Pinon Juniper Research Articles

Lee’s Tree

Out in these sparse pinon juniper woodson a rise between arroyos and far from anynarrow black snake of running watergrows a crone of a juniper several hundredyears old her trunk deeply scored and s...

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.

Heavy Seasonal Grazing on Central Arizona Piñon–Juniper Rangeland: Risky Business?

On the Ground • This pinon–juniper rangeland in central Arizona experienced heavy seasonal (late-spring/early-summer) grazing, but with above average, well-timed and evenly distributed precipitation for the time of year; both cool- and warm-season native grasses recovered. • If this study had been conducted on rangeland that was typically more heavily grazed, and more susceptible to erosion, and done later in the growing season, the risk of exceeding targeted end-of-season grazing utilization would have been greater. • Planning for, or reacting to, grazing utilization that exceeds targeted levels should take site-specific risk factors into consideration.

Reduced transpiration response to precipitation pulses precedes mortality in a piñon–juniper woodland subject to prolonged drought

Global climate change is predicted to alter the intensity and duration of droughts, but the effects of changing precipitation patterns on vegetation mortality are difficult to predict. Our objective was to determine whether prolonged drought or above-average precipitation altered the capacity to respond to the individual precipitation pulses that drive productivity and survival. We analyzed 5yr of data from a rainfall manipulation experiment in piñon-juniper (Pinus edulis-Juniperus monosperma) woodland using mixed effects models of transpiration response to event size, antecedent soil moisture, and post-event vapor pressure deficit. Replicated treatments included irrigation, drought, ambient control and infrastructure control. Mortality was highest under drought, and the reduced post-pulse transpiration in the droughted trees that died was attributable to treatment effects beyond drier antecedent conditions and reduced event size. In particular, trees that died were nearly unresponsive to antecedent shallow soil moisture, suggesting reduced shallow absorbing root area. Irrigated trees showed an enhanced response to precipitation pulses. Prolonged drought initiates a downward spiral whereby trees are increasingly unable to utilize pulsed soil moisture. Thus, the additive effects of future, more frequent droughts may increase drought-related mortality.

Variability of historical forest structure and fire across ponderosa pine landscapes of the Coconino Plateau and south rim of Grand Canyon National Park, Arizona, USA

We undertook reconstructions of historical ponderosa pine forest structure and fire regimes across an entire landscape to expand understanding of spatial variability in forest structure and dynamics. The study area includes the ponderosa pine forests of the Coconino Plateau, Arizona, USA. Using General Land Office survey data and newly developed methods, we examined surveyor descriptions of overstory and understory composition and structure across 60,998 ha. For 41,214 ha of forests, we reconstructed density, basal area, diameter-class distributions, and fire severity and used GIS to analyse their relationships with topography. Ponderosa pine forests were continuous in only 34 % of the 60,998 ha landscape. In 40 %, they were mixed with pinon–juniper, 24 % was pure pinon–juniper and 2 % were grass or shrubs. In ponderosa pine forests, the focus of this study, mean tree density was 144.2 trees ha−1; 18.8 % of the landscape had low tree density ( 200 trees ha−1). Small trees ( 50 % of all trees on 47 % of the landscape and large trees (>40 cm) composed >50 % of all trees on 21 % of the landscape. Low-severity fire likely structured the forest on 59 % of the landscape while 39 % was structured by mixed-severity fire, likely including small, patchy crown fires. Forest parameters displayed wide variability across environmental gradients. Broader-scale reconstructions revealed a much more spatially complex forest that was structured by wide range of fire severities. Variability in ponderosa pine forests was often under-reported in past studies, but is important in perpetuating biological diversity.

Density-Dependent Ecohydrological Effects of Piñon–Juniper Woody Canopy Cover on Soil Microclimate and Potential Soil Evaporation

Many rangeland processes are driven by microclimate and associated ecohydrological dynamics. Most rangelands occur in drylands where evapotranspiration normally dominates the water budget. In these water-limited environments plants can influence abiotic and biotic processes by modifying microclimate factors such as soil temperature and potential soil evaporation. Previous studies have assessed spatial variation in microclimate and associated ecohydrological attributes within an ecosystem (e.g., under vs. between woody canopies) or across ecosystems (e.g., with differing amounts of woody canopy cover), but generally lacking are assessments accounting systematically for both, particularly for evergreen woody plants. Building on recently quantified trends in near-ground solar radiation associated with a piñon–juniper gradient spanning 5% to 65% woody canopy cover, we evaluated trends in soil temperature and associated estimates of potential soil evaporation as a function of amount of woody canopy cover for sites overall and for associated canopy vs. intercanopy locations. Quantified soil temperature trends decreased linearly with increasing woody canopy cover for intercanopy as well as canopy patches, indicating the coalescing influence of individual canopies on their neighboring areas. Notably, intercanopy locations within high-density (65%) woody canopy cover could be as much as ∼10°C cooler than intercanopy locations within low-density (5%) cover. Corresponding potential soil evaporation rates in intercanopies within high-density woody canopy cover was less than half that for intercanopies within low density. Our results highlight ecohydrological consequences of density-dependent shading by evergreen woody plants on soil temperature and potential soil evaporation and enable managers to rapidly estimate and compare approximate site microclimates after assessing amounts of woody canopy cover. Such predictions of microclimate have general utility for improving management of rangelands because they are a fundamental driver of many key processes, whether related to understory forage and herbaceous species or to wildlife habitat quality for game or nongame species. Muchos procesos en los pastizales están definidos por microclimas y sus dinámicas ecohidrológicas asociadas. Muchos pastizales se localizan en zonas áridas donde la evapotranspiracio‘n normalmente es el flujo dominante del balance hídrico. En estos ambientes donde el agua es escasa, las plantas pueden influenciar procesos ecológicos, bióticos y abióticos, mediante la modificación de factores micro-climáticos, como temperatura del suelo el potencial de evaporación desde la superficie. Estudios previos han definido que la variación en microclimas y los atributos asociados con la eco-hidrología dentro de los ecosistemas (por ejemplo debajo del dosel vs. en espacios entre el dosel aé de dos árboles) o a través de los ecosistemas (por ejemplo con diferentes cantidades de cobertura de dosel). Sin embargo, se carece generalmente de la determinación sistemática de ambos, particularmente para las plantas arbustivas siempre verdes. Basándose en tendencias cuantificadas recientemente para la radiación solar cerca de suelo en un gradiente de pino-junípero abarcando una cubierta de 5% a 65% de cobertura de dosel, se evaluaron las tendencias en la temperatura del suelo y se desarrollaron estimaciones asociadas con el potencial de evaporación de suelo en función de la cantidad de cubierta arbórea tanto para sitios en general (en función de la cobertura), como para aquellos asociados con la cubierta contra sitios ubicados entre los árboles (no directamente debajo de las copas). Las temperaturas del suelo cuantificadas tendieron a decrecer linealmente con el incremento en la cobertura arbórea en los espacios entre árboles, asícomo los espacios cubiertos por los árboles, indicando la relación entre la influencia de las copas individuals sobre sus a‘reas vecinas. Notablemente, los espacios entre árboles dentro de lugares con altas densidades (65%) de cubierta arbórea pueden ser hasta 10uC más fríos que los espacios entre árboles dentro de una densidad baja de cobertura aérea (5%). Con respecto al potencial de las tasas de evaporación en los espacios entre árboles en las áreas con niveles altos de cubierta de dosel, resultó siendo menos de la mitad de la que ocurriría en espacios igualetne abiertos, pero localizados en zonas con baja cobertura de dosel arbóreo. Nuestros resultados resaltan los efectos eco-hidrológicos de la sombra producida por los árboles sobre la temperatura del suelo y el potencial de evaporación del suelo, y que dependen de la cantidad y densidad de árboles en el paisaje. Estos resultados permiten a los manejadores una rápida estimación y comparación del microclima en diversos sitios, después de determinar la cantidad de cubierta arbórea. Tales predicciones de microclimas tienen una utilidad general para mejorar el manejo de pastizales porque son fundamentales para muchos procesos esenciales, si se relacionan con pastos que se encuentran debajo de la cobertura arbórea, asícomo con las especies herbáceas o para la calidad del habitad de la vida silvestre de especies cinegéticas y no cinegéticas.

Redistribution of Runoff Among Vegetation Patch Types: On Ecohydrological Optimality of Herbaceous Capture of Run-On

A central tenant of ecohydrology in drylands is that runoff redistribution from bare to vegetated patches concentrates the key limiting resource of water, which can then enhance vegetation growth and biomass. Conversely, a reduction in vegetation patches, particularly those associated with herbaceous plants, can lead to a threshold-like response in which bare patches become highly interconnected, triggering a large increase in hillslope runoff and associated erosion. However, generally lacking is an assessment of how maximization of run-on to herbaceous patches relates to minimization of hillslope-scale runoff. To illustrate how runoff redistribution potentially changes in response to conversion of herbaceous patches to bare ones, we used a spatially distributed model, SPLASH (Simulator for Processes at the Landscape Surface–Subsurface Hydrology), with an example of a semiarid pinon–juniper woodland hillslope with seven combinations of bare and herbaceous patch cover, culminating in complete loss of herbaceous patches, for a 1-yr design storm. As expected, the amount of hillslope runoff increased curvilinearly with reductions in herbaceous cover as runoff per cell increased from bare patches and run-on per cell increased for herbaceous patches. Notably, the total amount of run-on to all herbaceous patches was greatest when the amount of bare cover was intermediate, highlighting a trade-off between the source area for generating runoff and the sink area for capturing run-on. The specific nature of patch–hillslope runoff redistribution responses certainly depends on several site-specific conditions, but the general nature of the response exhibited in our example simulation may be indicative of a general type of response applicable to many rangelands. We suggest that a more robust suite of such relationships could be valuable for managing rangelands by enabling explicit accounting for optimality and trade-offs in biomass per herbaceous patch, total herbaceous cover, and prevention of hillslope-scale connectivity of bare patches that triggers a large increase in runoff and associated erosion.

Habitat selection of rodents along a piñon–juniper woodland–savannah gradient

The biodiversity of pinon-juniper (P-J) woodlands of western North America has received increasing attention from conservationists because of concerns about woodland invasion into adjacent shrub-steppe communities. Small mammals contribute substantially to the faunal diversity of P-J woodlands, but the responses of small mammals to the inherent structural complexity of these woodlands have not been well described. We used occupancy modeling and ordination to describe habitat selection along a woodland-savannah gradient of 4 species of rodents, including 2 putative P-J woodland specialists, Peromyscus truei and Tamias dorsalis .W e accounted for the influences of season and prior conspecific capture on detectability. P. truei and T. dorsalis preferred old-growth woodland sites near rock outcrops with high canopy and bare-ground cover and low herb and shrub cover. Tamias minimus preferred savannah sites with high shrub and grass cover farther from rock outcrops. We found no evidence of resource selection along the gradient by Perognathus parvus. Our results provide insight into the role of habitat selection in facilitating coexistence among closely related species within P-J woodlands and suggest that management efforts that better discriminate between old, presettlement stands and young, invasive stands may enhance regional biodiversity. We demonstrate an effective application of occupancy modeling for describing habitat selection of cryptic rodents, which are particularly prone to imperfect detection. DOI: 10.1644/09-MAMM-A-060.1.

Historical and Modern Disturbance Regimes, Stand Structures, and Landscape Dynamics in Piñon–Juniper Vegetation of the Western United States

Pinon–juniper is a major vegetation type in western North America. Effective management of these ecosystems has been hindered by inadequate understanding of 1) the variability in ecosystem structure and ecological processes that exists among the diverse combinations of pinons, junipers, and associated shrubs, herbs, and soil organisms; 2) the prehistoric and historic disturbance regimes; and 3) the mechanisms driving changes in vegetation structure and composition during the past 150 yr. This article summarizes what we know (and don't know) about three fundamentally different kinds of pinon–juniper vegetation. Persistent woodlands are found where local soils, climate, and disturbance regimes are favorable for pinon, juniper, or a mix of both; fires have always been infrequent in these woodlands. Pinon–juniper savannas are found where local soils and climate are suitable for both trees and grasses; it is logical that low-severity fires may have maintained low tree densities before disruption of fire regimes following Euro-American settlement, but information is insufficient to support any confident statements about historical disturbance regimes in these savannas. Wooded shrublands are found where local soils and climate support a shrub community, but trees can increase during moist climatic conditions and periods without disturbance and decrease during droughts and following disturbance. Dramatic increases in tree density have occurred in portions of all three types of pinon–juniper vegetation, although equally dramatic mortality events have also occurred in some areas. The potential mechanisms driving increases in tree density—such as recovery from past disturbance, natural range expansion, livestock grazing, fire exclusion, climatic variability, and CO2 fertilization—generally have not received enough empirical or experimental investigation to predict which is most important in any given location. The intent of this synthesis is 1) to provide a source of information for managers and policy makers; and 2) to stimulate researchers to address the most important unanswered questions.

Piñon–Juniper Woodland Use by Cattle in Relation to Weather and Animal Reproductive State

We conducted a study to determine the role of pinon-juniper (PJ) woodland in providing shelter for cattle at a site in central New Mexico. Positions of 16 cows, 8 pregnant or nursing (PN) and 8 nonpregnant-nonlactating (NPNL), grazing a PJ woodland-grass steppe mosaic were recorded every 5 min by Global Positioning System during late winter and early spring in 2004 and 2005 (eight different cows in each year). Hourly weather variables were also recorded at a weather station located at our research site. Weekly fecal samples were collected from all collared cattle (n 5 16) to determine botanical composition of diets. Decreasing air temperatures, increasing relative humidity, winds out of the northwest (all of which are associated with heat loss), and increasing short-term thermal stress were associated with a detectable (P # 0.05) increase in PJ-woodland preference of PN and NPNL cows. Days to/from calving date was a significant predictor of PJ-woodland preference of PN cows (P # 0.05), which showed highest PJ-woodland preference on the day before or immediately after calving date. Preference for PJ woodland by all cows, averaged across the study period, increased with the increasing proportion of days with cold short-term thermal stress (P , 0.01) and decreasing availability of open shortgrass forage (P , 0.01). PN and NPNL cows exhibited detectably different grazing patterns (P 5 0.01). PN cows explored smaller areas (P , 0.01) and traveled shorter distances (P 5 0.053) than NPNL counterparts in any given day. Winterfat (Krascheninnikova lanata (Pursh) A. Meeuse & Smit) was the only plant species analyzed that was detectably more abundant (P 5 0.05) in NPNL vs. PN diets, particularly during the week surrounding calving in 2005. Our data suggest that PJ woodland with abundant understory can play an important role in providing shelter for nursing or dry cattle during winter, particularly in years when forage availability is scarce.

Predicting floodplain boundary changes following the Cerro Grande wildfire

AbstractA combined ArcView GIS–HEC modelling application for floodplain analysis of pre‐ and post‐burned watersheds is described. The burned study area is located on Pajarito Plateau near Los Alamos National Laboratory (the Laboratory), where the Cerro Grande Wildfire burned 42 878 acres (17 352 ha) in May 2000. This area is dominated by rugged mountains that are dissected by numerous steep canyons having both ephemeral and perennial channel reaches. Vegetation consists of pinon–juniper woodlands located between 6000 and 7000 ft (1829–2134 m) above mean sea level (MSL), and Ponderosa pine stands between 7000 and 10000 ft MSL (2134–3048 m). Approximately 17% of the burned area is located within the Laboratory, and the remainder is located in upstream or adjacent watersheds. Pre‐burn floodplains were previously mapped in 1990–91 using early HEC models as part of the hazardous waste site permitting process. Precipitation and stream gauge data provide essential information characterizing rainfall–runoff relationships before and after the fire. They also provide a means of monitoring spatial and temporal changes as forest recovery progresses. The 2000 summer monsoon began in late June and provided several significant runoff events for model calibration. HEC–HMS modelled responses were sequentially refined so that observed and predicted hydrograph peaks were matched at numerous channel locations. The 100 year, 6 h design storm was eventually used to predict peak hydrographs at critical sites. These results were compared with pre‐fire simulations so that new flood‐prone areas could be systematically identified. Stream channel cross‐sectional geometries were extracted from a gridded 1 ft (0·3 m) digital elevation model (DEM) using ArcView GIS. Then floodpool topwidths, depths, and flow velocities were remapped using the HEC–RAS model. Finally, numerous surveyed channel sections were selectively made at crucial sites for DEM verification. These evaluations provided timely guidance that influenced the decision to construct several flood detention structures that were completed in September 2000. Published in 2001 John Wiley & Sons, Ltd.

Coadaptations of the Clark's Nutcracker and the Pinon Pine for Efficient Seed Harvest and Dispersal

Clark's Nutcracker (Nucifraga columbiana) is one of four species of corvids that commences harvesting, transporting, and caching the seeds of pinon pine (Pinus edulis) in mid—August. Caching continues until inclement weather intervenes or the seed crop is depleted. Nutcrackers are efficient at collecting seeds from the trees because the birds discriminate edible and aborted seeds, select cones with higher than average number of good seeds and appear to concentrate on those trees that produce cones with large numbers of good seeds. The use of a sublingual pouch allows the nutcracker to carry up to 95 pinon pine seeds per trip (x = 55). A pouch full of seeds may be carried as far as 22 km from the collecting area (the pinon—juniper woodland, elevation ~ 1800 m) to communal caching areas where the seeds are buried in clumps in subterranean caches at a depth of 2 to 3 cm. These caching areas are on steep, south—facing slopes that are usually free of snow by late winter. Although solitary nesters, the birds, during the nonbreeding season, often form flocks when harvesting seeds. A flock of 150 nutcrackers cached between 3.3—5.0 X 106 pinon pine seeds in the autumn of a good cone crop. Each bird caches between 2.2 and 3.3 X its needed energetic requirements for the insect—free portion of the year. Some of the unrecovered seeds germinated and grew. The pinon pine reaches its highest density in relatively dry areas below the elevational range of other members of the genus Pinus, but ranges up to 3,100 m into the mixed coniferous forest. This pine has developed a number of traits that enhance its efficiency to be located and dispersed by the birds. The seeds are unusually large, of high energy value, and have relatively thin seed coats. The large size improves the germination potential of the seed but also attracts predators and dispersal agents. The seed coat color is markedly different for edible and aborted seeds, thus labeling them for visually oriented seed harvesters. Most pinon pine cones are oriented outward and upward which increases illumination of the seeds and tends to hold them in the cone. The pinon pine displays the seeds in its cones more readily than wind—dispersed pines by opening the seed—bearing cone scales to a uniform angle. Pinon pine seeds are retained for a long period of time in the cone because they are held in deep depressions on the cone scales by small flanges. This constellation of features indicated an evolutionary strategy on the part of the pinon pine to exploit and encourage members of the seed—caching guild to disperse the seeds. Deposition sites are presumably more favorable for germination than those obtained by simply broadcasting the seeds over a wide area. Individual seedlings potentially experience immediate intraspecific competition because the seeds are cached in clumps. Only one seedling, presumably the strongest, fastest—growing individual, survives. The benefits of this system to the nutcracker are that the bird has a supply of energy for the most unproductive months of the year. The bird also breeds in late winter or early spring, using the stored seeds for reproductive energy.

Mechanisms of Competitive Exclusion Between Two Species of Chipmunks

Two species of chipmunks, Eutamias dorsalis and E. umbrinus exclude each other from certain elevations on isolated mountain ranges in the central Great Basin. Competitive success is determined by habitat; dorsalis excludes umbrinus from the sparse pinon—juniper forests at lower elevations and umbrinus excludes dorsalis from the denser forests at higher altitudes. The two species occur together only in a very narrow strip of intermediate habitat. Observation of the behavior and interactions of the two species within this overlap zone resulted in the following explanation for the mutual exclusion. E. dorsalis, the more aggressive and more terrestrial species, chases umbrinus from those areas where the trees are so widely spaced that umbrinus must flee on the ground. The competitive advantage immediately shifts to the more social and arboreal umbrinus when the trees are sufficiently large and dense that their branches interlock. In these habitats umbrinus readily escapes dorsalis by fleeing through the trees over routes that the more aggressive species cannot follow. In such situations the aggressive nature of dorsalis actually becomes competitively disadvantageous because the more social umbrinus is so numerous that dorsalis wastes a great deal of time and energy on fruitless chases. The differences between the two species in aggressive behavior apparently represent adaptations to the density of cover and food resources in their habitats. The main mechanisms of the competitive interaction between these two chipmunks (interspecific aggression, the ability of the subordinate species to utilize some feature of the habitat to escape from the dominant species, and aggressive neglect on the part of the dominant species) may frequently be important in cases of competitive exclusion between highly mobile animals.