Simulating Lightning-Induced Tree Mortality in the Dynamic Global Vegetation Model LPJ-GUESS.

Area of Science:

• Forest Ecology
• Climate Science
• Ecosystem Modeling

Background:

• Lightning is a significant disturbance in forest ecosystems, particularly causing large tree mortality in tropical forests.
• Current ecosystem models do not account for lightning-induced tree mortality.
• Understanding lightning's impact is vital for accurate forest dynamics and carbon cycle projections.

Purpose of the Study:

• To implement and evaluate a lightning mortality module in the LPJ-GUESS dynamic global vegetation model.
• To explore the local and global impacts of lightning on forest ecosystems.
• To assess the role of lightning in tree mortality and dead biomass globally.

Main Methods:

• Developed a stochastic lightning mortality module for LPJ-GUESS, dependent on cloud-to-ground lightning density and forest structure.
• Calibrated and validated the module using data from a Panamanian forest site.
• Applied the model to tropical and temperate forests globally using alternative lightning density datasets.

Main Results:

• The model accurately simulated lightning-induced tree mortality in the Panamanian forest.
• Global simulations indicate lightning kills 301-340 million trees annually, contributing 0.21-0.30 GtC yr⁻¹ of dead biomass.
• Forest biomass would be 1.3%-1.7% higher without lightning, with highest mortality in African tropical forests.

Conclusions:

• Lightning plays a substantial role in global forest ecosystems and carbon cycling.
• More data on lightning-induced tree mortality across diverse forest types is needed for model improvement.
• Integrating lightning mortality into ecosystem models is essential for reliable future vegetation and carbon cycle projections, especially with increasing lightning activity.