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NATURAL FOREST COVER MONITORING OF A REGION 
AFFECTED BY DESERTIFICATION PROCESSES: GILBUES - PI 
Ana Lücia Costa de Oliveira-Galväo 
Flávio Simas de Andrade 
IBAMA - DIRPED 
Centro de Sensoriamento Remoto 
SQN 410, Bloco H, Apto. 104 - Asa Norte 
70865-080 - Brasília, DF - Brazil 
ISPRS Commission VII / Working Group 6 
ABSTRACT 
Situated on the southern part of Piauí State, the Municipality of Gilbues, and four other neighbouring 
states constitute the most extensive and continuous desertification nucleus in Brazil. The expansion of 
local degradation processes motivated the present forest cover monitoring survey that was based on 
multistage data analysis. This investigation manipulated data from 1990-1993 and compared them with 
the figures from 1980-1981. The resulting information was obtained association visual interpretation of 
TM and MSS satellite imagery and detailed field observation. An evaluation of the existing 
physiognomic classes and their respective areas was performed utilizing PC ARC/INFO Software. 
Simultaneously, a multiphase analysis of the deteriorate areas and the different vegetation types was also 
carried out. The results achieved provide evidence that Gilbues' natural forest cover is being substituted 
gradually by anthropic physiognomies. These modifications characterize the development of a biotic 
retrogression process. 
091