No abstract

No abstract

Clear cutting in tropical forests is common. A newer phenomenon, selective logging, is evident in Amazonia when examined with high-resolution satellite data. We have quanti® ed selective logging by digitizing satellite imagery and have found that it is much more di cult to detect than clear cutting. Selective logging is likely under-reported in satellite imagery-based estimates of change in Amazonia as the visible signal of selective logging may be evident for only a limited time. We have found that the areas a ected by selective logging have increased over time and have become more widely distributed. Little land selectively logged, perhaps 10%, was converted to pasture. Selective logging altered 12% of the total forested area of one study region, yet was undetectable in satellite imagery three years later. It is unclear how long the visual clues of selective logging will remain apparent in satellite imagery in subsequent years.

The forests of Russia cover a larger area and hold more carbon than the forests of any other nation and thus have the potential for a major role in global warming. Despite a systematic inventory of these forests, however, estimates of total carbon stocks vary, and spatial variations in the stocks within large aggregated units of land are unknown, thus hampering measurement of sources and sinks of carbon. We mapped the distribution of living forest biomass for the year 2000 by developing a relationship between ground measurements of wood volume at 12 sites throughout the Russian Federation and data from the MODIS satellite bidirectional reflectance distribution function (BRDF) product (MOD43B4). Based on the results of regression-tree analyses, we used the MOD43B4 product to assign biomass values to individual 500 m × 500 m cells in areas identified as forest by two satellite-based maps of land cover. According to the analysis, the total living biomass varied between 46 and 67 Pg, largely because of different estimates of forest area. Although optical data are limited in distinguishing differences in biomass in closed canopy forests, the estimates of total living biomass obtained here varied more in response to different definitions of forest than to saturation of the optical sensing of biomass.

Objective measurements of rates of deforestation, especially in the tropics, have been elusive. We report the development and use of a series of techniques for use of existing satellite imagery for measurement of rates of deforestation in the tropics. The techniques have been applied in the Brazilian state of Rondonia in the southwestern Amazon Basin, the site of a large Brazilian resettlement project, started in the early 1970s. Application of special techniques for detecting change using Landsat imagery showed that between 1976–1978 and 1978–1981 the rate of deforestation increased by a factor of 2 from 620 km2 yr−1 to 1270 km2 yr−1 in the 109,000‐km2 section of Rondonia studied with Landsat imagery. A combination of the Landsat and NOAA 7 advanced very high resolution radiometer imagery was used to provide an estimate of the total extent of deforestation in Rondonia by 1982. The area was 11,400 km2 or 43% of the total area of the project and 6% of the state. The techniques are highly promising and, with further development, can be used to estimate the extent and rates of deforestation globally.