Hurricane Katrina Flattened Oaks, Spared Pines

Over two-thirds of trees in certain types of forests located thirty miles from the track of Hurricane Katrina were downed by the high winds.

Meanwhile, other stands just twelve miles from the storm's eye got away with half that damage.

An analysis of tree losses in Mississippi's De Soto National Forest shows that whether trees survived Katrina's raging winds has more to do with the age and setting of a forest stand, and less with the intensity of wind.

De Soto National Forest stretches between Biloxi and Hattiesburg, Mississippi. Hurricane Katrina passed as close as seven miles from the National Forest's west boundary on August 29, 2005.

For about four hours, as the hurricane moved inland, the De Soto forest was hit by sustained winds of 85 to 100 miles per hour and gusts of 140 miles an hour. During that time the storm also dumped an average of five-and-a-half inches of rain.

Researchers from the University of South Carolina found that patches of trees up to 30 years old made it through the storm intact. Their stems were flexible enough to bend under the intense winds while staying rooted.

The hardest hit were older stands dominated by oaks, sweetgum and other hardwoods, or loblolly pine. Bottomland forests near streams suffered heavy losses. Even 18 miles from the hurricane track, these types of forests had more than two-thirds of their trees toppled. The moist and loosely-packed soils of floodplains made their trees more vulnerable to blowdown.

Uplands areas growing mostly pines received comparatively little damage. Some got away unscathed, while others usually lost no more than one-third of their trees. Any pine patches farther than nine miles from the hurricane's path escaped heavy damage.

As with the hardwood-dominated stands, pine stands that were older, near streams and close to the hurricane track suffered the most damage. Where hardwoods mixed with the pines, a higher proportion of trees also got knocked down by the hurricane.