Search

Arbuscular mycorrhizal fungi (AMF) are drivers of plant communities as they influence plant competition by increasing plants’ root absorptive surface. As such, AMF could be an important tool for ecological restoration. However, a lack of research using AMF in sagebrush steppe communities implies a need for more assessments of its efficacy. Here, we assessed the ability of a commercial inoculum to colonize and influence growth of three native Artemisia spp. (sagebrush) shrubs and the exotic Taeniatherum caput-medusae (medusahead). We expected to increase colonization and biomass production with the addition of the inoculum. Before testing the inoculum, its viability was examined using Trifolium incarnatum (crimson clover) in autoclaved soil. Next, a factorial greenhouse experiment was conducted to evaluate the target species when grown in live or autoclaved field soil from a disturbed (early seral) site. Inoculation resulted in an average root colonization of 24.82% ± 4.86% for T. incarnatum but failed to colonize any of the sagebrush steppe species in autoclaved soil and had little to no influence on colonization in live soil. All sagebrush steppe species were colonized by AMF in live soil, and biomass production averaged 889 mg, 530 mg, 323 mg, and 1 852 mg, respectively; however, average biomass for all species was greater when grown in autoclaved soils (1 620 mg, 706 mg, 371 mg, and 3 902 mg, respectively). Our results reveal differential effects of a commercial AMF inoculum on root colonization of Artemisia spp. and T. incarnatum and highlight the need to assess the efficacy of AMF inoculum before field application.

An improved understanding of the relationships among vegetation, groundwater level, and microtopography is crucial for making well-informed management decisions in areas with shallow groundwater resources. We measured plant species abundance/composition and richness in relation to depth to groundwater (DTW) and microtopography in Owens Valley, California, particularly in areas where DTW ranged from 0 to 4 m. Sampling occurred along 67 vegetation transects across three community types. Relationships between DTW and community composition were evaluated using non-metric multidimensional scaling (NMS), while non-parametric multiplicative regression was used to relate DTW and microtopography to species abundance. The dominant gradient in species composition (NMS Axis 1) explained ~51% of variation in our distance matrix and was most strongly associated (r = 0.55) with DTW. The graminoids Juncus arcticus, Leymus triticoides, and Distichlis spicata had strong affinities toward areas with the shallowest DTW ( 2.0 m). Variation in microtopography affected species abundance and increased species richness for vegetation communities at either extreme of the water table gradient, shallow, and deep DTW but not the intermediate DTW. Findings indicate that desert plant communities from shallow aquifers have adapted to different DTW and microtopography conditions and that considering those adaptations may be important to manage groundwater and vegetation resources in these areas.

Aims In the Oregon of USA, the control of western juniper (Juniperus occidentalis) is an accepted rangeland management practice to restore sagebrush steppe habitats of importance to wildlife and livestock. The effects of juniper cutting on ecosystem nitrogen, however, have not been well addressed although woody plant control has important implications for local watershed management and regional nitrogen pools. Methods We quantified ecosystem nitrogen stocks in two adjacent watersheds, comprised of a treated watershed (most juniper removed) and an untreated watershed (juniper not removed). Thirteen years after juniper removal, we measured aboveground nitrogen stocks for juniper trees, shrubs, grasses and litter in both watersheds. We also measured belowground nitrogen stocks (roots and soil) in both watersheds at two soil depths (0–25 and 25–50 cm). Important Findings Aboveground nitrogen stocks were 6.9 times greater in the untreated than in the treated watershed considering the much larger aboveground biomass. However, root nitrogen stocks were 3.1 times greater in the treated one due to the gain of understory root biomass associated with juniper cutting. Soil nitrogen stocks at both 0–25 and 25–50 cm depths were not affected by juniper removal. Overall, total ecosystem nitrogen stocks did not differ between the treated (9536 kg N ha−1) and untreated (9456 kg N ha−1) watersheds. The greatest ecosystem nitrogen accumulation (at least 95% total ecosystem nitrogen) resided belowground (soil 0–50 cm and roots) in both watersheds. This study provides evidence that the benefits of juniper removal can be attained without significantly affecting the capacity of ecosystem nitrogen storage.

Invasive annual grasses such as cheatgrass (Bromus tectorum L.) outcompete native grasses, increase fire frequency, and impact the functionality and productivity of rangeland ecosystems. Preemergent herbicide treatments are often used to control annual grasses but may limit timely restoration options due to negative effects on concurrently planted desired seeded species. We tested the efficacy of activated carbon-based herbicide protection coatings applied to individual bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Love) seeds for protecting seedlings from injury associated with pre-emergent herbicide (imazapic) application in a laboratory environment. Emergence of coated seed averaged 57% ± 5% compared with bare seed, which had 14% ± 10% emergence with imazapic application. Seedling height for coated seed averaged 7.56 ± 0.6 cm compared with 2.26 ± 0.4 cm in uncoated bare seed in the presence of imazapic. Coated seeds produced 87% more plant biomass than uncoated seeds. Our laboratory results suggest that treating individual seeds with an activated carbon-based coating dramatically reduces negative effects of pre-emergent herbicide on desired seeded species. Field studies are needed to confirm these results in an applied restoration context.

Aims Although increases in precipitation variability in arid ecosystems are projected due to climate change, the response of desert shrub communities to precipitation change has not been fully elucidated. Such knowledge is important since drought-adapted plants exhibit varied mechanisms of survival that may contribute to species coexistence. Methods We tested the responses of eight drought-adapted plants, a mix of graminoids, shrubs and forbs to three summer precipitation scenarios (1.3, 2.6 and 3.9 cm per month) in a common garden experiment in the Great Basin (Owens Valley, California). Changes in mineral nutrient uptake (carbon, nitrogen, phosphorus, potassium, calcium, magnesium, manganese, copper, boron, zinc, iron and sodium) and gas exchange parameters (photosynthetic rate and stomatal conductance) were investigated in the studied species. Important Findings Two graminoids (Sporobolus airoides and Leymus triticoides) and one salt tolerant shrub species (Atriplex confertifolia) responded to increased water availability with increases in photosynthetic rate and/or stomatal conductance. There was a significant correlation between water availability and uptake of nutrients for five out of eight species. Artemisia tridentata, with higher rates of photosynthesis, contained greater amounts of potassium, copper and boron, while Juncus arcticus, with higher rates of photosynthesis, contained greater amounts of magnesium and iron, and less sodium. Juncus arcticus and three salt-adapted species (A. confertifolia, Distichlis spicata and S. airoides) exhibited correlations with stomatal conductance and concentrations of nutrients. Results indicate that differential physiological response mechanisms to increased moisture and associated nutrient uptake strategies in drought-adapted species may mediate coexistence under increased summer precipitation.

A common argument for western juniper (Juniperus occidentalis) control in Oregon is the amount of water saved due to reduction in the number of trees. Yet a good understanding of water use by mature trees and sapling regrowth following mature juniper removal has not been documented. Such information is important to better assess how much water can be saved by juniper control. We used sap flow sensors to monitor water use by mature juniper in a control area and saplings in an area where juniper control occurred in 2005. Sap flow data collected between May 2017 and Sep 2019 showed the period of highest water use was in the summer, although this varied each year. In July 2017 (wettest yr of the study), mature trees used 144 L/d, approximately twice as much as in the average of July 2018 and 2019 (dry yr). During the period of maximum water uptake, mature trees used between 45 and 69 times more water than saplings depending on precipitation and, consequently, soil water availability. In summary, 1) juniper water use varies greatly with precipitation and 2) because of the large difference between mature and sapling trees, juniper control results in considerable water savings, even after a 14-yr period of juniper regrowth.

The sagebrush steppe has presented increasing levels of degradation. The addition of arbuscular mycorrhizal fungi (AMF) and biochar have been suggested to restore ecosystems. However, little is known about their effects on sagebrush steppe plants. We tested three sources of AMF inoculum: soil from a disturbed site (Inoculum A), soil from an undisturbed site (Inoculum B), and commercial inoculum (Inoculum C), all with and without biochar, to test if they could mediate growth of Pseudoroegneria spicata (native perennial), Taeniatherum caput-medusae (early seral; exotic annual) and Ventenata dubia (early seral; exotic annual) under greenhouse conditions. We measured AMF colonization and biomass. We hypothesized that the plant species would be differently affected by the inoculum types. The colonization of T. caput-medusae and V. dubia was greatest when inoculated with Inoculum A (38.8% and 19.6%). In contrast, the colonization of P. spicata was greatest with Inoculum B and Inoculum C (32.1% and 32.2). Biochar decreased biomass production but increased colonization with Inoculum A for P. spicata and V. dubia and with Inoculum C for T. caput-medusae. This study reveals the response of early and late seral sagebrush steppe grass species to contrasting sources of AMF and suggests that late seral plant species respond better to late seral inocula.

Protected-area sagebrush steppe ecosystems are few in number and increasingly important to the North American conservation network as sagebrush steppe faces growing threats from land use, climate change, and invasive species. We analyzed the distribution and abundance of native perennial and invasive annual plants to better understand patterns of plant invasion within two protected areas: John Day Fossil Beds National Monument (JODA), located in central Oregon, and Craters of the Moon National Monument and Preserve (CRMO), located in southeast Idaho. We used multivariate analysis to examine vegetation monitoring datasets and illuminate geographic variation in plant cover along gradients of well-known aspects of resistance to plant invasion (elevation, exposure [slope and aspect], precipitation and proximity to disturbance). Topographically mediated resistance to invasion appeared to manifest in the park with greater topographic variability (JODA), while increased elevation was more strongly associated with resistant sites in the park, which spanned a greater elevational gradient (CRMO). Factors that may mitigate moisture-mediated resistance also differed between sites. Slope and aspect were factors of apparent resistance for bunchgrass communities in JODA, while high crop year precipitation appeared to benefit medusahead (Taeniatherum caput-medusae [L.] Nevski) and the weedy native subshrub broom snakeweed (Gutierrezia sarothrae [Pursh] Britton & Rusby) over bunchgrasses and Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young). Increased elevation and distance to disturbed areas were the most important factors of resistance in forb-rich communities at CRMO, with the invasive annuals cheatgrass (Bromus tectorum L.), tumblemustard (Sisymbrium altissimum L.), and Descurainia spp. Webb & Bethel. invading in low elevations and in close proximity to roads or agricultural fields. Such complexity underscores the idiosyncratic nature of the manifestation of resistance and the need for place-based empirical studies to provide information for guiding protected-area management.

Arbuscular mycorrhizal fungi (AMF) may exert profound influences on ecosystem resilience and invasion resistance in rangelands. Maintenance of plant community structure through ecological feedback mechanisms such as facilitation of nutrient cycling and uptake by host plants, physical and chemical contributions to soil structural stability, and mediation of plant competition suggest AMF may be important facilitators in stressful arid environments. Plant-AMF interactions could influence succession by increasing native plant community resilience to drought, grazing, and fire and resistance to exotic plant invasion. However, invasive exotic plants may benefit from associations with, as well as alter, native AMF communities. Furthermore, questions remain on the role of AMF in stressful environments, specifically the mycorrhizal dependency of sagebrush (Artemisia spp.) steppe plant species. Here, we review scientific literature relevant to AMF in rangelands, with specific focus on impacts of land management, disturbance, and invasion on AMF communities in sagebrush steppe. We highlight the nature of AMF ecology as it relates to rangelands and discuss the methods used to measure mycorrhizal responsiveness. Our review found compelling evidence that AMF mediation of resilience to disturbance and resistance to invasion varies with plant and fungal community composition, including plant mycorrhizal host status, plant functional guild, and physiological adaptations to disturbance in both plants and fungi. We conclude by outlining a framework to advance knowledge of AMF in rangeland invasion ecology. Understanding the role of AMF in semiarid sagebrush steppe ecosystems will likely require multiple study approaches due to the highly variable nature of plant-AMF interactions, the complex mechanisms of resilience conference, and the unknown thresholds for responses to environmental stressors. This may require shifting away from the plant biomass paradigm of assessing mycorrhizal benefits in order to obtain a more holistic view of plant dependency on AMF, or lack thereof, in sagebrush steppe and other semiarid ecosystems.

Efficient water use in urban landscapes is a common objective throughout the western United States. Vegetative species promoted for their drought tolerance characteristics are often included in landscapes designed for resource conservation. However, water requirements of most common landscape species have not been quantified. This is especially true for xerophytic species. This lack of landscape plant water requirement data is a significant constraint on the design of efficient irrigation systems and management practices affecting urban landscape water use. Current irrigation practices often fail to consider the unique physiology of xerophytic species, and irrigation scheduling models may not be appropriate for xeric landscapes using xerophytic vegetation as the primary method of reducing water use. This work describes the seasonal patterns of growth and xylem water status for four regionally native xeric shrub species planted in an unirrigated urban landscape in the semi-arid environment of central Oregon. The four species (Artemisia tridentata, Holodiscus microphyllus, Ericameria nauseosa, and Ribes cereum) exhibited substantial growth over the course of 18 months without irrigation in a heavily modified urban soil profile. Water potential of the four species was strongly correlated with surface (10 cm) soil moisture (r ≥ 0.90), less so with reference monthly evapotranspiration (r ≤ 0.55), and only weakly with water vapor deficit (r ≤ 0.22). In A. tridentata and H. microphyllus, xylem water potential became more negative during the growing season and tracked the seasonal decline in soil moisture. In contrast, the xylem water potential of E. nauseosa and R. cereum tracked soil moisture early in the season but became less responsive to soil moisture in the driest months, suggesting different drought adaptation strategies in these species. Three of the four species showed no visual signs of drought stress and maintained acceptable aesthetics even as soil moisture decreased to less than 10%. However, R. cereum exhibited a drought dormancy strategy that made it less aesthetically desirable. These results suggest that extreme xerophytic shrubs provide an opportunity for significant reductions in water use in urban landscapes.

An improved understanding of the relationships among vegetation, groundwater level, and microtopography is crucial for making well-informed management decisions in areas with shallow groundwater resources. We measured plant species abundance/composition and richness in relation to depth to groundwater (DTW) and microtopography in Owens Valley, California, particularly in areas where DTW ranged from 0 to 4 m. Sampling occurred along 67 vegetation transects across three community types. Relationships between DTW and community composition were evaluated using non-metric multidimensional scaling (NMS), while non-parametric multiplicative regression was used to relate DTW and microtopography to species abundance. The dominant gradient in species composition (NMS Axis 1) explained ~51% of variation in our distance matrix and was most strongly associated (r = 0.55) with DTW. The graminoids Juncus arcticus, Leymus triticoides, and Distichlis spicata had strong affinities toward areas with the shallowest DTW (1.5 m). One salt-adapted species Sporobolus airoides and one shrub Ericameria nauseosa dominated areas with intermediate DTW (1.5-2.0 m), whereas the shrubs Atriplex torreyi, Sarcobatus vermiculatus, and Artemisia tridentata were dominant in areas with deeper DTW (2.0 m). Variation in microtopography affected species abundance and increased species richness for vegetation communities at either extreme of the water table gradient, shallow, and deep DTW but not the intermediate DTW. Findings indicate that desert plant communities from shallow aquifers have adapted to different DTW and microtopography conditions and that considering those adaptations may be important to manage groundwater and vegetation resources in these areas.

Cultivation of C3 and C4 crops in semi-arid regions will be severely constrained as global temperatures rise. Consequently, alternative crops need to be sought out that adapt well to heat and drought and are productive despite limited access to water. Traits, such as crassulacean acid metabolism (CAM), enable economically important species such as those in the Agave genus adapt to drought and high temperatures. The succulence and high efficiency of agaves, which enables them to produce biomass with little water, underscores their feasibility as an alternative crop for semi-arid regions, such as the Sonoran Desert in the southwestern U.S. In this paper, we offer a review of the suitability for cultivation of agaves via dryland farming, particularly by rock mulching techniques used by pre-Columbian, Sonoran Desert farmers. This analysis dovetails with information also provided on the biological traits of Agave and its historical and present utilization. Pre-Columbian, Hohokam dryland farmers used rock mulching in the form of rock piles to cultivate agaves. Rock piles acted as a type of mulch to harvest rainfall and to retain soil moisture, which allowed the Hohokam to intensively cultivate agaves during multi-year droughts. Remains of Hohokam rock mulching for agave production can be found at archaeological sites in central Arizona, which provides evidence of the utility of dryland farming and ancient agricultural innovation to reconcile water scarcity in the region. Moreover, the use of rock piles likely bolstered Agave productivity in marginal lands. Although little is known of historic rock mulching to cultivate agaves and its biological implications on plant productivity we suggest its application as a dryland farming model could be a sustainable strategy in the U.S. Southwest.

Ecological restoration of many arid zones is a pressing issue because of recurrent loss of plant cover. Here, we conducted a germination and growth study of three framework plant species, native to the Chihuahuan Desert in Northern Mexico, to optimize the establishment for arid zone restoration. The plant species were Zinnia grandiflora Nutt., Menodora scabra A. Gray, and Yucca elata (Engelm.) Engelm, which were selected for their potential for restoration as drought tolerant species. We evaluated seed germination, survival, and biomass allocation of seedlings under four (high, medium, low, and very low) simulated rainfall sequences as irrigation treatments. Rainfall sequences were obtained from a previous study that considered 35 years of precipitation records. Each sequence is accounted for 20% of probability of a wet, normal, low, or very low year in terms of precipitation occurring in the study area. Germination was conducted in controlled greenhouse conditions and seeding was done in pots con...

The role of fire in restoration of sagebrush plant communities remains controversial mainly because of paucity of information from long-term studies. Here, we examine 15-year post-fire responses of big sagebrush (Artemisia tridentata ssp wyomingensis) and broom snakeweed (Gutierrezia sarothrae), the two most abundant native shrubs at the John Day Fossil Beds National Monument, a protected area in north-central Oregon, USA. Fire effects were studied along gradients of topography and community type through time post-burn. Community types were distinguished as brush, plots dominated by big sagebrush and woodland, plots with a significant presence of Western juniper (Juniperus occidentalis) trees. Fire reduced big sagebrush cover in brush plots up to 100% and in woodland plots up to 86%. Broom snakeweed cover declined by 92% and 73% in brush plots and woodland plots, respectively. Big sagebrush did not show signs of recovery 15 years after burning regardless of topography and community type while broom snakeweed populations were clearly rebounding and prospering beyond pre-burn levels. Our results showed that an area initially dominated by big sagebrush (cover of big sagebrush 10-20%, cover of broom snakeweed 2-4%) dramatically shifted to an area dominated by broom snakeweed (cover of big sagebrush

Western juniper expansion is one of the largest threats to conserving sagebrush steppe ecosystems in the northwestern United States. Juniper expansion has degraded the sagebrush steppe by altering fire regimes and outcompeting shrubs and herbaceous vegetation for limited resources. We characterized the effect of juniper removal in a severely degraded sagebrush steppe habitat for 3 yr following juniper cutting. In addition, we measured the effect of low-intensity seasonal grazing on plant community recovery through cattle exclusion treatments. We monitored plant community composition (exotic annual grasses, preferred grasses, preferred forbs, and shrubs); fuel loads; and juniper recruitment in a factorial design of juniper removal and grazing exclusion. We found that although there were significant differences between cut and uncut juniper treatments, there were no consistent trends across all 3 yr. Our results suggest that other factors, such as timing of precipitation, may also have strong short-term effects on plant community composition. We detected no significant grazing effects during the study period, suggesting the current grazing regime is appropriate for the area. The cutting of juniper increased total fuel loads and herbaceous fuel loads. Compared with open interspace, a twofold increase in juniper seedlings and saplings was detected beneath juniper piles, which will act as sources for future juniper encroachment.

Aloe (Aloe barbadensis Miller) is a water deficit-tolerant plant. Products obtained from the leaf have a high commercial value in the medical, food and cosmetological industries. The aim of this study was to evaluate the growth and development of aloe (Aloe barbadensis M.) plants and the quality of its gel when applying bat guano extract (BGE) and seaweed extract (SE) in different soil moisture contents. A split-plot randomized block design was used with three replicates. The large plots were soil moisture contents: low (13 to 17 %), medium (18 to 22 %) and high (23 to 27 %); the medium plots were the BGE doses (0 and 20 L∙ha-1∙year-1), and the small plots the SE doses (0 and 20 L∙ha-1∙year-1). At 152, 238 and 458 days after the first application of the biofertilizers (DAFAB), plant height (cm), leaf length, width and thickness (cm), gel weight (g) and concentration of total soluble solids (TSS, %) in the gel were measured. Leaf width and thickness were higher when the soil moisture content was close to field capacity (23 to 27 %), while leaf length and width were higher in the first two evaluations when the moisture content was medium (18-22 %). The TSS concentration did not show significant statistical differences (P ≤ 0.05) in any treatment. At the end of the evaluation cycle (458 DAFAB), BGE increased leaf width and thickness.

We evaluated growth and physiology of three wetland graminoids (Distichlis spicata, Leymus triticoides, and Juncus arcticus) as affected by surface and subsurface water. These species are common in western USA and were collected from two areas: Bishop, California and Burns, Oregon. Our hypotheses were: 1) the use of surface water by plants is higher than the use of subsurface water and 2) there are population differences in the response of the species to available water. The species of study were grown in two-layer pots with soil water content in the upper and lower layers independently controlled. The first hypothesis was partially supported by our results, but variability existed among species. However, when all species had equal access to both surface soil water and subsurface water plants tended to preferentially use surface water. We also found that J. arcticus can display reverse hydraulic lift when growing with no subsurface water. The second hypothesis was clearly supported by results. Although the mechanism is not clear, it is possible that an area with periodic and predictable shallow groundwater underlying a dry or saline soil layer, such as the California site, might favor plant populations with high proficiency in water uptake by deeper roots.

Plant propagation is essential for the restoration of degraded ecosystems. Arid areas sustain some drought tolerant plant species such as Yucca elata (Engelm.) Engelm. and Menodora scabra A. Gray. It is widely accepted that drought can increase in intensity and frequency under the current scenario of climate change. Therefore, we conducted a germination study to test these two native plant species of the Chihuahuan desert under different levels of osmotic stress and to determine their response under different levels of drought. In both species, increasing levels of drought affected germination, but germination of Y. elata was not inhibited (13 % of germination) even at -1.5 MPa, while germination of M. scabra was inhibited (0 % germination) at this osmotic potential. These responses show germination of Y. elata is less affected by drought than germination of M. scabra. Therefore, this represents different potential alternatives of reproduction in restoration programs for these species. Whereas Y. elata may be successfully reproduced by seed under dry field conditions, M. scabra may require seedling production and field transplantation or the use of nursing plants in the field.

This greenhouse study evaluated nitrogen and sodium relations of three desert graminoids (Distichlis spicata, Leymus triticoides, and Juncus arcticus) as affected by availability of surface water, subsurface water or both. These species are amply distributed in desert wetlands of western USA where surface and subsurface water are differentially available. Plants of the three species were collected from two areas of ecological distribution: Bishop, California and Burns, Oregon. Because nitrogen and sodium uptake by plants is highly linked to water availability we established three general hypotheses for this study: (1) nitrogen uptake would be greater when plants have surface water available, (2) sodium uptake would be greater when plants do not have surface water available, and (3) there are populations’ differences in the response of the species to water availability. We grew plants in two-layer pots in which soil water content in the upper and lower layers was controlled independently. The first...

Atriplex species are tolerant to salinity and water stress and thus they are suitable for restoration of many degraded ecosystems. In addition, many Atriplex species offer good value as forages. We compared growth and leaf chemistry of Atriplex canescens, a well-known halophyte, and A. acanthocarpa, a poorly-studied species, as affected by salinity in a greenhouse study. Seeds and soil were collected in northern Mexico, the native range of these species. Plants were grown in pots containing native soil and irrigated with NaCl solutions of 0, 50, and 100 mM. Shoot growth of A. canescens declined 37% as NaCl treatments increased from 0 to 100 mM while shoot growth of A acanthocarpa was not significantly affected by salinity. The high salt tolerance of A. acanthocarpa was linked to a high accumulation of leaf sodium (Na) (7- to 13-fold higher than A. canescens). A. acanthocarpa had also higher growth rate than A. canescenes, making the former species a good candidate for cultivation, especially under...

Following western settlement, fire was suppressed directly and indirectly by Euro-American land management practices. Currently, reintroduction of fire into sagebrush steppe systems may be desirable, but long-term fire effects are not well-known. In this 15-year study we used a generalized linear mixed modeling approach to analyze the response of native and invasive grass species to fire in anan Artemisia tridentata subsp. wyomingensis (Wyoming big sagebrush) community in north-central Oregon, United States. This study examined responses of Bromus tectorum (cheatgrass), Pseudoroegneria spicata (bluebunch wheatgrass), and Poa secunda (Sandberg bluegrass) along gradients of community type and topography through time post fire. Community types were identified as either A. tridentata subsp. wyomingensis dominant (brush plots) or Juniperus occidentalis (western juniper) dominant (woodland plots). Cover of B. tectorum was greatest in brush plots. B. tectorum cover increased significantly 5 yr post burn...

The wide range of environmental conditions in which Opuntia ficus-indica (L.) Miller grows implies a great variability in fruit yield and fruit ripening, among other aspects. There is scarce scientific knowledge about fruit yield and fruit quality dependence on within-tree factors such as plant architecture, fruiting cladode position and cladode characteristics, especially over multiple growing seasons. In this work, we addressed the dependence of fruit attributes to the weight of fruiting cladodes for the ‘Rojo Pelon’ variety using the boundary line approach and including a 3-year database (2012–2014). Our results suggest that 14.4 g to 33 g (depending on the year) could be the minimum fruiting cladode dry weight (CDW) required for producing fruits. In general, above 156 g CDW or cladode excess dry weight, the number of fruits per cladode decreased. Considering data from the three years, cladodes with 1497 g of fresh weight were able to produce mean fruit weight per fruiting cladode (MFWC) of 154 g. The maximum load (1602 g) occurred on fruiting cladodes with 1629 g of fresh matter, and corresponded to 2014. These fruiting cladodes grew during 2013, the wettest year of the study (rainfall of 556.2 mm). Remarkably, fruiting cladode excess dry and fresh matter required for producing fruit could be important factors to avoid high variation between productivity levels in successive years. These attributes may be convenient indexes for predicting which cladode will produce fruits.

Quaking aspen, Populus tremuloides, has experienced severe declines in recent years in part due to the effects of changing climate and extreme drought. This study set out to investigate these effects by assessing associations of climatic, edaphic and topographic variables with physiological drought stress in aspen. The study took place on the Zumwalt Prairie in northeastern Oregon, a semi-arid bunchgrass prairie where aspen occur in isolated stands associated with riparian areas and late-season persistence of snow drifts. Using a 33-year time series of Landsat imagery to detect associations of aspen stands late-season snow cover and field measurements of soil moisture in aspen stands during 2017, we found while snow dominated stands were associated with greater soil moisture during spring, levels had equilibrated to those of other upland stands by summer. Measurements of predawn and midday stem Ψ in multiple height classes of aspen ramets revealed associations of both shallow soil moisture and vapor pressure deficit with physiological drought stress in aspen. Analysis of soil texture class revealed an important association with midday stem Ψ, with finer textured soils associated with decreased stem Ψ in comparison to coarser textured soils. While neither topographical characteristics nor snow cover were found to be important drivers of drought stress, topographical curvature was found to have a strong influence on summer soil moisture in upland stands. These findings contribute to our understanding of aspen physiology, drought ecology and landscape hydrology toward the xeric margin of aspen’s range. This information can help land managers anticipate and adapt to changing climates and understand their effects on key plant species such as aspen.

The encroachment of western juniper (Juniperus occidentalis) trees represents a substantial problem in Oregon rangelands because of the displacement of understory vegetation of importance to wildlife and livestock. Therefore, the control of this species is a common ecological restoration practice. However, western juniper control may also affect the carbon sequestration capacity for an area, although this effect is not well understood. Our study site was a paired watershed in central Oregon where western juniper trees were cut in one watershed (treated, 116 ha) and were left intact in another (untreated, 96 ha). Thirteen years after control, we quantified aboveground carbon stocks for western juniper trees, shrubs, grasses, and litter in both the treated and untreated watersheds. We also quantified belowground carbon stocks (roots and soil) in both watersheds at two soil depths (0−25 cm and 25−50 cm). Aboveground carbon stocks were 5.8 times greater in the untreated than in the treated watershed. On the other hand, root carbon stocks were 2.6 times greater in the treated than in the untreated watershed. Soil carbon stocks at both 0−25 cm and 25−50 cm depth were not affected by juniper control. Overall, total ecosystem carbon stocks (average 137.6 Mg C ha−1) were not different between watersheds. Most carbon resided belowground (soil 0−50 cm and roots); 84% and 97% of the total ecosystem carbon, respectively, was found in the untreated and treated watershed. Juniper control represents benefits such as habitat restoration for native wildlife, increased forage for livestock, and restoration of hydrological functions. Our study provides basis to suggest that the benefits of juniper control can be attained without substantially affecting the potential for ecosystem carbon sequestration.

Most of carbon in grasslands comes from underground biomass, particularly in arid grassland ecosystems. However, estimation of root biomass in these ecosystems has been poorly studied. In this study was analyzed the correlation between above ground plant variables and root biomass to develop statistical models for reliable root biomass estimations. Twenty-six plant species were collected within grazing-excluded grasslands. Linear, exponential and logarithmic regression models were performed for each species and for the whole data set to determine the variables that best predicted root biomass. Only Frankenia gypsophila and Dalea gypsophila showed root/shoot ratio (RSR) higher than one. Enneapogon desvauxii and Atriplex acantocarpha had a RSR close to one. Eight species showed statistical significance in at least one of the correlation analyses but only Tiquilia canescens, Bouteloua gracilis, Machaerantera pinnatifida, Lesquerella fendleri, and Atriplex acanthocarpa had both statistical significance and acceptable coefficient of determination (r2 ≥0.50). Using the Marquardt exponential method, 14 out of 15 studied species showed a high determination coefficient and statistical significance. This method was adequate (r2=0.853) to estimate root biomass for the whole set of plants from plant height and crown diameter.

We analyzed temporal and spatial patterns of water use by a functionally-diverse group of Great Basin plant species and determined their water use rates at the whole-plant and individual-leaf scales under variable summer watering. Species studied were the desert grasses Distichlis spicata and Sporobolus airoides, the desert shrubs Artemisia tridentata, Ericameria nauseosa, and Atriplex confertifolia; the wetland/riparian plants Juncus arcticus, Leymus triticoides, and Salix exigua; and the annual exotic Salsola tragus. Plant species were individually grown in 5.8 m2 plots in a common garden in eastern California. Three irrigation treatments in the form of monthly pulses were applied during the summer: low (1.3 cm), medium (2.6 cm), and high (3.9 cm), in addition to a nonirrigated control. Whole-plant water uptake characteristics were determined by soil water depletion at different soil depths, while leaf transpiration was determined by gas exchange. Whole-plant water extraction and leaf transpiration vari...

The effects of western juniper (Juniperus occidentalis) control on understory vegetation and soil water content were studied at the watershed-scale. Seasonal differences in topsoil (12 cm) water content, as affected by vegetation structure and soil texture, were evaluated in a 96-ha untreated watershed and in a 116-ha watershed where 90% juniper was removed in 2005. A watershed-scale characterization of vegetation canopy cover and soil texture was completed to determine some of the potential driving factors influencing topsoil water content fluctuations throughout dry and wet seasons for approximately one year (2014&ndash, 2015). We found greater perennial grass, annual grass, and shrub cover in the treated watershed. Forb cover was no different between watersheds, and as expected, tree canopy cover was greater in the untreated watershed. Results also show that on average, topsoil water content was 1% to 3% greater in the treated watershed. The exception was during one of the wettest months (March) evaluated, when soil water content in the untreated watershed exceeded that of the treated by &lt, 2%. It was noted that soil water content levels that accumulated in areas near valley bottoms and streams were greater in the treated watershed than in the untreated toward the end of the study in late spring. This is consistent with results obtained from a more recent study where we documented an increase in subsurface flow residence time in the treated watershed. Overall, even though average soil water content differences between watersheds were not starkly different, the fact that more herbaceous vegetation and shrub cover were found in the treated watershed led us to conclude that the long-term effects of juniper removal on soil water content redistribution throughout the landscape may be beneficial towards restoring important ecohydrologic connections in these semiarid ecosystems of central Oregon.

In a previous article, Beschta et al. (Environ Manag 51(2):474-491, 2013) argue that grazing by large ungulates (both native and domestic) should be eliminated or greatly reduced on western public lands to reduce potential climate change impacts. The authors did not present a balanced synthesis of the scientific literature, and their publication is more of an opinion article. Their conclusions do not reflect the complexities associated with herbivore grazing. Because grazing is a complex ecological process, synthesis of the scientific literature can be a challenge. Legacy effects of uncontrolled grazing during the homestead era further complicate analysis of current grazing impacts. Interactions of climate change and grazing will depend on the specific situation. For example, increasing atmospheric CO₂ and temperatures may increase accumulation of fine fuels (primarily grasses) and thus increase wildfire risk. Prescribed grazing by livestock is one of the few management tools available for reducing fine fuel accumulation. While there are certainly points on the landscape where herbivore impacts can be identified, there are also vast grazed areas where impacts are minimal. Broad scale reduction of domestic and wild herbivores to help native plant communities cope with climate change will be unnecessary because over the past 20-50 years land managers have actively sought to bring populations of native and domestic herbivores in balance with the potential of vegetation and soils. To cope with a changing climate, land managers will need access to all available vegetation management tools, including grazing.

Agave salmiana is a native plant species harvested for the commercial production of mezcal (Agave spirits) in the highlands of central Mexico. The objective of this study was to identify vegetation changes in natural communities where A. salmiana has been differentially harvested for commercial purposes. Three plant community categories were identified in the state of Zacatecas based on their history of A. salmiana utilization: short (less than 10 years of use), moderate (about 25 years), and long (60 or more years). Species cover, composition, and density were evaluated in field surveys by use category. A gradient of vegetation structure of the communities parallels the duration of A. salmiana use. A. salmiana density was greatest (3,125 plants ha(-1)) in the short-use areas and less (892 plants ha(-1)) in the moderate-use areas, associated with markedly greater density of shrubs (200%) and Opuntia spp. (50%) in moderate-use areas. The main shrubs were Larrea tridentata, Mimosa biuncifera, Jatropha dioica and Buddleia scordioides while the main Opuntia species were Opuntia leucotricha and Opuntia robusta. A. salmiana density was least (652 plants ha(-1)) in the long-use areas where shrubs were less abundant but Opuntia spp. density was 25% higher than in moderate-use areas. We suggest that shrubs may increase with moderate use creating an intermediate successional stage that facilitates the establishment of Opuntia spp. Long-term Agave use is generating new plant communities dominated by Opuntia spp. (nopaleras) as a replacement of the original communities dominated by A. salmiana (magueyeras).

We evaluated invasive exotic weeds and plant species diversity in relation to depth to groundwater (DTW) and microtopography in areas with DTW from 0·3–4 m in Owens Valley, California. Transects dominated by common plant species of the area were read at 1-cm intervals, and species cover was obtained at different scales: 1-m transect portions (microsites), whole transects (68 m average length), and the whole study area. Species richness and the Shannon–Wiener diversity index were obtained in microsites. DTW and microtopographical variation (soil-surface relative elevations) were jointly measured along the vegetation transects. Found in 34% of the sampled transects, the annual Bassia hyssopifolia was the most common exotic weed of the area. Its cover in the whole study area was only 0·9%, but it was the second most dominant species (19% cover) in microsites. B. hyssopifolia coexisted mainly with herbaceous species, typically in places with shallow groundwater (average

This study was designed to better define the nature of the relationship among vegetation, groundwater level and microtopography in an arid area where depth to groundwater (DTW) was 0–4 m. Plant cover, DTW and relative elevations were jointly measured along 67 vegetation transects throughout the Owens Valley, CA, USA. These transects were dominated by major species of the area: Artemisia tridentata, Atriplex torreyi, Ericameria nauseosa, Distichlis spicata, Juncus arcticus, Leymus triticoides, Sarcobatus vermiculatus and Sporobolus airoides. Plant species occurrence was associated with different DTW. J. arcticus and D. spicata occurred more frequently in areas with the shallowest groundwater ( 2·0 m). Species were also linked to different microtopographic positions: L. triticoides and J. arcticus were mainly restricted to depressions whereas A. torreyi and A. tridentata were widely distributed in higher positions on the microtopographical gradient. Only 6% of the variation in vegetation cover was accounted for by DTW throughout the study area (N = 820). Cover of individual species was usually unaffected by DTW variation. Results suggest that species distribution is linked to groundwater conditions, but cover of vegetation is only partially affected by DTW variation. This is possible because water tables in our study area are within the rooting depth of most species and plants appear to be well adapted to shallow DTW variations. Copyright © 2011 John Wiley & Sons, Ltd.

Arid and semiarid rangelands are suitable for responsible biosolids application. Topical application is critical to avoid soil and vegetation disturbance. Surface-applied biosolids have long-lasting effects in these ecosystems. We conducted a 10-year research program investigating effects of biosolids applied at rates from 0 to 90 dry Mg ha−1on soil water infiltration; runoff and leachate water quality; soil erosion; forage production and quality; seedling establishment; plant physiological responses; nitrogen dynamics; biosolids decomposition; and grazing animal behavior and management. Biosolids increased soil water infiltration and reduced erosion. Effects on soil water quality were observed only at the highest application rates. Biosolids increased soil nitrate-nitrogen. Biosolids increased forage production and improved forage quality. Biosolids increased leaf area of grasses; photosynthetic rates were not necessarily increased by biosolids. Biosolids effects on plant establishment are expected only under moderately favorable conditions. Over an 82-mo exposure period, total organic carbon, nitrogen, and total and available phosphorus decreased and inorganic matter increased. Grazing animals spent more time grazing, ruminating, and resting in biosolids-treated areas; positive effects on average daily gain were observed during periods of higher rainfall. Our results suggest that annual biosolids application rates of up to 18 Mg ha−1are appropriate for desert rangelands.

The EDYS (ecological dynamics simulation) model was used to simulate vegetation growth resulting from different experimental treatments for Bromus tectorum control at Yakima Training Center, Washington. The treatments tested in the field for 4 years were seeding, sucrose application, and a combination of seeding and sucrose application. These treatments included burning to favor their implementation. A control plant community with no manipulations was also monitored in the study. The simulations of plant production were not significantly different from the observed field results in 90% of the comparisons, supporting the validity of the model. In long-term simulations, the population of B. tectorum ceased to dominate the plant community in about 12 years regardless of the treatments. Subsequently, the successional patterns were affected by the treatments. The control and sucrose treatments produced similar successional trends dominated mainly by shrubs (Artemisia tridentata and Chrysothamnus nauseosus). In contrast, both seeding treatments, including the one with sucrose, produced successional trends dominated by grasses, which reflected the seed mix composition. Seeding had more lasting effects than sucrose application. However, the seeded species only started to dominate the seeded areas when the dominance of B. tectorum was reduced. The long-term simulations provided projections that were difficult to envision solely based on the results of the 4-year field experiment.

The EDYS model was used to simulate plant production in burned and unburned communities dominated by Bromus tectorum at the US Army Yakima Training Centre, Washington. Model results were validated with 4 years of field data obtained in experiments designed specifically for this study. Subsequently, 50-year simulations of plant production were conducted with normal precipitation for the area and with no disturbances such as grazing or military training. Our simulations of plant production were not significantly different (p>0.05) from observed results of burned and unburned communities in 90% of the comparisons, indicating that EDYS adequately simulated the dynamics of this system. Long-term simulations indicated that annual species, primarily B. tectorum, dominated burned and unburned plant communities for 13–15 years, after which, annuals were replaced by perennials. B. tectorum, however, remained five years longer in the burned than in the unburned community, suggesting that fire favors the persistence of this species in invaded areas. Although B. tectorum dominated both plant communities during the initial simulation period, its production fluctuated greatly. The main perennials that replaced B. tectorum were Chrysothamnus nauseosus, Artemisia tridentata, and Agropyron cristatum. Our long-term modelling results are supported by previous field observations in which annual species are replaced by perennials in the absence of disturbances.

The objective of this study was to quantify the leachate concentration of macronutrients and trace elements obtained through intact soil columns containing two rangeland soils with different texture and amended with biosolids. This was done to evaluate the possibility that surface application of biosolids could adversely affect subsurface water quality via leaching. Biosolids were applied on the surface of the soil columns at 0 (control), 7, 18, 34, or 90 Mg ha−1 in dry basis. Results indicated that biosolids did not increase NO3 − − N leaching, except for the application of 90 Mg ha−1 in the Stellar soil (Calciargid), the finer-textured soil. In the Armesa soil (Haplocalcid), the coarser-textured soil, all leachate NO3 − − N concentrations were higher than the maximum contaminant limit (MCL) for drinking water established by USEPA, irrespective of biosolids treatment. Orthophosphate leaching occurred mostly in the Stellar soil and was favored by biosolids application. Of the trace elements that are regul...

Vegetation cover and production were evaluated after nearly 7 years of livestock grazing exclusion and shrub control in an area with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico. An exclosure was established to prevent livestock grazing. In half of the excluded area, the main shrub, Larrea tridentata, was mechanically controlled. Outside the exclosure, heavy livestock grazing occurred as customary and shrubs were not controlled. Absence of grazing resulted in 50% higher grass cover and 35% higher total biomass. Larrea tridentata cover was twice as high on the grazed area as on the ungrazed area. Vegetation cover was dominated by grasses (42%) in the ungrazed area, whereas in the grazed area, cover was equally divided between grasses (28%) and shrubs (27%). Shrub control did not affect vegetation cover or herbage production. Multivariate analysis confirmed that inside the excluded area, shrub control had little impact on the plant community. The effect of grazing, however, clearly distinguished the community outside the exclosure from that inside the exclosure.

The transpiration coefficient (Kc) method estimates evapotranspiration as a proportion of the evapotranspiration of a reference crop growing in ideal conditions. This approach was designed for irrigated crops and assumes that plants are not subjected to resource limitations. Other assumptions are that plants have high leaf area index and little stomatal resistance to water loss. These conditions are not common for arid-land vegetation. However, mainly due to its simplicity, some studies have proposed the use of transpiration coefficients as a method of determining evapotranspiration in arid environments. In this article, the documented applications of the Kc method in arid environments and their accuracy are reviewed. We also critically discuss the physiological and agronomic concepts that support the Kc method as they relate to water-limited environments. The Kc method typically overestimates water use when plants encounter suboptimal conditions of soil water because it does not consider stomata...

Although changes in depth to groundwater occur naturally, anthropogenic alterations may exacerbate these fluctuations and, thus, affect vegetation reliant on groundwater. These effects include changes in physiology, structure, and community dynamics, particularly in arid regions where groundwater can be an important water source for many plants. To properly manage ecosystems subject to changes in depth to groundwater, plant responses to both rising and falling groundwater tables must be understood. However, most research has focused exclusively on riparian ecosystems, ignoring regions where groundwater is available to a wider range of species. Here, we review responses of riparian and other species to changes in groundwater levels in arid environments. Although decreasing water tables often result in plant water stress and reduced live biomass, the converse is not necessarily true for rising water tables. Initially, rising water tables kill flooded roots because most species cannot tolerate the associated low oxygen levels. Thus, flooded plants can also experience water stress. Ultimately, individual species responses to either scenario depend on drought and flooding tolerance and the change in root system size and water uptake capacity. However, additional environmental and biological factors can play important roles in the severity of vegetation response to altered groundwater tables. Using the reviewed information, we created two conceptual models to highlight vegetation dynamics in areas with groundwater fluctuations. These models use flow charts to identify key vegetation and ecosystem properties and their responses to changes in groundwater tables to predict community responses. We then incorporated key concepts from these models into EDYS, a comprehensive ecosystem model, to highlight the potential complexity of predicting community change under different fluctuating groundwater scenarios. Such models provide a valuable tool for managing vegetation and groundwater use in areas where groundwater is important to both plants and humans, particularly in the context of climate change.

This study evaluated growth patterns of Mexican oregano (Lippia berlandieri) under salt stress and tested the hypothesis that this species is salt tolerant. Plants were grown in Hoagland solution with no NaCl added (control) and with increasing NaCl concentrations added to produce osmotic potentials of −0.30, −0.45, −0.60, −0.90, and −1.20 MPa. Relative growth rate decreased linearly and leaf weight decreased 9-fold as osmotic potential decreased from control to −1.20 MPa. We therefore concluded that, compared to other non-halophytes, Mexican oregano is only moderately tolerant of salinity. Root growth was less affected by salinity than leaf and stem growth. Relative growth rate of Mexican oregano varied from 0.01 to 0.08 g/g/d. These low values suggest a slow recovery process for plants in native stands subject to continuous harvesting. Resumen Este estudio evaluo los patrones de crecimiento del oregano mexicano (Lippia berlandieri) bajo condiciones de estres salino y probo la hipotesis de que e...

This study evaluated the interactive effect of biosolids, time of application, and soil water on plant N concentration and uptake by Bouteloua gracilis (blue grama) and Hilaria mutica (tobosagrass) grown in pots. Biosolids were surface-applied to the soil of the pots either in the spring or the summer at rates of 0, 7, 18, 34, and 90 dry Mg ha−1. All of the pots were irrigated weekly to achieve 40% or 80% of field capacity soil water. The maximum increase in B. gracilis tissue N concentration due to biosolids application with respect to control was 41% in plants grown under the higher irrigation regime and only 15% in those plants grown under the lower irrigation regime. In H. mutica, the higher irrigation level produced an average of 20% higher tissue N concentration than the lower irrigation level across all biosolids application rates. Both species had a much higher N uptake (3.5- to 6.3-fold) under the higher than under the lower irrigation regime due to the large increase in shoot biomass caused by t...

Although some studies have demonstrated that application of biosolids enhances biomass production of desert grasses, there is a lack of information regarding the physiological mechanisms of this enhanced production. The main objective of this study was to evaluate how gas exchange and leaf area production of blue grama ( Bouteloua gracilis ) and tobosagrass ( Hilaria mutica ) are affected by different rates and seasons of biosolids application and irrigation regimes. Plants of both species were transplanted in pots and maintained under a rain-out shelter. Pots were treated either in the spring or summer with biosolids at rates of 0, 7, 18, 34 and 90 dry Mg ha −1 and irrigated at either 40 or 80% field capacity soil water content. The increase in biosolids rates produced increases in leaf area that did not always correspond with increases in photosynthetic rates ( P n ). This suggests that achieving a well-developed canopy was more important than increasing P n per se. However, plant responses to biosolids application varied with irrigation regimes and between species. A decrease in P n of blue grama treated with 34 Mg ha −1 of biosolids was, in part, due to stomatal closure to modulate water loss and possibly to relocation of N for root growth. Under 80% field capacity, tobosagrass seemed to have a less conservative strategy in regulating g s than blue grama. Spring application of biosolids resulted in higher P n than summer application. Photosynthetic rates of blue grama and tobosagrass were not always related to tissue N concentrations.

This research evaluated the effects of level and season of biosolids application and irrigation regime on shoot and root biomass production of blue grama ( Bouteloua gracilis (H.B.K.) Lag. ex Steud.) and tobosagrass ( Hilaria mutica (Buckl.) Benth.), two perennial, warm season grasses of Chihuahuan Desert rangelands. Plants of both species were transplanted to pots and maintained under a rain-out shelter. The plants were treated either in the spring or summer with biosolids at levels of 0, 7, 18, 34, and 90 dry Mg ha −1 and irrigated at 40% or 80% field capacity soil water content. In general, biosolids increased shoot biomass of both species, which was partly a result of the increased soil NO 3 -N concentrations that followed biosolids application. More biomass was allocated to the roots of the grasses when biosolids and irrigation levels were low. In contrast, more biomass was allocated to the shoots when biosolids and irrigation levels were high. Shoot biomass production and soil NO 3 -N concentrations were enhanced more by the spring application of biosolids than by the summer application. The season of application influences the beneficial effect of biosolids on desert grasses.

Shrubland ecosystems are less studied than grasslands regarding the role of domestic grazing on ecosystem degradation in the world, but particularly in Mexico. Of special concern is the paucity of research on soil hydrological responses to the impact of livestock. Here, we assessed the role that specific soil and surface characteristics play in soil hydrology as a response to goat grazing intensity in two different soil types, Regosol and Vertisol, in the Tamaulipan thornscrub of north-eastern Mexico. At each soil unit, a set of grazing regimes was identified, including heavy grazing (HG), moderate grazing (MG) and a no-grazing (NG) reference area, and selected soil properties and plant cover were evaluated. In Regosol sites, soil organic matter varied among all grazing regimes (4.6% higher on NG and 2.1% higher on MG with respect HG) and no dissimilarities on bulk density were recorded. For Vertisol sites, soil bulk density increased with grazing intensity (16% higher on MG and 37% higher on HG with respect to NG) whereas plant cover linearly decreased from 86% in NG to 29% in MG and 9% in HG sites. Soil organic matter content for Regosol, and plant cover and soil bulk density for Vertisol appeared as the best indicators of water infiltration and moisture retention for the grazing conditions assessed. Differences in those key driving variables may help explain surface hydrology responses to goat grazing in rangeland soils of Tamaulipan thornscrub ecosystems and possibly on similar rangelands around the world. Clear signs of vegetation degradation were also observed, manifested by a loss in species diversity and plant cover, especially under heavy grazing. This reflects unsustainable livestock management practices that should be avoided. This study contributes to improve our understanding of rangeland degradation processes and justifies devising more sustainable grazing management schemes.

This study measured water-use efficiency of wildland vegetation at the whole-plant level during two contrasting years to better understand ecosystem responses to precipitation fluctuations in the Great Basin, USA. Biome-representative species included grasses (Distichlis spicata, Leymus triticoides, and Sporobolus airoides), desert shrubs (Artemisia tridentata, Atriplex confertifolia, and Ericameria nauseosa), wetland/riparian plants (Glycyrrhiza lepidota, Juncus arcticus, and Salix exigua), and an exotic annual (Salsola tragus). Plants were grown in 5·8 m2 plots in a common garden in eastern California. Four watering treatments were applied monthly during two summers: control (no water other than natural precipitation), low (1·3 cm), medium (2·6 cm), and high (3·9 cm). Water-use efficiency, here termed water to production (WTPa), was the ratio of water transpired to aboveground biomass produced. Biomass production was 50% lower and WTPa was five times higher during 2009 than 2010. WTPa decreased with watering during 2009 but increased with watering during 2010. Year differences determined vegetation productivity and response to summer watering and were related to the lower winter/spring precipitation during 2009 than 2010. Desert shrubs were more drought tolerant than grasses and wetland plants. Yet, an increase in summer precipitation would primarily benefit herbaceous species and not desert shrubs. Desert shrubs achieved greater standing crop but lower root-to-shoot ratio (RSR) than herbaceous species. Nonetheless, the grass S. airoides had the greatest standing crop overall, mainly because of its greater root production (RSR 5·5). Species differences in growth, WTPa, and biomass allocation should be considered in land management and conservation practices. Copyright © 2012 John Wiley & Sons, Ltd.

Mountain environments are currently among the ecosystems least invaded by non-native species; however, mountains are increasingly under threat of non-native plant invasion. The slow pace of exotic plant invasions in mountain ecosystems is likely due to a combination of low anthropogenic disturbances, low propagule supply, and extreme/steep environmental gradients. The importance of any one of these factors is debated and likely ecosystem dependent. We evaluated the importance of various correlates of plant invasions in the Wallowa Mountain Range of northeastern Oregon and explored whether non-native species distributions differed from native species along an elevation gradient. Vascular plant communities were sampled in summer 2012 along three mountain roads. Transects (n = 20) were evenly stratified by elevation (~70 m intervals) along each road. Vascular plant species abundances and environmental parameters were measured. We used indicator species analysis to identify habitat affinities for non-native species. Plots were ordinated in species space, joint plots and non-parametric multiplicative regression were used to relate species and community variation to environmental variables. Non-native species richness decreased continuously with increasing elevation. In contrast, native species richness displayed a unimodal distribution with maximum richness occurring at mid-elevations. Species composition was strongly related to elevation and canopy openness. Overlays of trait and environmental factors onto non-metric multidimensional ordinations identified the montane-subalpine community transition and over-story canopy closure exceeding 60% as potential barriers to non-native species establishment. Unlike native species, non-native species showed little evidence for high-elevation or closed-canopy specialization. These data suggest that non-native plants currently found in the Wallowa Mountains are dependent on open canopies and disturbance for establishment in low and mid elevations. Current management objectives including restoration to more open canopies in dry Rocky Mountain forests, may increase immigration pressure of non-native plants from lower elevations into the montane and subalpine zones.