Ecological strategies and disturbance response of tropical forest trees: insight from functional trait variation

Tropical forests store 40% of terrestrial carbon, process six times as much carbon as is released through fossil fuel use, and are epicenters of biodiversity. Despite all that we know about tropical forests, there remains much to discover about variation in ecological strategies, differences in the way species acquire limited resources through dissimilarities in construction and allocation patterns. We also know little as to how this variation shapes the resilience of tropical tree communities to disturbance. These forests are increasingly threatened by global change stressors, such as anthropogenic land-use and climate change. Recent advances in ecological literature show that more insight into differences in ecological strategies among tropical forest species can be gained by going beyond species distributions to also examine functional trait variation. Functional traits are morphological and physiological traits that reflect allocation strategies thought to be important determinants of fitness. In the first two chapters of my dissertation, I quantified wood density and anatomical variation at multiple scales, and related this variation to ecological strategies of tropical forest tree species. The last two chapters examined effects of historical disturbance on the composition and temporal dynamics of tropical forest communities. In addition to wood density, other traits studied in these later chapters were maximum height and diameter. Across my dissertation, the scales spanned ranged from intra-individual, intra-specific, interspecific, community and temporal levels, across two tropical forests, the 50 ha CTFS plot in BCI, Panama, and the 5.2 ha long-term forest plots in Kibale National Park, Uganda. With the functional trait approach, my dissertation demonstrated several novel patterns, including 1) linear radial increases in wood density are typical of fast-growth high mortality tropical tree species, while slow-growth low mortality species show a range of radial changes in wood density including non-linear trends 2) greater variation in ecological strategies when wood density is decomposed into anatomical components, with functional consequences for species growth and mortality of saplings but not adult trees, 3) persistence of the effects of selective logging on the taxonomic and structural composition but not functional composition of a tropical forest 45 years after, and 4) inadequacy of classical successional models that assume recovery to pre-disturbance conditions for predicting the effects of selective logging on tropical forest dynamics