David L. Skole

Tropical Deforestation and Habitat Fragmentation in the Amazon: Satellite Data from 1978 to 1988

Landsat satellite imagery covering the entire forested portion of the Brazilian Amazon Basin was used to measure, for 1978 and 1988, deforestation, fragmented forest, defined as areas less than 100 square kilometers surrounded by deforestation, and edge effects of 1 kilometer into forest from adjacent areas of deforestation. Tropical deforestation increased from 78,000 square kilometers in 1978 to 230,000 square kilometers in 1988 while tropical forest habitat, severely affected with respect to biological diversity, increased from 208,000 to 588,000 square kilometers. Although this rate of deforestation is lower than previous estimates, the effect on biological diversity is greater.

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.

Carbon emissions from tropical deforestation and regrowth based on satellite observations for the 1980s and 1990s

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 Administrations 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 remote-sensing 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−1 for the 1980s and 1990s, respectively. Compared with previous estimates of 1.9 (0.6–2.5) Pg⋅yr−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.

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.

Deforestation in Costa Rica: A Quantitative Analysis Using Remote Sensing Imagery1

Accurate estimates of forest cover and forest fragmentation are critical for developing countries such as Costa Rica, which holds four to five percent of the world’s plant and bird species. We estimated forest cover for Costa Rica using Landsat 5 Thematic Mapper satellite scenes acquired between 1986 and 1991. In 1991, 29 percent (ca 14,000 km2) of the land cover of Costa Rica was closed forest cover; of that forested area, ca 30 percent is protected by national conservation policies. Forest loss in a study area representing ca 50 percent of Costa Rica’s territory during a five-year period (1986–1991) was 2250 km2, and the estimated deforestation rate was ca 450 km2/yr, or ca 4.2 percent/yr, of remaining forest cover. Forests are almost completely eliminated from the Tropical Moist Forest and Premontane Moist Forest life zones, and the level of fragmentation of remaining forests may be more advanced than previously thought.

Secondary Forest Expansion in the Brazilian Amazon and the Refinement of Forest Transition Theory

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 ...

The 1 km resolution global data set: needs of the International Geosphere Biosphere Programme†

Abstract Examination of the scientific priorities for the International Geosphere Biosphere Programme (IGBP) reveals a requirement for global land data sets in several of its Core Projects. These data sets need to be at several space and time scales. Requirements are demonstrated for the regular acquisition of data at spatial resolutions of 1 km and finer and at high temporal frequencies. Global daily data at a resolution of approximately 1 km are sensed by the Advanced Very High Resolution Radiometer (AVHRR), but they have not been available in a single archive. It is proposed, that a global data set of the land surface is created from remotely sensed data from the AVHRR to support a number of IGBPs projects. This data set should have a spatial resolution of 1 km and should be generated at least once every 10 days for the entire globe. The minimum length of record should be a year, and ideally a system should be put in place which leads to the continuous acquisition of 1 km data to provide a base line d...

Changes in the landscape of Latin America between 1850 and 1985 II. Net release of CO2 to the atmosphere

Abstract The net release of carbon to the atmosphere from deforestation in Latin America was calculated for the period 1850–1985. Changes in the area of forests were described in a companion paper. Here, the stocks of carbon in vegetation and soils of major ecosystems, and changes in these stocks of carbon as a result of disturbance, were used to calculate the net annual flux of carbon. The total net release of carbon between 1850 and 1985 was about 30 × 1015 g (range 17–35 × 1015 g). The land uses responsible for the emissions of carbon were increased areas of pastures (42% of the total emissions), croplands (34%), degraded lands (19%), and shifting cultivation (5%). Logging and the establishment of plantations contributed or accumulated negligible amounts of C over this 135-year period. The annual releases of C to the atmosphere increased over the period 1850–1985; half of the total release occurred after 1960. By 1985 the net release was 0.67 × 1015 g C year−1 (range 0.39–0.82 × 1015 g C). The relative contributions of different land uses to this flux were different from those over the long-term. The greatest single source of C in 1985 resulted from increases in the area of degraded lands (37% of the net flux), and the importance of shifting cultivation increased to almost 20%. The range of estimates calculated here for the current net flux of C is lower than earlier estimates of the range. The range results from uncertainties in the rates of land-use change, in the types of ecosystems cleared and the stocks of C in these ecosystems, and in the rates of decay and regrowth of organic matter associated with land-use change.

Fourier analysis of multi-temporal AVHRR data applied to a land cover classification

Abstract A signal processing technique is presented and applied to annual patterns of the Global Vegetation Index (GVI) derived from the Advanced Very High Resolution Radiometer (AVHRR) to examine the frequency distribution of the multi-temporal signal. It is shown that frequencies of the signal are linked to integrated GVI, seasonal variability and subseasonal variability of the land cover type. These characteristics are used to derive a land cover classification.

Changes in the landscape of Latin America between 1850 and 1985 I. Progressive loss of forests

Abstract Reduction in the area of forests in Latin America between 1850 and 1985 was estimated from changes in the major uses of land, including permanent croplands, pastures, shifting cultivation, logging, and degradation. Changes in croplands were documented through historical statistics. The types of forests and other natural ecosystems converted to croplands were estimated from a comparison of maps of natural vegetation with maps of agriculture. Changes in the area of pastures were inferred from changes in the number of cattle and stocking rates. Estimates of the rate of deforestation for shifting cultivation were available only in recent years. Before 1940 the area in shifting cultivation was assumed constant; between 1940 and 1985 the increase in area was assumed to accelerate. In recent decades, the area of forests has decreased more rapidly than increases in the areas of croplands and pastures. This additional loss of forests is thought to have resulted from the replacement of degraded agricultural land, and was estimated to have occurred historically according to different assumptions. The results showed that, between 1850 and 1985, about 370 × 106 ha of forest (28% of the forest area in 1850) were replaced by some other type of ecosystem. Most of was due to the expansion of pastures (44% of the reduction), croplands (25%), degraded lands (20%), and shifting cultivation (10%). The use of alternative data and assumptions gave estimates of total deforestation that ranged between 313 and 412 × 106 ha (25–30% of the area in 1850). The largest uncertainties were related to historical rates of degradation and shifting cultivation, and to the types of ecosystems converted to human uses. Use of satellite imagery can eliminate most of these uncertainties after 1975.