Juniperus Monosperma Research Articles

Restoring frequent fire to dry conifer forests delays the decline of subalpine forests in the southwest United States under projected climate

Abstract In southwestern US forests, the combined impact of climate change and increased fuel loads due to more than a century of human‐caused fire exclusion is leading to larger and more severe wildfires. Restoring frequent fire to dry conifer forests can mitigate high‐severity fire risk, but the effects of these treatments on the vegetation composition and structure under projected climate change remain uncertain. We used a forest landscape model to assess the impact of thinning and prescribed burns in dry conifer forests across an elevation gradient, encompassing low‐elevation pinyon‐juniper woodlands, mid‐elevation ponderosa pine and high‐elevation mixed‐conifer forests. Our results demonstrated that the treatments decreased the probability of high‐severity fires by 42% in the study area. At low elevation, the treatments did not prevent loss in forest cover and biomass with decreases in Pinus edulis and Juniperus monosperma abundances. At mid‐elevation, changes in fire effects maintained a greater diversity of tree species by favouring the maintenance of cohorts of old trees, in particular Pinus ponderosa which accumulated 5.41 Mg ha−1 more above‐ground biomass than without treatments by late‐century. Treatments in dry conifer forests modified fire effects beyond the treated area, resulting in increased cover and biomass of old Picea englemannii and Abies lasiocarpa cohorts. Synthesis and applications: Our findings indicate that thinning and prescribed burning can enhance tree species diversity in dry conifer forests by protecting old cohorts from stand‐replacing fires. Moreover, our results suggest that treatments mainly implemented in dry pine forests with high risk of high‐severity fires can be beneficial for subalpine species conservation by reducing the chance that high‐severity fire at mid‐elevation is transmitted into high‐elevation forest.

Metabolomic evidence of independent biotransformation pathways for terpenes in two specialist mammalian herbivores (genus Neotoma).

Herbivory is common in mammals, yet our understanding of detoxification processes used by mammals to biotransform plant secondary compounds (PSCs) is limited. Specialist herbivores are thought to have evolved detoxification mechanisms that rely more heavily on energetically cheap Phase I biotransformation reactions to process high levels of PSCs in their diets. We explored this hypothesis by comparing the urinary metabolite patterns of two specialist herbivores (genus Neotoma). Neotoma stephensi is an obligate specialist on one-seeded juniper (Juniperus monosperma). Neotoma lepida is a generalist forager across its range, yet populations in the Great Basin specialize on Utah juniper (J. osteosperma). While both juniper species have high levels of terpenes, the terpene profiles and quantities differ between the two. Individuals from both woodrat species were fed diets of each juniper in a cross-over design. Urine, collected over a 24-h period, was extracted and analyzed in an untargeted metabolomics approach using both GC-MS and HPLC-MS/MS. The obligate specialist N. stephensi excreted a unique pattern of Phase I metabolites when fed its native juniper, while N. lepida excreted a unique pattern of Phase II metabolites when fed its native juniper. Both woodrat species utilized the Phase II metabolic pathway of glucuronidation more heavily when consuming the more chemically diverse J. osteosperma, and N. stephensi utilized less glucuronidation than N. lepida when consuming J. monosperma. These results are consistent with the hypothesis that obligate specialists may have evolved unique and efficient biotransformation mechanisms for dealing with PSCs in their diet.

Where can managers effectively resist climate-driven ecological transformation in pinyon-juniper woodlands of the US Southwest?

Pinyon-juniper (PJ) woodlands are an important component of dryland ecosystems across the US West and are potentially susceptible to ecological transformation. However, predicting woodland futures is complicated by species-specific strategies for persisting and reproducing under drought conditions, uncertainty in future climate, and limitations to inferring demographic rates from forest inventory data. Here, we leverage new demographic models to quantify how climate change is expected to alter population demographics in five PJ tree species in the US West and place our results in the context of a climate adaptation framework to resist, accept, or direct ecological transformation. Two of five study species, Pinus edulis and Juniperus monosperma, are projected to experience population declines, driven by both rising mortality and decreasing recruitment rates. These declines are reasonably consistent across various climate futures, and the magnitude of uncertainty in population growth due to future climate is less than uncertainty due to how demographic rates will respond to changing climate. We assess the effectiveness of management to reduce tree density and mitigate competition, and use the results to classify southwest woodlands into areas where transformation is (a) unlikely and can be passively resisted, (b) likely but may be resisted by active management, and (c) likely unavoidable, requiring managers to accept or direct the trajectory. Population declines are projected to promote ecological transformation in the warmer and drier PJ communities of the southwest, encompassing 37.1%-81.1% of our sites, depending on future climate scenarios. Less than 20% of sites expected to transform away from PJ have potential to retain existing tree composition by density reduction. Our results inform where this adaptation strategy could successfully resist ecological transformation in coming decades and allow for a portfolio design approach across the geographic range of PJ woodlands.

Understory Vegetation Response to Thinning Pinyon-Juniper Woodlands

Portions of the western United States, extending from west Texas to eastern Oregon, are thin to densely populated with juniper (Juniperus spp.) woodlands. Managing tree densities, such as through mechanical thinning, has numerous ecological implications for rangeland watersheds and wildlife habitat. The objective of this study was to determine vegetation response to juniper removal in a pinyon (Pinus edulis Engelm)− and juniper (Juniperus monosperma Engelm)− dominated landscape in north-central New Mexico. Herbaceous cover and standing crop were collected from six 1.00- to 1.35-ha catchments situated within the New Mexico State University (NMSU)−Santa Fe Ranch, Santa Fe County, New Mexico, before treatment and at 5 and 10 yr following juniper removal. About 70% of mature juniper trees were cut in 2009 in three of the catchments (treated) while the remaining catchments were left as controls (untreated). Herbaceous cover and standing crop were measured in 2009 (pretreatment), 2014, and 2019 (post treatment) to test our hypothesis that juniper reductions would significantly increase herbaceous standing crop. After 10 yr, gravel, grass, and forb cover were comparable in the treated and the untreated, whereas bare soil cover was significantly decreased in the treated (30% ± 2.5) compared with the untreated (42% ± 2.5). Litter cover in the treated was higher (18% ± 2.6) than the untreated (5% ± 2.6). Herbaceous standing crop significantly increased in the treated compared with the untreated. Standing crop of grass in the treated was two to three times greater than the untreated. Forb standing crop was not influenced by treatment but increased over time in both treatments. Study findings provide land managers with critical information regarding one-seed juniper clearing effects on herbaceous vegetation response in the warm-climate rangeland ecosystems of the southwestern United States.

Mastication Treatments Increase Perennial Herbaceous Cover Across Soil Types in Southeastern Colorado Piñon-Juniper Woodlands

Tree-removal treatments have been broadly applied across piñon-juniper ecosystems of the western United States to reduce tree cover, stimulate understory plant production, and promote habitat for shrub- and grassland-obligate wildlife species. Mastication treatments have become an increasingly common approach, yet the efficacy of these treatments can vary on the basis of a variety of factors, including soil characteristics, woodland structure, and grazing pressures. Here, we assessed vegetation responses to mastication treatments across three dominant soil types in two-needle piñon (Pinus edulis Engelm. [Pinaceae])−one-seed juniper (Juniperus monosperma [Engelm.] Sarg.) woodlands in southeast Colorado, United States, a region characterized by monsoonal precipitation, limited presence of introduced plant species, and relatively high grazing intensity by cattle and wildlife. We found that mastication treatments were effective at increasing herbaceous plant cover and species diversity (by 1.2 × and 1.5 ×) and at reducing the amount of exposed soil (60% reduction) 3 yr following treatment. This was mainly due to increases in native perennial grasses. Further, there were limited (and insignificant) increases in cover of annual plants and low abundance of introduced species in treated plots. Understory plant responses to treatment were similar across soils with a range of available water capacities. The increase in understory plant cover and richness paired with the low abundance of introduced species suggests that mastication treatments increase forage production for cattle and wild ungulates. In addition, the lack of soil type differences in treatment response suggests that mastication treatment placement does not need to prioritize soil type and can instead focus on other key areas of importance, such as wildlife habitat connectivity, historic woodland structure, and treatment feasibility.

Using derivative thresholds to resolve conflicting habitat management strategies

Habitat management efforts for multiple species with contrasting habitat requirements can be challenging, particularly on small landscapes where large-scale heterogeneity may not be a viable solution. We sought to utilize derivative functions from species-response curves to identify thresholds along an environmental gradient for two species with differing responses to juniper cover. We estimated percentages of one-seed juniper (Juniperus monosperma) cover around loggerhead shrike (Lanius ludovicianus) and gray vireo (Vireo vicinior) nests in central New Mexico in 2016–2020 to better understand tolerance of juniper expansion for these two species of conservation concern. Species-response curves were derived from generalized additive mixed-effect models, with year as a random effect and a local regression smoother. Loggerhead shrike nests were more likely to occur in areas without junipers at the 170-m radius spatial scale. Nest-site selection declined as percent juniper cover increased. Gray vireo nests were most likely to be found in areas with approximately 11 % juniper cover at the 100-m radius spatial scale. Derivative functions were used to find juniper percentages where the rate of change in species' response was most negative for loggerhead shrikes and most positive for gray vireos. The rate of change in nest-site selection decreased the fastest at 13 % and increased the fastest at 4 % juniper cover for loggerhead shrike and gray vireo, respectively. These results suggest that maintaining juniper percentages between 4 and 13 % at relatively broad spatial scales would likely increase available nesting habitat both species. We demonstrate how derivative functions can be used to estimate the rate of change of species' response to environmental gradients and an application of such thresholds to resolve conflicting habitat management for two species of conservation concern.

Dispersal Patterns of One-Seed Juniper Seeds Contained in Mammal Scats and Bird Pellets

We conducted a two-year study in New Mexico, USA, to determine the role of birds, lagomorphs, mesocarnivores, and porcupines in one-seed juniper (J. monosperma (Englem.) Sarg.) seed dispersal. We established random plots: (1) around cone-bearing juniper trees in the woodland; (2) around non-cone-bearing juniper trees in the woodland; (3) in woodland/grassland transition zones; and in (4) grassland habitats near juniper woodlands. We estimated seed density and tallied the number of plots with seeds deposited by each disperser group. Birds deposited the highest number of seeds/ha under the canopy of cone-bearing trees. Mesocarnivores were responsible for the highest average seed deposition in all other habitats. In juniper cone-bearing tree habitats, birds deposited seeds in 100% of plots under-canopy and 93% of plots outside-canopy. Seeds deposited by lagomorphs were observed in plots across all sampled habitats. Overall, seed deposition was greatest around cone-bearing juniper trees, followed by non-cone-bearing juniper trees, woodland-grassland transition zones, and grassland habitats. Birds deposited seeds primarily under cone-bearing tree perch sites. Lagomorphs deposited seeds widely in relatively high numbers across all habitats and are likely responsible for the greatest number of one-seed juniper seeds deposited on the soil surface at our research site.

Response of Soil Moisture to Infrequent Heavy Defoliation of Chemically Thinned Juniper Woodland

In semiarid regions of the western United States, there is heightened interest in tree removal to increase water availability for other uses such as forage growth and groundwater recharge. This study was conducted in central New Mexico to determine the effects of heavy infrequent defoliation of chemically thinned juniper woodland (Juniperus monosperma) on soil moisture. Each of three cattle-grazing exclosures (CD, FG, and KI) was instrumented: 1) beneath trees with a set of three soil moisture probes (0−25, 25−50, and 50−75 cm depth) and one soil temperature probe under live trees (control) and dead trees (herbicide-treated); and 2) between trees with one soil moisture and one soil temperature probe in control and herbicide-treated intercanopy plots. Each plot had three clipped and three unclipped subplots. Mean daily maximum surface soil temperature was highest (17.19°C) in intercanopy, intermediate (16.13°C) under herbicide-treated, and lowest (14.90°C) under control trees. Topsoil moisture (0−25 cm depth) was different among treatment combinations from late July to early September 2006. Thus, the control unclipped combination had the highest topsoil moisture while the herbicide-treated unclipped combination had the lowest topsoil moisture. Comparing other depths, control unclipped plots had higher soil moisture in the middle layer (25−50 cm) and bottom layer (50−75 cm) than at the top from late August to early November 2006. Results imply that clipping on chemically thinned juniper woodlands does not increase soil moisture at any depth, yet macropore flow and water absorption on deep soil layers, underneath live trees, might help to store soil moisture for longer periods in water-limited environments.

Age-Dependent Search Behavior in the Colorado Checkered Whiptail (Aspidoscelis neotesselatus)

We compared movement and space use patterns of foraging adult and juvenile Colorado checkered whiptails (Aspidoscelis neotesselatus) in pinyon pine–juniper woodland. Through focal observations, we characterized (1) movement paths as a series of step lengths and turn angles at 30-s intervals, and (2) habitat use reflected by the proportion of time spent in different vegetation types and in the open. Adults and juveniles differed in both movement and habitat use. Adults spent more time in the open and in association with mountain mahogany (Cercocarpus montanus), while juveniles were more frequently found in association with dead wood, grass, and juniper (Juniperus monosperma). Adults also moved greater distances than juveniles and made use of larger areas. Movement patterns differed between age classes, with adults having longer step lengths. Adults and juveniles also engaged in different step length–turn angle sequences. For both classes, movement characteristics differed with habitat type.

Plant wax and carbon isotope response to heat and drought in the conifer Juniperus monosperma

Plant waxes, including n-alkanes, are commonly used for a wide range of paleo-applications. Several common traits of n-alkanes that are used as paleo-proxies include chain length distribution and average chain length (ACL), as well as plant wax carbon and hydrogen isotopic compositions. The effect of climate on plant wax traits has been the subject of many studies, but a common challenge with modern calibrations is disentangling the effects of species (genetic), temperature, and precipitation from one another. Here, we explore the effect of temperature and drought, independently and combined, on plant wax composition of the species Juniper monosperma in a large ecosystem-scale field manipulation experiment. We find that n-alkane concentrations significantly increase with temperature, but other parameters (including ACL) are not affected. These results support physiological studies that identify n-alkanes as an important barrier to water loss within the plant cuticle. Combined with prior studies, it appears that changes in ACL within sediments are likely controlled by changes in species composition rather than directly by changes in climate. We find little variation in the carbon isotopic composition (δ13C) of n-alkanes across the treatments whereas bulk leaf δ13C values are higher in the heat and drought treatment. Because leaf δ13C values represent a weighted C assimilation signal, these values reflect differences in leaf gas exchange among treatments, whereas the n-alkanes are synthesized when water availability is higher and differences among treatments are not significant enough to influence their values. These results have important implications for using n-alkane traits, including ACL and δ13C values, for paleoenvironmental reconstructions.

Insights from recent fires into juniper savanna dynamics at Wupatki National Monument, Arizona, USA

• We tested the hypothesis that recurrent fires may limit juniper expansion into southwestern semiarid grasslands and savannas. • Seven large fires at Wupatki National Monument, Arizona, burned 38% of the grasslands and dynamic savannas between 1995 and 2017. • Mortality of one-seed junipers ( Juniperus monosperma ) was >50% among smaller trees (<2 m tall), <40% among larger trees (>2 m tall), and 0% in trees >4 m tall. • Herbaceous vegetation recovered within 2 to 3 years postfire. • This suggests that fires may have limited juniper expansion historically and that fire may be an option for controlling juniper expansion and restoring grassland/savanna ecosystems today.

Morphological and Molecular Identification of Mycobiota Associated with Juniperus monosperma (Engelm.) Sarg. Blight in Mexico

The aim of the investigation was to identify the agents associated with blight in Juniperus monosperma at Lirios region, Arteaga, Coahuila. Botanical material was collected at Lirios, Arteaga, and taken to the laboratory. Pathogens were isolated in ADP culture medium and identifying by morphological criteria and molecular using primers ITS1 and ITS4. DNA extraction by the Dellaporta method, the visualization of obtained DNA was performed by electrophoresis on a 2% (p/v) agarose gel. DNA quantification was performed on a NanoDrop 1000 spectrophotometer, and DNA amplification was carried out in the Veriti thermocycler. Obtained sequences were aligned and compared with those available in the GenBank database of the National Center for Biotechnology Information (NCBI), using the BLAST algorithm (Basic Local Aligment Search Tool) to find conserved sequences. Pathogens were inoculated in stems of J. monosperma. The agents associated with blight were Alternaria sp., Aspergillus sp. and Rosellinia sp. and the sequence obtained compared with BLAST coincided only with Alternaria sp. and Aspergillus sp. with the access codes KP027305.1 and MG551283.1, respectively. According to data taken in field, Alternaria sp. behaved as the highest prevalence species and severity associated with blight in J. monosperma, and Rosellinia sp. in laboratory conditions.

Atmosphere‐Soil Interactions Govern Ecosystem Flux Sensitivity to Environmental Conditions in Semiarid Woody Ecosystems Over Varying Timescales

AbstractWater and CO2 flux responses (e.g., evapotranspiration [ET] and net ecosystem exchange [NEE]) to environmental conditions can provide insights into how climate change will affect the terrestrial water and carbon budgets, especially in sensitive semiarid ecosystems. Here, we evaluated sensitivity of daily ET and NEE to current and antecedent (past) environment conditions, including atmospheric (vapor pressure deficit [VPD] and air temperature [Tair]) and moisture (precipitation and soil water) drivers. We focused on two common southwestern U.S. (“Southwest”) biomes: pinyon‐juniper woodland (Pinus edulis, Juniperus monosperma) and ponderosa pine forest (Pinus ponderosa). Due to differences in aridity, rooting patterns, and plant physiological strategies (stomatal and hydraulic traits), we expected ET and NEE in these ecosystems to respond differently to atmospheric and moisture drivers, with longer response timescales in the drier pinyon‐juniper woodland. Net sensitivity to drivers varied temporally in both ecosystems, reflecting the integrated influence of interacting drivers and antecedent precipitation patterns. NEE sensitivity to VPD and soil moisture (and ET sensitivity to deep soil moisture [Sdeep]) was higher in the ponderosa forest. ET and NEE in both ecosystems responded almost instantaneously to Tair, VPD, and shallow soil moisture (Sshall), and increases in any of these drivers weakened the carbon sink and enhanced water loss. Conversely, Sdeep and precipitation influenced ET and NEE over longer timescales (days to months, respectively), and higher Sdeep enhanced the carbon sink. As climate changes, these results suggest hotter and drier conditions will weaken the carbon sink and exacerbate water loss from Southwest pinyon‐juniper and ponderosa ecosystems.

A 3-dimensional model of Pinus edulis and Juniperus monosperma root distributions in New Mexico: implications for soil water dynamics

(1) To develop a 3D root distribution model for pinon-juniper woodland using only tree species, sizes and locations as input. (2) To interpret a two-year time series of soil moisture relative to root distributions. The study was conducted in a pinon (Pinus edulis (Englem.)) -juniper (Juniperus monosperma (Englem.) Sarg.) woodland in New Mexico. We extracted roots from 720 soil blocks (30 cm × 10 cm × 10 cm) cut from the walls of three 10-m long and 1.5-m deep trenches. Roots were sorted by species and diameter class. Distribution models were developed for the dry weight of roots ≤5 mm in diameter. Soil water content and water potentials were measured in soil profiles under tree cluster and canopy gaps for 2 years, including a protracted dry-down period. Pinon had twice the root dry mass of juniper, similar to the ratio of canopy projection areas. Root densities were ca. 50% lower in soils under canopy gaps compared to tree clusters and the species ratio did not significantly differ between clusters and gaps. Pinon root density declined faster with soil depth and distance from the stem compared to juniper. A hard caliche layer at 60–80 cm soil depth had no apparent effect on the already low root density at that depth. Overall, the models explained 66% (pinon) and 54% (juniper) of the spatial variation in root density at the scale of sampled soil blocks. During an 8-month dry period, soil moisture declined faster in regions of higher root density: in shallow soil and under tree clusters. This left a reserve of plant-available soil water in the deep soil under canopy gaps. Horizontal variation in root density in these open woodlands is predictable and an important component of the dynamic interactions between plant and soil. Under wet and dry conditions, soil water content is substantially different under tree clusters and canopy gaps.

Allometric Relationships for Predicting Aboveground Biomass and Sapwood Area of Oneseed Juniper (Juniperus monosperma) Trees.

Across the semiarid ecosystems of the southwestern USA, there has been widespread encroachment of woody shrubs and trees including Juniperus species into former grasslands. Quantifying vegetation biomass in such ecosystems is important because semiarid ecosystems are thought to play an important role in the global land carbon (C) sink, and changes in plant biomass also have implications for primary consumers and potential bioenergy feedstock. Oneseed juniper (Juniperus monosperma) is common in desert grasslands and pinyon–juniper rangelands across the intermountain region of southwestern North America; however, there is limited information about the aboveground biomass (AGB) and sapwood area (SWA) for this species, causing uncertainties in estimates of C stock and transpiration fluxes. In this study, we report on canopy area (CA), stem diameter, maximum height, and biomass measurements from J. monosperma trees sampled from central New Mexico. Dry biomass ranged between 0.4 kg and 625 kg, and cross-sectional SWA was measured on n = 200 stems using image analysis. We found a strong linear relationship between CA and AGB (r2 = 0.96), with a similar slope to that observed in other juniper species, suggesting that this readily measured attribute is well suited for upscaling studies. There was a 9% bias between different approaches to measuring CA, indicating care should be taken to account for these differences to avoid systematic biases. We found equivalent stem diameter (ESD) was a strong predictor of biomass, but that existing allometric models underpredicted biomass in larger trees. We found SWA could be predicted from individual stem diameter with a power relationship, and that tree-level SWA should be estimated by summing the SWA predictions from individual stems rather than ESD. Our improved allometric models for J. monosperma support more accurate and robust measurements of C storage and transpiration fluxes in Juniperus-dominated ecosystems.

Germination of One-Seed Juniper Seeds Distributed by Different Frugivore Groups

One-seed juniper (Juniperus monosperma [Englem.] Sarg.) encroachment into grassland habitats is facilitated by a diverse group of frugivores. To test seed germination after gut passage, we collected pellets or scats containing mature seeds from four frugivore groups: passerine (perching) birds, lagomorphs (hares and rabbits), mesocarnivores (coyotes and foxes), and porcupines. For comparison of germination success, we also evaluated seeds from intact, nondigested one-seed juniper cones. We conducted germination trials under three different scenarios: 1) imbibed bare seeds (a measure of potential germination); 2) seeds still encased within a frugivore deposited pellet or scat matrix or still in a nondigested cone; and 3) matrix-free seeds that had gone through the matrix germination trials and then were freed from the matrix (a simulation of seeds that become dislodged from scats or pellets). In the bare seed trials, germination was highest (70.8% ± 7.4%) for seeds digested by mesocarnivores and was 63.9% ± 5.7% for porcupines, which was higher (P < 0.05) than germination of seeds from bird pellets (33.3% ± 7.7%). Germination of seeds from all frugivores, including lagomorphs (51.4% ± 7.2%), was higher (P < 0.05) than for seeds encased in cones (9.7% ± 3.2%). The germination percentage of seeds still encased in frugivore pellets or scats was highest for birds (40.1 ± 4.2) and was significantly lower (P < 0.05) for other frugivores. Seeds freed from all frugivore deposition matrices showed a second pulse of germination activity, especially seeds from lagomorph pellets. Germination success differences can influence the nature of one-seed juniper woodland infill and encroachment into bordering grasslands, which can lead to loss of soil health, lower grass biomass production, and a diminishment of habitat quality for grassland-dependent wildlife species.

Terpenes May Serve as Feeding Deterrents and Foraging Cues for Mammalian Herbivores.

Terpenes, volatile plant secondary compounds produced by woody plants, have historically been thought to act as feeding deterrents for mammalian herbivores. However, three species of woodrats, Neotoma stephensi, N. lepida, and N. albigula, regularly consume juniper, which is high in terpenes, and N. stephensi and N. lepida are considered juniper specialists. By investigating the terpene profiles in Juniperus monosperma and J. osteosperma, which are browsed or avoided by woodrats in the field, and recording the caching and consumption of juniper foliage by woodrats in the lab, we have evidence that terpenes may serve as feeding and/or foraging cues. The obligate specialist N. stephensi chose to forage on trees higher in p-cymene and preferred to consume juniper rather than caching it in a laboratory setting. These observations provide evidence that terpenes serve as a feeding cue and that the obligate specialist's physiological mechanism for metabolizing the terpenes present in juniper may negate the need for caching. The facultative specialist N. lepida chose to forage on trees lower in four terpenes and cached more juniper than the obligate specialist N. stephensi, providing evidence that terpenes serve as a feeding deterrent for N. lepida and that this woodrat species relies on behavioral mechanisms to minimize terpene intake. The generalist N. albigula foraged on trees with higher terpenes levels but consumed the least amount of juniper in the lab and preferred to cache juniper rather than consume it, evidence that terpenes act as foraging but not feeding cues in the generalist. Our findings suggest that volatile plant secondary compounds can act as feeding and/or foraging cues and not just feeding deterrents in mammalian herbivores.

Insects of Dominant Shrub Communities at Pawnee and Comanche National Grasslands, Colorado

Terrestrial insects associated with shrubs at Pawnee National Grassland in northeastern Colorado and Comanche National Grassland in southeastern Colorado were identified to family or genus with some taxa to species. Six species of grassland shrubs were sampled using a funnel-bucket method each month from June-September 2014 and 2015. Insect diversity and abundance differed between the grasslands. Chrysomelidae, Cicadellidae, Cleridae, Formicidae, Meloidae, and Miridae were abundant at Pawnee National Grassland, primarily from four-winged saltbush (Atriplex canescens) (Pursh.) Nutt). Acrididae, Aphididae, Chrysomelidae, Cleridae, Coccinellidae, Formicidae, Lygaeidae, Miridae, and Reduviidae collected from sandsage (Artemisia filifolia Torr.), four-winged saltbush, rabbitbrush (Ericameria nauseosa (Pallas ex. Pursh), greasewood (Sarcobatus vermiculatus (Hook) Torr.), skunkbush (Rhus trilobata Nutt.), and one-seed juniper (Juniperus monosperma (Engelm.) were abundant at Comanche National Grassland.

Reductions in tree performance during hotter droughts are mitigated by shifts in nitrogen cycling.

Climate warming should result in hotter droughts of unprecedented severity in this century. Such droughts have been linked with massive tree mortality, and data suggest that warming interacts with drought to aggravate plant performance. Yet how forests will respond to hotter droughts remains unclear, as does the suite of mechanisms trees use to deal with hot droughts. We used an ecosystem-scale manipulation of precipitation and temperature on piñon pine (Pinus edulis) and juniper (Juniperus monosperma) trees to investigate nitrogen (N) cycling-induced mitigation processes related to hotter droughts. We found that while negative impacts on plant carbon and water balance are manifest after prolonged drought, performance reductions were not amplified by warmer temperatures. Rather, increased temperatures for 5years stimulated soil N cycling under piñon trees and modified tree N allocation for both species, resulting in mitigation of hotter drought impacts on tree water and carbon functions. These findings suggest that adjustments in N cycling are likely after multi-year warming conditions and that such changes may buffer reductions in tree performance during hotter droughts. The results highlight our incomplete understanding of trees' ability to acclimate to climate change, raising fundamental questions about the resistance potential of forests to long-term, compound climatic stresses.

Controlling One-Seed Juniper Saplings With Small Ruminants: What We Have Learned

On the Ground • Protein supplements and polyethylene glycol increased juniper intake by small ruminants in all seasons except fall, when PSM concentrations were greatest. • Terpenes were affected by season and sapling size, and were related to juniper intake by small ruminants. • Small sapling browsing occurred most frequently in summer. Debarking of branches on taller saplings was greatest in spring. • Ten years later, juniper kill ranged from 5-14%. Growth suppression was still evident after 10 years; browsed saplings averaged 13 cm shorter than controls. • Strategies to target grazing of one-seed juniper are more likely to succeed if aligned with periods when PSM are lowest.