Statistical methods for estimating species richness of woody regeneration in primary and secondary rain forests of Northeastern Costa Rica

The study of plant communities requires a basic understanding of the abundance, distribution, and number of species present. Yet, in obtaining this information, scientists can rarely sample the entire community or area of interest. In practice, data from numerous small sub-samples provide a basis for extrapolating to a larger area, Such extrapolating must take into account the well-supported observation that estimates of local species richness depend strongly on the number of individuals and the area sampled (Gleason, 1922; Preston, 1948). Although researchers must rely heavily on extrapolations for many kinds of ecological studies, relatively little attention has been focused on improving the accuracy, applicability, and accessibility of species-richness estimators in vegetation studies, particularly in higly diverse tropical ecosystems. If robuts and accurate statistical estimators of species richness that are reasonably insensitive to sample size can be found, they can serve to provide a quantitative basis for identifying conservation priorities, for comparative biogeographic or regional studies, and for assessing long-term changes in species richness. Bunge and Fitzpatrick (1993) and Colwell and Coddington (1994) provided a broad overview of statistical approaches for estimating species richness form samples. Here, we evaluated the performance of several of these methods in estimating species richness of young woody regeneration in six tropical forest sites. We compared the performance of various estimation techniques within individual sites as well as across a range of sites differing in successional status and in woody species abundance and spatial distribution. We focused specifically on two size classes of wood regeneration: 1) established seedlings 1m in height, but