Aspectos demograficos de Aspidosperma polyneuron Muell. Arg. (Apocynaceae) em dois fragmentos de floresta semidecidua no municipio de Campinas, SP

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The population dynamics and the spatial-temporal variation in the size and spatial structures of an emergent tree species, Aspidosperma polyneuron, were studied in two semideciduous forests, the Reserva Municipal de Santa Genebra (SG) and the Mata do Ribeirão Cachoeira (RC), in the Southeast of Brazil. The annual mortality, recruitment and . growth rates of adult individuaIs (dbh _ 5 cm) were analyzed in a l-ha area in SG in two periods, the first between 1982/1985 (to) and 1994/1995 (ti) and the second between ti and 1999 (t2). In half of this area, the same parameters were calculated for saplings (dbh <5 cm) between ti and t2. For this last period, data were also analyzed with a matrix model, and analyses of sensitivity and elasticity were performed. Size strucutre and spatial distribution of individuals were compared among ti and t2 in the same area. The population structure of two other O.5-ha are as with similar physiognomy, one in the very SG and another in RC, was described. Both size and spatial structures varied among the three areas, and the differences were higher within each fragment than among fragments. The results suggest that the mechanisms governing the population dynamics of A. polyneuron vary among close and similar localities, and highlight the necessity of future studies on the factors which cause these differences. A temporal variation in the size frequency distribution of the individuals with dbh <5 cm was observed, but not of those with dbh _ 5 cm. The spatial structure was temporally stable, suggesting that the processes determining it are also constant over time. The number of saplings decreased between ti and t2 and that of adults between to and t2 at a rate of 2.7% per year due to the low rate of recruitment in these classes (2.1 % and 0.4%, respectively). The diameter growth rate was slow in the young (0.02 crn/year), as well as that in adults (0.04 crn/year). A significant proportion of individuals did not show any increase in height (8 to 37%, depending on the size class) or showed decrease in it (21 to 30 %). The studied period may represent only a phase of decline in a natural cycle of stochastic fluctuations in the number of individuaIs. It is also possible that density-dependent processes are regulating the high density of the species in the study area. A third possibility is that the incidence of mechanical damage, owing to the high crown infestation of lianas, are preventing the saplings from reaching the reproductive stage. According to the analysis with the matrix model, the control of lianas as well as the planting of seedlings of the species would be necessary to reverse the process of decline. Together with more evidence on the degradation of the forest, the results of the present study might represent an alert, which indicates the necessity of intervention with the aim of guaranteeing the stability of the population in the study area

ASSUNTO(S)

demografia ecologia vegetal

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