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Although deforestation rates in the Brazilian Amazon are well known, the extent of the area affected by forest degradation is a notable data gap, with implications for conservation biology, carbon cycle science, and international policy. We generated a long-term spatially quantified assessment of forest degradation for the entire Brazilian Amazon from 1992 to 2014. We measured and mapped the full range of activities that degrade forests and evaluated the relationship with deforestation. From 1992 to 2014, the total area of degraded forest was 337,427 square kilometers (km2), compared with 308,311 km2 that were deforested. Forest degradation is a separate and increasing form of forest disturbance, and the area affected is now greater than that due to deforestation. [ABSTRACT FROM AUTHOR]

Abstract: Many studies have assessed the process of forest degradation in the Brazilian Amazon using remote sensing approaches to estimate the extent and impact by selective logging and forest fires on tropical rain forest. However, only a few have estimated the combined impacts of those anthropogenic activities. We conducted a detailed analysis of selective logging and forest fire impacts on natural forests in the southern Brazilian Amazon state of Mato Grosso, one of the key logging centers in the country. To achieve this goal a 13-year series of annual Landsat images (1992–2004) was used to test different remote sensing techniques for measuring the extent of selective logging and forest fires, and to estimate their impact and interaction with other land use types occurring in the study region. Forest canopy regeneration following these disturbances was also assessed. Field measurements and visual observations were conducted to validate remote sensing techniques. Our results indicated that the Modified Soil Adjusted Vegetation Index aerosol free (MSAVIaf) is a reliable estimator of fractional coverage under both clear sky and under smoky conditions in this study region. During the period of analysis, selective logging was responsible for disturbing the largest proportion (31%) of natural forest in the study area, immediately followed by deforestation (29%). Altogether, forest disturbances by selective logging and forest fires affected approximately 40% of the study site area. Once disturbed by selective logging activities, forests became more susceptible to fire in the study site. However, our results showed that fires may also occur in undisturbed forests. This indicates that there are further factors that may increase forest fire susceptibility in the study area. Those factors need to be better understood. Although selective logging affected the largest amount of natural forest in the study period, 35% and 28% of the observed losses of forest canopy cover were due to forest fire and selective logging combined and to forest fire only, respectively. Moreover, forest areas degraded by selective logging and forest fire is an addition to outright deforestation estimates and has yet to be accounted for by land use and land cover change assessments in tropical regions. Assuming that this observed trend of land use and land cover conversion continues, we predict that there will be no undisturbed forests remaining by 2011 in this study site. Finally, we estimated that 70% of the total forest area disturbed by logging and fire had sufficiently recovered to become undetectable using satellite data in 2004. [Copyright &y& Elsevier]

Selective logging degrades tropical forests. Logging operations vary in timing, location, and intensity. Evidence of this land use is rapidly obscured by forest regeneration and ongoing deforestation. A detailed study of selective logging operations was conducted near Sinop, State of Mato Grosso, Brazil, one of the key Amazonian logging centers. An 11-yr series of annual Lansdat images (1992¿2002) was used to detect and track logged forests across the landscape. A semiautomated method was applied and compared to both visual interpretation and field data. Although visual detection provided precise delineation of some logged areas, it missed many areas. The semiautomated technique provided the best estimates of logging extent that are largely independent of potential user bias. Multitemporal analyses allowed the authors to analyze the annual variations in logging and deforestation, as well as the interaction between them. It is shown that, because of both rapid regrowth and deforestation, evidence of logging activities often disappeared within 1¿3 yr. During the 1992¿2002 interval, a total of 11 449 km2 of forest was selectively logged. Around 17% of these logged forests had been deforested by 2002. An intra-annual analysis was also conducted using four images spread over a single year. Nearly 3% of logged forests were rapidly deforested during the year in which logging occurred, indicating that even annual monitoring will underestimate logging extent. Great care will need to be taken when inferring logging rates from observations greater than a year apart because of the partial detection of previous years of logging activity. [ABSTRACT FROM AUTHOR]

This article examines forest change in the Brazilian Amazon in light of forest transition theory. We draw on satellite-based land cover data matched in a geographic information system (GIS) to census-based social and agricultural data for Brazilian municipalities at multiple time points. Subregions with distinct settlement histories serve as proxies for different stages along the forest transition, theorized to exhibit depletion of forest cover, eventually followed by a recovery. Satellite images allow for distinctions between primary (old-growth) and secondary (successional) forests, but the data indicate more successional forests than expected. We argue that biophysical impediments (e.g., poor soils) and social obstacles (e.g., capital scarcity) led to limited land settlement, low incomes, urbanization, and a shift from crops to pasture, resulting in the rapid expansion of secondary forests without primary forest depletion. These findings call for refinements in forest transition theory that can better account for land cover changes in tropical regions of non-OECD countries. [ABSTRACT FROM AUTHOR]

This paper presents models of secondary forests ("regrowth") in the Brazilian Amazon using social indicators as explanatory factors. We draw on a spatially explicit data set containing satellite-based estimates of secondary growth, matched to census-based social indicators for municipalities in the region. The models overcome several shortcomings in previous efforts: they use smaller units of analysis to capture local heterogeneity; they include a conceptually broad range of measures to reduce omitted variable bias; they allow for estimation of separate coefficients and error terms for three distinct subregions to observe variable effects across the region and manage heteroskedasticity; and they incorporate spatial information to account for spatial autocorrelation and obtain unbiased estimates of coefficients. The findings indicate that longstanding settlement and traditional activities have positive effects on the extent of secondary forests, but in-migration and non-traditional land use exert growing influences on forest regrowth as well, especially in frontier areas of the Amazon. [ABSTRACT FROM AUTHOR]

Discusses the effect of tropical deforestation on biological diversity. Destruction of habitat; Isolation of fragments of formerly contiguous habitat; Edge effects between forest and deforested areas; Use of Landsat Thematic Mapper for determining extent of deforestation; Study of the Brazilian Amazon for 1978 and 1988.

Carbon fluxes from tropical deforestation and regrowth are highly uncertain components of the contemporary carbon budget, due in part to the lack of spatially explicit and consistent information on changes in forest area. We estimate fluxes for the 1980s and 1990s using subpixel estimates of percent tree cover derived from coarse (National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer) satellite data in combination with a terrestrial carbon model. The satellite-derived estimates of change in forest area are lower than national reports and remotesensing surveys from the United Nations Food and Agriculture Organization Forest Resource Assessment (FRA) in all tropical regions, especially for the 1980s. However, our results indicate that the net rate of tropical forest clearing increased ≈10% from the 1980s to 1990s, most notably in southeast Asia, in contrast to an 11% reduction reported by the FRA. We estimate net mean annual carbon fluxes from tropical deforestation and regrowth to average 0.6 (0.3-0.8) and 0.9 (0.5-1.4) petagrams (Pg)·yr[sup -1] for the 1980s and 1990s, respectively. Compared with previous estimates of 1.9 (0.6-2.5) Pg·yr[sup -1] based on FRA national statistics of changes in forest area, this alternative estimate suggests less "missing" carbon from the global carbon budget but increasing emissions from tropical land-use change. [ABSTRACT FROM AUTHOR]