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Figure 1. Conception of the dynamic of the soil fertility in pasture after the conversion of forest 
STUDY AREA 
The study area is located in the southeast part of the State of Rondónia, Brazil, Ariquemes, Cacaulándia, Jaru and 
Theobroma counties. This area is well known as one of the most exploited areas by human activities in Amazon, 
showing typical colonial development structure known as “fish bone”. 
The conversion of primary forest to pasture has been the main form of land exploitation in the past decades. This kind 
of land cover occupies relatively extensive areas that can reach up to 2000 ha. Other land use practices occur onl small 
or medium properties (<100ha), in which some annual and perennial crops, such as rice, beans, coffee and banana, in 
addition to grassland. Some second growth forest can be observed as a result of the pasture/crops abandonment or in 
areas that were intensively used cocoa and rubber production in past decades. 
3. METHODOLOGY . 
Temporal sequences of Landsat TM images (path/row 231/067, bands 3, 4 and 5) were used for the classification of 
pasture ages (since forest/pasture conversion). The time series consisted of 5 scenes acquired as follows: 12/jul/1987, 
30/jul/1988, 28/jul/1993, 08/03/ 1995, 04/jul/1996 and 07/jul/1997. Initially these images were geometrically registered 
to the image 1995, previously georeferenced by using grand control points obtained through GPS (Alves. 1998), using 
the nearest neighbor interpolation algorithm. After image registration, images were to 3,000 by 3,900 subset pixel, 
corresponding to an area of 10.530 km?. As stated above, the main goal of this study was to establish the pasture 
chronossequence by categorizing the pasture into different ages in order to choose sampling sites for analysis of soil 
fertility dynamic. To achieve that purpose, the following procedure was developed. 
3.1 Shade fraction image 
Since the shade image derived from spectral mixture analysis can provide a high degree of separability between mature 
forest area and non-forest area (or land use area), it can be useful to detect the conversion of forest to land use area in a 
given period (Shimabukuro, 1997). The spectral mixture model was applied to all images with the constrained least 
squares method (Shimabukuro and Smith, 1991). A pure spectra for component “vegetation”, “soil” and “shade” were 
acquired directly from each image consisted with bands 3, 4 and 5, by analyzing spectra signature on band 4 and band 5 
scatter plot. 
  
1034 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 
  
  
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