Structure and dynamics of a semideciduous seasonal forest fragment in the Piracicaba region, São Paulo State, Brazil

Este estudo foi realizado em um fragmento de Floresta Estacionai Semidecidual de 9,5 ha localizado em Piracicaba, SP, denominado de Mata do Pomar, o qual sofreu dois incêndios em passado recente. O estudo está voltado para as seguintes hipóteses: i) as espécies arbóreas e os grupos sucessionais diferenciam- se com relação às taxas de recrutamento e mortalidade; ii) as eco-unidades identificadas através de uma técnica denominada de Avaliação Ecológica Rápida apresentam composição e diversidade de espécies diferenciadas; iii) as síndromes de dispersão diferem com relação ao número de indivíduos recrutados e a densidade de indivíduos jovens. Dessa forma, tem três objetivos: i) analisou-se o recrutamento, mortalidade e mudança do tamanho populacional das espécies arbóreas e dos grupos sucessionais num período de quatro anos (1991 a 1995) e também comparou a sua recente estrutura com outros dois fragmentos de Floresta Estacionai Semidecidual: um fragmento de mesma área (fragmento Santa Rita-9,5 ha) e outro fragmento de tamanho cerca de nove vezes superior (fragmento Capuava-86,0 ha); ii) foram fornecidas medidas quantitativas de riqueza, diversidade e composição florística de espécies arbóreas das quatro eco-unidades identificadas neste fragmento de floresta; iii) avaliou-se a relação das síndromes de dispersão com o recrutamento (indivíduos 5 cm de DAP novos ingressos em 1995) e a densidade de indivíduos jovens (indivíduos 50 cm de altura e 50 cm of height and 15 individuals/ha ) had high recruitment and low mortality, which resulted in a pronounced population increase. Pioneer and gap-opportunist species presented a greater increase in plant density than shade-tolerant canopy and shade-tolerant understory species. The fragment has 50% less tree species than Santa Rita and "Capuava" fragments, although with the same size of "Santa Rita" fragment. Further, the Mata do Pomar fragrnent has a high local dominance by few species. Different patterns of floristic composition, richness and diversity were found for the four identified eco-units (capoeira baixa-CB, "capoeira alta tipo 1 -CA 1, capoeira alta tipo 2-CA2, mata madura-MM). Richness and diversity were higher in CA2 and MM than CB and CA 1. Pioneer species were well represented in the CB and CA 1, gap- opportunist in the CA2; shade-tolerant canopy species and shade-tolerant understory species in MM. For saplings, density, richness and diversity were lower in low capoeira and this eco-unit was well represented by pioneer and gap-opportunistic species. CA 1, despite having the same richness and diversity of CA2 and MM, had lower density and it was well represented by pioneer and gap-opportunistic species. ln contrast, shade-tolerant canopy species and shade-tolerant understory species were well represented in MM. The higher number of species belong to zoocory and anernocory syndrornes. The zoocory was well represented in pioneer and shade- tolerant understory groups and the anemocory by the gap-opportunist group. The mumber of individuais recruited and sapling density were related with both successional groups and dispersai modes, i.e, the majority of the species and individuais were not dependent of animal dispersai, but were mainly represented by pioneer and gap-opportunist species. The main conclusions of this study were: i) it is likely that the density of shade- tolerant overstory and shade-tolerant understory groups will decrease, increasing the local dominance of pioneer and opportunistic species and autocoric and anemocoric species, thus reducing tree diversity; ii) the eco-units identified through the Rapid Ecological Assessment method were significantly correlated to different forest structures and thus can be used in defining conservation strategy and management of semideciduous seasonal forest fragments; iii) the strategies of conservation biodiversity in semideciduous seasonal forest fragments in the São Paulo State should consider the anthropogenic disturbance in the identification of conservation priorities