Incorporating Explicit Crown Damage into a Vegetation Demographic Model to Assess Impacts on Mortality and Carbon Turnover

Abstract:

Crown damage can account for over 25% of canopy turnover in tropical forests and is a strong predictor of tree mortality. However, vegetation models typically assume that trees have perfect allometries with complete crowns, which could lead to biases in estimates of aboveground biomass, light levels through the canopy, and a failure to capture lags associated with drivers of mortality. We incorporated a representation of crown damage into the Functionally Assembled Terrestrial Ecosystem Simulator (FATES), a demographic vegetation model that simulates vertical competition for light among cohorts of forest trees. In line with expectations, we find that a loss of crown biomass caused a reduction in growth and an increase in carbon starvation mortality in damaged trees. However, growth rates in the understory increased due to increased light availability. Overall, plot aboveground biomass and carbon residence times decreased as a result of the explicit representation of crown damage. In simulations with multiple Plant Functional Types (PFTs) differences in PFT susceptibility to damage, and their ability to recover, caused shifts in PFT abundances relative to control simulations without damage. Ongoing work is focused on linking crown damage to explicit drivers including droughts and lightning strikes, and benchmarking results against forest census and remote sensing data. Results demonstrate that even independent of explicit drivers, crown damage is an important process to capture within vegetation models due to its impact on successional dynamics and carbon turnover.