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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.

Studies of vegetation patterns on small desert mountains have rarely been conduct- ed. The purpose of this study was to evaluate the influence of aspect and elevation on vegetation of Mt. Summerford, a small desert mountain characteristic of the Basin and Range Province of southwestern United States and northern Mexico. Vegetation was randomly sampled on 4 aspects and 3 elevations (0-80 m, 80-160 m, and 160-240 m) of the mountain. South (S) and west (W) aspects had lower grass cover and higher shrub density than east (E) and north (N) aspects. Grass cover decreased as elevation increased on E and N exposures. In contrast, grass cover increased as elevation increased on S and W exposures. A high density of succulent species was found on lower elevations of the S and W aspects. The most frequent species on the mountain were Bouteloua curtipendula, Bouteloua eriopoda, Muhlenbergia porteri, Aristida ternipes, Aloysia wrightii, Ericameria lari- cifolia, Gutierrezia sarothrae, Fouquieria splendens, Dasylirion wheeleri, and Opuntia. Composition of these species, as a mosaic unit, was significantly different among the aspect-elevation units. Species richness was higher in S and W than in E and N aspects. Differences in vegetation patterns were attributed to differential water and nutrient availability on aspects and elevations. This study sug- gests that topographical change is responsible for vegetation patterns in mountains less than 500 m high.