Hurricane Michael Impacts Woodyard Hammock

When Dr. William Platt established a long-term study of the Woodyard Hammock old-growth beech-magnolia forest on Tall Timbers in 1978, he had hurricanes in mind. He was interested in how tropical storms would contribute to perpetuation of this ancient forest by knocking over or snapping some of the canopy trees and thereby letting light into treefall gaps, where the next generation of trees would compete for light as they grow. Eight years after setting up the 12-acre study plot, it took a direct hit from Hurricane Kate, a category 3 hurricane, which created many treefall gaps and overall increased open sky by about 60%. During the following two decades tree numbers went from about 10,000 to almost 20,000, and since then have returned to near pre-hurricane levels as trees outcompete each other in the gaps.

This fall we had just began our biennial census of each tree 2 cm in diameter or greater, when Hurricane Michael made a glancing blow to the Tallahassee area, toppling trees but not equaling the damage of Kate, or Michael's terrible damage further west. Even so, we have recorded tip-ups or snapped trunks of about 60 trees that were in the canopy or subcanopy. This damage, combination with that from hurricanes Irma in 2017 and Hermine in 2016, will no doubt initiate another wave of recruits that will influence the forest's structure and composition for decades, maybe centuries.

An interesting lesson we are learning from Woodyard Hammock is how seedlings growing very slowly under the forest canopy before gaps are created, called "advanced regeneration," influence the future composition of the forest by becoming the trees that fill the gaps when they form. More specifically, we are learning that the composition of the advanced regeneration changes considerably over the years, which can drive the community one way or the other when a storm creates gaps. For example, when Hurricane Kate hit, there was a preponderance of seedlings of hophornbeam (Ostrya virginiana), which dominated the gaps during the following two decades. Now hophornbeam seedlings are scarce, but seedlings of southern magnolia (Magnolia grandiflora), American beech (Fagus grandifolia), and sweetgum (Liquidambar styraciflua) are abundant, increasing their odds in the newly formed gaps. As the long-term study continues into the future, we will see who the winners are.

Woodyard Hammock Census

L-R: Intern Gianna Tarquinio and Field Ecologist Allie Snyder conduct the Woodyard Hammock biennial tree census after Hurricane Michael.

Woodyard Hammock Seedlings

Seedling of southern magnolia and acorn of swamp chestnut oak