- Spatial structure of Aspidosperma polyneuron in two semi-deciduous forests in Southeast Brazil - 41 Journal of Vegetation Science 15: 41-48, 2004 © IAVS; Opulus Press Uppsala. Abstract. Description of the spatial structure of vegetation is the first step in generating hypotheses regarding underlying processes. It is also important to take into account variation in spatial structure between different localities to be able to distinguish between life history traits and the influence of environment on population processes. Correlogram analysis was used to examine spatial recruitment and mortality patterns of Aspidosperma polyneuron, an emergent tree species, at Reserva Municipal de Santa Genebra (SG), a forest fragment in southeast Brazil. The spatial structure of individuals was compared with two areas with similar physiognomy, one in the same forest and another at Mata do Ribeirão Cachoeira (RC), a semi-deciduous forest located ca. 14 km away. Seed- ling, sapling and adult mortality occurred in clumps, while seedling recruitment occurred mostly in one region of the area. The spatial pattern varied among the three study areas, and the differences were higher between fragments than within SG. The adults showed a negative correlation in space with sap- lings and seedlings in one of the SG areas, which could be a consequence of intraspecific competition, or the influence of density or distance dependent natural enemies. However, this pattern was not observed in the other areas. The results suggest that the mechanisms governing the spatial population dynam- ics of A. polyneuron vary among nearby and similar localities. Keywords: Apocynaceae; Correlogram; Emergent tree; Popu- lation dynamics; Spatial variation. Nomenclature: Carvalho (1994); Lorenzi (1992). Abbreviations: bd = Basal diameter; RC = Mata do Ribeirão Cachoeira; SG = Reserva Municipal de Santa Genebra. Introduction The spatial distribution of individuals of tree species may be studied at different scales, from biogeographic to the arrangement of individuals within a community. At the largest scales, all species show a clumped pattern resulting from the spatial heterogeneity of suitable envi- ronmental conditions (Lieberman & Lieberman 1994). But within a community, the spatial pattern of individu- als may be, at various scales, random, uniform or may show different degrees of aggregation. The study of this pattern can give insights in population dynamics and intra or interspecific competition (Forget et al. 1999). Within a community the most frequent spatial ar- rangement found in tropical tree species is a decrease in clumping from the smaller to the larger size classes (Henriques & Souza 1989; Oliveira-Filho et al.1996; He et al. 1997; Martens et al. 1997; Barot et al. 1999; Condit et al. 2000). The clumping of individuals may be a consequence of limited dispersion, vegetative reproduc- tion or environmental heterogeneity (Phillips & Mac- Mahon 1981; Hutchings 1997). Density or distance dependent mechanisms, such as influence of natural enemies (Janzen 1970; Connell 1971), competition be- tween seedlings or between seedlings and adults (Howe & Smallwood 1982; Clark & Clark 1984) can cause a seedling distribution discordant with the distribution of dispersed seeds, resulting in a spatial segregation be- tween juveniles and adults. This spatial segregation could also be caused by shifting in the environmental requirements through ontogeny (Clark & Clark 1992; Dalling et al. 2001). Therefore, different processes may result in the same pattern, and the spatial distribution of individuals may be caused by the interaction of different mechanisms (He et al. 1997; Grau 2000). The description of spatial structure is the first step in working out hypotheses about the underlying processes, which should then be tested in further studies (Barot et Spatial structure of Aspidosperma polyneuron in two semi-deciduous forests in Southeast Brazil Fonseca, Marisa Gesteira 1* ; Martini, Adriana Maria Zanforlin 2 & Santos, Flavio Antonio Maës dos 3 1 Programa de Pós-graduação em Biologia Vegetal, Departamento de Botânica, Instituto de Biologia, CP 6109, Universidade Estadual de Campinas, 13083-970, Campinas, SP, Brazil; 2 Departamento de Ciências Biológicas, Universidade Estadual de Santa Cruz, Rodovia Ilhéus-Itabuna Km 16, 45650-000 Ilhéus, BA, Brazil; 3 Departamento de Botânica, Instituto de Biologia, CP 6109, Universidade Estadual de Campinas, 13083-970, Campinas, SP, Brazil; * Corresponding author; Fax +551937886168; E-mail marisa_fonseca@yahoo.com.br