H. F. Del Valle

Ecological lessons and applications from one century of low external-input farming in the pampas of Argentina

Ecology may benefit from long term, large scale experiments on low intensity farming to test theoretical principles and convert them into practical lessons. One century of land conversion in the Argentine pampas, and its effect on critical ecological properties, were analysed and discussed. Land transformation has resulted in significant changes of land use, land cover, energy flow, nutrient dynamics, hydrology, and the trade-offs between productivity, stability and sustainability. The analytical procedure involved the complementary utilisation of different data sources and approaches. The study was focused on large geographical scales: the entire pampas and its five ecoregions. Results were interpreted under the theoretical framework of succession in ecology. The historical conversion of natural grasslands into cultivated grasslands and croplands was not homogeneous, determining a variety of land use and land cover patterns. Due to its higher productivity, much more energy, nutrients and water were mobilised in the rolling pampas than in the other ecoregions. This study provides lessons about how the energy flow, the nutrient dynamics and the hydrological process are modified by land transformation under low external-input conditions. Technical coefficients to be applied in emerging fields of environment administration such as ecological-monitoring, environmental accounting and auditing, agro-ecological certification, land evaluation and allocation, and land management, can also be supplied by this kind of studies.

Status of desertification in the Patagonian region: Assessment and mapping from satellite imagery

Desertification advance in the Patagonian region is the main socioecological problem. However, in this region the precise location, extent, severity, and characteristics of desertification are often unknown. The objectives of this research were (1) to evaluate, classify, and interpret the status of desertification, based on biological and physical indicators in the Patagonian arid, semiarid, and subhumid region of Argentina; (2) to develop a map of desertification with recommendations for decision makers; and (3) to create a methodology to determine accurately the distribution of land degradation from satellite imagery. Data were obtained from selected cloud‐free scenes of the National Oceanographic and Atmospheric Administration/Advanced Very High Resolution Radiometer “large‐area coverage” (NOAA/AVHRR LAC), existing data, and intensive field observations. The combination of the coarse‐resolution satellite data of this study with fine‐resolution satellite data [Landsat multispectral scanner (MSS)] were t...

Remote Sensing of Land Degradation: Experiences from Latin America and the Caribbean

Land degradation caused by deforestation, overgrazing, and inappropriate irrigation practices affects about 16% of Latin America and the Caribbean (LAC). This paper addresses issues related to the application of remote sensing technologies for the identification and mapping of land degradation features, with special attention to the LAC region. The contribution of remote sensing to mapping land degradation is analyzed from the compilation of a large set of research papers published between the 1980s and 2009, dealing with water and wind erosion, salinization, and changes of vegetation cover. The analysis undertaken found that Landsat series (MSS, TM, ETM+) are the most commonly used data source (49% of the papers report their use), followed by aerial photographs (39%), and microwave sensing (ERS, JERS-1, Radarsat) (27%). About 43% of the works analyzed use multi-scale, multi-sensor, multi-spectral approaches for mapping degraded areas, with a combination of visual interpretation and advanced image processing techniques. The use of more expensive hyperspectral and/or very high spatial resolution sensors like AVIRIS, Hyperion, SPOT-5, and IKONOS tends to be limited to small surface areas. The key issue of indicators that can directly or indirectly help recognize land degradation features in the visible, infrared, and microwave regions of the electromagnetic spectrum are discussed. Factors considered when selecting indicators for establishing land degradation baselines include, among others, the mapping scale, the spectral characteristics of the sensors, and the time of image acquisition. The validation methods used to assess the accuracy of maps produced with satellite data are discussed as well.

Micromorphological, physical, and chemical characteristics of soil crust types of the central Patagonia region, Argentina

Abstract The objectives of this work were: (i) to document the micromorphological, physical, and chemical properties of soil crusts types; and (ii) to determine the factors that control crust formation. Soil crusts as Av‐horizons were studied in three different soil classifications: Typic Calciorthid, Typic Haplargid, and Typic Natrargid. The Av‐horizons showed common characteristics such as high silt and low organic matter contents. The high exchangeable sodium percentage (ESP) is considered the main cause of crust formation in the Av‐horizons of the Haplargid and Natrargid. The crusts lying below the desert pavement consist of an upper zone of laminated sands, silts and clays, large vesicles, and a very dense lower zone with few and small vesicles. The size of the vesicles differ greatly among the three studied crusts. The vesicular layers of the Natrargid are more developed than of other soils. The typical shape of vesicles is rough walled on the upper half and smooth at the bottom. The walls of larger...

Radar remote sensing of wind-driven land degradation processes in northeastern Patagonia

Wind-driven land degradation negatively impacts on rangeland production and infrastructure in the Valdes Peninsula, northeastern Patagonia. The Valdes Peninsula has the most noticeable dunefields of the Patagonian drylands. Wind erosion has been assessed at different scales in this region, but often with limited data. In general, terrain features caused by wind activity are better discriminated by active microwaves than by sensors operating in the visible and infrared regions of the electromagnetic spectrum. This paper aims to analyze wind-driven land degradation processes that control the radar backscatter observed in different sources of radar imagery. We used subsets derived from SIR-C, ERS-1 and 2, ENVISAT ASAR, RADARSAT-1, and ALOS PALSAR data. The visibility of aeolian features on radar images is mostly a function of wavelength, polarization, and incidence angle. Stabilized sand deposits are clearly observed in radar images, with defined edges but also signals of ongoing wind erosion. One of the most conspicuous features corresponds to old track sand dunes, a mixture of active and inactive barchanoid ridges and parabolic dunes. This is a clear example of deactivation of migrating dunes under the influence of vegetation. The L-band data reveal details of these sand ridges, whereas the C-band data only allow detecting a few of the larger tracks. The results of this study enable us to make recommendations about the utility of some radar sensor configurations for wind-driven land degradation reconnaissance in mid-latitude regions.

Erosion of subsurface horizons in Northeastern Patagonia, Argentina

Degradation processes and their association with spatial and lithological discontinuities in argillic horizons of nine profiles in northeastern Chubut province were examined. Twelve test pits were used as stratigraphic controls. The reconstruction of the upper limit of the argillic horizons and its position in relation to the soil surface was performed in different topographical positions. Lateral discontinuities may have been due to the erosion of surface and argillic horizons in the intermound area, or to the development of desert pavements and vesicular layers, which may or may not be buried. The lithological discontinuities that were not associated with the erosion processes may be caused by (1) profile development on different parent materials, as a result of lateral facial variations, (2) development of different profiles under different conditions of moisture as related to paleomicrorelief. The observed shapes of the argillic horizons associated with water erosion suggest that the surface peds of t...

Improving the discrimination of vegetation and landform patterns in sandy rangelands: a synergistic approach

Soil erosion is a key factor in land degradation processes in the sandy rangelands of the Peninsula Valdés of Patagonia, Argentina. Mapping landform and vegetation patterns is important for improving prediction, monitoring and planning of areas threatened by sand and shrub encroachment. This paper investigates the contribution of optical sensors, such as the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and textural measures derived from microwave Radarsat Advanced Synthetic Aperture Radar (ASAR) to their discrimination. An evaluation is undertaken to compare the classification accuracy achieved by specific regions of the spectrum and their synergistic use in an object‐oriented approach. Image segmentation and object‐oriented classifications were applied to the datasets. This required defining appropriate fuzzy membership functions for characterizing active and stabilized lineal dunes and the main vegetation classes. Improvements in the discrimination of active and stabilized dunes (vegetated by either scrub or grass) were achieved by using an object‐oriented classification that integrated microwave and visible near‐infrared (NIR) data. Changes in surface roughness caused by different vegetation types stabilizing the dunes affected the radar backscattering. Whereas Radarsat enabled a clear separation of scrub‐stabilized dunes, Terra‐ASTER showed superior performance in the cartography of grass‐stabilized dunes. The synergistic use of microwave and visible and near‐infrared (VNIR) data yielded a substantial increase in the discrimination and mapping of landform/vegetation patterns.

Atmospheric and fuel conditions related to the Puerto Madryn Fire of 21 January, 1994

, 1990). This area is prone towildfires during late spring and summer, when hightemperatures are coupled with low relative humidity.Lightning, careless campers, hunters and sometimesranchers are responsible for igniting most of these fireswhich, in general, are small and easy to control becausethey occur in heavily grazed areas, where fuel loadlacks horizontal continuity. In some areas, however, and especially aroundPatagonian coastal cities, many ranches have beenabandoned for various reasons. The lack of grazing hasallowed the recovery of vegetation, increasing theshrub and grass components. In these particular areas,the rate of decomposition of standing dead material tolitter and then to organic matter is very slow, and thisaccumulation of fine and medium-sized dead fuelsnotably increases the fire hazard. On 21 January 1994, at about 1430 (local time), a wild-fire was detected in a rangeland area 10 km west ofPuerto Madryn in north-eastern Patagonia. Threecrews with a total of 25 people were dispatched from the Puerto Madryn Volunteer Fire-FightersDepartment to suppress what at the beginning wasthought to be a small, easy to control, rangeland fire. Atabout 1730, the fire activity increased remarkably; achange in wind direction transformed the south flankof the fire in its head, and in a few minutes the fire wasout of control. The radio contact with the fire foremanwas lost and the rapid spread of the fire overran the 25fire-fighters; no one survived. This case study, aimed at determining the atmosphericand fuel conditions that led to the worst disaster in thewildland fire-fighting history of Argentina, has the fol-lowing specific objectives:(a) to determine the fuel load and vegetational charac-teristics of the burned area;(b) to describe fire behaviour characteristics; and(c) to describe the interaction of the synoptic weatherpattern, the local atmospheric conditions, and thefire behaviour.The analysis of this case is a contribution to the world-wide knowledge of extreme fire behaviour in different

Contribution of Open Access Global SAR Mosaics to Soil Survey Programs at Regional Level: A Case Study in North-Eastern Patagonia

The Japan Aerospace Agency (JAXA) recently released multi-temporal global SAR mosaics derived from a 4-year data acquisition project (2007–2010) of the Advanced Land Observing Satellite (ALOS) PALSAR, L-band at 25 m spatial resolution. These open access data sets could assist traditional soil surveys and/or digital soil mapping programs undertaken at regional and subregional scales. Through improving mapping accuracy and reducing fieldwork time, together with digital identification and classification of landscape types and geomorphic features, soil survey programs could be completed over extensive areas currently lacking reliable soil information. Argentina is a country that needs to establish operational digital soil mapping (DSM) initiatives to address challenges and potential solutions of soil surveys at detailed and semi-detailed scales. These efforts could provide useful soil information to complement or update existing soil survey data, and document methods and results. Although remote sensing has been recognized as an efficient technology to support data gathering and information generation for soil and terrain mapping, the Argentine national knowledge of how to operationalize these techniques is still incomplete. Limited research has been carried out on the potential of microwave remote sensing data for spatial estimation of different topsoil properties, excepting soil moisture. This chapter intends to narrow down this knowledge gap by assessing the potential of ALOS PALSAR image mosaics for identifying and mapping land covers, as soil cartographic base, or as a value-added layer for integration in thematic soil mapping. The chapter also analyses changes in L-band backscatter overtime, and their relation to land degradation processes. To this end, a test area covering the north-eastern Patagonia region was chosen for its diversity of geology, geomorphology, soil, and land use, as well as for the existing soil expertise and an ongoing regional soil-mapping project.

A remote sensing and fuzzy multi-objective linear programming approach to model impact of land management decisions on ecosystem services of rangelands

This paper presents an approach to explicitly determinate optimal stocking rates based on trade-offs between guanaco density and livestock grazing intensity on rangelands of Patagonia, Argentina. As sheep farming becomes less profitable in this region, farmers and ranchers need to focus on sustainable wildlife harvesting as alternative income generation. We developed a methodology for spatially-explicit assessment and mapping of stocking rates based on tradeoffs and synergies between ecosystem services and livestock grazing intensity on rangelands. Forage use for livestock production, carbon sequestration, wildlife conservation and soil erosion are the ecosystem services and disservices evaluated over a gradient of grazing intensity. We show how rangelands stocking rate determination can be converted into a multi-objective optimization problem that can be solved using a Fuzzy Multi-Objective Linear Programing (MOLP).