for future drought resilience in these highly vulnerable ecosystems and synthesize the current state of knowledge on how to enhance woodland resilience to drought coupled with high temperatures and associated disturbances. We present a landscape prioritization framework for guiding management goals and practices that requires prioritization of efforts based on the need for action and the probability of a positive outcome. Four guiding factors include historical woodland structure and drivers of long‐term landscape change, current vegetation structure and composition, future climate suitability, and habitat and resource value. In summarizing the strength of evidence supporting our recommendations, we identify critical knowledge gaps and highlight the importance of adaptive management strategies that reflect current uncertainties. This will ultimately allow for improved management of diverse semiarid woodland ecosystems that are undergoing substantial changes due to past and present land use, biological invasions, and climate change.

Solar and sensor geometry, not vegetation response, drive satellite NDVI phenology in widespread ecosystems of the western United States

Satellite-derived phenology metrics are valuable tools for understanding broad-scale patterns and changes in vegetated landscapes over time. However, the extraction and interpretation of phenology in ecosystems with subtle growth dynamics can be challenging. US National Park Service monitoring of evergreen pinyon-juniper ecosystems in the western US revealed an unexpected winter-peaking phenological pattern in normalized difference vegetation index (NDVI) time-series derived from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. In this paper, we assess the validity of the winter peaks through ground-based observation of phenology and examination of solar and satellite geometry effects. To test the premise of a true vegetation response, we analyzed NDVI values extracted from a time series of ground-based digital camera (‘phenocam’) images collected September 2017 to December 2018 in a pinyon-juniper woodland in Arizona, US. Results show pinyon and juniper growth peaked in the warm season, as did the other species in the phenocam field of view. NDVI time series from four other sensors (Landsat 7, Sentinel-2, VIIRS, and Proba-V) confirmed that winter peaks in this ecosystem are not limited to MODIS products. Examination of NDVI time series (2003–2018) derived from daily 250-m MODIS data in the broader pinyon-juniper ecosystem revealed that solar-to-sensor angle, sensor zenith angle, and forward/back-scatter reflectance explained >80% of intra-annual variability. Solar-to-sensor angle exerted the greatest control, and the direction of its correlation (positive) was the opposite of that which would be expected if it were driven by vegetation greenness. Solar-to-sensor angle is controlled seasonally by solar zenith angle and daily by variations in satellite overpass geometry. We mapped winter peaks across the western US in Google Earth Engine using 500-m MODIS MCD43A4 data, which correct for reflectance differences caused by view angle. In areas where winter vegetation peaks are ecologically improbable (i.e., locations with sub-freezing December temperatures), consistent winter peaks (≥ 14 years in 2003 to 2018) are widespread in both pinyon-juniper and non-pinyon-juniper conifer ecosystems; winter peaks are common (≥ 5 years in 2003 to 2018) across areas of shrubland. We attribute winter peaks to the positive correlation of NDVI with solar-to-sensor angle and solar zenith angle in combination with sparse, vertically oriented evergreen vegetation canopies. Increasing shadow visibility has been shown to increase overall NDVI, and the prevalence of the winter peaking in evergreen western sparse canopy ecosystems is consistent with this hypothesis. The extent of winter peaking patterns may have been previously overlooked due to temporal compositing, curve fitting, and incomplete snow screening.

Monitoring pinyon-juniper cover and aboveground biomass across the Great Basin

Since the mid-1800s pinyon-juniper (PJ) woodlands have been encroaching into sagebrush-steppe shrublands and grasslands such that they now comprise 40% of the total forest and woodland area of the Intermountain West of the United States. More recently, PJ ecosystems in select areas have experienced dramatic reductions in area and biomass due to extreme drought, wildfire, and management. Due to the vast area of PJ ecosystems, tracking these changes in woodland tree cover is essential for understanding their consequences for carbon accounting efforts, as well as ecosystem structure and functioning. Here we present a carbon monitoring, reporting, and verification (MRV) system for characterizing total aboveground biomass stocks and flux of PJ ecosystems across the Great Basin. This is achieved through a two-stage remote sensing approach by first using spatial wavelet analysis to rapidly sample tree cover from very high-resolution imagery (1 m), and then training a Random Forest model which maps tree cover across the region from 2000 to 2016 using temporally-segmented Landsat spectral indices obtained from the LandTrendr algorithm in Google Earth Engine. Estimates of cover were validated against field data from the SageSTEP project (R2 = 0.67, RMSE = 10% cover). Biomass estimated from cover-based allometry was higher than estimates from the Forest Inventory and Analysis Program (FIA) at the plot-level (bias = 5 Mg ha−1 and RMSE = 15.5 Mg ha−1) due in part to differences in tree-level biomass allometrics. County-level aggregation of biomass closely matched estimates from the FIA (R2 = 0.97) after correcting for bias at the plot level. Even after many previous decades of encroachment, we find forest area (i.e. areas with ≥10% cover) increasing at a steady rate of 0.46% per year, but 80% of the 9.86 Tg increase in biomass is attributable to infilling of existing forest. This suggests that the known consequences of encroachment such as reduced water availability, impacts to biodiversity, and risk of severe wildfire may have been increasing across the region in recent years despite the actions of sagebrush steppe restoration initiatives.

Stand Dynamics of Pinyon-Juniper Woodlands After Hazardous Fuels Reduction Treatments in Arizona

Pinyon-juniper ecosystems occur extensively across western North America, and at the landscape scale, variation in structure and composition is influenced by topographic position, soils, disturbance history, and local climate. The persistent pinyon-juniper woodland is a common structural form, and though they are known to be infrequent-fire systems, there is increasing interest in implementation of hazardous fuels reduction treatments in woodlands, especially in the wildland-urban interface. Few studies have quantified stand dynamics following fuels reduction treatments in persistent woodlands or compared treatment outcomes to conditions that develop under natural disturbance and successional processes. In 2004, we established a randomized, replicated study in woodlands of northern Arizona, and monitored stand dynamics and understory responses to determine how stand-level changes differed between common fuels reduction approaches. We compared the resulting structure with a conceptual state-and-transition model. Results showed that, over the 11 yr after treatment, juniper tree densities decreased by 8.4% and 0.9% but increased by 14.0% and 27.3% in Control, Burn, Thin, and Thin + Burn treatments, respectively. Pinyon tree densities decreased by 1.1% and 3.3%, increased by 12.2%, and decreased 7.9% in Control, Burn, Thin, and Thin + Burn treatments, respectively. All treatments showed fuel load reductions throughout the 11-yr study period and minimal rebound of tree recruitment toward pretreatment conditions. Prescribed fire alone (Burn) maintained persistent woodland conditions. Thinning treatments substantially reduced small tree densities and, with the addition of prescribed fire, produced losses of large trees. Thinning with prescribed fire (Thin + Burn) tended to produce conditions qualitatively unlike those described by our state-and-transition model. Evaluation of these commonly used fuels treatments against our state-and-transition model suggested that concerns regarding loss of ecological integrity may be warranted.

THEORETICAL AND SOCIOECOLOGICAL CONSEQUENCES OF FIRE FOODWAYS

Archaeological investigations of the effects of anthropogenic fire on the subsistence economies of small-scale societies, particularly those of the prehispanic northern American Southwest, are embryonic in scope and disciplinary impact. When burning has been mentioned in such studies it typically has been with reference to its alleged effectiveness in clearing land or deforesting areas for maize agriculture. In this article, in contrast, we present the results of our initial efforts to estimate the yield and socioecological consequences of cultivating a common fire-responsive ruderal—amaranth—whose growth is enabled by anthropogenic burning of understory vegetation in the Southwest's pinyon-juniper ecosystems. With data from the Upper Basin (northern Arizona), we show that, in an area that is not environmentally conducive to maize production, populations could be supported with systematic, low-intensity anthropogenic fires that promoted the growth of amaranth and other ruderals, such as chenopodium, which consistently dominate archaeobotanical and pollen assemblages recovered from a variety of archaeological and sedimentary contexts in the region. Based on this evidence, as well as modern fire ecological data, we propose that fire-reliant ruderal agriculture, in contrast to maize agriculture, was a widespread, sustainable, and ecologically sound practice that enhanced food supply security independently of variation in soil fertility and precipitation.

Optimizing regulatory requirements to aid in the implementation of compensatory mitigation

Optimizing regulatory requirements to aid in the implementation of compensatory mitigation

Disturbing Developments: An Archaeobotanical Perspective on Pinyon-Juniper Woodland Fire Ecology, Economic Resource Production, and Ecosystem History

It has long been thought that the only means by which the American Southwest's extensive pinyon-juniper woodlands, with their inherently low primary productivity, could have supported indigenous populations during prehispanic times was with the transformative consequences associated with the widespread cultivation of low-moisture-intolerant domesticated plants, principally maize (Zea mays L.). In this paper we present an alternative to this orthodox view which posits that anthropogenic fire was a vegetation-community management technology that was used to create disturbance patches and to propagate abundant, edible seed-rich ruderals in them. This perspective allows us, as well, to introduce and illustrate the interpretive possibilities of a conceptual scheme that focuses on three resource production types—cultivated wild plants, gathered wild plants, and domesticated plants—with multi-contextual macrobotanical data from a partially burned and rapidly abandoned multi-room settlement (occupied between AD 1070–1080) located south of the Grand Canyon in northern Arizona. By integrating these data with previous archaeobotanical, pollen, and sedimentary micro-charcoal studies, we propose that the systematic cultivation of wild plants in pyrogenic resource patches was a sustainable practice that enhanced food-supply security by insulating populations from the effects of short-term environmental variability and long-term climate change that challenge maize farmers. Importantly, these investigations indicate that low-intensity burning did not involve widespread deforestation, as some models of Holocene climate change suggest, and that prehistoric depopulation and modern fire suppression have altered fundamentally the composition and economic potential of contemporary pinyon-juniper ecosystems.

Modeling regional variation in net primary production of pinyon–juniper ecosystems

Spatial dynamics of carbon fluxes in dryland montane ecosystems are complicated and may be influenced by topographic conditions and land tenure. Here we employ a modified version of the Carnegie Ames Stanford Approach (CASA) ecosystem model to estimate annual net primary production (NPP) at a fine spatial resolution (30m) in pinyon–juniper (P–J) woodlands of the Colorado Plateau. NPP estimated by CASA was generally comparable to validation data from a statistical NPP model and field observations. We then compared modeled NPP results with spatial layers of topography and managed grazing to assess the influences of these factors on NPP. At the regional scale, there was a positive correlation between elevation and NPP (r2=0.20, p<0.0001), mainly due to an orographic effect, but slope and slope facing-derived dryness indices failed to explain modeled variation in NPP. Topographic analyses based on six terrain aspect classes showed that cooler and wetter north-facing slopes yielded higher NPP than did south-facing slopes. A multiple regression consisting of three numerical topographical attributes (elevation, slope and a dryness index) yielded the highest predictability for CASA NPP (adjusted r2=0.24, p<0.0001). Modeled NPP of a grazed site was significantly higher than that of an ungrazed site. Combining the results from this study and previous research efforts suggests that grazing may be correlated with higher woody vegetation cover, which elevates NPP in P–J woodlands of the Colorado Plateau. The findings reveal that the spatial pattern of NPP is complex, and can be strongly affected by topographic and/or anthropogenic factors even in relatively remote areas of this dryland region.

Predicting Age of Pinyon and Juniper Using Allometric Relationships

Abstract Management of pinyon-juniper ecosystems often is hampered by insufficient tree age structure data. We developed allometric relationships based on visible and easily measured tree characteristics as tools for predicting tree age. In this study, we tested tree height, diameter at root collar, and crown radius using both single- and multiple-regression analyses to determine which attributes best correlated with tree age. Because soil type and site productivity often affect growth rates of pinyon and juniper, three common soil types in northern Arizona were assessed to determine variation in regression equations. Stepwise regression analysis determined that height and diameter at root collar of juniper were the best variables for predicting age. For pinyon, crown radius on basalt-derived soil and diameter at root collar on limestone-derived soil were the variables of best fit; however, we suggest using diameter at root collar across all sites. We developed models from these allometric relationships to aid in the management of the pinyon-juniper ecosystem.

ISSR and AFLP analysis of the temporal and spatial population structure of the post-fire annual, Nicotiana attenuata, in SW Utah

BackgroundThe native annual tobacco, Nicotiana attenuata, is found primarily in large ephemeral populations (typically for less than 3 growing seasons) after fires in sagebrush and pinyon-juniper ecosystems and in small persistent populations (for many growing seasons) in isolated washes typically along roadsides throughout the Great Basin Desert of the SW USA. This distribution pattern is due to its unusual germination behavior. Ephemeral populations are produced by the germination of dormant seeds from long-lived seed banks which are stimulated to germinate by a combination of unidentified positive cues found in wood smoke and the removal of inhibitors leached from the unburned litter of the dominant vegetation. Persistent populations may result where these inhibitors do not exist, as in washes or along disturbed roadsides. To determine if this germination behavior has influenced population structure, we conducted an AFLP (244 individuals), ISSR (175 individuals) and ISSR+ AFLP (175 individuals) analysis on plants originating from seed collected from populations growing in 11 wash and burns over 11 years from the SW USA.ResultsGenetic variance as measured by both ISSR and AFLP markers was low among sites and comparatively higher within populations. Cluster analysis of the Utah samples with samples collected from Arizona, California, and Oregon as out-groups also did not reveal patterns. AMOVA analysis of the combined AFLP and ISSR data sets yielded significantly low genetic differentiation among sites (Φct), moderate among populations within sites (Φsc) and higher genetic differentiation within populations (Φst).ConclusionsWe conclude that the seed dormancy of this post-fire annual and its resulting age structure in conjunction with natural selection processes are responsible for significantly low among sites and comparatively high within-population genetic variation observed in this species.

Changes in Vegetation Structure after Long-term Grazing in Pinyon-Juniper Ecosystems: Integrating Imaging Spectroscopy and Field Studies

We used field studies and imaging spectroscopy to investigate the effect of grazing on vegetation cover in historically grazed and ungrazed high-mesa rangelands of the Grand Staircase‐Escalante National Monument, Utah, USA. Airborne hyperspectral remote sensing data coupled with spectral mixture analysis uncovered subtle variations in the key biogeophysical properties of these rangelands: the fractional surface cover of photosynthetic vegetation (PV), nonphotosynthetic vegetation (NPV), and bare soil. The results show that a high-mesa area with long-term grazing management had significantly higher PV (26.3%), lower NPV (54.5%), and lower bare soil (17.2%) cover fractions in comparison to historically ungrazed high-mesa pinyonjuniper rangelands. Geostatistical analyses of remotely sensed PV, NPV, and bare soil were used to analyze differences in ecosystem structure between grazed and ungrazed regions. They showed that PV was spatially autocorrelated over longer distances on grazed areas, whereas NPV and bare soil were spatially autocorrelated over longer distances on ungrazed areas. Field data on the fractional cover of PV, NPV, and bare soil confirmed these remote sensing results locally. Field studies also showed a significantly higher percentage composition of shrubs (27.3%) and forbs (30.2%) and a significantly lower composition of grasses (34.4%) and cacti (1.1%) in grazed areas. No significant difference between grazed and ungrazed mesas was found in percentage composition of trees or in the number of canopies per hectare. Our combined remote sensing and field-based results suggest that grazing has contributed to woody thickening in these pinyon‐juniper ecosystems through an increase in shrubs in the understory and intercanopy spaces. These results improve our understanding of broad-scale changes in pinyon‐juniper ecosystem structural composition and variability due to longterm grazing.

INTRA- AND INTERSPECIFIC VARIATION FOR SUMMER PRECIPITATION USE IN PINYON–JUNIPER WOODLANDS

In the arid southwest of North America, winter precipitation penetrates to deep soil layers, whereas summer ''monsoon'' precipitation generally wets only surface layers. Use of these spatially separated water sources was determined for three dominant tree species of the pinyon-juniper ecosystem at six sites along a gradient of increasing summer precipitation in Utah and Arizona. Mean summer precipitation ranged from 79 to 286 mm, or from 18% to 60% of the annual total across the gradient. We predicted that, along this summer rainfall gradient, populations of dominant tree species would exhibit a clinal off-on response for use of water from upper soil layers, responding at particular threshold levels of summer precipitation input. This prediction was largely supported by our observations of tree water source use over a two-year period and from irrigation ex- periments. Hydrogen and oxygen stable isotope ratios ( dD and d 18 O) of tree xylem water were compared to that of precipitation, groundwater, and deep and shallow soil water to distin- guish among possible tree water sources. dD-d 18 O relationships and seasonal xylem water potential changes revealed that trees of this ecosystem used a mixture of soil water and recent precipitation, but not groundwater. During the monsoon period, a large proportion of xylem water in Pinus edulis and Juniperus osteospermawas from monsoon precipitation, but use of this precipitation declined sharply with decreasing summer rain input at sites near the regional monsoon boundary in Utah. Quercus gambelii at most sites along the gradient used only deep soil water even following substantial inputs of summer rain. Pop- ulations of Quercus at sites with the highest average summer precipitation input, however, predominantly used water in upper soil layers from recent summer rain events. Soil tem- perature correlated with patterns of summer precipitation use across the gradient; high soil temperatures north of the monsoon boundary may have inhibited surface root activity for some or all of the three tree species. Irrigation experiments with deuterium-labeled water revealed that Quercus gambeliiin northern Arizona and southern Utah did not use water from surface layers. In contrast, Juniperus osteosperma at these sites responded significantly to the irrigations: between 37% and 41% of xylem water originated from irrigations that wetted only the top 30 cm of soil. Responses by Pinus edulis to these irrigations were variable; uptake of labeled water by this species was greater in September at the end of the summer than during the hot midsummer period. Inactivity of Pinus roots in midsummer supports the hypothesis that root activity in this species is sensitive to soil temperature. Seasonal patterns of leaf gas exchange and plant water potential corresponded to the seasonality of rainfall at different sites. However, no correlation between a species' ability to use summer rainfall and its tolerance to water deficits at the leaf level was found. Midday stomatal conductance (gs) for Pinus needles approached zero at predawn water potentials near 22 MPa, whereas gs in Quercus and Juniperus declined to zero at 22.8 and 23.7 MPa, respectively. The relationship between photosynthesis (A) and gs was similar among the three species, although Quercus maintained higher overall rates of gas exchange and tended to operate higher on the A/gs curve than the two conifers. At sites in eastern Arizona where Quercus fully used moisture from summer rains, leaf gas exchange characteristics were similar to those of Pinus and Juniperus.

Acid and alkaline phosphatase dynamics and their relationship to soil microclimate in a semiarid woodland

The seasonal dynamics of acid and alkaline phosphatase activity (μg p-nitrophenol released g −1 soil h −1), soil water potential and temperature, and the relationship of phosphatase activity to plant and soil microbial processes underneath Juniperus monosperma canopies and Hilaria jamesii-dominated intercanopy areas were studied in a northern Arizona pinyon–juniper ecosystem. Alkaline phosphatase activity was significantly higher in soils under junipers (126.5±3.9 μg p-nitrophenol g −1 soil h −1) than in intercanopy soils (106.6±4.0 μg p-nitrophenol g −1 soil h −1), and significantly exceeded acid phosphatase activity by a factor of 6. Seasonal high phosphatase activities were up to 2.4 times greater than seasonal lows. Activities were maximal in summer and winter. Juniper soils were cooler than intercanopy soils except during the coldest months of the year, when they were up to 2.7°C warmer. Intercanopy soils were up to 6.2°C warmer than juniper soils, and had the highest (30.0±0.3°C) and the lowest average temperatures (2.3±0.2°C). Soil microclimate explained as much as 20% of the variation in acid and alkaline phosphatase. Temperature and water potential together were better predictors of phosphatase activity than either one alone. The soil water potential class −0.1 MPa≥ ψ>−0.5 MPa was the most frequent best predictor of phosphatase activity, especially alkaline phosphatase. The winter peak in alkaline phosphatase activity is attributed to a buildup of phosphatase released into the soil from dying soil organisms, and the desorption and reactivation of previously accumulated phosphatase.

Plant Spatial Pattern and Nutrient Distribution in Pinyon-Juniper Woodlands Along an Elevational Gradient in Northern New Mexico

Plant and soil resource spatial patterns were measured in pinyon-juniper communities in northern New Mexico over an elevational gradient that also served as a water-availability gradient to examine the role of resource competition and resource availability in determining plant spatial patterns. Total canopy coverage increased with increasing elevation. Percent coverage of juniper declined with elevation and, with the exception of one site, that of pinyon increased. Water appeared to be a strong factor in the maintenance of stand structure and plant distribution in this pinyon-juniper ecosystem. Plant water stress was greater during the dry season at the low-elevation, low-density sites than at the upper-elevation, higher-density sites. At the upper-elevation sites, plant distributions were significantly more clumped than at the drier sites; only at these low-elevation sites was there a significantly negative relationship between plant size and distance to nearest neighbor and a trend toward regular spacin...

Biomass distribution and productivity of Pinus edulis—Juniperus monosperma woodlands of north-central Arizona

Above-ground biomass distribution, leaf area, above-ground net primary productivity and foliage characteristics were determined for 90- and 350-year-old Pinus edulis-Juniperus monosperma ecosystems on the Colorado Plateau of northern Arizona. These ecosystems have low biomass, leaf area and primary productivity compared with forests in wetter environments. Biomass of the 350-year-old pinyon-juniper stand examined in this study was 54.1 mg ha −1; that of the 90-year-old stand was 23.7 mg ha −1. Above-ground net primary production averaged 2.12 mg ha −1 year −1 for the young and 2.88 mg ha −1 year −1 for the mature stand; tree production was about 80% of these values for both stands. Projected ecosystem leaf area (LAI) of the stands was 1.72 m 2 m −2 and 1.85 m 2 m −2, respectively. Production efficiency (dry matter production per unit leaf area) was 0.129 kg m −2 year −1 for the young, and 0.160 kg m −2 year −1 for the mature stand. Production efficiency of the study sites was below the 0.188 kg m −2 year −1 reported for xeric, pure juniper stands in the northern Great Basin. Biomass of pinyon-juniper ecosystems of northern Arizona is generally below the 60–121 mg ha −1 reported for pinyon-juniper stands of the western Great Basin in Nevada. A climatic gradient with summer precipitation decreasing between southeast Arizona and northwest Nevada occurs in the pinyon-juniper region. Great Basin pinyon-juniper ecosystems lie at the dry-summer end of this gradient while pinyon-juniper ecosystems of the Colorado Plateau lie at about the middle of this gradient. In spite of wetter summers, pinyon-juniper ecosystems of northern Arizona are less productive than those of the Great Basin.

Potential variation of nitrogen transformations in pinyon-juniper ecosystems resulting from burning

Forest floor litter, duff, and underlying soils were assembled in laboratory microcosms representing pinyon, juniper, and interspace field conditions. Burning removed more than 95% of both N and C from the litter, with losses from the duff dependent on soil moisture conditions. No significant changes in total N or C were noted in the soil. Immediate increases were observed in soil NHinf4sup+, decreasing with depth and related to soil heating. The greatest increases were noted in both the pinyon and juniper soils that were dry at the time of the burn, with interspace soils exhibiting the least changes. Soil NHinf4sup+closely approximated the controls on day 90 after the burns in all treatments. Ninety days after the burn microbial biomass N was highest in the controls, followed by the wet and then the dry-burned soils, in both the pinyon and juniper microcosms. This was inversely related to the levels of accumulated NOinf3sup-. Nitrifying bacteria populations were indirectly correlated to soil temperatures during the burn. Population levels 90 days after the burn showed increases in both the wet- and the dry-burn treatments, with those in the pinyon treatments exceeding those found in the nitial controls of pinyon soils.

Selenium kidney/liver ratios in rock squirrel populations from grassland and pinyon-juniper ecosystems

Selenium levels in liver and kidney tissues were determined for rock squirrels ( Spermophilus variegatus) trapped within a distinct elevational gradient (grassland to pinyon-juniper ecosystem; alkaline to acidic soil) within the confines of the Kirtland Air Force Base Military Reservation in central New Mexico. Selenium levels in tissues were determined by graphite furnace atomic absorption spectrophotometry. Selenium kidney/liver ratios determined for rock squirrels decreased as elevational gradient increased ( r = −0.9403) in the pinyon-juniper ecosystem and increased as elevational gradient increased in the grassland ecosystem ( r = 0.9493). Other tests of significance ( t test, α 0.05) also support the inverse relationship between selenium kidney/liver ratios in grassland and pinyon-juniper ecosystems.

Nongame Wildlife Responses to Chaining of Pinyon-Juniper Woodlands

Nongame wildlife responses to chaining of pinyon-juniper (Pinus edulis-Juniperus osteosperma) woodland were studied in 1977 in the Piceance Basin, Colorado. Vegetation and small-mammal populations were sampled on a mature pinyon-juniper woodland (control) and areas chained 1, 8, and 15 years previously. Breeding-bird populations were studied on the areas chained 8 and 15 years previously, the control area, and on the edge between a mature woodland and an area chained 10 years previously. Ten species of breeding birds were observed on the unchained area, whereas only 3 and 4 species were observed on the 8and 15-year-old chained areas, respectively. Bird densities on the unchained area (29 territories/10 ha) were more than double those on the chained areas (11/10 ha). Five of 17 species breeding on the edge area used both vegetation types. Only 1 species was found exclusively on the edge area. Small mammals were more abundant on chained than unchained areas. Species composition of the catch varied among the chained and unchained areas; species diversity was greatest on the unchained area. Adverse effects on nongame wildlife could be minimized by favoring survival of shrubs and young trees, retaining selected cavity trees, and limiting widths of clearings when chaining pinyon-juniper. J. WILDL. MANAGE. 45(2):381-389 Pinyon-juniper woodlands dominate over 200,000 km2 of the southwestern United States (Lanner 1975). Vast areas of these woodlands have been cleared over the past 30 years to stimulate production of forage for big game and livestock. Chaining (dragging a heavy anchor chain between 2 bulldozers) has been and remains a method widely used for clearing tracts of pinyon-juniper (Short and McCulloch 1977). Major coal and oil shale deposits occur in the pinyon-juniper ecosystem. Mining of these deposits will result in appreciable impacts on local wildlife populations. Pinyon-juniper chaining has been employed in past mitigation efforts associated with energy developments (Voigt and Nagy 1979), and will provide a potential means of mitigating big game losses resulting from mining impacts. Despite the relatively large-scale use of pinyon-juniper chaining in the past, nongame wildlife responses to this habitat manipulation are poorly understood. A number of authors have described avian and small-mammal communities in pinyon-juniper woodlands (e.g., Hardy 1945; Miller 1946; Shepherd, unpubl. rep., Colorado Div. Wildl. Fed. Aid Proj. W-101-R-14, 1972; Austin and Urness 1976). The effects of clearing pinyon-juniper on small mammals have been studied to some extent (Turkowski and Reynolds 1970, Baker and Frischknecht 1973, Turkowski and Watkins 1976), but studies of the responses of bird communities to such habitat alterations are lacking. The objectives of this study were to: (1) describe vegetation, breeding-bird populations, and small-mammal populations on selected chained and unchained areas of pinyon-juniper woodland, (2) evaluate the effects of chaining on these 1 Present address: School of Forest Resources and Conservation, University of Florida, Gainesville, FL 32611. 2 Present address: Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI 48824. 3 Present address: Wyoming Game and Fish Department, Box 6249, Sheridan, WY 82801. J. Wildl. Manage. 45(2):1981 381 This content downloaded from 207.46.13.174 on Sun, 10 Jul 2016 04:51:45 UTC All use subject to http://about.jstor.org/terms 382 NONGAME WILDLIFE IN PINYON-JUNIPER. O'Meara et al. populations, and (3) formulate recommendations for maximizing benefits to this fauna when clearing pinyon-juniper for range improvement and wildlife mitigation. We acknowledge the field assistance of J. Gebhard, H. D. Gibbs, R. Kahn, and J. G. Mitchell, Colorado State University. R. F. Labisky, W. R. Marion, and T. E. Rogers, University of Florida, reviewed the manuscript. Funds for the study were provided by the U.S. Fish and Wildlife Service, Office of Biological Services, contracts 14-16-0008-2016 and 14-16-0008-

Distribution of Arceuthobium divaricatum and Phoradendron juniperinum (Viscaceae) on the South Rim of Grand Canyon, Arizona

The distribution and effects of the mistletoes Arceuthobium divaricatum Engelm. on Pinus edulis Engelm. and Phoradendron juniperinum Engelm. on Juniperus osteosperma (Torr.) Little on the pinyon-juniper vegetation type on the south rim of Grand Canyon National Park were investigated. Fire was the most limiting factor in the distribution of the mistletoes. The incidence of infection increased as trunk diameter and height increased in both pinyon and juniper. Arceuthobium divaricatum had the more serious impact on its host in respect to both vigor and mortality. Both mistletoes appear to be in equilibrium with their hosts at this time. Two mistletoes of the pinyon-juniper ecosystem of the Grand Canyon are Arceuthobium divaricatum Engelm. and Phoradendron juniperinum Engelm. Research on A. divaricatum and P. juniper- inum has been extremely limited because the trees infected have not been economically important as timber resources. With rising in- terest in utilization of the resources of the pinyon-juniper vegetation type, especially in a recreational capacity, effective management of these stands will be paramount in national parks and recreation areas (Clary 1975). Information on the site preferences and environmental factors that predispose the host trees to mistletoe infection will fa- cilitate management of diseased stands. This study was conducted to determine the distribution and effects of dwarf mistletoe on pinyon (Pinus edulis Engelm.) and true mistletoe on juniper (Juniperus osteosperma (Torr.) Little) on the South Rim at Grand Canyon Na- tional Park, Arizona.

The Role of Area, Heterogeneity, and Favorability in Plant Species Diversity of Pinyon-Juniper Ecosystems

The effects of area, environmental heterogeneity, and site favorability on plant species diversity and slope of the species—area curves were evaluated at thirty study sites in shrub—dominated communities within the pinyon—juniper zones of central Utah and northern New Mexico. Species diversity, as measured by total number of species per site, varies widely (24—87 species per hectare). Plant species diversity is highly correlated with increasing size of the area at each site (average r2 = .92). Environmental heterogeneity is also strongly positively heterogeneity account for > 98% of the variation in species number. Overall site heterogeneity and favorability combine to account for 74% of the observed variation in species number at Utah sites and 84% among New Mexico sites. Species diversity within these communities is largely controlled by two abiotic variables: (1) the amount of available moisture and (2) the number of different soil types within the site. Slope of the species—area curve (z—value) varies widely among the several study sites (.09—0.28). The observed values overlap expected z—values for continental communities. Environmental heterogeneity is shown to be positively associated with z—value. At Utah sites, heterogeneity of site solar irradiation, potential soil moisture, and soil depth explain 66% of the variation in z—values. At New Mexico sites, heterogeneity of solar irradiation, soil depth, and surface rock cover account for 90% of the variation in observed z—values.