Annual Tree Health and Mortality Survey of the Harvard Forest CTFS-ForestGEO Plot 2021-2024

The rate of tree mortality has been increasing, but why and where? Understanding the scope and scale of tree mortality is important because tree death can have a large impact on carbon dynamics and reduce biodiversity quickly. Mortality events most often occur at the scale of the individual or a small group of trees in a forest. Our ability to detect shifts in tree mortality and determine the causal factors responsible is defined by the intensity, scale, and frequency of our observations. Currently, most observations are too coarse in spatial scale and too infrequent in time to determine causal factors of mortality or how they vary across space and time and lack detail of why a tree died. Determining the uncertainty in tree mortality associated with the scale of observation is critical for making well informed estimates of carbon dynamics and predictions of forest community trajectories. The macroecological challenge lies gathering enough data on the ground to allow scaling up to broad regions with remote sensing products that can detect mortality events and changes in biomass at landscape and continental scales while minimizing uncertainty in our estimates. Our objective is to address this challenge and build scalable models of tree mortality with underlying factors associated with tree death. Each July for four years, we collected annual health and mortality data on all trees ≥10 cm diameter at breast height across the 35 ha ForestGEO megaplot at Harvard Forest. We assessed tree health by assigning any of 20 factors associated with death to all trees. We also collected crown metrics including the position in the canopy strata, percentage of crown structure intact, and percentage of crown living.