Efficient floristic inventory for the assessment of tropical tree diversity: A comparative test of four alternative approaches

Biodiversity inventory as a tool for guiding conservation planning at a local scale is under used, especially in tropical countries where technical capacity is often limited. Here four inventory protocols (one ad hoc, one fixed count and two fixed area methods) are tested for their efficiency and statistical robustness when applied to the woody floras of a Mexican seasonally dry tropical forest. They are tested for their ability to distinguish between sites not only by number of species (richness), but also by number of threatened species, and finally in their application to complementary reserve selection exercises. Whilst the ad hoc method is shown to have the advantage of high efficiency and is technically undemanding, where possible the statistically more robust fixed count or fixed area methodologies are recommended. However, the much used fixed area method of Gentry [Gentry, A.H., 1982. Patterns of neotropical plant species diversity. Evol. Biol. 15, 1–84] that uses 2 m × 50 m plots is shown to be inefficient. Only when comparison with other previously published assessments is a priority should the 2 m × 50 m fixed area method be considered, and then efficiency may be increased by widening the plots and distinguishing between those stems that fall within a notional 2 m plot and those outside of it. Both prioritisation by number of species and complementarity analysis, using the ‘greedy’ algorithm, are shown to be sensitive to choice of inventory protocol, suggesting that consideration is given to how species lists are obtained in reserve selection exercises.