After making landfall in Florida and Louisiana, Hurricane Katrina struck the northern Gulf Coast near the mouth of the Pearl River at the Mississippi-Louisiana border on 29 August 2005. The 125-mile-per-hour winds, exceptional storm surge, and heavy precipitation and flooding associated with the hurricane caused tragic loss of life and extensive damage to human infrastructure as well as to ecosystems throughout Mississippi.
The most widespread ecological impact of Hurricane Katrina was damage to millions of trees caused by high winds. The US Department of Agriculture’s Forest Service estimated timber losses of up to 3 billion cubic feet with a commercial value of about $1.3 billion across nearly 3.5 million acres of forestland in Mississippi alone. Damage was particularly severe within sixty miles of the coast, although forests throughout the state were affected. Even where trees were not blown down, the combination of high winds and intense precipitation defoliated trees and damaged tree crowns, depositing large amounts of leaf litter and woody debris on the ground and in streams.
The wind caused a variety of immediate damage. Most directly, Hurricane Katrina resulted in a reduction in standing forest biomass and shifts in forest composition because of differences in species susceptibility to high wind speeds. Nearly 20 percent of the standing volume of timber was destroyed, with up to a 40 percent loss near the coast; by comparison, 1969’s Hurricane Camille made an almost identical landfall but resulted in an average loss of only 11 percent of standing volume. Such changes influenced suitability and usage of habitat for animal species. For example, roughly half of all cavity trees for the endangered red-cockaded woodpecker in the De Soto National Forest were lost, and migratory birds had to shift their habitat usage in the Pearl River bottoms and likely on several barrier islands off the Mississippi coast. Exposure to higher levels of sunlight caused by fallen trees increased the susceptibility of forestlands to invasive nonnative species such as Chinese tallow tree (Triadica sebifera) and cogon grass (Imperata brasiliensis), which are prevalent in the damaged areas.
In addition to altering plant and wildlife habitat, the dead and damaged trees greatly increased fuel for wildfires, a problem exacerbated by a moderate to severe drought in the months after the hurricane. The downed trees also served as a haven for forest insects and diseases, including southern pine beetle and black turpentine beetle, which thrive on fallen trees and can harm living trees. Decomposition and combustion of dead and downed trees has also led to the release of large quantities of carbon dioxide into the atmosphere.
The second major cause of ecological damage associated with Katrina was the storm surge, which was exceptionally high as a consequence of the massive size of the hurricane, the strength of the system just prior to landfall, the intense low central pressure at landfall, and the shallow offshore waters. Estimates from a range of sources indicate that the surge was between twenty-four and thirty feet along the portion of the Mississippi coast centered on St. Louis Bay (including the communities of Waveland, Bay St. Louis, Pass Christian, and Long Beach) and was between seventeen and twenty-two feet along the eastern half of the Mississippi coast from Gulfport to Pascagoula. It penetrated at least six miles inland and up to twelve miles inland along bays and rivers, crossing Interstate 10 in many locations.
The storm surge affected coastal ecosystems through two mechanisms. Mechanical damage resulted from the dynamic force of the water itself—for example, when the surge moved sediment from wetlands, beaches, and coastal barrier islands to other land areas. The storm surge and waves from Hurricane Katrina completely inundated several barrier islands off the Mississippi coast, including Petit Bois, Horn, East Ship, West Ship, Cat, and the Chandeleur Islands, resulting in significant land loss, submersion of wildlife habitat, and damage to seagrass beds. These islands serve as buffers against hurricanes and storm surges and provide important wildlife habitat, and the loss of associated seagrass beds can affect the aquatic life that spawns, nests, and feeds there. Damage to oyster beds from siltation and contamination was also high along the northern Gulf Coast. Mechanical damage to vegetation, such as bark stripping and uprooting, as well as burial by deposited sediments was particularly notable on barrier islands and in the narrow belt along the coastline near US Highway 90.
In addition, inundation by seawater in the surge zone led to extensive changes in soil characteristics, including salinity, pH, conductivity, and soil chemistry, and salt spray contributed to defoliation of trees, particularly pines. Such changes can lead to extended tree mortality and slow forest recovery.
While Hurricane Katrina had a number of short-term ecological effects, the longer-term impacts will be under investigation for years to come. Many of the initial effects will likely be short-lived, but in some coastal systems storm effects may have pushed ecosystems past a threshold, resulting in extensive and potentially irreversible damage.
- Douglas Brinkley, The Great Deluge: Hurricane Katrina, New Orleans, and the Mississippi Gulf Coast (2007)
- William H. Cooke, Katarzyna Grala, David Evans, and Curtis Collins, Journal of Forestry (December 2007)
- Gaye S. Farris, Gregory J. Smith, Michael P. Crane, Charles R. Demas, Lisa L. Robbins, and Dawn L. Lavoie, eds., Science and the Storms: The USGS Response to the Hurricanes of 2005 (2007)
- Hermann M. Fritz, Chris Blount, Robert Sokoloski, Justin Singleton, Andrew Fuggle, Brian G. McAdoo, Andrew Moore, Chad Grass, and Banks Tate, Journal of Geotechnical and Geoenvironmental Engineering (May 2008)
- John A. Kupfer, Aaron T. Myers, Sarah E. McLane, and Ginni Melton, Ecosystems (February 2008)
- Pervaze A. Sheikh, Congressional Research Service Report for Congress (February 2006)
- James Patterson Smith, Hurricane Katrina: The Mississippi Story (2012)