Establishing Native Grasses in a Big Sagebrush–Dominated Site: An Intermediate Restoration Step

Many semiarid rangelands in the Great Basin, U.S.A., are shifting dominance to woody species as a consequence of land degradation including intense livestock grazing and fire suppression. Whereas past rehabilitation efforts in Big sagebrush (Artemisia tridentata) steppes removed the shrub and added introduced forage grasses to successfully shift communities from shrublands to grasslands, current consensus is that native species should be included in restoration projects and that retention of some woody plants is desirable. We examined the potential for interseeding grasses into dense shrub communities as a precursor to thinning shrubs and releasing grasses from shrub interference. We compared seedling establishment of the native grass, Bluebunch wheatgrass (Pseudoroegneria spicata), with that of the Eurasia grass, Crested wheatgrass (Agropyron desertorum), in dense Ar. tridentata stands. Shrubs may play an important role as nurse plants for seedling establishment (reduced solar radiation, ‘‘island of fertility’’ effect) but result in highly contrasting light environments and root interference for seedlings. In experimental plots, we examined effects of Ar. tridentata shade levels (0, 40, 70, and 90% reduction of solar radiation) and initial root exclusion (present/absent) on the establishment and growth of P. spicata and Ag. desertorum seedlings. With this design we evaluated the interference effects of Ar. tridentata on the two grasses and identified the most beneficial microsites for grass restoration in Ar. tridentata– dominated communities. We predicted seedling survival and growth to be greater under moderate shade (40% reduction) and limited root competition than under no or strong shade conditions (0 and 90%) and unrestricted root interactions. Fifty to 85% of the P. spicata and Ag. desertorum seedlings survived the dry summer months of 1995 and 1996 and the intervening winter. Neither shading nor root exclusion from Ar. tridentata affected final seedling survival of either species. Seedling biomass of both grass species was negatively affected by initial root interactions with Ar. tridentata. However, the analysis of seedling biomass variability (coefficient of variation) indicated that in all shade and root-exclusion treatments, some seedlings of both species developed to large individuals to survive in Ar. tridentata–dominated rangelands. Thus, the use of interseeding techniques shows promise for restoring herbaceous species in dense Ar. tridentata stands and should be given further consideration when shrub retention is an important consideration

Biological soil crust effects and responses in arid ecosystems: recent advances at the species level

La costra biológica del suelo (CBS) es un componente complejo del ecosistema que engloba diferentes organismos (líquenes, musgos, hepáticas, cianobacterias, hongos, algas) presentes en las primeras capas de suelo. La CBS se encuentra en una amplia variedad de ecosistemas, aunque generalmente es más abundante en ecosistemas donde la cobertura de plantas vasculares es escasa, como los ecosistemas áridos. En estos ecosistemas, la CBS contribuye considerablemente a su biodiversidad y funcionamiento. Debido a la gran dificultad para la identificación de especies de estas comunidades, la mayoría de la investigación sobre la CBS se ha desarrollado a escala de comunidad y grupo morfológico. A este nivel, se ha podido observar el gran potencial de estas comunidades de contribuir a la estructura y dinámica del ecosistema: interaccionan con las primeras capas del suelo y con otros organismos, participan en la fijación de carbono y nitrógeno, así como en procesos hidrológicos y en el ciclo de nutrientes. Sin embargo, avances recientes en el conocimiento de la CBS arrojan interesantes y marcadas diferencias en la ecología y el papel funcional de las distintas especies que la componen, con las consecuentes implicaciones en la gestión y conservación de estas comunidades y de los ecosistemas que habitan. En particular, se han observado respuestas específicas en términos de presencia, abundancia y frecuencia ante diversos factores ambientales (variables climáticas, tipo de sustrato, presencia de plantas vasculares y perturbación por pastoreo – recuperación natural), así como un efecto a nivel de especie sobre las propiedades del suelo.Biological soil crusts (BSCs) constitute a complex component of the ecosystem formed by different organisms (lichens, mosses, liverworts, cyanobacteria, fungi, algae) associated with soil surface. These communities are present in a wide variety of ecosystems; however, their abundance is generally higher in arid environments with sparse vegetation cover. In these ecosystems, BSCs greatly contribute to biodiversity and ecosystem functioning. Due to technical difficulties in species identification, most studies on BSCs have been carried out at community and morphotype levels. These studies have emphasized the potential role of BSCs in defining ecosystem structure and functioning by: interacting with topsoil layers and other soil organisms, participating in carbon and nitrogen fixation, and also in hydrological and nutrient cycling. Notwithstanding, recent advances in our knowledge about BSCs show substantial and interesting differences in the ecology and functional roles of BSC species, with marked implications in the management and conservation of these communities and their ecosystems. Particularly, it has been observed that BSC presence, abundance and frequency respond differently to diverse environmental factors (climatic variables, soil type, presence of vascular plants, and grazing disturbance - natural recovery) at the species level, and also do BSC effects on topsoil properties.Este trabajo ha sido parcialmente financiado por la Comunidad Autónoma de Madrid (Proyecto REMEDINAL2, S2009/AMB-1783) y el Ministerio de Ciencia e Innovación (Proyecto EPICON, CGL2010-22049)

Differences in plant cover and species composition of semiarid grassland communities of central Mexico and its effects on net ecosystem exchange

"Changes in land use across the semiarid grasslands of northern Mexico have driven a decline of plant cover and alteration of plant species composition. A number of different plant communities have resulted from these changes. Their implications, however, on the carbon (C) cycle and regional carbon balance are still poorly understood. Here, we examined the effects of plant cover loss and changes in species composition on net ecosystem CO2 exchange (NEE) and their biotic and abiotic controls. NEE was measured in five representative plant community types within a semiarid grassland by temporarily enclosing the entire aboveground ecosystem using a chamber method (i.e., geodesic dome). Sites included an oat crop (crop), a moderately grazed grassland (moderate grazing), a 28 yr-old grazing exclosure (exclosure), an overgrazed site with low perennial grass cover (overgrazed), and an overgrazed site presenting shrub encroachment (shrub encroachment). For natural vegetation, rates of standardized daytime NEE for sites with a high plant cover (exclosure and moderate grazing) were similar (P > 0.05) as compared to sites with low plant cover (overgrazed and shrub encroachment). However, yearly total nighttime NEE (carbon loss) was more than double (P < 0.05) for sites with high plant cover compared to sites with low cover, resulting to slight C sinks for the low plant cover sites, and neutral or sources for the high plant cover sites as accounted by daytime and nighttime NEE annual balance. Differences in plant cover and its associated biomass defined the sensitivity to environmental controls. Thus, daytime NEE in low plant cover sites reached light compensation points at lower photosynthetic photon flux density than those from high plant cover sites. Differences in species composition did not influence NEE rates even though there were transient or permanent changes in C3 vs. C4 functional groups. Our results allowed the detection of the large variability and contribution of different plant communities to regional C balance in patchy landscapes. Identification of the role of landscape patches in the regional C balance as either sinks or sources may provide tools allowing land use management strategies that could favor C uptake in patchy landscapes.

Richness and density of grassland bird species assessed by two methods

"Dentro de las aves, las de pastizal son de las más amenazadas en el mundo. En México, estos ecosistemas se han visto afectados por el sobre-apacentamiento con ganado doméstico y la conversión a la agricultura. Para desarrollar planes de conservación es necesario evaluar las poblaciones y utilizar herramientas precisas que permitan conocer el estado de éstas. El objetivo del estudio fue comparar el conteo de aves por transecto y el puntual, para contrastar su efectividad al estimar la riqueza de especies y densidad de poblaciones, mediante cuatro diferentes distancias de detección en tres tipos de hábitats: pastizal mediano abierto, sabana y áreas agrícolas, las cuales diferían en su cubierta vegetal. La cuantificación se realizó en el periodo invierno-primavera 2004 - 2005. Las densidades más altas se obtuvieron con la técnica del conteo puntual en los intervalos de 0 - 25 y 25 - 50 m. El mayor número de especies se detectó con ambos métodos en las distancias de 0 a 75 m. Los resultados son consistentes para las dos estaciones y los tres hábitats, por lo que es posible combinar los métodos probados cuando se realicen inventarios referentes a la diversidad de aves de los pastizales semiáridos de México.""Inside the birds group, the grassland birds are the most threatened in the world. In Mexico, these ecosystems have been affected by overgrazing by domestic livestock and conversion of soil to agriculture. To develop conservation plans is necessary to evaluate birds populations and the use of tools that help us to accurately assess the status of bird populations. The main objective of our study was to compare two bird-count methods (transect and point count), to contrast the effectiveness of estimating species richness and population densities at four detection distances in three contrasting grassland habitats: open middle grassland, savanna grassland and agriculture lands, these habitats differ in vegetation cover. Bird counts were conducted during winter 2004 and spring 2005. Estimated population densities were highest when using the PC method at distances of 0 - 25 m and 25 - 50 m. The greatest number of species was detected when both methods at distances of 0 to 75 m. These results were consistent for both seasons and for the three grassland habitats, in base to these results, combining both methods when realizing birds' diversity inventories in Mexican semiarid grasslands.

Contrasting Impacts of Grazing on Soil Properties and Plant Communities between Semiarid and Temperate Rangeland Ecosystems

We discuss how grazing by large herbivores as a land use option does not necessarily involve a trade-off in terms of soil carbon (C) storage, by presenting results from field grazing gradient experiments from rangeland ecosystems under different climatic conditions in semiarid grasslands from Central Mexico and temperate ecosystems from Northern England. In general, moderate grazing pressure did not reduce soil C in both ecosystems after comparisons with long-term grazing exclusions, and moderate grazing even showed higher soil C in the semiarid area. In the semiarid area, our results are likely explained by grazing tolerance of plant species in moderate grazing pressure, and by effects of herbivores on plant community structure and proportion of bare soil in heavy grazing pressure. In the temperate area, C losses might be more linked to temperature-limitation on heterotrophic soil C respiration. Our results indicate that moderate grazing is compatible with soil C storage, although we also provide warnings against this generalisation under scenarios of climate warming

A Network of Transdisciplinary Observation Mechanisms as a Digital Source of Knowledge on Rangeland, to Communicate and Exchange at Local, Regional and Global Scales

For several decades, interventions geared towards the development of drylands have been the catalysts of much change in a rapidly evolving world, and learning how to build sustainable trajectories that take into account both cultural and contextual variations is becoming of increasingly great import. As local problems become intertwined, and given the difficulty of large-scale collective action, understanding these dynamics requires cognizance of all levels of knowledge governance systems and their interactions. So far as rangelands are concerned, the lack of easily accessible documentation encompassing all knowledge to date is a major impediment to their sustainable development. With this in mind, polycentric governance would allow for centralized decision-making, which would then give rise to solutions that could be adapted to local conditions. Recent advances in technology and the proliferation of data are creating new opportunities for monitoring the progress and performance of multi-scale development efforts, and indeed new and non-traditional data sources will be paramount to the success of such endeavours. For instance, participatory observation is an emerging example of a non-traditional data source that is already making a significant contribution, and has fostered engagement at the community level. We seek to demonstrate the value of implementing transdisciplinary observation mechanisms—here, in relation to Southern Countries’ pastoral systems—and to provide concrete examples of how such mechanisms can be adopted for mainstreaming the use of data from a variety of sources, thereby facilitating the implementation of a sustainable development agenda as part of a continuous learning process. This project has been managed within the framework of the Agadir Platform, infrastructure supported and implemented by Ibn-Zohr University, Morocco

Comparación en la germinación de semillas y crecimiento de plántulas entre gramíneas nativas y exóticas del pastizal semiárido

Exotic African grasses have been introduced into deteriorated semiarid grasslands in northern Mexico to stop soil erosion and improve land productivity. These species are characterized by larger size and greater seed productivity than natives, traits which may contribute to eventual displacement of native grasses. Invasion of natural ecosystems alters species composition and ecosystem functioning, making identification of the traits and mechanisms used by successful invaders vital to controlling this problem. A comparison was done of seed germination potential and seedling biomass allocation in two native grasses (Bouteloua gracilis and B. curtipendula) and five exotic African grasses (Eragrostis curvula, E. lehmanniana, E. superba, Melinum repens and Panicum coloratum). Treatments consisted of washed and unwashed seeds and sterilized and unsterilized soils. Only E. superba exhibited higher (PEn los pastizales del norte de México se han introducido gramíneas de origen africano, con el propósito fundamental de controlar la erosión del suelo e incrementar la productividad. Estas especies en lo general exhiben mayor talla y mayor producción de semilla, por lo que existe el riesgo, en caso de su naturalización, de que desplacen a las especies nativas. La invasión de ecosistemas semiáridos por estas especies exóticas ocasiona múltiples problemas, por lo que es fundamental identificar con anticipación los mecanismos que contribuyen a su propagación. En ensayos con condiciones controladas se trabajó con las gramíneas nativas Bouteloua gracilis y B. curtipendula así como las exóticas africanas Eragrostis curvula, E. lehmanniana, E. superba, Melinum repens y Panicum coloratum. El estudio examinó la germinación de semillas y la asignación de biomasa en plántulas, en condiciones de esterilización de semilla y suelo (semilla lavada y no lavada más suelo esterilizado y no esterilizado). En el presente estudio solamente E. superba superó los porcentajes de germinación (

Potential distributional patterns of three wild ungulate species in a fragmented tropical region of northeastern Mexico

"In the northernmost American tropical forests of eastern Mexico, we analyzed the potential distribution of three ungulate species, Odocoileus virginianus, Mazama temama and Pecari tajacu, in response to several physical, climatic, biological, and anthropogenic variables, in order to identify environmental factors affecting distribution and potential key areas for ungulate conservation. Current presence records for these species were gathered, and potential distribution models were built using Maximum Entropy niche modeling (MaxEnt). Model suitability surfaces were used to calculate remaining potential habitat areas in the region, as well as the potential sympatric area and representation of these areas in Natural Protected Areas. Biological and anthropogenic variables were the best species distribution predictors. Landscape composition (the proportion of different land-use and land-cover classes: forest, agriculture, and pasture) within approximately 120 ha, was the most important variable for all models, influencing each species differently with respect to their tolerance of altered habitats. The remaining potential area of all three species is fragmented and has apparently been nearly lost in plains (<14% remaining). Distribution models allowed us to detect an important location in the western portion of our study area which may function as a large biological corridor in the Sierra Madre Oriental mastogeographic province, a region heavily transformed by land use change. In the context of habitat transformation, management promoting quality matrix at the landscape level promises to be a viable alternative for ungulate conservation in tropical regions of Mexico.

Seed germination and seedling growth in native and exotic grasses in the semiarid grasslands of Northern Mexico

"En los pastizales del norte de México se han introducido gramíneas de origen africano, con el propósito fundamental de controlar la erosión del suelo e incrementar la productividad. Estas especies en lo general exhiben mayor talla y mayor producción de semilla, por lo que existe el riesgo, en caso de su naturalización, de que desplacen a las especies nativas. La invasión de ecosistemas semiáridos por estas especies exóticas ocasiona múltiples problemas, por lo que es fundamental identificar con anticipación los mecanismos que contribuyen a su propagación. En ensayos con condiciones controladas se trabajó con las gramíneas nativas Bouteloua gracilis y B. curtipendula así como las exóticas africanas Eragrostis curvula, E. lehmanniana, E. superba, Melinum repens y Panicum coloratum. El estudio examinó la germinación de semillas y la asignación de biomasa en plántulas, en condiciones de esterilización de semilla y suelo (semilla lavada y no lavada más suelo esterilizado y no esterilizado). En el presente estudio solamente E. superba superó los porcentajes de germinación (P<0.05) de las especies nativas, sin embargo debido a la mayor producción de semillas por las especies exóticas, al menos dos de éstas superaron la producción potencial de propágulos de las nativas. El lavado de semilla favoreció mayor germinación en las tres especies de Eragrostis, mientras que la esterilización de suelo (P<0.05) inhibió germinación de B. curtipendula y E. curvula. Estos resultados sugieren mecanismos inhibidores y que facilitan la germinación, mediados posiblemente por microorganismos, mismos mecanismos se observaron en el crecimiento de plántulas.""Exotic African grasses have been introduced into deteriorated semiarid grasslands in northern Mexico to stop soil erosion and improve land productivity. These species are characterized by larger size and greater seed productivity than natives, traits which may contribute to eventual displacement of native grasses. Invasion of natural ecosystems alters species composition and ecosystem functioning, making identification of the traits and mechanisms used by successful invaders vital to controlling this problem. A comparison was done of seed germination potential and seedling biomass allocation in two native grasses (Bouteloua gracilis and B. curtipendula) and five exotic African grasses (Eragrostis curvula, E. lehmanniana, E. superba, Melinum repens and Panicum coloratum). Treatments consisted of washed and unwashed seeds and sterilized and unsterilized soils. Only E. superba exhibited higher (P<0.05) germination rates than the native species. Due to their overall higher seed production, potential propagule production was highest in two of the exotic grasses (E. superba and E. curvula). Seed washing favored higher germination in the three Eragrostis grasses, whereas soil sterilization inhibited germination in B. curtipendula and E. curvula (P<0.05). Seedling growth variables indicated similar effects in biomass allocation. Propagule production is not necessarily the factor that most facilitates invasive success by an exotic grass species, while the lack of pathogenic microorganisms and/or presence of growth promoting microorganisms may play a vital role.