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Soil processes in arid ecosystems are strongly controlled by resource scarcity. Grazing intensification can induce changes in ecosystem processes through multiple pathways, adding new constraints to those of local conditions. We focus on grazing-induced changes in litter traits and soil environment that may affect litter decomposition and N dynamics in temperate grass-shrub steppes. We performed three litterbag decomposition experiments to evaluate: i) the effect of litter traits in a common garden (ex situ), ii) the effect of soil environment using a foreign common litter substrate (in situ), and iii) the interactive effects of litter traits and soil environment (grazed vs. exclosure communities, reciprocal transplants in situ). Field experiments were replicated in three blocks with paired plots under a long-term exclosure (> 25 years) and under year-round sheep grazing. Local litter included mixtures of species of grasses and shrubs, separately. Grazing exclusion did not alter litter decomposition rates, either through changes in litter traits or in soil environment. Nevertheless, N released during grass litter decomposition was 286% higher in exclosures than in grazing communities. The difference was associated to changes in litter C:N ratio. The effects were maintained when results were integrated to the entire litter community. Our study suggests that litter decomposition rates in arid steppes are strongly controlled by local drivers. Ungulate grazing does not have an important influence on litter mass loss, but it can exert a strong control on N flux during decomposition, by changing grass litter traits.

Livestock grazing has degraded many arid and semi‐arid rangelands around the world, and the drier climate predicted by climate change scenarios may amplify these effects and even lead to catastrophic vegetation shifts. We assess the long‐term effects (1900–2100) of grazing and rainfall on various aspects of vegetation structure including the grass‐shrub balance, the maintenance of spatial vegetation patterns, and the decline or recovery of palatable grasses (e.g. Poa ligularis) on a cover and/or density basis. We used the eco‐hydrological and individual‐based simulation model DINVEG for this purpose, which describes the spatiotemporal dynamics of Patagonian grass‐shrub steppes based on six decades of field research (1955–2018). Rainfall and grazing affected the simulated vegetation structure in different ways. Total plant cover was mostly influenced by rainfall, but the cover of palatable grasses was mostly influenced by stocking rate. Dry conditions and low stocking rates (122 mm/year and 0.2 sheep/ha). High stocking rates and/or drier conditions caused only gradual shifts in spatial vegetation patterns, but maintained the observed positive association for grasses around shrubs. In contrast, shrub encroachment was associated with repulsion between grasses and shrubs and the formation of shrub clusters into a matrix of scattered less palatable grasses. Plant compositional changes occurred through grass species replacement (e.g. P. ligularis is replaced by Pappostipa humilis) and the associated hysteresis effect of palatable grass species: model simulations suggest that 2–3 decades of heavy and year‐long continuous grazing can drive palatable grasses to close to extinction, whereas natural recovery of degraded steppes may take 100 years or longer. Synthesis and applications. Desertification and climate change challenge grazing management in semi‐arid rangelands, especially in already degraded ecosystems. Management that alternates between years of grazing and resting was effective to maintain the cover of palatable grasses, but this allowed for only very slow recovery of degraded steppes. While drier climate and grazing may not change the overall spatial patterns of vegetation, our results are rather pessimistic regarding the short‐term recovery of palatable grasses. This will require increasing complexity in ecosystem restoration efforts, combined with interventions such as sowing, watering, reseeding or major changes in land use.

Ecological modeling that includes plant population processes as a critical determinant of vegetation dynamics is useful for sustainable rangeland management. However, we know little about how long-term sheep grazing pressure drives the plant community structure through changes in different native grass species at both individual and population levels. In this study, we hypothesized that plant populations perform differently under different grazing management due to their specified preference by livestock animals. We also tested whether grazing-rest management, aimed at increasing long-term rangeland sustainability, improves the plant growth of forage grass species. We evaluated plant density, individual morphology and plant-size distribution of dominant grass populations in permanent exclosures and open fields under moderate and intensive grazing pressures in Patagonian steppes (South America). We also examined the effects of seasonal grazing-rest managements on the growth and tillering (asexual reproduction) of forage species plants, using temporary mobile exclosures. Grazing intensity changed population density and structure according to species. Compared to permanent exclosures, moderate grazing maintained the plant density of palatable species highly preferred by sheep, reduced the standing-dead biomass proportion of individual plants, and promoted the green biomass of tussocks. Conversely, intensive grazing (double stocking rates) decreased the plant density and individual size of species highly preferred by sheep, and increased the plant density of non-preferred species. Grazing-rest enhanced forage grass species growth and reproduction compared with year-round grazing management, especially during the growing season of a wet year. Our studies support that sheep can be managed to control the plant-size distribution of dominant grass species, their population dynamics, and thereby the overall forage availability at the community level. Both moderate grazing and grazing-rest management can improve the forage availability and preserve the dominant native grasses. We suggest applying a plant population dynamics perspective to facilitate sustainable management of global rangelands.

AimsArid ecosystem soil processes are strongly bottom-up controlled by resource scarcity. However, grazing intensification can induce changes through multiple pathways and spatio-temporal scales. For example, by changing litter quality and site environmental conditions. Our purpuse was to understand the relative importance of top-down and bottom-up controls of litter decomposition and N dynamics in the Patagonian grass-shrub steppes.MethodsWe performed three litterbag decomposition experiments to evaluate: i) the interactive effects of litter traits and site environmental conditions (grazed vs. exclosure communities) (reciprocal transplants in situ), ii) the net effect of litter traits in a common garden (ex situ), and iii) the net effect of site environmental conditions using a foreign common litter substrate (in situ). The study was performed on three pairs of sites with areas under a long-term exclosure (> 25 years) or under year-round sheep grazing. Local litter included main community species composition and was sorted by grass and shrubs material. ResultsGrazing exclusion did not significantly alter litter decomposition, either through changes in grass litter traits that control decomposition or through changes in the site environmental conditions. Nevertheless, N released during litter decomposition was 286% higher in exclosures than in grazing commumnities. The difference was associated to changes in the grass litter chemical quality. The effects were maintained when we integrated results from the entire litter community. Conclusion Our study suggests that decomposition rates in arid steppes are mainly bottom-up determined, but top-down controls shaping grass litter traits importantly alter the flux of N during decomposition.

Fil: Easdale, Marcos Horacio. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Patagonia Norte. Estacion Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche; Argentina

Transhumant pastoralism is a mobile livelihood strategy in many mountainous, arid and semi-arid regions worldwide. The knowledge of pastoral communities and their lifestyle are strongly rooted in the historical evolution of their own experience in the region, which has largely been part of their social adaptation strategies to environmental variability. However, other recent processes such as urbanization, land-use change, land grabbing and agricultural intensification have promoted the fragmentation of the landscape in this type of regions, thus threatening many mobile farming systems. Our aim was to study the predominant resources and perceptions in the discourse of transhumant pastoralists who are spatially distant from urban areas, with less relative contact with modern lifestyle and consequently, facing certain restrictions on resources availability. The study was oriented to explore the perceptions and adaptations of pastoral families with respect to the problems, challenges, and opportunities that transhumant lifestyle is currently confronting in North-West Patagonia, Argentina. We developed a collective cognitive mapping based on individual semi-structured interviews and network analysis techniques aimed at identifying their predominant perceptions. Traditional cultural issues associated with forms of livelihood and transhumant lifestyle were dominantly manifested, but there were references to some key resources, problems, and opportunities rooted in modern or urban lifestyle system. This mixture of resources and strategies suggests an increasing urban-rural articulation, which is an adaptation to strengthen the current socio-ecological system regime. However, younger generations of transhumant pastoralists are growing in an urban-rural network, which challenges their lifestyles and future developmental pathways. Fil: Easdale, Marcos Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Over 65% of drylands are used for grazing of managed livestock. Understanding what drives grazing effects on the structure and functioning of rangelands is critical for achieving their sustainability. We studied a network of 239 sites across Patagonian rangelands (Argentina), which constitute one of the world's largest rangeland area. We aimed to (i) evaluate how aridity and grazing affect ecosystem structure and functioning and (ii) test the usefulness of the landscape function analysis (LFA) indices (stability, infiltration and nutrient cycling) as surrogates of soil functioning. Aridity decreased species richness and the cover of palatable grasses but increased the cover of palatable shrubs. Grazing pressure negatively impacted the cover of palatable grasses and species richness but did not affect the cover of shrubs. Aridity had direct and indirect negative relationships with the LFA indices. Grazing pressure had no direct effects on the LFA indices but had an indirect negative effect on them by affecting vegetation structure. The LFA indices were positively and negatively correlated with soil organic carbon and sand contents, respectively, suggesting that these indices are useful proxies of soil functional processes in Patagonian rangelands. Our findings indicate that aridity and overgrazing have convergent effects on the structure and functioning of ecosystems, as both promoted reductions in species richness, the cover of palatable grasses and soil functioning. Rangeland management activities should aim to enhance species richness and the cover of palatable grasses, as these actions could contribute to offset adverse effects of ongoing increases in aridity on drylands. Copyright © 2017 John Wiley & Sons, Ltd.

In general, there is more knowledge about aboveground structure and processes than about those belowground. It has been proposed that plants are belowground territorial and root segregation explains species coexistence. We explored this idea by studying root intermingling of perennial graminoid plants in an arid Patagonian steppe. We extracted soil samples under target species. Additionally, we buried root traps filled with sieved soil to quantify root colonization close to plants (zone of high influence), of five dominant graminoid species. We sorted root biomass by species from samples and traps using a root-trait taxonomic key with 95% accuracy. Both studies indicated that the zone of high influence is occupied by roots of target and neighbor species (1–4 species) but showed differences in relative biomass of species. After 4 months, species with high root RGR show dominance in traps. This soil pre-emption seems transitory because in the descriptive study dominant species predominated independently of target species. We propose that coexistence among active roots of several species could be explained by different soil occupation rates in the zone of high influence. More studies are needed in relation with resource use in order to comprehend relationship between above and belowground biomass distributions. Fil: Reyes, María Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Bare soil is an idiosyncratic and important feature of arid ecosystems that can be affected by human land use such as domestic grazing intensification. Here we focused on the study of individual bare soil areas (BSA) and their long-term dynamics using DINVEG (spatially-explicit simulation model). In Patagonian rangelands we photographed BSA in grazed and ungrazed stands (n = 50). Compared with exclosure, grazing increased the size of the BSAs (17%, p

Fil: Herrero Jáuregui, Cristina. Complutense University of Madrid. Departament of Biodiversity, Ecology and Evolution. Madrid, Spain. Fil: Arnaiz Schmitz, Cecilia. Autonomous University of Madrid. Socio - Ecosystems Laboratory. Madrid, Spain. Fil: Reyes, María Fernanda. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina. Fil: Telesnicki, Marta Cecilia. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina. Fil: Hernández Agramonte, Ignacio. University of Tartu. Department of Botany. Institute of Ecology and Earth Sciences. Tartu, Estonia. Fil: Easdale, Marcos H. Instituto Nacional de Tecnología Agropecuaria (INTA). Centro Regional Patagonia Norte. Estación Experimental Agropecuaria Bariloche (EEA Bariloche). San Carlos de Bariloche, Río Negro, Argentina. Fil: Schmitz, María Fe. Complutense University of Madrid. Departament of Biodiversity, Ecology and Evolution. Madrid, Spain. Fil: Aguiar, Martín Roberto. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA). Buenos Aires, Argentina. Fil: Gómez Sal, Antonio. University of Alcalá. Life Sciences Department. Ecology. Alcalá, Spain. Fil: Montes, Carlos. University of Madrid. Socio - Ecosystems Laboratory. Madrid, Spain. Erratum grafs.

Research linking functional traits to competitive ability of coexisting species has largely relied on rectilinear correlations, yielding inconsistent results. Based on concepts borrowed from natural selection theory, we propose that trait?competition relationships can generally correspond to three univariate selection modes: directional (a rectilinear relationship), stabilising (an n-shaped relationship), and disruptive (a u-shaped relationship). Moreover, correlational selection occurs when two traits interact in determining competitive ability and lead to an optimum trait combination (i.e., a bivariate nonlinear selection mode). We tested our ideas using two independent datasets, each one characterising a group of species according to (a) their competitive effect on a target species in a pot experiment and (b) species-level values of well-known functional traits extracted from existing databases. The first dataset comprised 10 annual plant species frequent in a summer-rainfall desert in Argentina, while the second consisted of 37 herbaceous species from cool temperate vegetation types in Canada. Both experiments had a replacement design where the identity of neighbours was manipulated holding total plant density in pots constant. We modelled the competitive ability of neighbours (i.e., the log inverse of target plant biomass) as a function of traits using normal multiple regression. Leaf dry matter content (LDMC) was consistently subjected to negative directional selection in both experiments as well as to stabilising selection among temperate species. Leaf size was subjected to stabilising selection among desert species while among temperate species, leaf size underwent correlational selection in combination with specific leaf area (SLA): selection on SLA was negative directional for large-leaved species, while it was slightly positive for small-leaved species. Synthesis. Multiple quadratic regression adds functional flexibility to trait-based community ecology while providing a standardised basis for comparison among traits and environments. Our analyses of two datasets from contrasting environmental conditions indicate (a) that leaf dry matter content can capture an important component of plant competitive ability not accounted for by widely used competitive traits, such as specific leaf area, leaf size, and plant height and (b) that optimum relationships (either univariate or bivariate) between competitive ability and plant traits may be more common than previously realised. Fil: Rolhauser, Andrés Guillermo. Universidad Nacional de San Juan; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Nordenstahl, Marisa. Universidad Nacional de San Juan; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Pucheta, Eduardo Raúl. Universidad Nacional de San Juan; Argentina

In the last decade, probably in response to global changes and the environmental crisis, the use of the term "social-ecological system" (SES) in scientific literature has grown. This is certainly a sign that the need and importance of transdisciplinary research has been recognized. Here, we explore whether the use of the term is a buzzword or, rather, actually represents a key concept in the integration of social and ecological research. We compiled a database of publications (N = 1289) that mentioned SES in the title, keywords and abstract. Subsequently, we analyzed the authors' affiliations, type of work (conceptual, empirical or review), study site, prevailing human use, temporal and spatial scales of the analysis, kind of variables analyzed (socioeconomic or biophysical), and the method/s used to integrate them. We detected four time spans in the use of the term (1975-1997, 1998-2006, 2007-2012, 2013-2016). Our results suggest that SES is a widely invoked concept in the study of the interface between social and ecological systems. Most works show some common elements, such as the analysis of resilience, ecosystem services, sustainability, governance and adaptive management. However, the majority of studies do not study SES as a whole, integrating both social and ecological variables and their feedback loops. We consider SES as a concept still in construction in order to build a necessary framework for the integration of social and ecological sciences. For a robust evolution, we recommend that one focus on: (i) A conscious, discussed and agreed effort of scientists to conduct the transdisciplinary research needed to study SES; and (ii) the development of methodological tools for the true integration of social and ecological data, This study was partly supported by the project, ECOGRADIENTS (CGL2014-53782-P), funded by the Spanish Ministry of Economy and Competitiveness (2015-074408)

Patch‐size distribution and plant cover are strongly associated to arid ecosystem functioning and may be a warning signal for the onset of desertification under changes in disturbance regimes. However, the interaction between regional productivity level and human‐induced disturbance regime as drivers for vegetation structure and dynamics remain poorly studied. We studied grazing disturbance effects on plant cover and patchiness in three plant communities located along a regional productivity gradient in Patagonia (Argentina): a semi‐desert (low‐productivity community), a shrub‐grass steppe (intermediate‐productivity community) and a grass steppe (high‐productivity community). We sampled paddocks with different sheep grazing pressure (continuous disturbance gradients) in all three communities. In each paddock, the presence or absence of perennial vegetation was recorded every 10 cm along a 50 m transect. Grazing effects on vegetation structure depended on the community and its association to the regional productivity. Grazing decreased total plant cover while increasing both the frequency of small patches and the inter‐patch distance in all communities. However, the size of these effects was the greatest in the high‐productivity community. Dominant species responses to grazing explained vegetation patch‐ and inter‐patch‐size distribution patterns. As productivity decreases, dominant species showed a higher degree of grazing resistance, probably because traits of species adapted to high aridity allow them to resist herbivore disturbance. In conclusion, our findings suggest that regional productivity mediates grazing disturbance impacts on vegetation mosaic. The changes within the same range of grazing pressure have higher effects on communities found in environments with higher productivity, markedly promoting their desertification. Understanding the complex interactions between environmental aridity and human‐induced disturbances is a key aspect for maintaining patchiness structure and dynamics, which has important implications for drylands management. Fil: Oñatibia, Gastón Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Boyero, Luciano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Domestic herbivores’ effect on vegetation is spatially heterogeneous, being one of the major causes of forage resources degradation. It has been proposed that paddock size controls grazing impact’s heterogeneity because as size decreases, herbivores’ utilization is spatially more even. However, this has not been critically evaluated in commercial-scale paddocks isolating paddock size effects from other factors influencing the interaction between herbivores and vegetation. Here we assessed how paddock size mediates the heterogeneity of continuous sheep grazing effects on vegetation, at constant stocking rate in Patagonian steppes. We selected three small (ca. 110 ha) and three large (ca. 1 100 ha) paddocks dominated by the same plant community. All paddocks contained a single watering point and presented similar shape. Total and specific plant cover, vegetation patchiness, population size distribution of dominant grass species, plant morphology, and sheep feces density were estimated at increasing distances from watering points. Relationships between vegetation variables and distance from the watering point were in most cases asymptotic exponential, although responses generally differed between small and large paddocks. In small paddocks, vegetation variables mostly reached a plateau at a short distance from the watering point (~ 200 m). Instead, in large paddocks, the changes in vegetation variables were larger and more gradual, and reached a plateau at much greater distances (~ 2 000 m). Vegetation heterogeneity throughout the paddock was lower in small than large paddocks. Our findings suggest that paddock size mediates the spatial pattern of grazing effects on vegetation. Reducing paddock size decreases grazing impacts spatial heterogeneity, which makes plant-animal interactions more predictable and might improve forage utilization efficiency. Fil: Oñatibia, Gastón Rafael. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Aguiar, Martin Roberto. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Las ciencias agropecuarias constituyen un vínculo académico entre sociología y ecología. Actualmente, existe la predominancia de una perspectiva tecnocrática orientada a aumentar la productividad y la eficiencia, con una impronta muy operativa e instrumental en el abordaje de muchos problemas complejos, relegando a segundo plano muchos otros aspectos que debieran abordarse en relación con la sustentabilidad y el desarrollo rural. El objetivo de este artículo es discutir el papel de las ciencias agropecuarias como nexo académico para abordar problemáticas socioambientales y la tensión que enfrenta la conservación de los ecosistemas rurales y el desarrollo territorial. The farming sciences are an academic link between sociology and ecology. Currently, there is a prevalent technocratic perspective intended to increase both the productivity and the efficiency with a strong instrumental and operative drive in order to cope with many complex problems. This way some other aspects have been put in the background, even though they should be considered when dealing with the rural development and sustainability. The paper aims to discuss on the role of the farming sciences as an academic link useful to cope with social-environmental problems and the tensions arising in the preservation of rural ecosystems and the territorial development. Fil: Easdale, Marcos Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Patagonia Norte. Estacion Experimental Agropecuaria San Carlos de Bariloche. Instituto de Investigaciones Forestales y Agropecuarias Bariloche. - Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Patagonia Norte. Instituto de Investigaciones Forestales y Agropecuarias Bariloche.; Argentina Fil: López, Dardo Rubén. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Background and Aims Dioecious plants are of particular concern in view of global environmental changes because reproductive females are more sensitive to abiotic stresses, thus compromising population viability. Positive interactions with other plants may counteract the direct effects of any abiotic environmental stress, allowing them to thrive and maintain a viable population in suboptimal habitats, although this process has not been tested for dioecious species. Furthermore, almost no data are available on the outcome of such species interactions and their link with local spatial patterns and sex ratios. Methods We set up a field experiment with Poa ligularis, a dioecious native grass from the arid grasslands of South America. We studied the interaction of male and female plants with cushion shrubs of contrasting ecological strategies. We experimentally limited direct shrub-grass competition for soil moisture and transplanted plants to evaluate the amelioration of abiotic stress by shrub canopies (i.e. sun and wind) on grasses. We also studied the distribution of naturally established female and male plants to infer process-pattern relationships. Key Results Positive canopy effects as well as negative below-ground effects were more intense for females than for males. Deep-rooted Mulinum spinosum shrubs strongly facilitated survival, growth and reproduction of P. ligularis females. Naturally established female plants tended to distribute more closely to Mulinum than co-occurring males. Female growth suffered intensive negative root competition from the shallow-rooted Senecio filaginoides shrub. Conclusions Interactions with other plants may reduce or enhance the effect of abiotic stresses on the seemingly maladapted sex to arid environments. We found that these biased interactions are evident in the current organization of sexes in the field, confirming our experimental findings. Therefore, indirect effects of climate change on population sex ratios may be expected if benefactor species abundances are differentially affected. Fil: Graff, Barbara Pamela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Almeida, Rocio Jezabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

In many Northern Hemisphere salt marshes, recovery of disturbance-generated bare areas usually occurs within a few years. However, in some southwestern Atlantic marshes, bare patches may remain unchanged for several years. Here we investigated biological and physical factors that might affect bare patch colonization in a Mar Chiquita coastal lagoon salt marsh (Argentina). We evaluated natural seedling emergence of the pioneer pickleweed plant Sarcocornia perennis, considering distance to mature plants and the herbivory/bioturbation exerted by the crab Neohelice granulata (using exclosures). Almost no seedling emergence was observed in patches distant from mature plants, while higher emergence resulted in close patches. Crab exclusion did not affect seedling counts. Nevertheless, most of these seedlings did not survive high-temperature months. We analyzed if colonization was favored by increasing the availability of S. perennis seeds, and we found similar seedling emergence in patches both close and distant to mature plants. As in the previous experiment, most of them did not survive the high-temperature months, but some seedlings could establish within crab exclosures. Finally, we used a shade cloth to reduce solar radiation, but this did not increase seedling survival, which was only favored in crab exclosures. In summary, our results suggest that seed availability, followed by the presence of crabs (but not solar radiation), affect the rate of patch recovery. Additionally, our results show that life-history traits (seed ecology) of the colonizer can be a key and are a usually overlooked driver of salt marsh secondary succession. Fil: Kaminsky, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. ; Argentina Fil: Alberti, Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. ; Argentina Fil: Iribarne, Oscar Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

Changes in land use often increase the provisioning ecosystem services at the cost of decreasing the regulating services. Thus, the appropriation of primary production to optimize the supply of forage for livestock production may undermine C and N storage, essential to maintain the integrity of ecological systems and the biosphere. The aim of this work was to study this trade-off by estimating the effect of grazing intensity on two provisioning and regulating ecosystem services (forage supply and C and N storage, respectively) in a 300 km2 Patagonian steppe. In areas with different historical sheep grazing regime (intensive, moderate and ungrazed), we estimated forage supply through the aboveground biomass of preferentially consumed species as well as total C and N storage in plants, through forage and non-forage aboveground biomass, litter and root biomass in the top 20 cm of soil. We found that forage supply and C and N storage were highest in moderately grazed areas and were positively correlated, indicating the absence of trade-offs between them. Grazing exclusion had no effect on total plant C and N, but decreased these stocks in green grass biomass in relation to moderate grazing. Intensive grazing decreased both provisioning and regulating services, markedly diminishing grass C and N stocks and grass forage compared to other conditions. Conversely, shrubs and roots were not influenced by grazing regime. This study provides evidence that in arid rangelands, an adequate grazing management could be a key control to complementarily maximize both provisioning and regulating ecosystem services. Fil: Oñatibia, Gastón Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Semmartin, María Gisela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

The article from Keeler and colleagues (2017) highlighted five relevant issues to modify how academic institutions may improve the linkage of the scientific community and societal needs. In this letter, we highlight some issues that, from our Latin American experience, may broaden the discussion.First, linking academia and society is an urgent need. However, it is difficult to think about mechanisms that allow the integration of academia with society as a whole. Society is far from homogenous. Different stakeholders may have opposite views of situations that from the academic sector are defined as a problem. For example, deforestation will be perceived as a problem by aboriginal communities but as a virtuous process by companies involved in land-grabbing. The strategies to build bridges with society must start from recognizing the diversity of stakeholders, their needs and worldviews, and the actual and potential conflicts.Second, we agree with Keeler and colleagues about the need to integrate departments of basic science with those of more applied sciences. However, we emphasize that the social links of research do not necessarily relate to how much research is applied versus basic. The contribution of those who work on fundamental issues materializes not only in providing the bases for further technological developments but also in the development of critical thinking in their students. Instead of applied versus basic, we must care about good versus bad science.Third, we agree with Keeler and colleagues about the need to break down the elitist academic structure. However, by definition, the elitist structure has positive feedbacks. The magnitude of cultural difference, prestige, and authority reinforce the isolation. It is necessary to foster counterforces, such as encouraging the incorporation into universities of sectors marginalized from high education. This not only allows a better contact with specific communities but also increased diversity in a broad sense. Since the ?Reforma Universitaria? (discussed below), many Latin American countries have public, autonomous, and gratuitous university systems. This academic system is an ?antielitist? mechanism.Fourth, academia has to lead the discussion and the search for solutions to the environmental crisis. However, this has limits. Academia is not in the best position to promote interinstitutional programs with an active participation of a variety of stakeholders. Governments should pull the academic sector by involving it in policies design.There are no panaceas for institutional arrangements. However, it is useful to observe the diversity of responses and to learn from them. Those of us who have completed postgraduate studies in US incorporated institutional models that allow us to look critically at our own universities. In Latin America, the discussion of the society?academia link has a long history. We want to highlight two characteristics, more or less common in public universities of Argentina and Uruguay. First, there is an explicit mandate in public-university statutes that all academic units must carry out teaching, research, and extension (Arocena and Sutz 2005). The extension mandate involves a direct relationship among faculty and stakeholders to clearly formulate a problem, contribute to its solution, support vulnerable actors, spread knowledge, raise awareness in society, and work with decision-makers. The second one is the cogovernance (co-gobierno in Spanish) of the university. The Academic Boards of Universities, the supreme governing body, are integrated with elected representatives from among professors, alumni, and students (and in some cases, administrative staff). The presence of alumni and students is an excellent mechanism to connect the academic world with social demands and to form leaders with broadened views. Keeler and colleagues indicate the need for ?an institutional revolution.? The previously outlined mechanisms of linking academia and society were, in fact, the result of a revolution, the so-called ?Reforma Universitaria,? promoted by the students of the Universidad Nacional de Córdoba (Argentina) in 1918 that later extended throughout Latin America. Fil: Paruelo, José. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Universidad de la República; Uruguay Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Question: Root biomass distribution and below-ground processes are the main drivers of plant community structure and dynamics in arid rangelands. However, despite their relevance, below-ground plant responses to disturbance regimes remain poorly understood. This knowledge is a pressing issue since most of our ideas derive from extrapolating above-ground ecological theory and data. Here, we asked how domestic grazing management changes (intensification and abandonment) impact on both below-ground species co-occurrence at microsite level (point-richness) in relation to above-ground patterns and below-ground biomass distribution of dominant graminoid species across different soil layers. Location: Patagonian steppe, Argentina. Methods: We sampled and compared ungrazed, moderately grazed and intensively grazed steppes. We evaluated below- and above-ground point-richness (microsite level: 6-cm diameter), as well as total and specific root biomass in the top 20 cm of soil along 50-m transects in commercial paddocks. Results: We found independence between fine-scale below- and above-ground responses. Below-ground point-richness was at least three times higher than above-ground point-richness. Besides, below-ground point-richness decreased from 4.2 species in ungrazed sites to 3.4 species in intensively grazed ones. Neither grazing intensification nor abandonment changed total root biomass, although intensification changed the root biomass composition, reducing preferred and increasing non-preferred grass species. Strikingly, below-ground point-richness and total root biomass did not differ between microsites covered and not covered by vegetation. This pattern was not affected by grazing. Conclusions: Our findings showed a higher degree of fine-scale below-ground species co-occurrence than above-ground in this Patagonian steppe. The intensification of grazing slightly decreased below-ground species co-occurrence and changed root composition (species abundance), although grazing management did not modify the high degree of independence between below- and above-ground structure. Even though intensive grazing markedly decreases above-ground biomass, total below-ground biomass does not vary along a wide range of grazing conditions. In general, most of our knowledge about vegetation responses to grazing is based on above-ground information, assuming that below-ground patterns and processes are analogous to those above-ground. This study suggests that below- and above-ground community structure at fine-scale are not strongly correlated and they can be differentially affected by grazing. Fil: Oñatibia, Gastón Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Reyes, María Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Aims: In arid communities, it has been proposed that individual plants can extend their roots beyond their canopy exploring neighbouring bare ground areas. This becomes relevant in systems where the vegetation is distributed in patches surrounded by bare soil. However, whether roots of different species may be overlapping under bare ground areas is still controversial. The factors controlling root responses when no plants appear to be directly influencing the gap among patches are still unclear. The aim of our study was to detect perennial grasses responses to an N enrichment pulse. Methods: In a semi-arid steppe (Patagonia, Argentina), we buried root traps filled with sieved soil with and without N addition, under bare soil patches. Traps were harvested after 4 and 6 months. Trap neighbourhoods (30 cm in diameter) included at least three of the dominant tussock species. After harvests, we identified species in the traps by root traits, and quantified diversity, biomass and specific relative growth rates. Important Findings: Bare ground areas show simultaneous root growth of different species. Diversity of perennial grass roots was higher with N addition than without it in the first harvest (4 months), but this difference disappeared in the second harvest (6 months). Root biomass was maximal after 6 months in N addition traps. Species preferred by herbivores (Bromus pictus and Poa ligularis) showed rapid growth and responses to N addition. Differences between harvests may be an indicative that N pulses interact with rising temperatures and soil water content as growing season progress. Fil: Reyes, María Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Soil patchiness is a key feature of arid rangelands. As root proliferation contributes to soil exploration and resource uptake, it is ecologically relevant to understand how species respond to soil heterogeneity and coexist. Campbell et al.'s influential 1991 hypothesis proposes that dominant species deploy root systems (scale) that maximize soil volume explored. Instead, subordinate species show accurate root systems that exclusively proliferate in nutrient-rich patches (precision). After many experiments under controlled conditions, the generality of this hypothesis has been questioned but a field perspective is necessary to increase realism in the conceptual framework. We worked with a guild of perennial graminoid species inside a grazing exclosure in an arid Patagonian steppe, a model system for ecological studies in arid rangelands for four decades. We buried root traps in bare ground patches with sieved soil, with or without a pulse of nitrogen addition, to measure specific root biomass and precision at 6 and 18 months after burial. We also estimated scale (root density) in naturally established plants, and root decomposition in litter bags. Several species grew in root traps. Dominant species showed the highest root biomass (in both harvests) and scale. Subordinate species grew more frequently with nitrogen addition and showed lower biomass and scale. Similar total root biomass was found with and without nitrogen addition. Species differed in root decomposition, but correcting species biomass by decomposition did not change our conclusions. We did not find a relation between scale and precision, indicating that Campbell's hypothesis is probably not supported in this Patagonian steppe. Soil resource acquisition differences probably do not utterly explain the coexistence of dominant and subordinate species because the steppe is also affected by large herbivore grazing. We propose that root proliferation in this steppe is the result of the interaction between individual density in the community and specific root growth rates. Fil: Reyes, María Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Aim: We studied the legacy effects of shrubs during the downgrade phase of high–cover patches. Specifically, are woody species able to modify environmental attributes at patch level to such an extent as to alter the colonization once they have vacated their original position? Methods: We monitored five environmental variables along an experimental four-stage downgrading gradient of high–cover patches during two years in cold- and warm-seasons, individual plant growth during three years, as well as the floristic composition of patches along the same gradient after 13 years. Results: The downgrade of high–cover patches reduces the aboveground protection due to the increase in wind speed (400–500%) and evaporation rate (43–160%) associated with shrub death and senescence. In addition, high–cover patches increase the total soil nitrogen (400–600%) and reduce the infiltration rate (44–73%) on the top layer. Leaf length and flower culms of grass tussocks were lower in bare soil patches (7.5 cm and 3) compared to whatever degradation stage of high–cover patches (9–10 cm and 18–32). Floristic composition after 13 years reveals that grass species occupied the patch stages differentially, with a disjunctive pattern among species within the Poa and Pappostipa genus. Conclusions: Legacy effects prompted by shrubs through changes in soil properties at the horizontal plane can conditioned the patch dynamics. The ability of different plant species to cope with the spatial heterogeneity at the horizontal plane should be included as a new criterion to define plant strategies from arid ecosystems according to the gap–phase dynamics and mosaic maintenance. Fil: Cipriotti, Pablo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Métodos Cuantitativos y Sistemas de Información; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Ecología; Argentina

Year-to-year variability in field seedling emergence in arid rangelands poses questions about the viability of perennial grasses threatened by overgrazing. There are practical difficulties in estimating long-term seedling emergence for perennial species with erratic behavior (high temporal variability). We present a novel approach combining seed germination studies, modeling, and field experiments to estimate long-term germination probability using Poa ligularis as a perennial grass model. Additional objectives were to evaluate: (i) germination requirements of different P. ligularis populations, (ii) field emergence behavior at two extreme locations within the distributional range in the southern region, and (iii) the influence of microsite or local soil on field emergence. Germination parameters were obtained from 8 populations collected across a 12° latitude transect. Germination parameters were combined with a soil water model to estimate long-term germination (used as a proxy of field emergence) in the southernmost location. Germination requirements differed across populations and correlated with environmental conditions of collection sites, demonstrating ecological significance. Field experiments showed very low emergence. Simulations for the southern location indicated erratic emergence. Fifty percent of the years had nil simulated field emergence and the magnitude of the events, when occurred, was small. The magnitude of these events depended on the population, demonstrating an additional genetic constraint. Erratic field emergence arises from the mismatch between environmental conditions and germination requirements. Knowing favorable climatic conditions triggering seed germination (and thus emergence) events are key for opportunistic management of species with this erratic behavior.

In most arid ecosystems, the vegetation is organized into two-phase mosaics, where high-cover vegetation patches are interspersed in a matrix of low plant cover. We studied the role of the biotic interaction balance (competition/facilitation) between shrubs and grasses as a driver of patch dynamics and maintenance of two-phase vegetation mosaics. Following Watt's seminal model, we conducted two field experiments in which we manipulated different vegetation patches to obtain the different stages along the building and degradation dynamics of high-cover patches. In addition we applied two possible belowground competition treatments (natural and experimentally reduced). We measured plant variables (emergence, survival, height, flower culms) on grass seedlings and transplants. We integrated all plant measurements into a single positive and negative component, to calculate the net balance along three stages of the patch dynamics proposed. The net biotic interaction balance was negative during the early and mature stages of high-cover patches because the average standardized effect from the negative component was below −0.44, while the positive component was not different from zero. However, the net biotic interaction balance was positive during the degraded stages of high-cover patches because the negative average component was −0.37, while the positive component reached 0.58. The negative net effects during early and mature stages of high-cover patches can be explained by the occurrence of wet years, because high rainfalls hide the aboveground facilitation. Our findings point out the importance of complementary mechanisms to the interaction balance in the mosaic maintenance (e.g. trapping of seeds by shrubs) according to the inter-annual rainfall variability.

Fil: Cipriotti, Pablo Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Instituto de Investigaciones Fisiologicas y Ecologicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomia. Departamento de Metodos Cuantitativos y Sistemas de Informacion; Argentina

Summary 1. Dioecious plants frequently face sex-related resource allocation trade-offs. Differential traits of male and female plants can have important consequences that influence their direct and indirect interactions with neighbours and herbivores. 2. Gender differences in traits have been considered to be inherently linked to sex-biased ratios along environmental stress gradients. However, the mechanisms behind the variation in sex ratios with increasing biotic stress remain elusive. 3. We linked the results of process-based field experiments with fine-scale spatial patterns of naturally established plants (both sexes) at different grazing intensities. We demonstrated that slowgrowing females were better defended against insects and small mammals but were more susceptible than males to competition from neighbours. 4. In large-herbivore exclosures, we found that sex-biased spatial patterns at the microsite scale can be predicted from gender-specific traits, with females more segregated from competitors (unpalatable grasses) than males. Traits related to growth/defence trade-off in females, coupled with their higher competition costs than males, suggest that gender dimorphism in traits can directly influence species interactions and spatial organization. 5. In the presence of large herbivores, female individuals were preferentially browsed despite their larger investment in antiherbivore compounds. The greater distance of females from unpalatable competitors was the main determinant of female-biased consumption by domestic herbivores. Females growing close to neighbours successfully eluded browsing but also faced competition. Scaling up to a population level, population sex ratios drift from female- to male-bias with increasing domestic grazing intensity. 6. Synthesis: The sexual dimorphism in traits of a dioecious bunchgrass results in differential herbivory by natural enemies, differential competitive ability and differential spatial distribution of sexes. Domestic grazers disrupt this balance by shifting species interactions and their spatial organization. Changes in dioecious plant populations towards male-biased sex ratios with grazing intensity could not be predicted solely by gender-specific traits.

Ecosystem services are the benefits that society receives from nature, including the regulation of climate, the pollination of crops, the provisioning of intellectual inspiration and recreational environment, as well as many essential goods such as food, fiber, and wood. Rangeland ecosystem services are often valued differently by different stakeholders interested in livestock production, water quality and quantity, biodiversity conservation, or carbon sequestration. The supply of ecosystem services depends on biophysical conditions and land-use history, and their availability is assessed using surveys of soils, plants, and animals. The demand for ecosystem services depends on educational level, income, and location of residence of social beneficiaries. The demand can be assessed through stakeholder interviews, questionnaires, and surveys. Rangeland management affects the supply of different ecosystem services by producing interactions among them. Trade-offs result when an increase in one service is associated with a decline in another, and win–win situations occur when an increase in one service is associated with an increase in other services. This chapter provides a conceptual framework in which range management decisions are seen as a challenge of reconciling supply and demand of ecosystem services.

Many mountainous regions worldwide arecharacterized by harsh environments, scarce infrastructure,and extreme contrasts between mountains and neighboringplateaus and plains. Transhumance is a social adaptation tohandle geomorphological heterogeneity such as lowlandsand highlands, and to cope with environmental variability(seasonal and regional rainfall and snowfall). We studiedthe regional transhumant system with a network approachin the Andes of North Patagonia, Argentina. We measuredthe connectivity promoted by the seasonal movements ofherds and people (relationships) among different ecosystems(nodes), defined as winter and summer lands. Weidentified 238 networks. The highest frequencies correspondedto small network structures (dyads and triads),suggesting that landscape management is highly decentralized.Network complexity was positively related toecological richness and diversity of connected nodes.However, most networks were dependent upon a centralnode, suggesting vulnerable situations regardingdisturbances affecting such key nodes. The identification ofsocial?ecological traps of this mobile system providednovel insights for policy decision making, which otherwisewould not be evidenced with traditional approaches.Management proposals and policy making should considerthe spatial and temporal scales of transhumant pastoralism,in order to avoid problems derived from fixation logics,scale mismatches, and disconnection. Fil: Easdale, Marcos Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomia. Departamento de Recursos Naturales y Ambiente. Cátedra de Ecología; Argentina Fil: Paz, Raul Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Santiago del Estero; Argentina

A proposed refinement to the stress-gradient hypothesis requires consideration of the strategies of the interacting species and the characteristics of the stress factors. While the strength and direction of these interactions can be predicted for different ecosystems, this idea remains largely untested in the field. We performed a manipulative field experiment complemented with a descriptive study to test the predictions in a natural setting that represents the extreme end of a precipitation gradient. There, wind driven desiccation and water availability are the main stressors (non-resource and resource-based stresses, respectively). We evaluated the interaction between the shrub and grasses that are dominant in the Patagonian steppe. The species had differences in morpho-functional traits and drought tolerance that fit into the C-S axis of Grime's strategies. We experimentally separated root zones to limit direct competition for soil moisture and reduce the resource-based stress on grasses. We also manipulated the distance to shrubs to evaluate non-resource stress amelioration by canopies (e.g., sun and wind) on grasses. Finally, we evaluated the distribution of naturally established C and S grasses in the neighborhood of C and S shrubs to infer process-pattern relationships. Our growth data coincide to a large degree to the predictions. We found positive effects on the growth of beneficiaries when stress was non-resource based and when strategies differed (i.e., Cshrub-Sgrass and Sshrub-Cgrass). We also found strong negative effects when the abiotic stress was driven by water, particularly on C grasses. Additionally, shrubs only increased the survival of grasses when strategies differed (i.e., Cshrub-Sgrass and Sshrub-Cgrass). Our manipulative and descriptive study supported previous results that showed that stress-tolerant species are important for the persistence of competitive species at high stress. While the applicability and generality of these predictions remains to be tested with more field experiments, some ecological factors, such as stress types and species traits, can explain much of the variation in how dominant shrubs and grasses interact in this extreme arid environment. Moreover, this framework could be extended to specifically test the importance of facilitation under different levels of stress. Fil: Graff, Barbara Pamela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Many of the complex issues worldwide regarding environmental management and sustainable develo-pment require integrating the social and natural sciences. Nevertheless, while theoretical discussions have been increasingly developed, operative issues are still major barriers to integrated social-ecological analysis. The aim of this paper was to assess regional forage production in semi-arid rangelands as a key feature in social-ecological analysis, by using human organizational units (i.e. counties). We used these state-administrative units to explore demographic and farming indicators in order to address socio-productive implications of different regional forage production dynamics. We studied the forage spatial and temporal dynamics in two different large ecological regions: Monte and Patagonia, under a single administrative unit (i.e. province). Since forage production estimations in arid rangelands are not trivial, we tested two different methods. We found that inter-annual variability in forage production explained the main differences between regions. At a regional level, zones with higher temporal variability in forage production registered less rural residents and farm numbers, but inverse situations were registered at sub-regional scales. We found a non-linear relationship between forage production variability and rural population density. We proposed differentiated policy recommendations regarding rangeland management and animal husbandry, considering both the social and ecological contexts. © 2012 Elsevier Ltd. Fil: Easdale, Marcos Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Patagonia Norte. Estación Experimental Agropecuaria San Carlos de Bariloche; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Desertification threatens 70% of all dry lands worldwide by diminishing the provision of economic and ecosystem services. However, since long-term vegetation dynamics of semiarid ecosystems are difficult to study, the opportunities to evaluate desertification and degradation properly are limited. In this study, we tailored, calibrated and tested a spatially-explicit simulation model (DINVEG) to describe the long-term dynamics of dominant grass and shrub species in the semiarid Patagonian steppe. We used inverse techniques to identify parameterizations that yield model outputs in agreement with detailed field data, and we performed sensitivity analyses to reveal the main drivers of long-term vegetation dynamics. Whereas many parameterizations (10–45%) matched single field observations (e.g. grass and shrub cover, species-specific density, aboveground net primary production [ANPP]), only a few parameterizations (0.05%) yielded simultaneous match of all field observations. Sensitivity analysis pointed to demographic constraints for shrubs and grasses in the emergence and recruitment phase, respectively, which contributed to balanced shrub-grass abundances in the long run. Vegetation dynamics of simulations that matched all field observations were characterized by a stochastic equilibrium. The soil water content in the top layer (0–10 cm) during the emergence period was the strongest predictor of shrub densities and population growth rates and of growth rates of grasses. Grasses controlled the shrub demography because of the resource overlap of grasses with juvenile shrubs (i.e. water content in the top layer). In agreement with field observations, ecosystem function buffered the strong variability in precipitation (a simulated CV in ANPP of 16% vs CV in precipitation of 33%). Our results show that seedling emergence and recruitment are critical processes for long-term vegetation dynamics in this steppe. The methods presented here could be widely applied when data for direct parameterization of individual-based models are lacking, but data corresponding to model outputs are available. Our modeling methodology can reduce the need for long-term data sets when answering questions regarding community dynamics.

Objective: To contribute to the integration of key ecological concepts such as dynamic equilibrium, critical threshold, resistance and resilience to the ‘State and Transition Model’ (STM), in order to apply them in a more feasible way for rangeland management. Methods: Review and discussion of conceptual models and applied literature, including examples of rangeland dynamics. Results and Conclusions: We propose to enhance the STM considering two principal axes: (a) the x axis determined by structural ecosystem changes (vegetation and soil) and (b) the y axis determined by ecosystem functions and/or processes (recruitment, rain use efficiency). These axes define what we will call Structural–Functional State and Transition Model (SFSTM). Both axes of SFSTM make it possible to determine and quantify states and transitions, critical thresholds and to evaluate the resistance and resilience of an ecosystem to a given disturbance. The critical threshold is identified by structural and functional thresholds (x and y axes), thus defining the point where the ecosystem loses its resilience. Furthermore, in the supplementary file we provide examples with field data from Patagonia to illustrate the SFSTM. The proposed SFSTM has large implications for rangeland research and management, facilitating the understanding and integration of key concepts to enhance the STM. The identification of variables to assess structure and processes makes the model more useful.

We revisited a growth-form removal experiment after 12 years with the aim to compare the long-term population responses of three shrub species. Specifically, we were interested to know if the resource partitioning and plant interactions act as complementary mechanisms of the shrub-grass coexistence. In 1983 different plots from grass-shrub Patagonian steppes were submitted to three treatments: control, grass-, and shrub-removal during three consecutive years. In 1997 we studied nine plots from the original experiment and recorded all shrubs to compare shrub density, population size structure, vitality, spatial patterns and neighbourhood interferences of three native and co-dominant shrub species: Mulinum spinosum, Senecio filaginoides, and Adesmia volckmanni. After 12 years of recovery, shrubs as a growth-form group, fully re-established in plots where they were removed and attained 75% higher density in grass-removal plots than in control plots. However, long-term population responses of Mulinum, Senecio, and Adesmia to removals were distinctive. On the other hand, negative and positive interferences among shrub species and between shrubs and grasses generated a complex network. Morphological and functional differences in shrub and grass species and their interactions at population level and long-term could be a key to achieve a better comprehension of shrub-grass coexistence from semi-arid ecosystems. © 2010 Elsevier Ltd. Fil: Cipriotti, Pablo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Aguiar, Martin Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Past research has shown that changes in grazing-resistance traits may be associated with genetic changes in plant populations. Little is known about spatial genetic relationships within plant populations (spatial genetic structure) and any grazing effects on these relationships. Here we present observations of the fine-scale spatial genetic structure in three grass species in semiarid environments (Arizona, Mexico, and Argentina). In each environment, populations of a dominant grass species were sampled from two sites with contrasting livestock grazing histories. Plant genotypes were described with the use of amplified fragment length polymorphism markers. In Arizona, populations of sideoats grama (Bouteloua curtipendula var. caespitosa Gould and Kapadia) differed in that one has never experienced livestock grazing, whereas cattle have grazed the other. In the other two environments, populations exposed to long-term heavy grazing were examined, along with those that experienced either moderate grazing (Mexico, blue grama [Bouteloua gracilis {Willd. ex Kunt} Lag. ex Griffiths]) or extended exclusion of livestock (Argentina [Poa ligularis Nees ex Steud.]). Based on independent analysis of each population, we observed no differences in average gene diversity between populations of each species. With the use of analysis of molecular variance we found slight but significant genetic differentiation between populations with different grazing histories in Arizona and Argentina. Significant genetic structure was present in all populations and indicated an inverse relationship between spatial and genetic distance. Interestingly, this relationship was most pronounced in the cattle-free sideoats grama population, suggesting larger genetic neighborhood areas in the absence of livestock. Less distinct differences in spatial genetic structure associated with grazing history were evident in the other two species. We hypothesize that livestock grazing may lead to increased homogeneity in genetic structure at the landscape scale. Effectively examining this hypothesis presents many experimental challenges.

There is limited knowledge about root morphological differences at the species level. Consequently, plant ecological groups are largely defined on aboveground traits. Our hypothesis was that roots of graminoid species differ in morphological and functional attributes. In field and greenhouse studies, we measured morphological and functional root traits of eight dominant graminoids. Multivariate analyses of root traits arranged species into two groups. Species were unequivocally classified by either discriminant analysis or a taxonomic key. Traits that contributed most to identification were diameter, colour, and branching. Species from one group had large root diameters, more branching, and lower tensile strength, specific length, rate of new root generation, and RGR than the other group. The grouping by root traits matched previous classifications: one group had been described as more xerophytic, less preferred by livestock, and more delayed in phenology than the second group. Our study shows that (1) a set of root morphological traits may be reliably used to recognize species, and (2) root traits reflect the major ecological grouping of species, even when they all belong to the same growth form. For Patagonia and similar sites, our work will open the way to more detailed, specific-level studies on community underground organization.