Logged forests were found to contain less nutrients than old-growth forests and these differences were greater in logged forests that had recovered in stature. We modelled the millions of observations of mapped nutrient concentrations as a function of forest canopy height, elevation and disturbance history (i.e. logged vs. primary forest). Our models revealed that elevation is a major driver of nutrient availability in lowland tropical forests but, after holding elevation constant, logged forests contained fewer nutrients than old-growth forests and this difference was greatest in taller logged forests. We conclude that nutrient limitation becomes increasingly pronounced as forests produce more leaves and acquire biomass, with time after logging, that the effects of nutrient limitation become increasingly important. Our findings suggest that logged forests diverge from pristine forests in terms of their canopy chemistry. We caution that this may have resulted from changes in species composition and may make tropical forests less able to recovery, following future rounds of logging.
We acknowledge that our findings were produced through a remote-sensing exercise, expanding a high quality ground-based survey not designed to sample across all the gradients. A valuable next step would be to use predictions of nutrients, such as ours, to guide targeted field surveys so sample over gradients in nutrient availability, forest degradation and recovery.
This work was the culmination of a huge international collaboration between multiple universities, government agencies and funders, without whom it would not have been possible. For that we are extremely grateful.
Swinfield (2019) Global Change Biology