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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.

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.

An enhanced understanding of plant water uptake is critical for making better-informed management decisions involving vegetative manipulation practices aimed to improve site productivity. This is particularly true in arid and semiarid locations where water is a scarce, yet precious commodity. In this project, we evaluated the interannual and seasonal variability of soil moisture and transpiration in sapling, juvenile, and mature western juniper (Juniperus occidentalis) trees in a semiarid rangeland ecosystem of central Oregon, USA. Transpiration levels were greatest in mature juniper trees in an untreated juniper watershed (Jensen WS), while the lowest transpiration levels were observed in juniper saplings in a treated watershed (Mays WS) where most mature juniper trees were removed in 2005. Significant differences (p &le, 0.05) in leaf water potential levels observed between predawn and midday readings for all juniper growth stages indicated water is lost over the course of the day. Results showed seasonal precipitation was highly variable over the course of the study (2017 through 2019) and this was reflected in soil water available for tree uptake. This resulted in considerable intra- and inter-annual variation in transpiration. In years with greater winter precipitation amounts (2017 and 2019), juniper transpiration rates were highest during the summer, followed by spring, autumn, and winter. On average, transpiration rates during the summer in the wettest (329 mm) year 2017 were 115 and 2.76 L day&minus, 1 for mature and sapling trees, respectively. No data were collected for juvenile trees in 2017. In the drier (245 mm) year 2018, higher transpiration rates were observed in the spring. On average, spring transpiration rates were 72.7, 1.61, and 1.00 L day&minus, 1 for mature, juvenile, and sapling trees, respectively. Study results highlight the sensitivity of western juniper woodlands to variations in seasonal precipitation and soil moisture availability.

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.

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.

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...

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).

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.

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.

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.

El pasto rosado (Melinis repens) es una especie introducida de África que invade diversos ecosistemas. En México se encuentra en todos los Estados, y en Chihuahua es la especie dominante en extensas áreas depastizales. Las invasiones reducen la calidad y cantidad de los productos y servicios del ecosistema. No se sabe exactamente cuándo llegó al continente americano. Dependiendo de las condiciones climáticas puede comportarse como anual o perenne de vida corta. Produce abundante semilla durante años con precipitaciones por debajo de lo normal comparados con años lluviosos. La germinación de la semilla puede ser en presencia de luz o sin ella, la máxima germinación es entre 20 a 35 ºC; a -0.2 MPa se inhibe la germinación y el fuego no la afecta. Bajo condiciones de humedad y en las primeras etapas de desarrollo presenta una relación raíz parte aérea de 1.13 a 1.90 y una tasa de crecimiento relativo de 0.0034 a 0.15 mg g-1 d-1; además, reduce biomasa en 70 % cuando crece en suelo nativo comparado con suelo esterilizado. Si bien es un mal forraje por su valor nutricional, su principal uso es como forraje. Otros usos son ornamental, medicinal y como fito-remediador. La aplicación de fuego favorece su desarrollo y no se conoce un método de control. Por lo que el aprovechamiento como forraje es lo más viable. Al implementar una campaña de control es importante reducir el movimiento de estaespecie como parte de las actividades humanas.