Estrutura e dinâmica de populações arbóreas de um fragmento de floresta estacional semidecidual na região de Piracicaba, SP

Abstract

Tree populations structure and dynamics of a semideciduous seazonal forest fragment in the Piracicaba region, São Paulo state, BrazilFragmentation of tropical forests associated with anthropogenic disturbance can result in a loss of tree species and floristic composition change throughout the time in a forest fragment. To gather quantitative data regarding this hypothesis, this study was conducted in a 9.5 ha semideciduous seazonal forest fragment located in Piracicaba region, São Paulo state, Brazil. This fragment is named "Mata do Pomar", where two fires occurred in the recent past. In this fragment, recruitment, mortality and populational change of tree species were obtained in 4-year period (1991 and 1995). Different patterns of recruitment, mortality and populational change were found among tree species and ecological groups. The ten species more abundant in 1991 (class 1 -⊕ 15 individuals/ha ) presented 79.9% of recruitament, against only 7.5% and 9.0% of recruitment presented by density classes 2 (5.2 to 13.8 individuals/ ha) and 3 (1.7 and 3.4 individuals/ha), respectively. In particular, the three most abundant tree species in 1991, Bauhinia forficata, Aloysia virgata and Urera baccifera, all pioneer species, and Croton floribundus, an opportunistic species, were responsible for 75% of recruitment.Coupled with the high recruitment, these species also had low mortality, which resulted in a pronunciated population increasing. In the two lower density classes, 2 and 3, beyond the low recruitment, the pioneer and the opportunistic species presented 74.2% of recruitment. These last groups also presented a greater density gain than shade-tolerant canopy species and shade-tolerant understory species in the density classes 2 and 3. Beyond these results were also done a comparative analysis of this fragment with a fragment of same size ("Santa Rita" fragment -9.5 ha) and a fragment of 86 ha ("Capuava" fragment), both located in Piracicaba region.The "Mata do Pomar" fragment presents less of the half of tree species than "Santa Rita" and "Capuava" fragments, although with the same size of "Santa Rita" fragment. Further, the four most abundant tree species in the "Mata do Pomar" fragment, B. forficata, A. virgata, U. baccifera and T. micrantha are responsible for 62% of individuals, whereas the four most abundant tree species in "Santa Rita" and "Capuava" fragments are responsibles for only 30.6% and 23.2% of individuals, respectively, indicating a high local dominance in the "Mata do Pomar" fragment.This study demonstrates that strategies of conservation biodirversity in semideciduous seazonal forest fragments in the São Paulo state should consider the anthropogenic disturbance in the identification of conservation priorities.

Dinâmica da comunidade arbórea em uma floresta estacional semidecidual sob queimadas recorrentes

“…Ao contrário do esperado, o presente estudo mostrou maior riqueza e diversidade de espécies nas áreas da floresta queimadas duas vezes do que nas queimadas uma vez. Alguns estudos já verificaram diminuição na riqueza de espécies em áreas que sofreram perturbações (Nascimento et al 1999), no entanto, a intensidade e a frequência desses distúrbios podem contribuir tanto para diminuição como para o aumento da riqueza da comunidade. Isso está relacionado à severidade das perturbações, sendo que as extremas ocasionam a perda de espécies.…”

“…Especificamente no Brasil, florestas semidecíduas, têm sido estudadas com relativa frequência (Oliveira-Filho et al 1997; Nascimento et al 1999;Chagas et al 2001;Guilherme et al 2004;Appolinário et al 2005;Oliveira-Filho et al 2007;Paiva et al 2007;Higuchi et al 2008;Silva & Araujo 2009). No entanto, ainda são raros os estudos que analisam alterações estruturais e monitoram o desenvolvimento pós-fogo em florestas (Silva et al 2005;Melo et al 2007;Balch et al 2008).…”

Structure and dynamics of a woody plant community of a tropical semi-deciduous seasonal forest in the "Estação Ecológica do Panga", municipality of Uberlândia, Minas Gerais, Brazil

“…The greatest change observed was in relation to floristic composition, but the species that disappeared or were recruited were represented by just one or a few individuals. Species that were not abundant in the initial survey had a greater probability of disappearing locally, between a survey and the next one (Kellman et al 1998, Nascimento et al 1999, being able to reappear in a subsequent survey through migration or recruitment of individuals from the seed bank and seedlings or from the growth of young individuals that did not reach the minimum criterion for inclusion in the first survey (Pedroni 2001). The greater the time interval between the samplings, the larger the possibility of changes in floristic composition.…”

“…A high mortality rate was related by Phillips (1996) to global changes, such as an increase of CO 2 , and by Laurance et al (1998) and Nascimento et al (1999) to the effects of habitat fragmentation and microclimatic alterations. In EEP, the high rate was strongly influenced by the mortality of the Lithraea molleoides population.…”

Spatial variation in the structure and floristic composition of "restinga" vegetation in southeastern Brazil

“…In Brazil, where biodiversity is probably the highest in the world (World Conservation Monitoring Center 1992), most delimitation and characterization surveys have been restricted to one-hectare plots, with a few exceptions (e.g., Campbell 1994, Nascimento et al 1999. This is also true for the vegetation on the Brazilian sandy coastal plains ("restingas") where surveys often cover 1.0 hectare or less (e.g.…”