Survivors, not invaders, control forest development following simulated hurricane in New England

Hurricanes profoundly impact New England forests every 50-100 years but few studies have evaluated mechanisms of long-term forest dynamics following major windthrows. In 1990, the Harvard Forest initiated a large hurricane experiment in a 0.8 ha manipulation (pulldown) and 0.6 ha control area of a maturing Quercus rubra-Acer rubrum forest. In the pulldown, 276 trees were toppled, using a winch and cable, in the northwesterly direction of natural treefall from major hurricanes. Eighty percent of canopy trees and two-thirds of all trees >5 cm dbh suffered direct and indirect damage. We used twenty years of measurements to evaluate the mechanisms and trajectory of forest response after intense disturbance, and to revisit initial gap-dynamics hypotheses from this experiment and studies of the 1938 “Great Hurricane”.

Early analyses emphasized tree seedling establishment and sprouting by damaged trees as the dominant mechanisms of forest recovery in this extensive damaged area. However, despite 80% canopy damage and 8000 m² patch size, survivors controlled forest development. Residual oaks make up 40% of stand basal area after 20 years. The new cohort of trees, dominated by black birch advance regeneration, makes up 30% of stand basal area. There were shifts in understory vegetation composition and cover, but few species were gained or lost after 20 years. Stand productivity rebounded quickly (litterfall recovered to pre-disturbance levels in six years), but we predict that basal area in the pulldown will lag behind the control (which gained 6 m²/ha over 20 years) for decades to come. The life histories of the surviving species in the forest were the key to the resilience and rapid recovery in the pulldown, and explain why this forest’s responses contrast with predictions of gap theory and studies of the 1938 Hurricane.