Determining the ecophysiological limits of a narrow niche tropical conifer tree (Podocarpus trinitensis).

Many tropical species live close to their thermal limits within a narrow niche. Here, we investigate the ecophysiological limits of the tropical tree Podocarpus trinitensis, which is endemic to Trinidad and Tobago where most populations exist as isolated stands on hilltops. Five wild stands from a range of elevations were compared in the field with measurements of leaf temperature, canopy cover, stomatal conductance (gs), chlorophyll content and several chlorophyll fluorescence parameters.

Symbiotic N fixation is sufficient to support net aboveground biomass accumulation in a humid tropical forest.

Symbiotic nitrogen (N) fixation has been shown to support carbon storage in young regenerating tropical forests, but N-fixing trees can also be strong competitors with non-fixing trees, making it unclear which mechanism drives long term patterns in biomass accretion. Many tropical forests have excess N, but factors such as rising atmospheric CO or selective cutting practices might induce additional N demand. Here we combine decades of stem inventory data, in-situ measures of symbiotic N fixation, and simulations of N demand to evaluate demographic and biogeochemical controls on biomass dynamics in legume-rich lowland forests of Trinidad.