Sampling effort and factors influencing the precision of estimates of tree species abundance in a tropical forest stand

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Stand inventories are indispensable in community and population studies, diversity and conservation assessments, and pattern search, representing the first step towards understanding distribution and abundance variation of species in space. As species abundance descriptors ate estimated through sampling, the precision of the estimates is important to assess data scope. In a 6.5-ha area of a semideciduous Atlantic forest, SE Brazil, we randomly located 100 plots of 10 x 10m to sample trees with DBH >= 5 cm. We calculated the sampling error of estimates of density, frequency, dominance, and importance value index (IVI) for species with five or more adult individuals, and determined the number of plots necessary not to exceed sampling errors of 20%. Esenbeckia leiocarpa (Rutaceae), the most abundant species, was the only species for which sampling errors did not exceed 20%. The most appropriate criterion for evaluation of the sampling sufficiency for the inventory of the stand as a whole was the one based on the general sampling error of a set of the most abundant species. The estimates of density, frequency and IVI were influenced by the aggregation of individuals. The estimate of dominance had a greater influence of the basal area variation among individuals. Frequency had the greatest precision, dominance had the smallest, and density and I VI had intermediate precision.394377388Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Fitting abundance distribution models in tropical arboreal communities of SE Brazil

The species abundance distribution of ecological communities has been represented through several mathematical models, of which the most common are: geometric series, logseries, lognormal, and a type of broken stick, this latter found only in animal communities. There is no consensus on the underlying biological processes, but initial observations on plant communities related these models to equilibrium and high richness (lognormal), stress or disturbance and low richness (logseries and geometric series). Recently the value of these relationships was challenged, and other descriptors were considered better predictors of richness, disturbance and stress. We aimed at investigating how these models and their parameters, as well as dominance and evenness are related with species richness, stress and disturbance in six tropical forest communities, SE Brazil: two well-conserved fragments, two disturbed by fire, and two swampy forests (anoxic stress). The models did not show consistent relationships with richness, disturbance or stress. The parameters and indices of diversity a (logseries) and l (lognormal) varied closely with richness, and the dominance was larger in the communities submitted to stress or disturbance. Our results indicate the need of further studies in order to validate (or refute) the use of abundance distribution models for detection of patterns related to richness, stress or disturbance in tropical arboreal communities. On the other hand, richness and dominance did respond to disturbance and stress