In early September 1996, Hurricane Fran swept over the barrier islands of North Carolina and pushed inland toward Raleigh-Durham. As it approached, its winds became stronger than anyone had expected. Umstead State Park, a heavily forested area between the two cities, was hit particularly hard. Fran blew down thousands of trees, snapping power lines, wrecking buildings, and blocking over thirty miles of trails. The park was closed for eight months. But despite the devastation to the park’s built environment, the hurricane was probably beneficial to the park’s natural environment.
Today, the sky over Umstead Park was a sheet of high, gray clouds. Last night’s rain had left the forest glistening green and left the ground a damp carpet of pine needles and crushed leaves. A cool breeze blew through the understory. It was a perfect day for being out in the woods, and a pleasant taste of the coming autumn.
The forest was diverse, populated with three species of pine, six species of hickory, and a dozen species of oak. But this was my first time out in the southeastern mixed forests and I couldn’t identify most of them. The white oaks (Quercus alba) were huge, with thick trunks and low, spreading branches. They looked like old trees that might have already been growing when Umstead was formed from farmland in the 1930s.
Many of the parks in America’s eastern forests were created during this time — between the Civil War and the Great Depression — when eastern farms were abandoned for more easily cultivated grasslands to the west. As each park was designated, its forests began growing all at once from fields and pastures, resulting in forests with a similar look: tall, straight trees, evenly spaced over a lawn-like understory of grass and ferns.
These woods are undeniably pretty and pleasant to visit, but they’re missing something. Even though they are eighty, ninety, sometimes a hundred years old, they are immature. Like a city that has no cemetery because its inhabitants are all the same age, the trees are decades from a natural death, and the forest floor is strangely devoid of dead wood. But this wood, called coarse woody debris, might be the most important and conspicuous characteristic of a mature forest.
Coarse woody debris encompasses everything from broken branches to rotting stumps, from fallen trees to tipped-up roots. It accumulates naturally as a forest ages, and can account for over a quarter of all the wood in a mature forest. For people who have only seen young, manicured forests all their lives — and there are a lot of these people — the appearance of pervasive disorder created by coarse woody debris can be upsetting. It looks as if something’s gone wrong. But the truth is that it’s the sign of a healthy forest. Coarse woody debris increases the biodiversity of a landscape. It’s a way nutrients get recycled back to the earth. It’s habitat for mosses and fungi, shelter for small animals, home for insects, and a buffet for the animals that eat those insects. Have you ever watched a bear shred a rotten log looking for ants? That’s coarse woody debris he’s eating out of.
The benefits of coarse woody debris are now so well-known that foresters have developed techniques to accelerate its development. A guide published by the University of Massachusetts, for example, gives forest owners instructions on how to girdle trees so that they die and turn into standing snags, how to fell others so their logs rot on the forest floor, and how to create clearings around big trees so they can grow even bigger. By increasing the habitat diversity in a forest, these artificial means lead to a natural end. But these artificial techniques won’t be necessary in Umstead Park, thanks to Hurricane Fran.
I was walking next to murky, brown Sycamore Creek. It flowed silent and deep in some places, loud and rocky in others. The forest floor on both sides was littered with the coarse woody debris left by the hurricane. The fallen wood has made the forest mature, leaving it filled with a variety of microhabitats that hadn’t existed before, and leaving gaps in the canopy that let more sunlight into the understory. The forest has become more diverse, a mix of old trees and saplings, shady groves and sunny gaps that support a greater variety of wildlife than a uniform forest. Hurricane Fran’s impact was, so to speak, a windfall for the park’s environment.