THE ROLE OF TRADITIONAL AGROFORESTS IN THE CONSERVATION OF RAIN-FOREST BIRD DIVERSITY IN SUMATRA

Bird community composition and structure were compared among three different types of traditionally managed agroforests and the nearby primary forests in southwestern Sumatra during the breeding season. The agroforests were dominated respectively by rubber tree (Hevea brasiliensis), damar (Shorea javanica), and durian (Durio zibethinus) and were managed for cash crops (latex, resin, fruits, spices, coffee and timber). Although planted on formerly clearfelled and cultivated areas, these agroforests were highly diversified and structurally complex. Species relative abundance was obtained in 112 random samples of 50 individuals within limited census areas. The species were classified according to size, main diet, and observed habitat use. Eighty-three percent of all the regional pool of resident species were recorded at least once (excluding aerial, nocturnal, and aquatic species). Species richness, diversity, and equitability were all significantly lower (12% to 62% less) in every agroforest than in the primary forest, and the coefficients of similarity between the natural and managed forest communities were low (0.43-0.55). Less than half the lowland primary forest species known from western Sumatra were recorded in at least one agroforest. Among the 216 species occurring in samples, 56% significantly decreased in or disappeared from agroforests, whereas only 22% appeared or increased. The species most affected by the conversion of primary forests were large frugivores and large insectivores of the canopy and low understory, or terrestrial interior forest specialists. Species thriving in agroforests were small frugivores, foliage insectivores, and nectarivores often orginally associated with gaps. The factors affecting biodiversity in agroforests may involve reduced tree height, canopy foliage volume, vertical diversity of the vegetation structure, floristic richness, and associated variety of food resources. High hunting pressure may also be a factor. These multipurpose, traditionally managed agroforests still are a valuable compromise between conservation of tropical forest biodiversity and sustainable use of natural resources. They also function as buffer zones between densely populated and protected areas and are one of the most successful examples of silviculture of dipterocarps. Yet they are not equivalent to primary forests.