Cambios en el uso de la tierra en Argentina y Uruguay : marcos conceptuales para su análisis

Resumen en inglés incluidoEl ser humano modifica el territorio para llevar a cabo actividades productivas o construir viviendas. Estas modificaciones producen importantes cambios en la estructura y el funcionamiento de los ecosistemas, afectando en última instancia la propia calidad de vida de las personas. En este artículo en primer término describimos algunos de los cambios ocurridos en el uso de la tierra en buena parte de Argentina y Uruguay. Utilizamos conjuntamente información aportada por estadísticas oficiales de ambos países y datos resultantes del procesamiento y clasificación de imágenes satelitales. Nuestros análisis muestran que tanto el área agrícola como forestal se han expandido en los últimos años. En Argentina, la mayor expansión la tuvieron los cultivos anuales (desde un 4% a un 14.3%, entre 1988 y 2002) y particularmente la soja, tanto en la provincia de Buenos Aires como en las provincias del Norte Argentino. En Uruguay la mayor expansión entre los censos de 1990 y 2000, estuvo dada por los cultivos forestales, los cuales llegaron a ocupar más del 35 % del área de algunas secciones censales. Luego del 2000, la expansión de la soja también afectó el litoral uruguayo, donde varias secciones censales aumentaron su área de soja a tasas cercanas al 5% anual. En segundo término, presentamos el marco conceptual a los efectos de entender los procesos que determinan estos cambios y examinar su dinámica espacial y temporal. En base a este marco conceptual es posible modelar los cambios en el uso de la tierra a partiendo de la probabilidad de transición entre usos. Los controles de estas transiciones pueden ser ambientales (por ej. tipos de suelos, clima, etc.), económicos (por ej. margen bruto, precios internacionales, etc), sociales (por ej. disponibilidad de mano de obra, tenencia de la tierra, etc.), o políticos (por ej. la ley forestal, política impositiva, líneas de créditos, etc.). Finalmente usando la idea de servicios ecosistémicos presentamos un marco conceptual para la planificación del uso de la tierra considerando sus impactos ambientales, sociales, económicos y políticos

Improving ground cover monitoring for wind erosion assessment using MODIS BRDF parameters

Measuring and monitoring controls on wind erosion can facilitate detection and prediction of soil degradation important for food security. Ground cover is widely recognised as an important factor for controlling soil erosion by wind and water. Consequently, maintaining ground cover (e.g., vegetation, crop canopy, crop residue) is a recommended management practice which is widely adopted by farmers and land owners. Wind erosion is a lateral or horizontal process and the amount of ground cover needed to maintain lateral cover (L c = nbh/S where n roughness elements occupy ground area S and have b and h mean breadth and height, respectively) is not well-established. Soil may be removed from beneath or between crop and natural vegetation canopies depending on the width, height and distribution of cover types relative to wind direction and strength. Monitoring by repeated measurement or estimation of ground cover provides information to develop an understanding of its spatial and temporal variation. Fractional cover (f c) retrieved from optical satellite remote sensing (e.g., Moderate Resolution Imaging Spectroradiometer; MODIS) provides a consistent and repeatable measure of ground cover when viewed from above. Therefore, f c provides an areal assessment of components of ground cover. Fractional cover is consequently not the most appropriate approximation of the protection of the soil from wind erosion. Extant wind erosion model parameterisations of L c already benefit from the use of satellite-derived cover data (L fc). However, the parameterisations are not well developed. Here, we address the need for a dynamic (multi-temporal), moderate resolution and global metric for wind erosion assessment and modelling. We demonstrate the benefits of using L c within the context of monitoring ground cover for the assessment of wind erosion and review the basis for estimating ground cover using L c. We describe a new method for an albedo-based approximation of aerodynamic sheltering (L ω). We use ray-casting of rough surfaces from an existing wind tunnel study to establish a relation between measured L c and directional hemispherical reflectance ω dir(0°, λ), the so-called 'black-sky albedo' and its inverse to estimate shadow. The relation is confirmed to be dependent on the solar zenith angle (θ) and spectral (λ) confounding factors (e.g., soil moisture, soil mineralogy). We reduced the λ dependency of ω dir(0°, λ) by normalising with the MODIS (MCD43A1) BRDF parameter f iso to estimate albedo-based lateral cover (L ω) globally over space (500m pixels) and time (every 8days). We compared L ω with f c and L fc over time for selected locations in Australia and examined L ω across Australia and the USA using national biogeographic regions. Consistent with current approaches to estimating L c, our results were not field validated due to the dearth of ground-based measurements. However, our results demonstrate that L ω will improve wind erosion models particularly over large areas and L ω is likely to be a valuable source of decision-support information to guide policy makers and land managers on where, when and how to reduce wind erosion

Sectoral approaches to improve regional carbon budgets

Humans utilise about 40% of the earth's net primary production (NPP) but the products of this NPP are often managed by different sectors, with timber and forest products managed by the forestry sector and food and fibre products from croplands and grasslands managed by the agricultural sector. Other significant anthropogenic impacts on the global carbon cycle include human utilization of fossil fuels and impacts on less intensively managed systems such as peatlands, wetlands and permafrost. A great deal of knowledge, expertise and data is available within each sector. We describe the contribution of sectoral carbon budgets to our understanding of the global carbon cycle. Whilst many sectors exhibit similarities for carbon budgeting, some key differences arise due to differences in goods and services provided, ecology, management practices used, land-management personnel responsible, policies affecting land management, data types and availability, and the drivers of change. We review the methods and data sources available for assessing sectoral carbon budgets, and describe some of key data limitations and uncertainties for each sector in different regions of the world. We identify the main gaps in our knowledge/data, show that coverage is better for the developed world for most sectors, and suggest how sectoral carbon budgets could be improved in the future. Research priorities include the development of shared protocols through site networks, a move to full carbon accounting within sectors, and the assessment of full greenhouse gas budgets