JENS-PETER KRUEGER, GERHARD GEROLD
Georg-August-Universität Göttingen, Department of Landscape Ecology, Germany
This study attempts to develop a GIS-based methodology for the assessment of potential soil degradation areas in the main cultivation zone in the eastern Bolivian lowland. The region is characterised mainly by highly mechanized large scale agriculture.
Variables taken into account are data about soil (soil properties), climate (precipitation), land use (utilisation, system, cultivation period) and relief (topography) as well as land cover (type), administrative (concessions, colonisation areas) and infrastructure data (road network, network distance, settlements). Information about soils were derived from a departmental land use plan (PLUS) and several more detailed soil studies. All data were compiled together in a GIS data base.
We assessed the spatial and temporal patterns of deforestation as well as the conversion into different land use or land cover classes by processing 2 adjacent Landsat images (230-72, 230-73) for the years 1984, 1992 and 2001 each. The study area is limited to the area common to the images. It is located between the Andean foothills to the west and the Brazilian shield to the north-east and covers over five million hectares of mainly flat land. Almost 1.200.000ha forest were cleared between 1984 to 2001. The estimated annual deforestation rate increased from 40.339ha by 1992 to approximately 97.500ha by 2001. Thus, 73% of the total deforestation has occurred in the 1990s.
The soils are predominantly highly fertile (alluvial deposits) but due to an inherently fragile soil structure susceptible to compaction. Hence, a significant proportion of the soils have different levels of limitations for mechanized agriculture and requires careful management. According to the land use plan, 871.338ha (82,5%) of the soils in the study area used for cropping in 2001 have severe limitations, whereas 132.695ha (12,6%) are unsuited for cultivation. However, the combination of an inherently unstable soil structure with inappropriate soil management techniques and harsh climatic conditions (strong winds and a distinct inter-annual variability in precipitation) led to increasing soil degradation processes, followed by declining yields. Low land prices makes conservation unnecessary, so that ongoing soil degradation is most likely.
Keywords: Bolivia, GIS, soil degradation