Population dynamics of Garcinia lucida (Clusiaceae) in Cameroonian Atlantic forests.

Garcinia lucida Vesque (Clusiaceae) is a highly valued non-timber forest tree. The bark and the seeds are exploited and commercialised for medicinal purposes and palm wine processing in Cameroon, Gabon and Equatorial Guinea. The bark is often removed over almost the entire circumference of the stem, leading to high mortality. To identify the processes or the life stages that influence the population dynamics and to forecast the potential effects of harvesting, a demography study was carried and a matrix model was constructed to characterise the population dynamics of G. lucida in the South Cameroonian Atlantic humid forests. The study revealed that height and diameter growth values were very low and may constitute biological disadvantages for the dynamics of the species. The flowering and fruiting model, the absence of seed dormancy, and the high germination and seedling survival rates constituted advantages for the population dynamics, which is characterised by effective regeneration strategies. Rates of growth, survival and fecundity allowed calculations of transition probabilities of the matrix model. The value of the dominant eigenvalue (lambda) was 1.063, slightly higher than the value expected for stable populations. The sensitivities of lambda to changes showed that the population growth was most sensitive to changes in tree growth, particularly in the seedling stage. Elasticity analysis showed that growth and fecundity elements had much lower contributions to lambda, indicating that the harvesting of seeds may have a low impact on population growth. However, the population growth was highly sensitive to changes in survival probability, particularly among trees of 5-10 cm, diameter at breast height (dbh). The last stages, containing the large reproductive individuals over 10 cm dhb, which are interesting for the bark extraction, accounted for lowest elasticity, indicating that the extraction of bark may have at least a low impact on population growth. Thus, there maybe a good scope for sustainable extraction of G. lucida bark in these stages. The size-class 5-10 cm dbh proved by loop analysis to be the most important reproductive stage for population maintenance. However, individuals in this size-class are also exploited by forest gatherers, and increased exploitation pressure on trees in this size-class is likely to have a considerable impact on the population growth and to compromise the scope for sustainable exploitation of this resource. (C) 2002 Elsevier Science B.V All rights reserved