Compound impacts on forest carbon uptake and storage from wind, heat, and drought

Ecosystems can be damaged by extreme events such as hurricanes, heatwaves, and droughts. The frequency and/or intensity of these disturbances is expected to increase with anthropogenic climate change. Predicting the impacts of these changing disturbances is a key challenge for global change research. Heat and drought can change forests from net absorbers of carbon to net emitters. In addition, damage to forests during these events could alter their vulnerability to damage during tropical cycles. Meanwhile, wind damage opens up the canopy and increases light availability in the understory, potentially changing the species composition of the forest. But the long-term effects of wind damage on forests composition and carbon fluxes are not well understood and difficult to project. The proposed project will analyze the effects of compound threats from tropical cyclones, heat, and drought on the carbon cycle of coastal and inland forests. 

Advances in understanding of impact of compound disturbances on ecosystem carbon cycle would greatly benefit terrestrial ecosystem and dynamic global vegetation models, which are used to predict the future ecosystem structure and function and feedbacks between the carbon cycle and climate. For example, large-scale mortality due to warming and drying would result in additional carbon dioxide being released to the atmosphere, which would further exacerbate climate change.

We will use existing datasets and provide a comparison of findings from scales spanning satellite and airborne remote sensing data and ground-based observations. Our proposed work will leverage and synthesize existing data, including ground-based observations from DOE-supported resources and measurements collected at the Luquillo Long Term Ecological Research (LTER) site in Puerto Rico, LiDAR measurements of forest structure, as well as satellite-based data for broader regional analysis.

The proposed synthesis project will address research gaps through four objectives:

Objective 1: Create a database of compound events for our study area.

Objective 2: Apply a case study approach and machine learning methods to:

A) determine the impacts of heat extremes and drought (either separately or in tandem) on vulnerability of forests to damage from strong winds, and

B) determine the impacts of hurricane-related disturbance on vulnerability of forests to future drought and/or heat extremes.

Objective 3: Use data from Puerto Rico to understand the reasons for the impacts seen at a larger scale impacts and how they lead to either an increase or decrease in vulnerability.

Objective 4: Provide datasets that can be used by process-based models that represent forest structure and wind damage to improve their representations of carbon cycle responses to compound events and wind.

The outcomes of the project will be improved mechanistic understanding of the relationship between disturbance from heat, drought, and storms; and datasets useful for validating and improving ecosystem models and future projections of the forest carbon cycle.