Characterizing tropical tree species growth strategies : learning from inter-individual variability and scale invariance

Understanding how tropical tree species differ in their growth strategies is critical to predict forest dynamics and assess species coexistence. Although tree growth is highly variable in tropical forests, species maximum growth is often considered as a major axis synthesizing species strategies, with fast-growing pioneer and slow-growing shade tolerant species as emblematic representatives. We used a hierarchical linear mixed model and 21-years long tree diameter increment series in a monsoon forest of the Western Ghats, India, to characterize species growth strategies and question whether maximum growth summarizes these strategies. We quantified both species responses to biotic and abiotic factors and individual tree effects unexplained by these factors. Growth responses to competition and tree size appeared highly variable among species which led to reversals in performance ranking along those two gradients. However, species-specific responses largely overlapped due to large unexplained variability resulting mostly from inter-individual growth differences consistent over time. On average one-third of the variability captured by our model was explained by covariates. This emphasizes the high dimensionality of the tree growth process, i.e. the fact that trees differ in many dimensions (genetics, life history) influencing their growth response to environmental gradients, some being unmeasured or unmeasurable. In addition, intraspecific variability increased as a power function of species maximum growth partly as a result of higher absolute responses of fast-growing species to competition and tree size. However, covariates explained on average the same proportion of intraspecific variability for slow-and fast-growing species, which showed the same range of relative responses to competition and tree size. These results reflect a scale invariance of the growth process, underlining that slow-and fast-growing species exhibit the same range of growth strategies

Multivariate morphometric analysis and species delimitation in the endemic New Caledonian genus Storthocalyx (Sapindaceae)

Storthocalyx is one of four genera of Sapindaceae endemic to New Caledonia. The most recent taxonomic revision is >60 years old and is based on material that represents <10% of the collections available today. Four species are currently recognized: Storthocalyx chryseus, Storthocalyx leioneurus, Storthocalyx pancheri, and Storthocalyx sordidus, although a significant number of specimens cannot be assigned to any of them. One hundred and ninety-eight herbarium specimens were examined for an ascendant hierarchical classification and a principal coordinates analysis based on 19 morphological characters regarded as diagnostic at the species level (including those used in the original revision). The analyses revealed five morphologically well delimited groups that potentially correspond to species-level units. The resulting entities were then compared with nomenclatural types, which showed that four of them corresponded to the four currently recognized species and suggested that the fifth represents a well delimited, undescribed species. The analysis also showed that seven type specimens represent mixed gatherings comprising elements referable to two distinct species. The findings of the present study provide a basis for undertaking a taxonomic revision of Storthocalyx, including the description of the new species.(c) 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176, 127-146