Recently, it has been found that gap-filling, critically-light dependent trees may be responsible for the size structure and striking similarities among tropical forests (Farrior et al. 2016). Yet, those experienced in walking through tropical forests know that there are many charismatic species that seem to spend their whole lives in the understory – even flowering and setting seed in the shade. To better understand the ecological strategies of shade-tolerant species and their interactions with light-demanding species in tropical systems, we investigated differences in species’ light dependence using census data over ca. 30 years and functional trait information for over 300 tree species within the 50-ha Barro Colorado Island (BCI) Forest Dynamics plot in Panama.
Results/Conclusions
From analysis of tree species in the BCI forest, we find at least three specific strategies. First, we find the gap-seeking light dependent strategy that does indeed explain the underlying size distribution of all trees in this tropical forest. We also find a true understory strategy, where individuals of such species’ growth rate seems independent of light availability. And finally, we find an intermediate strategy, where individuals grow up in the understory and transition to the canopy – a light dependent species, but not a gap specialist. These strategies correlate with leaf and wood economics spectra. In particular, we find that species showing understory strategy have higher specific leaf area and greater wood density than light-demanding species, suggesting that functional strategies of tropical tree species can deviate from the expectation of a single fast-slow economics spectrum. Our study suggests that species functional traits influence variation in plant allocation in response to light levels, and provides a better understanding of the mechanisms shaping species distributions and community structure in diverse tropical forests.