Fernando Coronato

Soil nitrogen dynamics in northeastern Patagonia steppe under different precipitation regimes

Small-scale heterogeneity of plant cover and highly variable precipitation events in dry regions can strongly influence N dynamics. We evaluated the differences in N availability (Ni), N mineralization (Nmin), flush of microbial-N (N-MF) and soil moisture (SM) at 0–20 cm depth among four types of patches characteristic of heavily grazed areas in the northeastern Patagonia steppe of Larrea divaricata and Stipa spp. Soil samples were taken monthly during two years of differing annual precipitation (178 mm in 1994 and 325 mm in 1995). Ni and SM were also measured at 20–40 cm depth. Additionally, we estimated the potential N mineralization (pNmin) during two months in both winter and summer in laboratory incubations at 20% soil moisture and 25°C. Sampled patches included: undisturbed patches of shrubs and perennial grasses (GSP), incipient patches of Larrea divaricata and perennial grasses (IGSP), incipient patches of the perennial grass Stipa tenuis (GP), and bare soil (BS). Mineralization rates were much higher during the wet year, and higher in GSP and IGSP than in GP and BS. The prevailing form of Ni was NH4+–N, but pulses of NO3-–N were measured in field incubations when SM was higher than 10%; NO3-–N was also the main form of Ni in pNmin assays. Flush of microbial-N depended mainly on plant cover, following the sequence: GSP>IGSP>GP=BS. It was not correlated with soil moisture, except in the GSP patches, and exhibited lower values during the wet year. Available N (as NH4+–N) was higher in the subsurface than in the surface samples during the wet year. The relative importance of N-MF and Nmin as indicators of spatial and temporal changes in N dynamics, and the role of deep-rooted shrubs in the recovery of soil N fertility, are discussed.

The Physical Geography of Patagonia and Tierra del Fuego

Publisher Summary This chapter focuses on the physical geography of Late Cenozoic of Patagonia and Tierra del Fuego. This chapter discusses a junction of natural elements in the southern end of South America. Bedrock substratum and structure, climate, distribution of the superficial runoff, soils, and vegetation, all act together in a systematic, cause–effect relationship and form a group of homogeneous geographical spaces that are joined under first-order geological and atmospheric elements, such as tectonic plates and the general atmospheric circulation. The interaction of the wetter Pacific winds and the Andean Cordillera is the basic natural condition that determines the geographical aspects of the natural, physical environment of the southernmost end of South America. The pluvial and snow regime of the streams, the allochtonous character of the tableland streams, the development of contrasting biomes, such as jungle-like forests and rainshadow deserts, with a modest thermal regime are a consequence of the orographic barrier interaction with the air masses of the Southern Pacific anticyclonic centers and the polar front.

Spatial sex segregation in the dioecious grass Poa ligularis in northern Patagonia: the role of environmental patchiness

We examined the effect of environmental patchiness on the spatial segregation of the sexes in the dioecious anemophilus grass Poa ligularis. Because the species is sensitive to grazing, a better understanding of environmental factors that control its spatial distribution and abundance could improve conservation efforts. We hypothesized that (i) males and females are spatially segregated in the microenvironments created by plant patches as the result of sexual specialization in habitat and/or resources use, (ii) sexual specialization is related to different tolerance to competition and reproductive costs of males and females, and (iii) changes in patch structure affect the microenvironment and the intensity of spatial segregation of the sexes. We analyzed the spatial distribution of sexes at three sites with different plant and micro-environmental patchiness and performed a controlled competition experiment with different substitution of males and females. Our results showed that large plant patches created larger sheltered soil fertility islands than small patches. As patch size and their area of influence increased, the density and the spatial segregation of the sexes of P. ligularis also increased, resulting in biased habitat-specific sex ratios. In accordance with their higher reproductive costs, females were more frequent in sheltered (low air evaporative demand) and nitrogen-rich areas inside patch perimeters than males. Females were also better able to tolerate inter-sexual competition than males. In contrast, males tolerated low nitrogen concentration in soil and low sheltering, probably gaining advantage in pollen dispersal. Inter- and intra-sexual competition, however, affected the reproductive output of both sexes. From the point of view of conservation, environmental patchiness is important to the status of P. ligularis populations. The reduction of patch size limits the available microsites, biases the sex ratio towards males inside patches, increases inter- and intra-sexual competition, and it might be expected to decrease overall seed and pollen production and consequently potential recruitment.

Seed bank patterns of Festuca pallescens in semiarid Patagonia (Argentina): a possible limit to bunch reestablishment

The pre- and postdispersal spatial patterns of the germinable seed bank of Festuca pallescens were evaluated in semiarid grasslands of Patagonia disturbed by sheep grazing. Before dispersal, the seed bank showed spatial heterogeneity and was significantly smaller than the postdispersal seed bank. The postdispersal seed bank was uniformly distributed in patches of bare soil. The size of the germinable seed bank varied with the topographic condition of sites. On slopes, bunches exhibited more panicles and the germinable seed bank was larger after dispersal and smaller before dispersal as compared with upland sites. Losses of the germinable seed bank during autumn and spring are partially accounted for by germination rates. Predominant westerly winds influenced the patterns of seed dispersal, but other agents such as predation or sheet wash may also be active, especially on slopes. The low persistence of the seed bank of F. pallescens, particularly at canopy gaps, indicates that this may constitute a primary control of the regeneration of this species in semiarid grasslands of Patagonia. Management of these grasslands for restoration should accordingly include practices oriented to an adequate replenishment of the germinable seed bank at these places.

Windchill influence on thermal conditions in North Patagonia

The occurrence of windy conditions in Patagonia is well known. However there has been little attempt made concerning the wind cooling effect in the area. Because of windchill, equivalent temperatures may be quite different to the actual temperature. In Patagonia, constancy and wind strength determine a yet unexplored bioclimatic factor. This paper deals with windchill and the resulting equivalent temperatures in Puerto Madryn, Chubut, North Patagonia. This location may be considered as having the most favourable thermal conditions south of latitude 42°S, being a sheltered place near the sea-shore. Hourly values of windchill were calculated using Steadmans formula, based on records over 11 years. The results show that, even in such favourable conditions, windchill is an important feature of the Patagonian climate, and is perceived as being cooler than it actually is.

The Climate of Península Valdés Within a Regional Frame

Peninsula Valdes shares with the whole of Eastern Patagonia the main features of the regional climate, i.e. scarce rainfall, strong winds and cool-temperate temperatures. Not with standing it has an ill-defined climate because of its geographical location not far from the transitional area, where Pacific and Atlantic air masses merge. Also, because of its latitude (42°–43° S), the southward migration of the subtropical anticyclones is still noticeable over the area in summer. This chapter aims to explain the interplay between large scaled factors as the above-mentioned, and local ones as the almost insularity of the study area. A concise description of the climate is presented through the usual basic elements, temperature, precipitation, and wind. The maritime influence upon these variables is evaluated. It is shown that although mostly commanded by the rain-shadowed westerlies as the entire Patagonia, the climate of Peninsula Valdes has singularities that make it a less arid, more even, and milder climate which presents some Mediterranean features. Historic trends of rainfall and temperature are discussed and appear to be in agreement with global warming projections, according to which future scenarios would be drier and warmer in the Peninsula Valdes region.

Introducing Patagonia: An Approach from Geo-History

The uniqueness of Patagonia stems not only from its remote location on the world map but from several other geographic factors briefly discussed on this chapter, starting from some climatic features and sharp contrasts not found anywhere else. The last glaciation caused drainage deviations that complicated international boundary delimitation, which, in turn, hastened expansionism based on sheep farming of not always suitable lands. Widespread desertification is the major ecological consequence of this unwise process, developed at the expense of Native Patagonian peoples, some of whom have completely disappeared. From a terrestrial point of view, Patagonia is a geographic cul-de-sac, so aboriginal cultures were materially rudimentary; on the other hand, to seafarers Patagonia was on the inter-oceanic route and was a dangerous coast to be left behind as soon as possible. The unavoidable contact was dramatically contrasting and not always peaceful. With very low demographic density, and despite isolated cases of ecological mismanagement, the region still keeps an aura of pristine nature, enhanced by distance and legend. This chapter may seem incongruent in this volume, but it aims to place the readers in the wider scope of Patagonian geo-history, the human environment in which the research presented here was carried out.

Building New Human–Natural Systems for Sustainable Pasture Management in South America

On the basis of research conducted in three contrasting South American ecoregions (southern Patagonia, Argentina; the central Pampas and Campos, Uruguay; and western Amazonia, Brazil), this chapter aims to better understand the complex sets of reasons that have recently led local societies to adopt more sustainable pasture management in South America. After a brief overview of each of the three biomes, representative social–ecological systems of pastoralism are identified with the objective to describe their respective pasture management history, especially the colonization process and the settlement of the pioneers, and the successive farming systems, mainly the practices related to herd and pasture management, are compared. Finally, the main local and national policies regarding the livestock sector and landownership are analyzed. The evolution of the social–ecological systems of pastoralism in these ecoregions was assessed with a three-dimensional model of vulnerability based on the agroecosystem resilience, livelihood improvement, and institutional capability. The evolution of the mental models about livestock has also been analyzed to better understand the current perceptions of the local people and their scenarios for the future of livestock in their social–ecological systems. The results focused on the dynamics of rangeland management, the vulnerability of the pastoral social–ecological systems, and the evolution of the mental models of local people about livestock, so as to discuss the different rhythms of transformation and the existence of critical thresholds. Besides diverse land and social issues, it is imperative to intensify livestock production and increase the offer of new technologies, as well as to identify some relevant human dimension factors, such as the demand of local societies for collective livelihood improvement, the recent national and international environmental policies related to global warming and biodiversity, and the stronger awareness of consumers for sustainable development. In the context of global change, the practices of rangeland management will change in a more sustainable way, resulting in better society–environment interaction and human–nature integration.

Epigean Tenebrionids (Coleoptera: Tenebrionidae) from Leones and Tova-Tovita Islands (Chubut, Argentina) and Its Comparison with the Mainland Assemblage

Abstract. The Parque Interjurisdiccional Marino Costero Patagonia Austral (PIMCPA) protects over 180 km of Patagonian Atlantic coastline of northern San Jorge gulf, including an archipelago that comprises more than 39 islands. In this work, we studied the darkling beetles (Coleoptera: Tenebrionidae) of the two largest islands in the PIMCPA archipelago: Leones and Tova-Tovita. Tenebrionids are reported for first time in these islands, in addition, we described their species assemblage. Likewise, a comparison between the islands and the mainland was also performed. The GLM, MDS, ANOSIM and PCA methods were employed. Islands share the same tenebrionid species assemblage but they differ from that displayed on the mainland. Considering both islands as a whole, the insular assemblage shows lower species richness and diversity than those seen in the mainland. We identified eight species in the islands which belong to eight genera and four tribes. We also found that six of these species were shared among islands. Psectrascelis punctipennis Kulzer was exclusively recorded from the Tova-Tovita, while Platesthes kuscheli Kulzer from the Leones island. The island assemblage is mainly composed of nocturnal or crepuscular species [including Praocis (Hemipraocis) sellata bergi Burmeister, Patagonogenius quadricollis (Fairmaire), Emmallodera crenaticostata crenaticostata Blanchard and Scotobius akidioides akidioides Waterhouse], while several diurnal species of Nyctelia Berthold are the most common and diverse darkling beetles among mainland fauna. Additionally, we discuss the effects of the mainland distance, paleoclimate, and the origin of insular assemblages. Finally, other insular implications of tenebrionid beetles are discussed.