Ecogeography and human scenario in notheast Roraima, Brasil

RESUMO

In northern Brazil, the Northeast part of the State of Roraima is the most complex environment that occurs under Amazonian conditions. The "environmental stratification" approach, based essentially on pedological, geomorphological and vegetational studies was used, providing a rapid assessment of the ecogeography, its long-term possibilities and constraints. The integrated land use assessment of the stratified units was discussed. Among the four units, three main units occur on the extensive plain surface, forming a climatic gradient. The Caracaraí-Anauá unit is dominated by forest and campina vegetation, associated with latosols and hydromorphic podzols. The Lavrado unit is dominated by open grass savanna, with fire-resistant species and gallery forest featuring Buriti palms, resembling a "dambo"-like landscape. In most cases, the boundaries between these two units are abrupt forest/savanna contacts. The Surumu unit is characterized by xerophytic savanna with cactus, with semiarid species and sodic soils occurring on volcanic-acid rocks. Overall, the present tendency is for an invasion of forest vegetation into savanna areas. The process is directly related to the evolution of the "veredas de buritis"ecosystem and the capture of closed lakes and "dambo"-like swamps as "veredas de buritis" extend and landscape rejuvenation occurs. The main agronomic constraint is the very low nutrient status of the soils, allied to the high aluminum saturation in the Caracaraí-Anauá and Lavrado units, and the high sodium content, erosion hazard and stony soils in the Surumu unit. The carrying capacity and the resilience against changes of the units are generally very low. In spite of that, the overall extent of land colonization in Roraima increased by about 70 percent from 1980 to 1985, although small settlements increased by a disproportionate 242 percent over that period, mainly as a result of colonization in the forested Caracaraí-Anauá unit; in contrast, there was an absolute reduction of 23 percent in the number of very large settlements. The official land colonization policy was discussed, illustrating the human scenario in NE Roraima. The obsence of strategies for rural development is evident, and the current pattern of high mobility of these "colonos"(settlers) associated with seasonal burning and gold-mining are direct consequences of this ill-conceived policy...