AEROFORESTPY SYSTvIMS FOR INCREASING M{E PPDDUOT1ION OF WOO MXOD AND FODDER FROM NORMFAST BRAZIL

Three distinct climatic types are recognizable: a sub-humid zone with average precipitation of about 1500 mm, a semi-arid zone with a pronounced dry season but moderate precipitation in the rainy season, and an arid zone with average annual precipitation below 750 mm. The arid zone occupies approximately 50% of the area and extends from the north coast in the states of Ceará and Rio Grande do Norte, southward into the interior for a distance of about 1,300 km. The climate of the Northeast varies considerably from year to year in terms of the total amount of rainfall and its distribution within the rainy season. Short periods of little or no rainfall may occur at any time during the rainy season, and droughts are recurrent, especially in the arid regions. Rainfall variability in the Northeast also results in years of excessive rainfall, which can lead to serious problems associated with drought. The region's natural vegetation has been divided into four major ecological zones. The forest zone, originally tropical rain forest or tropical seasonal forest, has been virtually all removed due to agricultural and urban land use. The alvar, a transitional zone between the forest zone and the coast, is characterized by scattered trees alternating with a fairly dense layer of small trees and shrubs. The caatinga, which may be described as deciduous shrub forest of thorny small trees and shrubs and cacti, is not homogeneous, varying in density and composition depending on the amount of rainfall. Under the driest conditions, vegetation cover is discontinuous, with patches of bare ground and a high frequency of cacti. The caatinga exhibits significant changes from the wet to the dry season, with a reduction in vegetation cover and an increase in the frequency of cacti. The region's vegetation is also characterized by a high degree of heterogeneity, with a mix of tree species, shrubs, and herbaceous plants. The caatinga is an important ecosystem in the Northeast, providing a range of ecosystem services, including soil conservation, water cycling, and biodiversity conservation. The Brazilian Northeast region is densely populated, with a rapid increase in human population expected to reach about 65 million by the turn of the century. The region's land resources are under intense pressure, with the best land being utilized for plantation crops and grazing. The increase in rural population densities has led to over-exploitation of the vegetation in the caatinga for timber and fuelwood, exacerbating the region's environmental problems. The region is one of the most depressed in Brazil, both socially and economically. There is a shortage of both wood and food crops, and the situation is likely to worsen unless more productive and sustainable land management systems are evolved and practiced. The development of tree-based agroforestry systems with a view to increasing production and rehabilitating environmentally degraded areas is considered desirable.