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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, G00B03, doi:10.1029/2007JG000622, 2008

Objective indicators of pasture degradation from spectral mixture analysis of Landsat imagery

Eric A. Davidson

Woods Hole Research Center, Falmouth, Massachusetts, USA


Gregory P. Asner

Department of Global Ecology, Carnegie Institution, Stanford, California, USA


Thomas A. Stone

Woods Hole Research Center, Falmouth, Massachusetts, USA


Christopher Neill

Ecosystems Center, Marine Biological Laboratory, Woods Hole, Massachusetts, USA


Ricardo O. Figueiredo

Embrapa Amazônia Oriental, Belem, Pará, Brazil


Abstract

Degradation of cattle pastures is a management concern that influences future land use in Amazonia. However, “degradation” is poorly defined and has different meanings for ranchers, ecologists, and policy makers. Here we analyze pasture degradation using objective scalars of photosynthetic vegetation (PV), nonphotosynthetic vegetation (NPV), and exposed soil (S) derived from Landsat imagery. A general, probabilistic spectral mixture model decomposed satellite spectral reflectance measurements into subpixel estimates of PV, NPV, and S covers at ranches in western and eastern Amazonia. Most pasture management units at all ranches fell along a single line of decreasing PV with increasing NPV and S, which could be considered a degradation continuum. The ranch with the highest stocking densities and most intensive management had greater NPV and S than a less intensively managed ranch. The number of liming, herbiciding, and disking treatments applied to each pasture management unit was positively correlated with NPV and negatively correlated with PV. Although these objective scalars revealed signs of degradation, intensive management kept exposed soil to <40% cover and maintained economically viable cattle production over several decades. In ranches with few management inputs, the high PV cover in young pastures declined with increasing pasture age, while NPV and S increased, even where grazing intensity was low. Both highly productive pastures and vigorous regrowth of native vegetation cause high PV values. Analysis of spectral properties holds promise for identifying areas where grazing intensity has exceeded management inputs, thus increasing coverage of senescent foliage and exposed soil.

Received 15 October 2007; accepted 17 March 2008; published 23 July 2008.

Keywords: Amazon; pastures; Nova Vida; Paragominas; degradation.

Index Terms: 0480 Biogeosciences: Remote sensing; 0402 Biogeosciences: Agricultural systems; 0439 Biogeosciences: Ecosystems, structure and dynamics (4815); 0470 Biogeosciences: Nutrients and nutrient cycling (4845, 4850); 0428 Biogeosciences: Carbon cycling (4806).

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Citation: Davidson, E. A., G. P. Asner, T. A. Stone, C. Neill, and R. O. Figueiredo (2008), Objective indicators of pasture degradation from spectral mixture analysis of Landsat imagery, J. Geophys. Res., 113, G00B03, doi:10.1029/2007JG000622.