Juniper Woodlands Research Articles

Optimizing regulatory requirements to aid in the implementation of compensatory mitigation

Optimizing regulatory requirements to aid in the implementation of compensatory mitigation

Water limitations on forest carbon cycling and conifer traits along a steep climatic gradient in the Cascade Mountains, Oregon

Abstract. Severe droughts occurred in the western United States during recent decades, and continued human greenhouse gas emissions are expected to exacerbate warming and drying in this region. We investigated the role of water availability in shaping forest carbon cycling and morphological traits in the eastern Cascade Mountains, Oregon, focusing on the transition from low-elevation, dry western juniper (Juniperus occidentalis) woodlands to higher-elevation, wetter ponderosa pine (Pinus ponderosa) and grand fir (Abies grandis) forests. We examined 12 sites in mature forests that spanned a 1300 mm yr−1 gradient in mean growing-year climate moisture index (CMIgy ), computed annually (1964 to 2013) as monthly precipitation minus reference evapotranspiration and summed October to September. Maximum leaf area, annual aboveground productivity, and aboveground live tree biomass increased with CMIgy (r2 = 0.67–0.88, P < 0.05), approximately 50-, 30-, and 10-fold along this drier to wetter gradient. Interannual fluctuations in CMI affected the annual radial growth of 91 % of juniper, 51 % of pine, and 12 % of fir individuals from 1964 to 2013. The magnitude of the site-average growth–CMI correlations decreased with increased CMIgy (r2 = 0.53, P < 0.05). All three species, particularly fir, experienced pronounced declines in radial growth from c. 1985 to 1994, coinciding with a period of sustained below-average CMIgy and extensive insect outbreak. Traits of stress-tolerant juniper included short stature, high wood density for cavitation resistance, and high investment in water transport relative to leaf area. Species occupying wetter areas invested more resources in height growth in response to competition for light relative to investment in hydraulic architecture. Consequently, maximum tree height, leaf area : sapwood area ratio, and stem wood density were all correlated with CMIgy . The tight coupling of forest carbon cycling and species traits with water availability suggests that warmer and drier conditions projected for the 21st century could have significant biogeochemical, ecological, and social consequences in the Pacific Northwest.

Seasonal burning of juniper woodlands and spatial recovery of herbaceous vegetation

Decreased fire activity has been recognized as a main cause of expansion and infilling of North American woodlands. Piñon-juniper (Pinus-Juniperus) woodlands in the western United States have expanded in area 2–10-fold since the late 1800s. Woodland control measures using chainsaws, heavy equipment and prescribed fire are used to restore big sagebrush (Artemisia tridentata Nutt.) steppe plant communities and reduce woody fuel loading. Immediate objectives in the initial control of piñon-juniper are; (1) recovery of perennial herbaceous species to restore site composition, structure and processes (resilience) and resist invasion and dominance by invasive annual grasses (resistance) and (2) reducing woody fuel accumulations. Spanning a 7year period (2006–2012), we compared herbaceous recovery following cutting and prescribed fire on three sites in mid and late succession western juniper (Juniperus occidentalis spp. occidentalis Hook.) woodlands in southeast Oregon. Treatments were untreated controls, partial cutting followed by fall broadcast burning (SEP), clear-cut and leave (CUT), and clear-cut and burn in winter (JAN), and spring (APR). Cover of herbaceous species was measured in three zones; interspace, litter mats around tree stumps (stump), and beneath felled trees. In interspace zones of all treatments, comprising between 51% and 63% of site areas, perennial bunchgrasses dominated two sites and co-dominated with invasive annual grasses at one site after treatment. Burning in the JAN treatments, when fuel moisture and relative humidity were high and temperatures cooler, reduced disturbance severity in stump and felled tree zones, which maintained perennial herbaceous understories and prevented or limited the presence of invasive annuals. Burning felled juniper in SEP and APR treatments resulted in moderate to high fire severity in stump and felled tree zones. At two sites, these fires consumed all fuel up to the 1000-h fuel class, largely eliminated herbaceous perennials, and created islands within treatments that enhanced annual grass invasion and dominance. To maintain or boost site resilience and resistance following control of late successional woodlands, reducing piñon-juniper fuels by burning in winter provides managers with a low-impact option for conserving sagebrush steppe.

Canopy Interception for a Tallgrass Prairie under Juniper Encroachment

Rainfall partitioning and redistribution by canopies are important ecohydrological processes underlying ecosystem dynamics. We quantified and contrasted spatial and temporal variations of rainfall redistribution for a juniper (Juniperus virginiana, redcedar) woodland and a tallgrass prairie in the south-central Great Plains, USA. Our results showed that redcedar trees had high canopy storage capacity (S) ranging from 2.14 mm for open stands to 3.44 mm for closed stands. The canopy funneling ratios (F) of redcedar trees varied substantially among stand type and tree size. The open stands and smaller trees usually had higher F values and were more efficient in partitioning rainfall into stemflow. Larger trees were more effective in partitioning rainfall into throughfall and no significant changes in the total interception ratios among canopy types and tree size were found. The S values were highly variable for tallgrass prairie, ranging from 0.27 mm at early growing season to 3.86 mm at senescence. As a result, the rainfall interception by tallgrass prairie was characterized by high temporal instability. On an annual basis, our results showed no significant difference in total rainfall loss to canopy interception between redcedar trees and tallgrass prairie. Increasing structural complexity associated with redcedar encroachment into tallgrass prairie changes the rainfall redistribution and partitioning pattern at both the temporal and spatial scales, but does not change the overall canopy interception ratios compared with unburned and ungrazed tallgrass prairie. Our findings support the idea of convergence in interception ratio for different canopy structures under the same precipitation regime. The temporal change in rainfall interception loss from redcedar encroachment is important to understand how juniper encroachment will interact with changing rainfall regime and potentially alter regional streamflow under climate change.

Drought-induced piñon mortality alters the seasonal dynamics of microbial activity in piñon–juniper woodland

Piñon (Pinus edulis) – Juniper (Juniperus monosperma) (PJ) woodlands cover 17+ million hectares in the western USA. These woodlands have been particularly sensitive to recent changes in climate, with drought induced die-offs of piñon occurring across 1.5 million ha, since 2000, triggering large changes in the structure and function of these biomes. To assess the effects of this large scale mortality on soil processes, we analyzed rhizosphere extracellular enzyme activity (EEA) and fungal biomass in soil samples collected beneath tree canopies at two piñon–juniper woodland sites: one site where piñons were experimentally killed by girdling, and a paired intact site with no piñon mortality that served as a reference. We also quantified soil water content (SWC) from soil samples, and sap flow density fluxes as an indicator of tree physiological status. Soil EEA patterns varied as functions of the identity of the closest competitor trees, host-tree physiological status, and SWC. At the girdled site, we observed higher plant cell wall related decomposition activities under live juniper canopies, compared to dead piñon trees. In contrast, at the control site, we observed higher plant cell wall decomposition rates under live piñon rather than juniper canopies, particularly with higher soil moisture availability. At the site level, ordination plots for intact PJ woodlands showed a decreasing trend in microbial cell wall decomposition activity as soil water availability, and fungal biomass increased. We observed the opposite trend at the girdled site. Overall, these results suggest that widespread piñon mortality significantly affects the functional behavior of rhizosphere microorganisms at multiple scales, in part by shifting the focal substrates of microbial community decomposition.

Биоразнообразие фитоценозов заповедника «Утриш»

We consider data on a variety of different forest forming tree species in a unique facility of Mediterranean flora on Russian territory – State Nature Reserve "Utrish." Conifers are represented by three species of junipers (Juniperus exelsa Bieb., Juniperus foetidissima Willd., Juniperus oxycedrus L.), Rinus kochiana Klotsc, Pinus pityusa Stev., Taxus baccata L. Greek Juniper is a dominating one on the area of 563.2 hectares, followed by prickly juniper (52.8 ha) and stinking juniper (38.9 ha). Their age is ranged from 121 to 141 years. The average height of juniper woodlands, where juniper stands as forest formimg species ranges from 5.4 m, with an average diameter of 16.3 cm for forests with Juniperus oxycedrus dominance to 7.6 m with an average diameter of 27.1 cm, in the case of Juniperus foetidissima and 6.9 m with an average diameter of 26.2 cm for Juniperus exelsa. Hardwoods dominate in the composition of forests in the reserve. Oak forests cover an area of about 7500 hectares. Large areas are under European ash forests dedicated to wetter conditions in the valleys in the crevices and flattened sheltered gullies. Examples of these types are associated with forests and the dominance of the Caucasian hornbeam, field maple. Carpinus orientalis usually playing a role in the undergrowth juniper stands and oak forests with dominance of pubescent oak forms plantations in clearings. Conifers are dominant in the coastal part of the reserve, and oak forests are basic phytocenoses forming the forest reserve "Utrish".

Anchor Chaining’s Influence on Soil Hydrology and Seeding Success in Burned Piñon-Juniper Woodlands

Broadcast seeding is one of the most commonly applied rehabilitation treatments for the restoration of burned piñon and juniper woodlands, but the success rate of this treatment is notoriously low. In piñon-juniper woodlands, postfire soil−water repellency can impair seeding success by reducing soil−water content and increasing soil erosion. Implementing anchor chaining immediately after seeding can improve establishment of seeded species by enhancing seed-to-soil contact and may improve restoration success by decreasing soil−water repellency through soil tillage. The objectives of this research were to 1) determine if anchor chaining in postfire pinyon-juniper woodlands diminishes soil−water repellency, and 2) determine meaningful relationships between soil−water repellency, unsaturated hydraulic conductivity [K(h)], and the establishment of seeded and invasive species. Research was conducted on two study sites, each located on a burned piñon-juniper woodland that had severe water repellency and that was aerially seeded. At each location, plots were randomly located in similar ecological sites of chained and unchained areas. At one location, anchor chaining considerably improved soil hydrologic properties, reducing the severity and thickness of the water-repellent layer, and increasing soil K(h) 2- to 4-fold in the first 2 yr following treatment. At this same location, anchor chaining increased perennial grass cover 16-fold and inhibited annual grass and annual forb cover by 5- and 7-fold, respectively. Results from the second site only showed improvements in soil K(h); other hydrologic and vegetative treatment responses were not significantly improved. Overall, this research suggests that anchor chaining has the potential to improve restoration outcomes, though additional research is warranted for understanding the direct impact of anchor chaining on soil−water repellency without the interaction of a seeding treatment.

Biological Soil Crust Response to Late Season Prescribed Fire in a Great Basin Juniper Woodland

Expansion of juniper on U.S. rangelands is a significant environmental concern. Prescribed fire is often recommended to control juniper. To that end, a prescribed burn was conducted in a Great Basin juniper woodland. Conditions were suboptimal; fire did not encroach into mid- or late-seral stages and was patchy in the early-seral stage. This study evaluated the effects of the burn on biological soil crusts of early-seral juniper. Fire reduced moss cover under sagebrush and in shrub interspaces. Mosses were rare under juniper; their cover was unaffected there. Lichens were uncommon under juniper and sagebrush and therefore not significantly impacted there. Their cover was greater in shrub interspaces, but because the fire was spotty and of low intensity, the effects of burning were minimal. Compared with unburned plots, the biomass of cyanobacteria was diminished under juniper and sagebrush; it was reduced in the interspaces in both burned and unburned plots, presumably in response to generally harsher conditions in the postburn environment. Nitrogen fixation rates declined over time in juniper plots and interspaces but not in sagebrush plots. Although fire negatively affected some biological soil crust organisms in some parts of the early-seral juniper woodland, the overall impact on the crusts was minimal. If the intent of burning is to reduce juniper, burning of early-seral juniper woodland is appropriate, as most affected trees were killed. Control of sagebrush can likewise be accomplished by low-intensity, cool season fires without eliminating the crust component. Intense fire should be avoided due to the potential for greater encroachment into the shrub interspaces, which contain the majority of biological soil crust organisms. Burning early-seral juniper may be preferred for controlling juniper encroachment on rangeland.

Prolonged experimental drought reduces plant hydraulic conductance and transpiration and increases mortality in a piñon–juniper woodland

Plant hydraulic conductance (ks) is a critical control on whole-plant water use and carbon uptake and, during drought, influences whether plants survive or die. To assess long-term physiological and hydraulic responses of mature trees to water availability, we manipulated ecosystem-scale water availability from 2007 to 2013 in a piñon pine (Pinus edulis) and juniper (Juniperus monosperma) woodland. We examined the relationship between ks and subsequent mortality using more than 5 years of physiological observations, and the subsequent impact of reduced hydraulic function and mortality on total woody canopy transpiration (EC) and conductance (GC). For both species, we observed significant reductions in plant transpiration (E) and ks under experimentally imposed drought. Conversely, supplemental water additions increased E and ks in both species. Interestingly, both species exhibited similar declines in ks under the imposed drought conditions, despite their differing stomatal responses and mortality patterns during drought. Reduced whole-plant ks also reduced carbon assimilation in both species, as leaf-level stomatal conductance (gs) and net photosynthesis (An) declined strongly with decreasing ks. Finally, we observed that chronically low whole-plant ks was associated with greater canopy dieback and mortality for both piñon and juniper and that subsequent reductions in woody canopy biomass due to mortality had a significant impact on both daily and annual canopy EC and GC. Our data indicate that significant reductions in ks precede drought-related tree mortality events in this system, and the consequence is a significant reduction in canopy gas exchange and carbon fixation. Our results suggest that reductions in productivity and woody plant cover in piñon–juniper woodlands can be expected due to reduced plant hydraulic conductance and increased mortality of both piñon pine and juniper under anticipated future conditions of more frequent and persistent regional drought in the southwestern United States.

Generalization and evaluation of the process‐based forest ecosystem model PnET‐CN for other biomes

Terrestrial ecosystems play an important role in carbon, water, and nitrogen cycling. Process‐based ecosystem models, including PnET‐CN, have been widely used to simulate ecosystem processes during the last two decades. PnET‐CN is a forest ecosystem model, originally designed to predict ecosystem carbon, water, and nitrogen dynamics of temperate forests under a variety of circumstances. Among terrestrial ecosystem models, PnET‐CN offers unique benefits, including simplicity and transparency of its structure, reliance on data‐driven parameterization rather than calibration, and use of generalizeable relationships that provide explicit linkages among carbon, water and nitrogen cycles. The objective of our study was to apply PnET‐CN to non‐forest biomes: grasslands, shrublands, and savannas. We determined parameter values for grasslands and shrublands using the literature and ecophysiological databases. To assess the usefulness of PnET‐CN in these ecosystems, we simulated carbon and water fluxes for six AmeriFlux sites: two grassland sites (Konza Prairie and Fermi Prairie), two open shrubland sites (Heritage Land Conservancy Pinyon Juniper Woodland and Sevilleta Desert Shrubland), and two woody savanna sites (Freeman Ranch and Tonzi Ranch). Grasslands and shrublands were simulated using the biome‐specific parameters, and savannas were simulated as mixtures of grasslands and forests. For each site, we used flux observations to evaluate modeled carbon and water fluxes: gross primary productivity (GPP), ecosystem respiration (ER), net ecosystem productivity (NEP), evapotranspiration (ET), and water yield. We also evaluated simulated water use efficiency (WUE). PnET‐CN generally captured the magnitude, seasonality, and interannual variability of carbon and water fluxes as well as WUE for grasslands, shrublands, and savannas. Overall, our results show that PnET‐CN is a promising tool for modeling ecosystem carbon and water fluxes for non‐forest biomes (grasslands, shrublands, and savannas), and especially for modeling GPP in mature biomes. Limitations in model performance included an overestimation of seasonal variability in GPP and ET for the two shrubland sites and overestimation of early season ER for the two shrubland sites and Freeman Ranch. Future modifications of PnET‐CN for non‐forest biomes should focus on belowground processes, including water storage in dry shrubland soils, root growth and respiration in grasslands, and soil carbon fluxes for all biomes.

Structural and regenerative changes in old-growth piñon–juniper woodlands following drought-induced mortality

Two decades of drought and rising temperatures have triggered bark beetle outbreaks and extensive mortality of Colorado piñon (Pinus edulis) and Utah juniper (Juniperus osteosperma) across the southwest US. For example from 2002 to 2005, over one-third of the piñons in Mesa Verde National Park’s old-growth woodlands were killed by the bark beetle Ips confusus and other drought-related factors. Extensive wildfires have also burned through the Park over the last two decades, reducing the extent of old-growth woodlands by nearly one-half. We compared historical (1970–1990s) and recent (2005–2011) data to gauge the effects of the 2002–2005 mortality event on canopy structure, woody surface fuels, and tree recruitment. Large, mature piñons were the most susceptible to mortality; we measured significant reductions in piñon cover and diameter. Due to the loss of large trees, woodlands that were subjected to substantial mortality had reduced structural complexity relative to nearby unaffected stands. In a longitudinal fuels comparison, 2010–2011 fuels were compared to historical 1993 values in the same plots; we could not detect a change in woody fuel load. However when the 2010–2011 fuels are compared across mortality severity classes, there was a trend toward slightly greater 1–100h, greater 1000h fuel loads, and more litter in stands with higher levels of tree mortality. However, modeled surface fire behavior did not differ across mortality severity classes. Modeled crown fires needed higher wind speeds to spread from tree to tree in stands without tree mortality, but this is likely due to the inherently more open canopy structure in stands that resisted mortality rather than due to tree mortality per se. Post-mortality piñon reproduction and recruitment were recorded from 2005 to 2011 and compared with NPS monitoring data from 1975 to 1995. Cone production in 2005 was comparable to historical trends, but recent seedling and sapling densities were significantly below historical values. Yearly seedling and sapling density in 1975–2011 was positively correlated with precipitation during the sampling year and two years prior. The largest proportion of seedlings and saplings occurred under piñon or juniper canopies, and a smaller proportion under native shrubs. Given the loss of a substantial component of the adult trees, reduced stand structural complexity, and demonstrated need for moist conditions and nurse plants for effective recruitment, these old-growth woodlands may be vulnerable to decline under future warm and dry climate projections. Management strategies focusing on maintaining structural features of both the overstory and understory could help provide conditions for sustainable recruitment and contribute to the goal of conservation of rare old-growth piñon–juniper woodlands.

Packrat middens and the Holocene palaeohistory of Colorado piñon (Pinus edulis) in western Colorado

AbstractAimOur aim was to determine the age and dispersal history of Colorado piñon (Pinus edulis) in western Colorado during the early to late Holocene using radiocarbon‐dated needles and nutshells from packrat (Neotoma spp.) middens.LocationThe Uncompahgre Plateau (UP) comprises more than 600,000 ha of public and private lands in west‐central Colorado, USA. Elevations within UP range from 1400 to 3140 m and it is characterized by numerous deep canyons and flat‐topped mesas. The Upper Gunnison Basin (UGB) encompasses a 243,000‐ha area enclosed within the southern Rocky Mountains in south‐western Colorado, USA. It spans 2200–4300 m in elevation, with no outlet apart from the Black Canyon of the Gunnison lower than 2650 m.MethodsMiddens were sampled by breaking off small sections of solidified deposits located in caves and crevices that were then disaggregated in water with repeated rinsing to separate all the plant remains. Single conifer needles and nutshells from 28 middens were radiocarbon dated to determine the age and timing of dispersal into western Colorado.ResultsThirty‐two midden samples were collected, of which 28 produced identifiable plant remains that were radiocarbon dated. Piñon needles and/or nutshells were identified and radiocarbon dated from 20 of these middens from seven localities in UP. The results indicated that piñon did not become established in UP until c. 6000 yr bp, which contrasts with the nearby UGB, where piñon charcoal has been identified from seven archaeological sites with dates ranging from 8000 to 3000 yr bp.Main conclusionsOur data are consistent with a model of late Pleistocene/early Holocene piñon migration into the Colorado Plateau from Arizona and New Mexico before becoming established in western Colorado. The timing of the piñon migration into south‐central Colorado along the Rio Grande corridor from New Mexico remains uncertain. While piñon–juniper woodlands currently dominate the lower elevations of UP, piñon had disappeared from UGB by c. 3000 yr bp and remains absent there today except for a few isolated trees.

Fuel Reduction, Seeding, and Vegetation in a Juniper Woodland

Western juniper has increased in density and distribution in the interior Pacific Northwest since the late 1800s. Management goals for many juniper woodlands are now focused on reducing tree densities and promoting biodiversity, prompting the use of fuel reduction treatments. Fuel reduction often involves mechanical cutting and disturbances such as slash pile burning and skid trail formation. While these activities may reduce tree densities, the extent to which they will restore native biodiversity and community composition, particularly in woodlands invaded by exotic annual grasses, is unclear. We evaluated the effects of juniper cutting in two experiments of disturbance type (slash piles and skid trails) followed by three native seeding treatments (cultivar, locally sourced, and no seed) on vegetation in central Oregon. Prior to cutting, native perennial grass cover and richness were positively associated and exotic grass cover was negatively associated with juniper basal area. After cutting and 2 yr after seeding, species composition was altered for both disturbance types. Some seeded areas had higher total species richness, higher native species richness, higher cover of seeded species, and higher overall cover compared to areas that were not seeded. But seeding effectiveness in mitigating exotic species spread varied based on exotic species functional group, pretreatment propagule pressure, and experiment disturbance type. Neither seed mix lowered exotic grass cover. There was limited evidence that the cultivar mix outperformed the locally sourced native seed mix. In the short term, fuel reduction activities may have facilitated further conversion of this woodland to an exotic grassland, but longer-term evaluation is needed. In juniper woodlands that have been invaded by exotic species, fuel reduction activities may facilitate further invasion, and exotic species control may be needed to limit invasion and promote native vegetation.

Vegetation Management Across Colorado Plateau BLM Lands: 1950–2003

Large tracts of land across the western United States have been managed over the last century in an effort to increase forage production, reduce the risk of wildland fires, and/or restore ecosystem structure and function. Yet documentation of this land-treatment history is lacking. With the use of data collected from Bureau of Land Management (BLM) field offices across the Colorado Plateau, we quantified the number, spatial extent, and implementation cost of tree-reduction and seeding treatments done in piñon (Pinus edulis)–juniper (Juniperus osteosperma, Juniperus monophylla, Juniperus scopulorum) woodlands between 1950 and 2003. Over 247 000 hectares of land were treated, corresponding to 6.6% of the piñon–juniper vegetation type within BLM-owned lands. Tree-reduction treatments involving chaining, bulldozing, or cabling were most prevalent between the 1950s and 1970s, with over 163 000 ha of land treated with these methods. Prescribed burning became increasingly prevalent in the 1980s, with over 43 000 ha burned. In more recent years, hydroaxe treatments have become common (4 400 ha treated), but to a much lesser extent than prescribed burns. Over 60% of these tree-reduction treatments were done in conjunction with revegetation or seeding treatments. Implementation costs of these tree-reduction treatments were over $26.7 million, with the hydroaxe treatment having nearly three times the cost of implementation than all other tree-reduction treatments. The spatial extent of these tree-reduction treatments and associated implementation costs highlight the importance of research examining the efficacy of these treatments and the potential legacy effects. The land-use history reported in this study and the accompanying freely accessible on-line database is a useful tool to guide research and management objectives and methodology.

Different intra- and interspecific facilitation mechanisms between two Mediterranean trees under a climate change scenario.

In harsh environments facilitation alleviates biotic and abiotic constraints on tree recruitment. Under ongoing drier climate change, we expect facilitation to increase as a driver of coexistence. However, this might not hold under extreme abiotic stress and when the outcome depends on the interaction with other drivers such as altered herbivore pressure due to land use change. We performed a field water-manipulation experiment to quantify the importance of facilitation in two coexisting Mediterranean trees (dominant Juniperus thurifera and coexisting Quercus ilex subsp. ballota) under a climate change scenario. Shifts in canopy dominance favouring Q. ilex could be based on the extension of heterospecific facilitation to the detriment of conspecific alleviation. We found that saplings of both species transplanted under the canopy of nurse trees had greater survival probability, growth and photochemical efficiency. Intra- and interspecific facilitation mechanisms differed: alleviation of abiotic stress benefited both species during summer and J. thurifera during winter, whereas browsing protection was relevant only for Q. ilex. Facilitation was greater under the dry treatment only for Q. ilex, which partially agreed with the predictions of the stress gradient hypothesis. We conclude that present rainfall availability limits neither J. thurifera nor Q. ilex establishment. Nevertheless, under current global change scenarios, imposing increasing abiotic stress together with altered herbivore browsing, nurse trees could differentially facilitate the establishment of Q. ilex due to species-specific traits, i.e. palatability; drought, heat and cold tolerance, underlying species differences in the facilitation mechanisms and eventually triggering a change from pure juniper woodlands to mixed formations.

Utilizing National Agriculture Imagery Program Data to Estimate Tree Cover and Biomass of Piñon and Juniper Woodlands

With the encroachment of piñon (Pinus ssp.) and juniper (Juniperus ssp.) woodlands onto sagebrush steppe rangelands, there is an increasing interest in rapid, accurate, and inexpensive quantification methods to estimate tree canopy cover and aboveground biomass. The objectives of this study were 1) to evaluate the relationship and agreement of piñon and juniper (P-J) canopy cover estimates, using object-based image analysis (OBIA) techniques and National Agriculture Imagery Program (NAIP, 1-m pixel resolution) imagery with ground measurements, and 2) to investigate the relationship between remotely-sensed P-J canopy cover and ground-measured aboveground biomass. For the OBIA, we used eCognition® Developer 8.8 software to extract tree canopy cover from NAIP imagery across 12 P-J woodlands within the Sagebrush Steppe Treatment Evaluation Project (SageSTEP) network. The P-J woodlands were categorized based on the dominant tree species found at the individual sites for the analysis (western juniper, Utah juniper, and mixed P-J community). Following tree canopy cover extractions, relationships were assessed between remotely-sensed canopy cover and ground-measured aboveground biomass. Our OBIA estimates for P-J canopy cover were highly correlated with ground-measured tree canopy cover (averaged across all regions r = 0.92). However, differences between methods occurred for western and Utah juniper sites (P < 0.05), and were more prominent where tree canopy cover was > 40%. There were high degrees of correlation between predicted aboveground biomass estimates with the use of remotely-sensed tree canopy cover and ground-measured aboveground biomass (averaged across all regions r = 0.89). Our results suggest that OBIA methods combined with NAIP imagery can provide land managers with quantitative data that can be used to evaluate P-J woodland cover and aboveground biomass rapidly, on broad scales. Although some accuracy and precision may be lost when utilizing aerial imagery to identify P-J canopy cover and aboveground biomass, it is a reasonable alternative to ground monitoring and inventory practices.

Multidisciplinary, Multisite Evaluation of Alternative Sagebrush Steppe Restoration Treatments: The SageSTEP Project

This special issue presents short-term ecological effects of restoration treatments imposed as part of the Sagebrush Steppe Treatment Evaluation Project (SageSTEP), and summarizes public attitude survey results related to restoration efforts. Funded by the US Joint Fire Science Program (JFSP; 2005– 2011), the Bureau of Land Management (BLM; 2011 to present), the National Interagency Fire Center (2011 to present), and the US Fish and Wildlife Service (2010), SageSTEP was designed and implemented to provide treatment-related information to managers concerned about the rapidly changing condition of sagebrush steppe ecosystems in the US Interior West (McIver et al. 2010). At lower elevations, cheatgrass has become more dominant at the expense of native perennial bunchgrasses, in some locations shifting fire return intervals from.50–100 yr to,20 yr, and greatly increasing mean fire size (Whisenant 1990; Miller et al. 2011; Balch et al. 2012). At higher elevations, pinon pine and juniper woodlands have expanded and displaced sagebrush and other shrubs, in some places shifting fire return intervals from 10–50 yr to..50 yr, and significantly increasing mean fire severity (Miller and Heyerdahl 2008). Federal, state, and private land managers and owners have for many years attempted to arrest the conversion of sagebrush steppe communities into woodland and annual grassland and to restore native herbaceous communities by applying treatments such as prescribed fire, mowing, chaining, cutting, mastication, or herbicides. Substantial published information exists on the efficacy of such treatments in sagebrush steppe, but most studies are site-specific, short-term (Miller et al. 2013), and focused on few variables. Recognizing this, the BLM, in collaboration with the JFSP, solicited sagebrush steppe scientists and managers to design SageSTEP, a study that provides multisite, multidisciplinary, long-term information on treatment outcomes over a range of ecological conditions, and that also provides insight on cost and public acceptance of management practices. A planning grant was provided by JFSP in 2003 to design SageSTEP, and the study was ultimately funded by JFSP in 2005. SageSTEP addresses four principle objectives, each linked to one or more of the design features of the study:

Response of Conifer-Encroached Shrublands in the Great Basin to Prescribed Fire and Mechanical Treatments

In response to the recent expansion of piñon and juniper woodlands into sagebrush-steppe communities in the northern Great Basin region, numerous conifer-removal projects have been implemented, primarily to release understory vegetation at sites having a wide range of environmental conditions. Responses to these treatments have varied from successful restoration of native plant communities to complete conversion to nonnative invasive species. To evaluate the general response of understory vegetation to tree canopy removal in conifer-encroached shrublands, we set up a region-wide study that measured treatment-induced changes in understory cover and density. Eleven study sites located across four states in the Great Basin were established as statistical replicate blocks, each containing fire, mechanical, and control treatments. Different cover groups were measured prior to and during the first 3 yr following treatment. There was a general pattern of response across the wide range of site conditions. There was an immediate increase in bare ground and decrease in tall perennial grasses following the fire treatment, but both recovered by the second or third growing season after treatment. Tall perennial grass cover increased in the mechanical treatment in the second and third year, and in the fire treatment cover was higher than the control by year 3. Nonnative grass and forb cover did not increase in the fire and mechanical treatments in the first year but increased in the second and third years. Perennial forb cover increased in both the fire and mechanical treatments. The recovery of herbaceous cover groups was from increased growth of residual vegetation, not density. Sagebrush declined in the fire treatment, but seedling density increased in both treatments. Biological soil crust declined in the fire treatment, with no indications of recovery. Differences in plant response that occurred between mechanical and fire treatments should be considered when selecting management options.

Limits to understory plant restoration following fuel-reduction treatments in a piñon-juniper woodland.

National fuel-reduction programs aim to reduce the risk of wildland fires to human communities and to restore forest and rangeland ecosystems to resemble their historical structure, function, and diversity. There are a number of factors, such as seed bank dynamics, post-treatment climate, and herbivory, which determine whether this latter goal may be achieved. Here, we examine the short-term (2 years) vegetation response to fuel-reduction treatments (mechanical mastication, broadcast burn, and pile burn) and seeding of native grasses on understory vegetation in an upland piñon-juniper woodland in southeast Utah. We also examine how wildlife herbivory affects the success of fuel-reduction treatments. Herbaceous cover increased in response to fuel-reduction treatments in all seeded treatments, with the broadcast burn and mastication having greater increases (234 and 160 %, respectively) in herbaceous cover than the pile burn (32 %). In the absence of seeding, herbaceous cover only increased in the broadcast burn (32 %). Notably, fuel-reduction treatments, but not seeding, strongly affected herbaceous plant composition. All fuel-reduction treatments increased the relative density of invasive species, especially in the broadcast burn, which shifted the plant community composition from one dominated by perennial graminoids to one dominated by annual forbs. Herbivory by wildlife reduced understory plant cover by over 40 % and altered plant community composition. If the primary management goal is to enhance understory cover while promoting native species abundance, our study suggests that mastication may be the most effective treatment strategy in these upland piñon-juniper woodlands. Seed applications and wildlife exclosures further enhanced herbaceous cover following fuel-reduction treatments.

Non-equilibrium hillslope dynamics and irreversible landscape changes at a shifting pinyon–juniper woodland ecotone

Pinyon–juniper woodlands of the western United States frequently exist within topographically complex landscapes where varied slope aspect yields substantial, local microclimate variation. Vegetation composition and cover typically change markedly along the gradient of relatively mesic northern aspects to more xeric southern aspects. Ecohydrological processes including precipitation runoff, soil moisture storage, and erosion are strongly influenced by vegetation. In certain cases, reduction of plant cover may set self-enhancing feedbacks in motion that lead to further declines of both vegetation and soils, and in some cases, replacement of woodlands with more xerophytic vegetation. The first place such change is likely to occur is in the ecotone between the drier southern aspects and moister north aspects. We studied vegetation, soils, and soil erosion in two small (1–2ha) drainage basins in northeastern Arizona where pinyon–juniper woodlands occupy northern aspects, grading to shrub-dominated vegetation on more xeric southern aspects. Mapping of soil thickness, use of tree-root exposure to measure long-term soil erosion rates, and data on tree mortality and establishment indicate that the ecotone between woodland and more xerophytic vegetation has apparently been shifting for centuries, with a reduction in woodland vegetation. Erosion rates on xeric aspects ranged from 14 to 23cm per century in one basin and as much as 60cm per century in the other basin. In contrast, mesic aspects showed either no net soil losses over the last several centuries or rates significantly less than on the xeric aspects. Exposure of small roots (<5mm diameter) of cliff rose (Purshia stansburiana) directly overlying bare bedrock surfaces indicates that the process of denudation is ongoing and probably expanding in ecotonal areas. Mesic and xeric aspects exemplify “conserving” vs. “non-conserving” ecohydrologic systems in terms of their capacities to retain water and soils. The contrasting sets of self-enhancing feedback dynamics on xeric vs. mesic aspects not only produce different states in vegetation and soils, they also set in motion the production of pronounced geomorphic contrasts that probably require centuries to millennia to develop. The ongoing ecohydrological transitions in the more xeric aspects are in the process of transforming those hillslopes from smooth, curvilinear, soil-mantled, sediment transport-limited slopes to detachment-limited slopes characterized by an expanding area of bare bedrock steps and cliffs, and this transition is probably irreversible. Predicted temperature increases over the next century for the region are comparable to the present-day soil temperature differential on xeric vs. mesic aspects at the site. Soil temperature is the principal driver of soil water evapotranspirative losses, and because of the interdependent linkages between soil temperature, soil moisture, weathering, production and retention of soil, vegetation, and hydrological response, relatively small temperature increases will likely accelerate the ongoing environmental changes in this and similar areas.