Rapid tropical forest inventory: a comparison of techniques based on inventory data from western Amazonia

Floristic inventory is critical for conservation planning in tropical forests. Tropical forest inventory is hampered by large numbers of species, however, and is usually abbreviated by sampling only the tallest trees in the forest, an approach that remains time-consuming. In a systematic effort to identify better means of abbreviating inventory in western Amazonia, we defined four classes of inventory abbreviation and evaluated them for use in inventory: occurrence metric, measured for individual taxa (e. g., presence-absence); taxonomic resolution, the level to which stems are identified; diameter class, the classes included in inventory; and taxonomic scope, the taxon or taxa included in inventory. Using these four classes and all their possible combinations, we defined > 300 inventory abbreviations and evaluated them by conducting nine inventories near Iquitos, Peru. We evaluated these abbreviations with four criteria: correlation between the floristic patterns of the full and abbreviated inventories, mean number of stems per site, total number of taxa, and height of inventoried stems. Presence-absence inventories were generally interchangeable with abundance inventories, regardless of the use of other abbreviations. Genus-resolution inventory captured 80% of the floristic pattern of the full inventory, with an 80% reduction in number of taxa sampled, but did not reduce the number of stems sampled. Inventories based on diameter class, with either species or genus identifications, revealed a majority of the floristic pattern of the full inventories with a fraction of the stems and taxa, but they were indistinguishable in efficiency from random sampling. Taxonomic-scope abbreviations were more efficient than any other type of inventory, including random sampling, and required one-fifth the number of stems and taxa of diameter-class-based methods and one-twentieth the number of a full inventory. We believe that taxa-based inventory may provide the optimal instrument for biological survey and conservation planning in western Amazonia.