Walter Chomentowski

Annual fluxes of carbon from deforestation and regrowth in the Brazilian Amazon

The distribution of sources and sinks of carbon among the worlds ecosystems is uncertain. Some analyses show northern mid-latitude lands to be a large sink, whereas the tropics are a net source; other analyses show the tropics to be nearly neutral, whereas northern mid-latitudes are a small sink. Here we show that the annual flux of carbon from deforestation and abandonment of agricultural lands in the Brazilian Amazon was a source of about 0.2 Pg C yr-1 over the period 1989–1998 (1 Pg is 1015 g). This estimate is based on annual rates of deforestation and spatially detailed estimates of deforestation, regrowing forests and biomass. Logging may add another 5–10% to this estimate, and fires may double the magnitude of the source in years following a drought. The annual source of carbon from land-use change and fire approximately offsets the sink calculated for natural ecosystems in the region. Thus this large area of tropical forest is nearly balanced with respect to carbon, but has an interannual variability of ± 0.2 PgC yr-1.

Physical and human dimensions of deforestation in Amazonia

In the Brazilian Amazon, regional trends are influenced by large scale external forces but mediated by local conditions. Tropical deforestation has a large influence on global hydrology, climate and biogeochemical cycles, but understanding is inadequate because of a lack of accurate measurements of rate, geographic extent and spatial patterns and lack of insight into its causes including interrelated social, economic and environmental factors. This article proposes an interdisciplinary approach for analyzing tropical deforestation in the Brazilian Amazon. The first part shows how deforestation can be measured from satellite remote sensing and sociodemographic and economic data. The second part proposes an explanatory model, considering the relationship among deforestation and large scale social, economic, and institutional factors. 43 refs., 8 figs.

Effects of global change on carbon storage in tropical forests of South America

We used a process-based model of ecosystem biogeochemistry (MBL-GEM) to evaluate the effects of global change on carbon (C) storage in mature tropical forest ecosystems in the Amazon Basin of Brazil. We first derived a single parameterization of the model that was consistent with all the C stock and turnover data from three intensively studied sites within the Amazon Basin that differed in temperature, rainfall, and cloudiness. The range in temperature, soil moisture, and photosynthetically active radiation (PAR) among these sites is about as large as the anticipated changes in these variables in the tropics under CO2-induced climate change. We then tested the parameterized model by predicting C stocks along a 2400-km transect in the Amazon Basin. Comparison of predicted and measured vegetation and soil C stocks along this transect suggests that the model provides a reasonable approximation of how climatic and hydrologic factors regulate present-day C stocks within the Amazon Basin. Finally, we used the model to predict and analyze changes in ecosystem C stocks under projected changes in atmospheric CO2 and climate. The central hypothesis of this exercise is that changes in ecosystem C storage in response to climate and CO2 will interact strongly with changes in other element cycles, particularly the nitrogen (N) and phosphorus (P) cycles. We conclude that C storage will increase in Amazonian forests as a result of (1) redistribution of nutrients from soil (with low C:nutrient ratios) to vegetation (with high C:nutrient ratios), (2) increases in the C:nutrient ratio of vegetation and soil, and (3) increased sequestration of external nutrient inputs by the ecosystem. Our analyses suggest that C:nutrient interactions will constrain increases in C storage to a maximum of 63 Mg/ha during the next 200 years, or about 16% above present-day stocks. However, it is impossible to predict how much smaller the actual increase in C storage will be until more is known about the controls on soil P availability. On the basis of these analyses, we identify several topics for further research in the moist tropics that must be addressed to resolve these uncertainties.

Characteristics of bird species using forest and agricultural land covers in southern Costa Rica

Our understanding of why tropical forest species differ in their ability to inhabit agroecosystems is limited, despite the link between this ability and the likelihood of population decline for species inhabiting regions undergoing widespread conversion of forest to agriculture. We used logistic regression and data from southern Costa Rica to develop a model based on natural history characteristics to distinguish between forest species that did or did not use agricultural land covers. We sampled birds along 15 3.0-km routes, seven in forest and eight in agriculture, five times over three years. Each species was classified as an F-species, detected only in forest, a G-species, detected in both forest and agriculture, or an A-species, detected only in agriculture. Thirty percent of species were F-species, 42% were G-species, and 28% were A-species. Based on the logistic regression model, the likelihood of being a G-species, as opposed to an F-species, was low for species that were dependent on forest interior, had a stenophagous diet, and a small elevational range. Weight, resident versus migrant status, and whether or not a species was insectivorous, were not significant predictors of being a G-species. For all F–G species pairs, the model correctly predicted the G-species 70% of the time. The model provides a first step in identifying those characteristics that predispose forest species to use agricultural land. In addition, our results indicate that the structurally simple agricultural systems of the study region are of limited value for a large proportion of the regional species pool.

Conservation units: a new deforestation frontier in the Amazonian state of Rondônia, Brazil

Over the past several decades, the Brazilian State of Rondonia has been the destination of many rural migrants drawn from Brazils middle southern regions by massive government colonization projects. Factors such as explosive population growth, logging, mining, small-scale farming and ranching have synergistically fuelled deforestation in the state. The total area deforested in Rondonia in 1978 was 4200 km 2 . In 1988, the area increased to 30 000 km 2 , in 1998 to 53 300 km 2 and by the year 2003, a total of 67 764 km 2 of Rondonia was deforested. In response to the high rate of deforestation observed in Rondonia and other Amazonian states, state and federal agencies worked to create a network of conservation units (CUs) in Brazil during the 1990s that was signed into law (Law 9985/00) in 2000. The ability of these CUs to reduce the rate of deforestation was analysed. Remotely-sensed data from Landsat and thematic coverages were used to measure deforestation inside all CUs in Rondonia. A more detailed analysis of CUs with the highest levels of deforestation, including an analysis between soil types and deforestation and a forecast of potential future deforestation, was conducted. The creation of conservation units in Rondonia has been useful in curbing deforestation within their boundaries; however, many CUs face pressure from the combined activities of illegal loggers, cattle ranchers and small-scale farmers seeking new sources of timber and agricultural land. For example, an exponential increase in the amount of deforestation was observed in Rondonias Bom Futuro National Forest between 1992 and 2000. A regression model indicated a total of 20 500 ha deforested by 2002, while measurements from 2002 imagery showed an actual total deforestation of 20 720 ha. Should this trend persist, Bom Futuro National Forest could be completely deforested by 2017. CUs in Rondonia must be developed and implemented jointly by all stakeholders through the creation of partnerships between local communities, non-governmental organizations and government agencies.

Multi-temporal assessment of selective logging in the Brazilian Amazon using Landsat data

Large‐scale selective logging is a relatively new activity in the Amazon and its full consequences have yet to be evaluated. Impacts by selective logging alone have been estimated to increase approximately 4–7% of the annual carbon release from deforestation. In this research, visual interpretation and semi‐automated remote sensing techniques were applied to identify and map areas of selective logging in tropical terra firme (upland) forests together with the correlated multi‐annual measurement results for 1992, 1996, and 1999, for the Brazilian Amazon. The research results indicate that selective logging is rapidly increasing in both intensity (regional) and area (basin‐wide). By 1992, at least 5980 km2 of forest had been logged. During the 1992–1996 and 1996–1999 periods the area impacted expanded by an additional 10 064 km2, and 26 085 km2, respectively. Selective logging within protected areas increased more than twofold between 1992 and 1996, and more than fivefold between 1996 and 1999 in that region. We also estimated that at least 3689 km2 had been actively logged in 1992, an additional 5107 km2, and 11 638 km2, had been logged in 1996 and 1999, and at least 10% of total logged forests detected in 1999 were previously logged in the period of analysis.

Monitoring Selective Logging in Tropical Evergreen Forests Using Landsat: Multitemporal Regional Analyses in Mato Grosso, Brazil

Abstract 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 ...

Assessment of forest disturbances by selective logging and forest fires in the Brazilian Amazon using Landsat data

The rapid environmental changes occurring in the Brazilian Amazon due to widespread deforestation have attracted the attention of the scientific community for several decades. A topic of particular interest involves the assessment of the combined impacts of selective logging and forest fires. Forest disturbances by selective logging and forest fires may vary in scale, from local to global changes, mostly related to the increase of carbon dioxide released into the atmosphere. Selective logging activities and forest fires have been reported by several studies as important agents of land-use and land-cover changes. Previous studies have focused on selective logging, but forest fires on a large scale in tropical regions have yet to be properly addressed. This study involved a more comprehensive investigation of temporal and basin-wide changes of forest disturbances by selective logging and forest fires using remotely sensed data acquired in 1992, 1996, and 1999. Landsat imagery and remote-sensing techniques for detecting burned forests and estimating forest canopy cover were applied. We also conducted rigorous ground measurements and observations to validate remote-sensing techniques and to assess canopy-cover impacts by selective logging and forest fires in three different states in the Brazilian Amazon. The results of this study showed a substantial increase in total forested areas impacted by selective logging and forest fires from approximately 11,800 to 35,600 km2 in 1992 and 1999, respectively. Selective logging was responsible for 60.4% of this forest disturbance in the studied period. Approximately 33% and 7% of forest disturbances detected in the same period were due to impacts of forest fires only and selective logging and forest fires combined, respectively. Most of the degraded forests (∼90%) were detected in the states of Mato Grosso and Pará. Our estimates indicated that approximately 5467, 7618, and 17437 km2 were new areas of selective logging and/or forest fires in 1992, 1996, and 1999, respectively. Protected areas seemed to be very effective in constraining these types of forest degradation. Approximately 2.4% and 1.3% of the total detected selectively logged and burned forests, respectively, were geographically located within protected areas. We observed, however, an increasing trend for these anthropogenic activities to occur within the limits of protected areas from 1992 to 1999. Although forest fires impacted the least area of tropical forests in the study region, new areas of burned forests detected in 1996 and 1999 were responsible for the greatest impact on canopy cover, with an estimated canopy loss of 18.8% when compared to undisturbed forests. Selective logging and forest fires combined impacted even more those forest canopies, with an estimated canopy loss of 27.5%. Selectively logged forest only showed the least impact on canopy cover, with an estimated canopy loss of 5%. Finally, we observed that forest canopy cover impacted by selective logging activities can recover faster (up to 3 years) from impact when compared to those forests disturbed by fires (up to 5 years) in the Amazon region.

The Impact of Land Titling on Tropical Forest Resources

The impact of land tenure security on tropical deforestation and land management, more generally, is an issue that has received a great deal of discussion, and which possesses significant policy implications. If land tenure encourages planning over the long term, then the awarding of titles and the enforcement of private property rights may provide a decentralized approach to controlling rapid loss of forest. The economic theory on the role of tenure security on the management of assets such as land is well articulated, and in the case of tropical forest predicts a reduction in forest exploitation and destruction. Despite the conceptual appeal of the theoretical argument, little empirical work has been accomplished addressing specifically the role of secure land tenure on rates of forest clearance in tropical frontiers. The present chapter seeks to rectify this situation by combining data from a detailed survey of households with a time series of classified satellite images. In the summer of 1996, the authors conducted a survey along the Transamazon Highway in the state of Para, Brazil, compiling information from 347 lots belonging to small-holders. In addition to the survey, they compiled a six year time-series of classified Landsat TM images for an 11-year period between 1986 and 1997 (1986, 1987, 1988, 1991, 1992, 1997). These images cover the survey area and provide a dynamic account of the land cover changes for a sub-sample of the lots queried in the original survey. The chapter gives an account of the survey sample, and results of a statistical analysis addressing the impact of title on the commercial exploitation of hardwoods and on rates of deforestation. Given knowledge of the year of titling and a series of images bracketing 11 -years, the research considers, on a lot-by-lot basis, rates of deforestation before and after the awarding of title. The paper is concludes with a discussion of the implications of findings for policy.

Land Use and Land Cover Change in Southeast Asia

Southeast Asia is a culturally, environmentally, and geographically rich, diverse, and dynamic region. Comprised of eleven countries, it spans the Indochina and Malay peninsulas and the Malay Archipelago. Five nations, Cambodia, Laos, Myanmar, Thailand, and Vietnam, are entirely on the mainland. The remaining six, Brunei, East Timor, Indonesia, Malaysia, Philippines, and Singapore, are spread across thousands of islands. Coastal zones and river deltas, piedmont zones and mountain chains, with peaks reaching heights greater than 19,000 feet, characterize the region. The land cover and land use change patterns evident in Southeast Asia are as diverse and dynamic as the political, economic, and demographic spheres in these eleven nations.