Forest dynamics where typhoon winds blow.

Abstract

Tropical cyclones (TCs) sporadically cause extensive damage to forests. However, little is known about how TCs affect forest dynamics in mountainous terrain, due to difficulties in modelling wind flows and quantifying structural changes. Typhoon Mangkhut (2018) was the strongest TC to strike Hong Kong in over 40 yr, with gusts > 250 km h-1. Remarkably, the event was captured by a dense anemometer network and repeated LiDAR surveys across natural forests and plantations. We mapped long-term mean and extreme wind speeds using CFD models and analysed corresponding changes in canopy height, which uncovered TC-forest dynamics at unprecedented scales (> 400 000 pixels, 1108 km2). Forest height was more strongly limited by wind exposure than by background topography, a limitation attributable to a dynamic equilibrium between growth and disproportionate TC damage to taller forests. Counterintuitively, wind-sheltered forests also suffered heavy damage. As a result, canopies of wind-sheltered forests were more rugged, which contrasted with flat-topped forests at wind-exposed sites. Plantations were more susceptible to TCs compared to natural rainforests of similar stature (canopy height change -0.86 m vs -0.39 m). Our findings highlight TCs as important, often overlooked factor that fundamentally shapes forest structure and dynamics.