Roberto J. Fernández

Universidad de Buenos Aires | UBA · FAUBA-IFEVA-CONICET

La precipitación es determinante de múltiples procesos en zonas áridas. Abordar su variabilidad es difícil en áreas extensas y de baja densidad de registros como la Patagonia norte. El objetivo de este trabajo es caracterizar la variación temporal y espacial de las precipitaciones, y evaluar productos satelitales de lluvia para esta región. Con los...

Droughts are projected to increase in magnitude, frequency and duration in the near future. In rangelands, the provision of valuable ecosystem services such as forage supply for livestock productivity is intimately linked to rainfall patterns, which makes it particularly vulnerable to droughts. Nonetheless, rangelands can differ in their sensitivit...

Estimations of Net Ecosystem Exchange (NEE) are crucial to assess the carbon sequestration/carbon source capacity of agricultural systems. Although several global models have been built to describe carbon flux patterns based on flux tower data, South American ecosystems (and croplands in particular) are underrepresented in the databases used to cal...

Droughts are projected to increase in magnitude, frequency and duration in the near future. In rangelands, the provision of valuable ecosystem services such as forage supply for livestock productivity is intimately linked to rainfall patterns, which makes it particularly vulnerable to droughts. Nonetheless, rangelands can differ in their sensitivit...

Para afrontar el reto de alimentar a una población creciente que cambia su estilo de vida y su dieta y, al mismo tiempo, tratar de conservar los recursos naturales y proteger la biodiversidad, se proponen tres estrategias principales para lograr tales objetivos: 1) cambiar la forma de producir los alimentos en el campo (aumentando la eficiencia), 2...

Aim Numerous studies have assessed whether species niches are conserved in geographically separated regions. However, most of them were performed on invasive species, with the limitation that such species have likely not yet reached their potential distribution in the invaded region. Here we test the hypothesis of niche conservatism in the entire...

We evaluated the effect that integrating annual aboveground net primary production (ANPP) along different 12-month periods has on temporal models of productivity (ANPP as a linear function of annual precipitation). We studied Argentinean Patagonia, which encompasses a variety of climates and biomes. Using MODIS normalized difference vegetation inde...

RESUMEN La agronomía tradicional está siendo crecientemente cuestionada, oponiéndosele argumentos agroeco-lógicos que para muchos resultan de validez dudosa por "maniqueos" o "ideologizados". Aquí hacemos explícitos los principales postulados en pugna para clarificar las desavenencias más frecuentes, inten-tando separar los datos objetivos de las t...

La agronomía tradicional está siendo crecientemente cuestionada, oponiéndosele argumentos agroecológicos que para muchos resultan de validez dudosa por "maniqueos" o "ideologizados". Aquí hacemos explícitos los principales postulados en pugna para clarificar las desavenencias más frecuentes, intentando separar los datos objetivos de las tomas de po...

Trichloris crinita es una gramínea que se distribuye naturalmente de manera disyunta entre regiones áridas y semiáridas cálidas de Sudamérica y Norteamérica (i.e. distribución anfitropical). La especie es recomendada en ambos continentes para la restauración de pastizales naturales; sin embargo, todavía no se conocen aspectos básicos de la ecología...

ESTRUCTURA Y DIVERSIDAD GENÉTICA DE Trichloris crinita, GRAMÍNEA CON DISTRIBUCIÓN DISYUNTA ANFITROPICAL -----(Resumen)----- Trichloris crinita es una gramínea que se distribuye naturalmente de manera disyunta entre regiones áridas y semiáridas cálidas de Sudamérica y Norteamérica (i.e. distribución anfitropical). La especie es recomendada en ambo...

Plant species disjunctions have attracted the interest of ecologists for decades. We investigated Trichloris crinita, a native C4 perennial grass with disjunct distribution between subtropical regions of North and South America, testing the hypothesis that the species has a similar realized climatic niche in both subcontinents. The climatic niche o...

Introducción-- Conocer las condiciones climáticas que resultan adecuadas para la persistencia de una especie (es decir, su nicho climático) es importante tanto para entender su ecología como para establecer pautas de conservación y manejo (como, por ej., planificar la restauración de poblaciones). En este trabajo se investigó a Trichloris crinita,...

Background: Seed weight is a key fitness-related trait associated with plant adaptation and is commonly targeted in plant breeding. Aims: We evaluated seed weight variation within and between Trichloris crinita and Trichloris pluriflora across their geographical ranges in Argentina. Methods: Genetic variation in seed weight was evaluated through a...

Significance Global crop production tripled during the last 50 years, mainly by an increase in yield (production/area). We show that the energy embedded in the main oil-based inputs (machinery, fuel, and fertilizers) increased worldwide at a rate at first larger, but in the last decades slower, than crop production, resulting in a recent overall im...

Covering 16% of global land surface, dry forests play a key role in the global carbon budget. The Southern Hemisphere still preserves a high proportion of its native dry forest cover, but deforestation rates have increased dramatically in the last decades. In this paper, we quantified for the first time the magnitude and temporal variability of car...

Soil evaporation is a dominant water flux of flat dry ecosystems, reducing available water for plant transpiration. Vegetation plays a key role at controlling evaporation, especially by altering soil surface micro-meteorological conditions. Here we explored the vegetation cover effect on soil evaporation, differentiating the effects of canopy cover...

The conversion of dry woody rangelands into pastures can alter key soil physical properties that regulate ecosystem water circulation and storage. Based on three paired stands of native woodlands and pastures established 20 years ago in the southern Dry Chaco (San Luis, Argentina), we described contrasts in five soil physical properties using a sys...

Vegetation plays an important part in regulating water fluxes in ecosystems, specially in dry regions where a large fraction of precipitation is evapotranspirated. Here, we assessed how the replacement of native dry forests by pastures, with the aim of increasing livestock production, affects water flux partition in the Arid Chaco plains. We charac...

This paper is intended for young researchers with an environmental conscience, alerting them that a self-centred ecology can work against conservation and other desirable goals.

Highlights • This is a primer on why information is almost never sufficient to deal with complex problems. • Ways in which knowledge is being negotiated and co-produced with users are shown. • Political and ideological influence on the selection of problems and work teams is highlighted. • Distinction between environmental conscience and intellectu...

Vegetation plays an important part in regulating water fuxes in ecosystems, specially in dry regions where a large fraction of precipitation is evapotranspirated. Here, we assessed how the replacement of native dry forests by pastures, with the aim of increasing livestock production, affects water fux partition in the Arid Chaco plains. We characte...

Water stress modifies plant above- vs belowground biomass allocation, i.e., morphological plasticity. It is known that all species and genotypes reduce their growth rate in response to stress, but in the case of water stress it is unclear whether the magnitude of such reduction is linked to the genotype's growth potential, and whether the reduction...

Effectively managing net primary productivity in drylands, for grazing and other uses, depends on understanding how limited rainfall input is redistributed by runoff and runon among vegetation patches, particularly for patches that contrast between lesser and greater amounts of vegetation cover. Due in part to data limitations, ecohydrologists gene...

El aumento de los gases de efecto invernadero (GEI) en la atmósfera es el más comentado —y uno de los más estudiados— de los impactos humanos sobre el planeta por ser motor del cambio climático y de su consecuencia más general y conocida: el calentamiento global. Hay consenso acerca de que estos cambios serán en su mayoría perjudiciales, y por lo t...

The annual amount of precipitation inputs received by a site during a full year is considered a dominant spatial and temporal control of primary productivity and other related process in arid to subhumid ecosystems. However, to be effectively used by plants, these inputs have to escape runoff, favoured by large and less frequent precipitation event...

Existe acuerdo en la comunidad científica en que los problemas del planeta son muy serios. Hay datos confiables y alarmantes sobre el consumo no sustentable de energía, la pérdida de biodiversidad y los cambios acelerados en los ciclos de materiales (Rockström et al.2009). Los medios de comunicación se ocupan frecuentemente de estos temas, sobre to...

More than half of the dry woodlands (forests and shrublands) of the world are in South America, mainly in Brazil and Argentina, where in the last years intense land use changes have occurred. This study evaluated how the transition from woody- to grass-dominated system affected key ecohydrological variables and biophysical processes over 20,000 hec...

Distribution of water enables different ecological niches and the coexistence of species. This separation may be in space: vertically in the soil profile or horizontally by lateral root exploration; and in time, as plants may use water at different periods. This study focused on the soil-plant water relation in semiarid Patagonia. Water potential a...

The annual amount of precipitation inputs received by a site during a full year is considered a dominant spatial and temporal control of primary productivity and other related process in arid to subhumid ecosystems. However, to be effectively used by plants, these inputs have to escape runoff, favored by large and less frequent precipitation events...

In arid environments, water availability is the main limiting factor for primary production, and it is expected that not only drought-resistance, but also plant strategies for soil water use will be under natural selection. Our aim was to investigate the strategies of soil water use and the responses to water shortage that lead to variability in dr...

Disturbances in semiarid environments have revealed a strong connection between water, salt and vegetation dynamics highlighting how the alteration of water fluxes can drive salt redistribution process and long-term environmental degradation. Here, we explore to what extent the reciprocal effect, that of salt redistribution on water fluxes, may pla...

Since 1980, more than 40 countries have implemented long-term ecological research (LTER) programs, which have shown their power to affect advances in basic science to understand the natural world at meaningful temporal and spatial scales and also help link research with socially relevant outcomes. Recently, a disciplinary paradigmatic shift has int...

Despite general agreement regarding the adaptive importance of plasticity, evidence for the role of environmental resource availability in plants is scarce. In arid and semi-arid environments, the persistence and dominance of perennial species depends on their capacity to tolerate drought: tolerance could be given on one extreme by fixed traits and...

Water in plant xylem is often superheated, and therefore in a meta-stable state. Under certain conditions, it may suddenly turn from the liquid to the vapor state. This cavitation process produces acoustic emissions. We report the measurement of ultrasonic acoustic emissions (UAE) produced by natural and induced cavitation in corn stems. We induced...

Since 1980, more than 40 countries have implemented long-term ecological research (LTER) pro-grams, which have shown their power to affect advances in basic science to understand the natural world at meaningful temporal and spatial scales and also help link research with socially relevant outcomes. Recently, a disciplinary paradigmatic shift has in...

The Global Drylands Observing System proposed in this issue should reduce the huge uncertainty about the extent of desertification and the rate at which it is changing, and provide valuable information to scientists, planners and policy-makers. However, it needs careful design if information outputs are to be scientifically credible and salient to...

A field experiment was performed to improve understanding of the functional diversity of western Patagonian shrubs. Anarthrophyllum rigidum, Adesmia volckmanni, Berberis heterophylla, Mulinum spinosum, Schinus poligamus and Senecio filaginoides were compared in their capacity to absorb water from a 10-mm pulse enriched in deuterium and applied at t...

It has been proposed that aridity and grazing are convergent selective forces: each one selects for traits conferring resistance to both. However, this conceptual model has not yet been experimentally validated. The aim of this work was to experimentally evaluate the effect of aridity and grazing, as selective forces, on drought and grazing resista...

Paspalum dilatatum Poir., is a perennial C4 grass widely distributed in the Argentinean Pampas. The response to water availability for materials developed with forage-production purposes is unknown. We hypothesized that genetic differences between commercial varieties are reflected in their regrowth capacity under water stress. The effect of five l...

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La estructura y la dinámica de las poblaciones vegetales de los sistemas pastoriles están principalmente controladas por la competencia intra e interespecífica y por la herbivoría, en el marco impuesto por el ambiente edáfico y el clima. Las defoliaciones producidas por los herbívoros impactan directamente sobre las poblaciones vegetales, pero tamb...

Structure and dynamics of plant populations in pastoral systems are mainly controlled by inter and intraspecific competition and herbivory within the constraints imposed by soil characteristics and climate. Defoliations caused by herbivores have a direct impact on plant populations, but also an indirect effect through changes in the intensity of co...

In this millennium, global drylands face a myriad of problems that present tough research, management, and policy challenges. Recent advances in dryland development, however, together with the integrative approaches of global change and sustainability science, suggest that concerns about land degradation, poverty, safeguarding biodiversity, and pro...

The literature on whole-plant acclimation to drought is reviewed and it is proposed that leaf-level homeostasis in water status is attained during ontogeny largely thanks to whole-plant changes in physical resistance to liquid water flow caused by morphological and anatomical adjustments. It is shown that, in response to water deficits, plant resis...

Wheat plants (Triticum aestivum var. INTA x2018;Cinco Cerros’) were grown in pots with fine sand under a rain-out shelter to assess their response to a water shortage spanning most of the growth cycle. Three watering treatments, based on different thresholds of plant-available water, were started 8 weeks after sowing and maintained for 10 weeks. Af...

La textura del suelo como fuente de heterogeneidad; sus efectos sobre la oferta de agua para las plantas Introducción Uno de los mensajes más generales de este volumen-y de las enseñanzas del Profesor León, a quien está dedicado-es la existencia de heterogeneidad en los ecosistemas a múltiples escalas (CHANETON, 2005). Entre las escalas de menos de...

The 'pulse-reserve' conceptual model--arguably one of the most-cited paradigms in aridland ecology--depicts a simple, direct relationship between rainfall, which triggers pulses of plant growth, and reserves of carbon and energy. While the heuristics of 'pulses', 'triggers' and 'reserves' are intuitive and thus appealing, the value of the paradigm...

Summary • We hypothesized that plant growth reduction under water stress is caused primarily by a reduction of leaf-area ratio (LAR, leaf area per unit of total plant dry mass). • Two perennial Chihuahuan desert grass species (slow-growing Bouteloua eriopoda and fast-growing Eragrostis lehmanniana) were subjected over 6 wk to a combination of two w...

We report work on a cold, windy South American steppe dominated by tussock grasses and shrubs of small stature that, together, cover only half of the soil surface. Our objective was to find out why seedlings and juveniles of these dominant species are generally absent from the bare or poorly-populated spots (gaps) that exist between established ind...

The 88th Dahlem workshop on Integrated Assessment of the Ecological, Meteorological and Human Dimensions of Global Desertification was held at Freie Universität, Berlin, Germany, from 10 to 15 June 2001.

Eight perennial C-4 grasses from the Jornada del Muerto Basin in southern New Mexico show five-fold differences in relative growth rates under well- watered conditions (RGRmax). In a controlled environment, we tested the hypothesis that there is an inverse relationship (trade-off) between RGRmax and the capacity of these species to tolerate drought...

Two shrub species, dominant in western Patagonia, Argentina, exhibited different demographic behaviors under the effect of sheep grazing and of manipulated resource levels. Senecio filaginoides showed an increase in cover under increasing grazing pressures; the rise was explained by an increasing number of individuals and not by larger plants; this...

Aboveground net primary production (ANPP) of the Patagonian steppe in southwestern Chubut (Argentina) was estimated using a harvest technique to assess the herbaceous (mainly grass) component and a double sampling technique to evaluate shrub production. The latter requires the measurement of plant dimensions and the harvest of shrub biomass in smal...

A method for mapping coarse root distribution suitable for stony soils was developed. Each root is considered as a broken line, whose segments are fairly straight root portions. The spatial location of end points of these segments is recorded in the field through 3 coordinates: its distance from plant vertical axis, its depth, and its distance to t...