Estudio del NDVI mediante análisis multiescalar y series temporales utilizando imágenes SPOT, durante el período 1998-2012 en el Uruguay Resumen: Los índices de vegetación suponen una de las principales fuentes de información para el monitoreo y espacialización de la vegetación a distintas escalas, siendo el Normalized Difference Vegetation Index (NDVI) uno de los más utilizados. Este trabajo pretende describir y analizar la tendencia del NDVI en los sistemas ambientales de Uruguay, como una variable síntesis del comportamiento del sistema ambiental. Se aplicó un análisis multiescalar (país, cuenca, sitios), mediante la utilización del análisis de series temporales, siendo las imágenes SPOT 4 y 5, a través del programa del instrumento Vegetation (VGT) la fuente de información. Las series temporales analizadas mostraron un ajuste significativo del modelo de Autocorrelación Integrado de Medias Móviles (ARIMA), siguiendo una autocorrelación de orden 2, con nivel de integración de orden 1, ARIMA (211). Se observó una tendencia significativa a la baja del NDVI para el total de las unidades espaciales, siendo las unidades agrícolas (escala sitio) las que presentaron mayor tendencia a la baja. El desarrollo del estudio permitió construir una base de datos sin antecedentes en Uruguay, junto con la elaboración de una metodología precisa y robusta para el análisis espacio-temporal del NDVI. Se demuestra que la teledetección es una herramienta útil para la mejorar de la gestión de los sistemas ambientales.Palabras clave: NDVI, series temporales, SPOT, enfoque multiescalar, percepción remota. Study of the NDVI with multi-scale and time-series analysis using SPOT imagery during the period 1998-2012 in UruguayAbstract: Vegetation indices are a relevant source of information for spatial monitoring of vegetation at multiple scales. Among them, the Normalized Difference Vegetation Index (NDVI) is one of the most commonly used. This study aims to describe and analyze the spatial patterns of the NDVI in terrestrial systems in Uruguay at the onset of the 21st Century. A multiscalar approach (country, basin and sites) was applied using time series analysis of NDVI values obtained from SPOT 4 and 5 images through the program Instrument Vegetation (VGT). The analyzed time series showed a significant fit of the Autocorrelated Integrated Moving Averages (ARIMA) model, with an autocorrelation of order 2
Questions Increasing climate variability has major effects on forest productivity, as well as transitions between forest and savanna ecosystems. While drought‐induced declines in tropical forest productivity and forest loss is a global concern, forest expansion in subtropical South America predicted by climate models has received little attention. In the forest–grassland transition zone encompassing Uruguay, we ask: (1) how does climate variability affect woodland productivity and at what time scales; and (2) how do different woodland types (riparian, hillside and wooded savanna) differ in their sensitivity to climate variability? Location Forests and wooded savanna in Uruguay, subtropical southeast South America. Methods Primary productivity was measured as the fraction of photosynthetically active radiation (fPAR) based on monthly normalized difference vegetation index (NDVI) from multitemporal (1998–2012) SPOT imagery at a 1 km × 1 km resolution, covering 19% of Uruguayan woodlands. The effects of accumulated rainfall and mean temperature on the productivity of riparian and hillside forests and wooded savanna were evaluated using correlations and time series analysis over multiple time windows ranging from 1–24 mo. Results Inter‐annual rainfall variability and seasonal temperatures affected forest productivity even though average conditions were largely non‐limiting. Periods of exceptionally high rainfall and warm winters had positive effects on forest productivity, but hot summers had a negative effect on all woodland productivity. Riparian and hillside forest productivity was equally susceptible to drought, showing similar relationships to accumulated rainfall over multiple time periods, as well as similar susceptibility to high summer temperatures. Wooded savanna – a composite cover of trees and a grass/forb understorey – productivity was linked to seasonal rainfall over 3–6 mo, and in general showed the lowest correlation with inter‐annual variability in rainfall. Conclusions Results suggest functional convergence in the response of riparian and hillside forests to water deficit and hot summers. The increases in forest productivity with increasing rainfall and declining drought risk – as predicted by the IPCC for this region – are a potential mechanism for increased growth and future expansion of forests in this biogeographic transition zone.
Las áreas metropolitanas de América Latina transitan por diversos cambios territoriales que se han profundizado durante las últimas décadas. En este estudio se analizan las dinámicas territoriales que han ocurrido en la región noreste del Área Metropolitana de Montevideo, se considera a la segregación territorial y a los territorios estratégicos como conceptos claves para entender dichas transformaciones. En este sentido se emplean técnicas de Geoprocesamiento y se elabora un índice de estratificación socioeconómica. Los resultados indican un crecimiento sostenido de los procesos de urbanización sobre el uso rural y se evidencia un desarrollo acelerado de cambios en las distintas clases sociales donde el Estado es un actor clave para favorecer los procesos de segregación territorial.
Nuestro objetivo principal es analizar la configuración de los territorios agrarios del agronegocio en el Uruguay para los sectores de la silvicultura, la agricultura de secano y la ganadería vacuna, desde una perspectiva de la geografía agraria. Para ello realizamos una profunda caracterización de las fases del capital, la producción y la circulación de cada uno de los sectores. Los procedimientos empleados fueron, análisis bibliográfico, recolección y sistematización de los datos agropecuarios, y producción de cartografía temática a escala país. Las fuentes de datos fueron principalmente las diversas dependencias del Ministerio de Ganadería Agricultura y Pesca (MGAP). Ello permitió identificar en el espacio agrario del Uruguay los principales procesos de territorialización del agronegocio, evidenciando, por un lado, que existe una clara concentración espacial de los sectores analizados, y por otro lado, una tendencia en la centralización productiva tanto en la fase productiva como circulatoria del capital, caracterizada por el dominio de capitales transnacionales, reconfigurando los procesos de territorialización históricos del espacio agrario uruguayo.
The mapping and monitoring of forest ecosystems on a national scale is key to their management and conservation. Native forests in Uruguay are considered given their importance for biodiversity and ecosystem services. Here we evaluate the spatial distribution of the land cover class 'hillside and ravine forest'-a subclass of native forest characterized by patches and transition zones with native grasslands-using Landsat images (30 x 30 m) from 2014 and 2015 and high-resolution images from Google Earth. To evaluate spatial heterogeneity within hillside forests, we then used highresolution SPOT images of 1 km 2 from 1998-2012 to evaluate differences in the normalized difference vegetation index (NDVI) among canopy coverage categories. The hillside and ravine forest class were characterized as a composite cover class with an average canopy coverage of 69 ± 23%, variability of wich was reflected in NDVI values. The total area of this class in 2015 was estimated as 334,480 ha, somewhat less than an earlier 2008 estimate (384,240 ha). Among the potential errors in delineating hillside forests using Landsat images, there was the classification of «forest» in areas characterized by grassland and a tree canopy cover <25 %. This potential error in delimitation at broader scales led to the overestimation of hillside and ravine forest area in southeastern Uruguay, but an underestimation in northern Uruguay. Our study highlights the large discrepancies in the estimation of the distribution of hillside and ravine forest at different spatial scales, and also indicates the potential of NDVI to evaluate the heterogeneity of this forest within the same cover class.
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