Anthony Lee marks storm-damaged timber in Missouri’s Mark Twain National Forest. Credit: U.S.Forest Service
“Not much stands up to the highest wind speeds, except maybe live oak because of their growth habit and anchorage,” says Stanturf. “The farther inland you get, the wind energy dissipates, and you get less breakage and blowover,” he explains. “But even inland, you still get significant damage from the loss of major branches.”
Katrina’s damage extended as far north as Memphis, Tenn. A 2007 study published in Science used NASA satellite images to estimate 320 million trees dead or damaged in Mississippi and Louisiana alone from Hurricane Katrina. In combination with Hurricane Rita later that year, Hurricane Katrina was called “the largest single forestry disaster on record in the nation” by The Washington Post.
Damage inflicted by hurricanes depends on a variety of factors, including location, how the forest was managed and the age and height of a stand. While a loblolly pine plantation with trees 10 to 15 feet high may not sustain much damage, an older stand with 50-foot-tall trees of the same species would sustain more damage, according to Stanturf. In addition, because trees tend to support and protect other trees, there’s often more damage along openings in a forest, such as along roads or powerline swaths.
Beyond the wind damage, the storm surge that accompanied Hurricane Katrina damaged forests from the ground level. Sea waters surged more than three miles inland in some regions and more than 30 feet along much of the Mississippi coastline, causing the widespread damage inflicted by coastal flooding.
Forest recovery after a hurricane or other event depends on a particular forest’s management objective. Some hurricane-ravaged forests may be left to regenerate on their own, taking decades to a century to fully recover and reestablish. In some cases, cleanup is necessary to protect the forest from further destruction, as tree debris can become a breeding ground for insects and fungi. Other responses include salvage logging to recover the timber value that’s been lost and to reduce fire hazards, explains Stanturf. Seven years after Hurricanes Katrina and Rita, both replanted and surviving stands are recovering.
Though a post-hurricane or tornado forest isn’t initially the same type of forest that existed before the event, “it might develop into the same type of forest if managed well and if that is what a landowner wants and has the resources to accomplish,” explains Stanturf.
When heavy ice and wet snow coat tree limbs, the layers can be thick enough to break branches, twist limbs and crack tree crowns. Such an ice storm blanketed southern Missouri’s Mark Twain National Forest in 2009, snapping miles of telephone poles, limbs and trees.
After an ice storm or blizzard has passed through a forest, the first order of business is unblocking roads, especially roads that lead to residences, then clearing roads for larger vehicles. “We make sure people are safe first of all,” says Douglas Oliver, the Forest Service district ranger responsible for Mark Twain National Forest’s Poplar Bluff Ranger District. Then, trees are cleared from ditches, and workers ensure there aren’t hazardous trees or limbs dangling over recreation areas.
Similar to hurricane cleanup, timber may need to be salvaged before it rots and becomes worthless — or a breeding ground for pests. When the chainsaws stop, Oliver says, salvage teams have reported hearing swarms of insects boring into the downed wood. Such sheer volume of hungry insects can threaten nearby stands of surviving trees, likely weakened from the ice or wind.
Beyond insects, weakened, still-standing trees are vulnerable to disease and other physiological decline. At Mark Twain National Forest — where tornadoes and a 100-year flood have also occurred in the last five years — many surviving trees are more susceptible to ailments such as oak decline, which has afflicted red and black oak in the eastern U.S.
The summer after an ice storm or blizzard also can bring another danger. The layer of downed tree material can increase wildfire risk if conditions are extremely dry. Such a well-fueled fire could create catastrophic conditions to the point of soil sterilization, Oliver says.