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Who is cutting trees?

Nearly all the region's countries have laws that prohibit unauthorized cutting and burning of forests. But government officials charged with enforcing these regulations have long been hobbled by the difficulty of monitoring activities over thousands of square kilometers.

Infrared satellite imagery can be processed to detect subtle differences in the light reflected by healthy or degraded forests, cleared areas and other types of vegetation. That makes it ideal for tracking changes caused by logging and many other kinds of land use.

The Landsat image taken over Santa Rosa del Palmar, Bolivia in 1994 (See first photo on the left), was processed to highlight forested areas (dark green) and areas that have been logged and converted to various types of agricultural use (pink and light green). According to engineers at Aeroterra S.A., an Argentine firm that analyzed the image for a client, three distinct types of land use are visible in relatively close proximity. The large, rectangular plots in the lower right-hand corner belong to a Mennonite community that is practicing intensive, mechanized agriculture. The pattern of rounded, light-green clearings in the upper left-hand corner is probably the result of a planned land development program that established settlements at 5 km intervals. The more chaotic pattern of smaller plots in the lower left-hand corner indicates an older, ad hoc settlement with mixed agricultural uses.

The second picture shows a 1991 view of the reservoir behind the Salto del Guairá hydroelectric complex on the border between Paraguay and Brazil. The image shows that forests (color-coded in brown) have been cut right up to the water's edge in many places despite regulations that require a wide forest buffer along the entire perimeter of the reservoir. Without adequate forest cover, run-off erosion from farmed land can fill the reservoir with silt, endangering its future operation.

By combining images such as these with a GIS that includes land use regulations and ownership information, government officials stand a much better chance of detecting and stopping inappropriate land use. While up-to-date Landsat images formerly cost close to $5,000 each, not including processing fees, the price is expected to drop to less than $500 starting late 1999 when the latest Landsat satellite enters service. At that price, continuous satellite monitoring of land use will become an affordable option for many governments.

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