Hurricane Andrew and Louisiana's Coast

Home , Hurricane Andrew, Hurricane Audrey, Hurricane Betsy, Hurricane Camille

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National Biological Service Southern Science Center Lafayette, Louisiana

‘Current Address National Biological Service Northern Prairie Science Center Jamestown, North Dakota

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II Louisiana State University Baton Rouge, Louisiana and 162 National Biological Service {afayette, Louisiana

National Sea Grant Depository Pell Library Building - GSO University of Rhode Island Narragansett, RI 02882-1197USA “Hurricane” is the term used to describe Hurricane Camille, with sustained winds of the strongest of the windy, circulating more than 320 kph (200 mph), was the most storms- or cyclones-in the Atlantic and powerful hurricane ever recorded to hit the eastern Pacific oceans; in the western Pacific northern gulf coast. these kinds of storms are referred to as Although difference in wind speed is one typhoons. Most Atlantic hurricanes are born easy way to classify storms, hurricanes have in the southern Atlantic Ocean, off the coast other unusual characteristics. Some storms of Africa, in the months of June through move quickly and produce little rainfall, November each year. while others are slow and generate torrential During this time, winds off the west coast rain squalls with downfalls that often exceed of Africa sometimes converge, circulating 38 cm (15 inches). One characteristic that all counterclockwise. Often, these winds maintain storms share, however, is the location of the a low speed and travel across the Atlantic most powerful and dangerous winds. The Ocean as tropical waves, causing little more forward right quadrant of a hurricane-12:00 than rainfall on land masses they strike. to 3:00 on a clock face-is its strongest and At other times, when water temperatures most dangerous section, because it is fueled are warm enough and atmospheric conditions by the counterclockwise motion of the storm are correct, the wind speeds increase and as well as its forward movement. begin to form around a center, or eye. Hot, As the storm moves along the ocean sur- moist air from the ocean is pulled up into face, it becomes a complex, tight mass of wind the eye of the storm, which is now called a and rain. The eye becomes perfectly clear on tropical storm. As the air rises and cools, satellite pictures; larger hurricanes can have moisture condenses and is released as heavy an eye as large as 56.3 km (35 mi) across. The rain into the torrential winds circling the eye. hurricane’s eye is the area around which the The released energy is pumped into the winds rotate and is actually a calm area in the rotating cloud mass, making it rise and spin center of the storm. People have often been even faster. By the time the winds reach deceived into thinking that a storm had ended speeds of 119 kph (74 mph), the storm has when the eye passed over and were surprised become a hurricane. when destructive winds began again. As the spinning storm moves across the Hurricanes can contain and release ocean, unstopped by land, wind speeds enough energy to supply electricity to the increase. Hurricanes are commonly classified United States for a year. And hurricanes by the strength of their winds into five cate- carry the ocean along with them, bringing gories on the Saffir-Simpson Hurricane storm surges as high as 7.6 m (25 ft) above Intensity Scale. The weakest hurricanes, with sea level. Often the accompanying storm wind speeds of 119-153 kph (74-95 mph), are surge and associated floods are responsible referred to as Category I storms and cause for much damage in coastal areas. minimal damage primarily to plants and trees. Storms pursue unpredictable paths toward In 1992, Hurricane Andrew was a Category land. There is no set pattern in the journey IV storm with sustained wind speeds of 225 from their birth places off Africa, although kph (140 mph). Category V storms, such as they frequently move northwesterly to the Hurricane Camille in 1969, are the strongest Gulf of Mexico and eastern coasts of North and responsible for catastrophic damage. and Central America. A Fierce Storm

Figure l-Satellite image of Hurricane Andrew over the Gulf of Mexico.

strengthened to hurricane force- 120 kph (74 mph). The storm rapidly intensified and by August 23 had become a Category III hurricane (see “How Hurricanes Form,” inside front cover) with winds of 193 kph (120 mph). The next day, August 24, it struck the eastern coast of Florida and passed over the Florida peninsula in only six hours. As an even stronger hurricane with winds of 225 kph (140 mph-a Category IV storm), Hurricane Andrew moved northwesterly across the Gulf of Mexico. As people all along the Gulf of Mexico tried to predict its course, the hurricane’s second landfall was along Louisiana’s coast August 26. n mid-August 1992, television and the U.S. mainland but it was also one It first passed near the barrier radio audiences were alerted to a of the most intense. Figure 1) islands along the central gulf coast of potentially damaging hurricane Hurricane Andrew, with winds of the state with 225-kph (140-mph) that had formed in the Atlantic Ocean. 200 kilometers per hour (124 miles per winds and a storm surge of 2 m (7 ft). Satellite imagery showed a large hour), destroyed urban and other set- A combination of these winds and the swirling mass of clouds rotating around tled areas in Louisiana. It also swept resulting strong waves and storm surge an area of low pressure and heading across a variety of economically eroded 30-40 percent of Raccoon Island toward the continental United States. important natural ecosystems in south as well as the western arm of Whiskey On August 24, this hurricane struck Louisiana, including barrier islands, Island. This erosion reduced the sig- the eastern coast of Florida, passed coastal wetlands, and forested wet- nificant protection that those barrier over the Florida peninsula, entered the lands. A closer look at the life span of islands could offer to coastal marshes Gulf of Mexico, and moved north- this storm shows that its path of and swamps from future storms. westerly until it slammed into the destruction was inevitable. Hurricane Andrew then moved Louisiana coast on August 26. On August 14, satellite photogra- across the water between the islands Hurricane Andrew, as it was named phy first indicated a strong tropical and the Louisiana mainland and struck by the National Weather Service, wave off the west coast of Africa. This coastal marshes near Cypremort Point. caused over $27 billion worth of dam- weather pattern achieved tropical Large sections of marsh in western age in Florida and Louisiana. It was storm strength on August 17 and, by Terrebonne Parish received extensive not only the costliest storm to strike August 22, its winds had further physical damage. Figure Z-Path of Hurricane Andrew over satellite image of Louisiana. NATIONAL l3lOLOGlCAL SERVICE

Still very strong, the hurricane traveled through the swamps and forests of the Atchafalaya Basin. Aerial reconnaissance shortly after the storm revealed large tracts of downed and mangled forests. More than 40 percent of the bottomland hardwood forests in Iberia, St. Martin, and St. Mary parishes were severely damaged. By the time the storm neared Baton Rouge, its peak wind gusts were still near hurricane force 113 kph (70 mph). About 24 hours after Hurricane Andrew struck Louisiana, it took a northeasterly track and was finally downgraded to a tropical depression. On August 28, it merged with an advancing cold front and died in of coastal systems, helping alter the and monitored. Headed by the Pennsylvania. shapes of barrier islands, coastal National Biological Service’s Southern In just two weeks the hurricane marshes, and swamps and other wet- Science Center, 23 studies of the eco- created damages of $27.2 billion and land forests. Because scientists, fisher- logical impacts of Hurricane Andrew affected the incomes of many Florida men, and foresters alike have become were planned and completed. These and Louisiana residents for years. increasingly aware of the values of studies examined the short- and long- Hurricane Andrew passed over a these systems, interest in understand- term effects on coastal barrier islands, densely populated area in south ing, protecting, and restoring them wetlands, and swamps and bottom- Florida, which accounted for the bulk has been increasing as well. Recent land hardwood forests in Louisiana of the monetary losses and loss of passages of federal laws such as the and their wildlife. (Figure 2) ( lives. Its landfall in Louisiana was in Coastal Wetlands Planning, a sparsely settled area, but storm Protection, and Restoration Act of damages in the state still reached $2.5 1990 indicate that, among lawmakers billion. The fishery and aquaculture and the people they represent, there industries suffered enormous losses. is a growing appreciation of systems Although memories of the storm are that hurricanes affect. now fading, its impact can still be Three months after Hurricane seen and will be felt for years to come. Andrew, the U.S. Congress provided Storms such as Hurricane Andrew funds so that damages to Louisiana’s are significant forces in the evolution coastal resources could be assessed Barrier Islands

Figure 3-Overhead view of Isles Dernieres was scoured and breached by waves, shows overwash and island break up. and the plant communities were UNIVERSITY OF SOUTHWESTERN LOUISIANA essentially stripped away. In other areas, substantial overwash and sand deposition of 50-100 cm (20-39 inches) partially or completely buried plants. Deposited sand partially or com- near them, the Isles Dernieres lost an pletely covered plant communities of additional 30 percent of their land area. Isles Dernieres and other Louisiana Hurricane Andrew’s impact on barrier islands. Low island marsh Isles Dernieres varied considerably, communities, dominated by smooth depending on the position of an cordgrass, as well as marshes at high- island relative to the storm’s path. er elevations characterized by a mix- Islands farther to the west and closer ture of mangroves, saltwort, saltgrass, to the path of the storm suffered glasswort, smooth cordgrass, and greater alterations in shape and size wiregrass were buried. In some cases, than did islands on the eastern end of only the tops of the mangroves were the chain. The westernmost islands of still exposed to the air. the chain, Whiskey and Raccoon, Because plants on barrier islands were severely eroded. (Figure 4) are generally adapted to sand move-

the outermost land exposed to hurricanes, barrier islands often lose significant areas of beach and marsh. Storm waves associated with cold fronts and tropical storms continuously alter the shapes of these islands, but large storms like hurricanes can cause significantly more erosion in one event than several years of cold front passages. Other disruptive forces such as subsidence, sea-level Figure &Two aerial photographs of Raccoon Island, Isles Dernieres, before and after Hurricane rise, inadequate sediment supply, and Andrew, show that the island’s entire western spit was washed away. NASA AMES 1990, 1993 human disturbance work in concert with tropical and winter storms to On Trinity Island, in the eastern ment, salt spray, and low levels of degrade these islands. (Figure 3) part of the chain, large breaches of nutrients, it is not surprising that, Among the first habitats of coastal water up to 2 km (1 mi) long opened despite burial by sand and exposure Louisiana to experience the devastating across the island. The shoreline receded to the storm surge, the vegetation on effects of Hurricane Andrew were the 68 m (223 ft) in some areas, and there Trinity Island is rapidly recovering. barrier islands, Isles Dernieres. Over were significant overwashing and Throughout the recovery, both total the past 130 years, nearly 78 percent deposition of sand on back barrier plant cover and number of species of the land area in the Isles Dernieres wetlands. It is also likely that the entire have increased. The reestablishment island was submerged by the accom- chain had already been lost. The con- and growth of these plant communities panying storm surge. tinuous island arc present in 1853 had will help to stabilize the new sand Overwash and sand movement surfaces created by the strong storm deteriorated into a series of five narrow from Hurricane Andrew damaged islands. Recent photointerpretation island plant communities that protect winds, which continuously eroded has documented that between 1990 and the underlying layers of sand from and transported the sandy dune and 1992 after Hurricane Andrew passed eroding, but in some areas the land swale soils.

3 When Hurricane Andrew carried NOVEMBER 1993 beach sand across Trinity Island and deposited it on the back barrier wetland plant communities, it created habitats with environmental conditions different from those present before the MARCH 1994 storm. Changes in salinity and elevation resulted in a redistribution of plant species. For instance, increased elevation from sand deposition caused a shift in species dominance NOVEMBER 1994 from smooth cordgrass to wiregrass. Mangroves disappeared from higher sites but became established in the saltier lower sites. Many barren areas had still not CLASS Nov. ‘93 recovered from the hurricane three nBare Dunes 3 .58 4 7R 3.69 Beach 24.33 68.39 54.50 years later. Most recovery occurred Flat/Beach Bar 4.20 5.70 6.77 when new shoots grew from0 the run- Scrub Shrub 12.77 11.95 14.13 Figure 7a,b,c- Geographic information system s ners of adult plants that had survived nVegetated Dunes 2.95 2.91 4.78 show restoration of Raccoon Island. the storm. Because runners have to q Water 3.23 3.06 3.24 NATlONAL BlOLOGlCAL SERVICE nSalt Marsh 59.75 57.55 61.59 grow from adult plants, barren areas

as a persistent bank of seeds has not shrimp had reestablished to prestorm yet been established. The new sand levels, as had the populations of wad- deposits are barren surfaces swept by ing birds feeding in these habitats. wind that continually resuspends the Surprisingly, revegetation on the bay sands, making it difficult for seeds to side of the islands was strongly corre- accumulate and contribute to vegeta- lated with the presence of shrimp tion recovery Only in areas with exist- burrows, suggesting that the shrimp ing adult plants were germinated seeds influence the entrapment and growth found, because these plants provided of plant propagules. (Figure 6) a windbreak that allowed both sedi- Understanding how vegetation ments and seeds to accumulate. recovers from storms is important for Figure 5-Revegetation of barrier islands Barrier island beaches are also land managers. The state of Louisiana through runner growth of plants that survived important habitats for benthic inverte- began a beach restoration and nour- the storm. NATIONAL BIOLOGICAL SERVICE brates, including ghost shrimp. ishment operation to reestablish the Although not seen in the seafood mar- portions of Raccoon Island swept away kets of Louisiana, these burrowers are by Hurricane Andrew. The long-term distant from surviving vegetation will an important food for wading birds stability of these newly restored areas take a long time to regain plant cover. and are agents in nutrient cycling and may be significantly improved by the In addition, damage to new growth other sediment development process- establishment of vegetative cover. by nutria has been noted. This herbi- es. These shrimp suffered mass mor- (Figure 7a, b, c) vore can damage new shoots and may talities during the passage of Hurricane Natural resource managers must play a major role in the future estab- Andrew near Isles Dernieres. balance restorative sediment deposition lishment of vegetation. (Figure 5) Within two years of the hurricane, with possible further decimation of Dispersal and germination by shoreline populations of ghost reestablished ghost shrimp, which are seeds on Trinity Island were minimal, important in the barrier island ecosys- tem. For the greatest success, there Figure 6- Wildlife such as shrimp actually must be a combination of active man- helped to build back the barrier islands by agement, including the planting of overturning sediments as they burrowed. adult plants, and careful monitoring UNIVERSITY OF SOUTHWESTERN LOUISIANA of benthic shrimp populations. 4 Coastal Wetlands

urricanes and other storms sites, large pieces of soil and vegetation Where did these sediments origi- generally produce damaging were torn from the marsh and thrown nate? Careful measurements of sedi- winds, storm tides, and rain to the tops of levees or deposited into ment characteristics indicated that that flood inland coastal areas as well oil and pipeline canals, effectively some were introduced from outside as erode beaches and barrier islands. blocking them. Some of these pieces the coastal marsh system, while others Coastal wetlands help to dissipate the were as large as a small car. Other were redistributed from the bottoms of force of storm surges and can there- marsh sites were covered with 1.5-2 m shallow basins where the marsh sub- fore lessen the impact of these storms (5-7 ft) of wrack (plant debris), which strate had eroded. on areas farther inland. Damage to completely buried the existing vege- Coastal marshes closest to the path these valuable coastal wetlands them- tation. Areas that were not physically of the storm east of Atchafalaya Bay selves, however, can be quite severe. disrupted or covered with sediment had the thickest deposit of storm-gen- The effects of high winds and storm or wrack also appeared to lose plant erated sediment, which was 10-16 cm surges are most apparent as continu- cover because the salty gulf waters (4-6 inches) deep and most probably ous marsh is broken up into pieces, driven onshore by the hurricane came from the bottom of Atchafalaya channels are filled with debris, and “burned” the tops of the plants, killing Bay. As the storm approached, water areas of marsh are converted into the aboveground parts. was pulled from the bay by the force open water. (Figure 8a, b) Hurricane Andrew also introduced of the storm, exposing the sediments Other types of physical damage to large amounts of sediment into these of the shallow bay bottom. As the storm coastal wetlands were evident follow- coastal marsh systems. In some cases, passed the bay, this water rushed back ing the passage of Hurricane Andrew. vegetation was completely buried in and the resulting storm surge of Most striking was the widespread lat- while, in others, the sediment was 1.8 m (6 ft) mixed these sediments into eral compression of marsh, resulting deposited as a thin layer on the marsh the water column. As the storm surge in a series of accordion-like folds with surface but did not smother plants. moved over the marsh, it deposited ridges rising 2 m (7 ft) above the Sediments were deposited over large the sediments onto the surface. normal surface level. expanses of the coast, and even sites Subsidence and lack of sediment In other areas, the marsh was as far as 130 km (81 mi) from the path are critical factors affecting wetland scoured as portions were washed of the hurricane received significant loss in coastal Louisiana. To remain away, leaving open water. At some amounts. stable, coastal marshes must grow

Figure 8a, b-Two aerial photographs of coastal Louisiana, before and after Hurricane Andrew, show marsh break-up into open water. in height as rapidly as they sink and Bayou Chitigue, Louisiana affected, however, began to resprout sea level rises, but many portions of within six weeks of the storm. coastal Louisiana are isolated from Five days after the hurricane, the renourishment by sediment. Events salinity of some interior marsh sites such as winter storms and hurricanes, was still eight times higher than it was which suspend sediments in the water prior to the storm and, at one site in column, may partially off-set the effects western Terrebonne Parish, a wedge of subsidence and subsequent wetland of saltwater was still evident below loss by supplying needed sediment. the marsh surface 55 days after the Not all hurricanes appear to con- storm. Results from earlier studies of tribute as much sediment to the coastal Louisiana wetlands indicate that -l:..~...,.....,.....,.....,.....,.....,r environment as Hurricane Andrew JUll DW JW DlX JLln DW JLNl impounded marshes suffer more did. Whether they do depends on their ‘92 ‘93 ‘94 ‘95 extensive and long-term effects from idiosyncratic nature: wind velocity, saltwater than do marshes that drain Figure 9-Although winter storms and hur- storm tide height, angle of approach ricanes can deposit great amounts of sedi- freely. In one instance, the vegetation to the shore, and the availability of a ments and wrack on marshes (accretion), the of an impounded marsh on the chenier source of sediments. And even if hur- height and stability of the marsh (elevation) plain in southwestern Louisiana ricanes do contribute much sediment, sometimes remain unaffected. required four years to recover from it may not ultimately help certain NATIONAL BKXOGICAL SER”,CE the entrapment of saltwater driven coastal marshes maintain their eleva- ashore by a hurricane storm surge. tion relative to increasing sea level. hurricane-induced storm surge was At sites where researchers had In studying the effects of Hurricane still 1.7 m (6 ft) high with a salinity of prestorm data, they were readily able Andrew, scientists have found that, in 10-15 parts per thousand-about half to see how Hurricane Andrew caused certain areas of coastal Louisiana, even the salt in seawater. This saltwater changes in plant composition. Areas significantly increased contributions “burned,” and in many cases killed, with different types of storm damage, of sediment cannot completely coun- the aboveground portions of fresh including sediment addition, wrack, teract subsidence patterns, and marsh plants. This phenomenon was lateral compression, and scoured marshes will continue to be drowned seen as far away as the Pearl River, marsh, were affected quite differently. and lost. (Figure 9) In other areas, located on the border of Louisiana (Figure 10) additional sediment resulted only in a and Mississippi, over 180 km (112 mi) Surfaces at the compressed-marsh temporary increase in elevation that from the storm’s eye. Most of the plants sites were elevated, creating drier was slowly lost in following years. The increases in elevation were short- lived phenomena and these sites are returning to prestorm conditions. Proximity to the coast was not nec- essarily the primary factor that deter- mined damage to wetland vegetation. In many cases, salt marshes closest to the path of the hurricane showed the least signs of damage. On the other hand, freshwater plants in interior marshes suffered most from exposure to the moderately saline water that accompanied the storm surge as it moved inland. At research sites Figure l0-Depending on the type of damage suffered,coastal marsh plants recovered at 20-40 km (12-25 mi) from the coast, the different rates and some have yet to recover. NATIONAL BlOLOGlCAL SERVICE

6 habitat. The most dramatic changes in tible to increased erosion from hurri- species composition were in the com- cane winds and associated storm surges. pressed areas. Plants not typically Levees surrounding impoundments found in coastal marshes increased can also isolate marshes from avail- significantly because of the drier con- able sources of sediment, which can ditions. Figure 11) promote subsidence and result in Areas where sediment was deposited marsh loss. The sediment that enters did not change substantially in species an impounded marsh as a hurricane composition. In these sites, it is likely storm surge washes over the levee that the sediment will act as a fertilizer, Figure 11-Lateral compression caused the may be the only significant addition increasing the growth of the existing most significant damage and the longest of sediment received by the marsh vegetation. In areas with wrack depo- recovery for coastal marshes. since its enclosure. NATIONAL BlOLOGlCAL SERVICE sition, plants have recolonized very Hurricanes are valuable sources of slowly because the wrack must first sediment for coastal wetlands and decay enough to allow plants to grow such as lateral compression, erosion, may in the short-term be able to through the thick debris. and wrack deposition, will long-term counteract subsidence and slow the Virtually all of the study areas in adverse effects be seen. 03pre 12) process of the marsh’s interior frag- the coastal marsh had some degree of Areas where the marsh was totally mentation and degradation. Although disturbance after Hurricane Andrew. lost are unlikely to recover, worsening these sediments may not completely Although the kinds of species present the existing problems of coastal marsh counteract the subsidence associated in many sites changed, this change is erosion and degradation. In other with Louisiana’s coastal wetlands, likely to persist only in areas of com- cases, sediment added to the marsh they are an important addition in pressed marsh where increased sur- surface contributes to the health of areas cut off from normal sediment face elevations will last longer. these systems. supplies. Marsh managers should Ultimately, scientists have found The overall firmness and “health” consider these often opposing effects that the vegetation of these coastal of the marsh strongly influence the when considering restoration and marshes recovers fairly quickly from degree to which it is affected by storms. mitigation projects. The best way to the impacts of hurricanes and other Hurricane Andrew had a major impact protect wetlands from future hurri- tropical storms. Even areas where the on floating and weakly rooted wetlands, cane destruction is to promote the vegetation dies back because of salt but a much smaller effect on firmly inorganic and organic accretionary burn generally recover over time. rooted marshes. In the future, areas of processes that encourage a “healthy” Only in areas with dramatic changes, degraded marsh will be more suscep- marsh.

Wetland

Affected

Figure 12a, b- Satellite images inter- preted by computer software show that large areas of Louisiana’s coast were affected by Hurricane Andrew. Image (b) is an enlarge- ment of area marked with square on image (a). - Forested Wetlands

urricane Andrew diminished in strength after it made landfall east of Cypremort Point. The storm turned to the north- northeast, passing over the Atchafalaya Basin where more than 450 km 2 (174 mi’) of cypress-tupelo and bottomland hardwood forests were at risk. The storm stayed within the levee boundaries with wind speeds gradually weakening, but wind gusts of 112 kph (70 mph) were still recorded when the storm was 48 km (30 mi) west of Baton Rouge. The Atchafalaya Basin contains 35 percent of the remaining bottomland hardwood forest and swamp forests of the lower Mississippi floodplain. The two dominant forest-cover types include cypress-tupelo swamps, pri- Figure 13-Hurricane Andrew‘s tree-toppling path in the Afckafalaya Basin. marily in the southeast part of the basin, and mixed bottomland hardwood forests. The southwest portion basal area-the volume of their the trees in this area damaged. These of the basin has been subjected to high trunks-in areas exposed to the weaker stands were growing on loose soils rates of sedimentation since the con- and were quite susceptible to being struction of levees after the flood of influence of the storm. Trees in areas 1927 and the diversion of sediment- exposed to the full strength of the storm pushed over. Surprisingly, cypress- laden Mississippi River water. The lost over 60 percent of their basal area. tupelo stands were largely unaffected areas of new sediment are now domi- Bottomland hardwoods in the because the canopy tree species have nated by black and sandbar willow, southwest portion of the basin, domi- properties, such as extensive root sys- swamp cottonwood, and the exotic nated by willows, were especially tems, that make them resilient to hur- Chinese tallow. hard-hit, with more than 85 percent of ricane-force winds. (Figure 14) The impact of Hurricane Andrew varied greatly with forest type, the Figure IPAlfkougk species mixture, canopy (tree top) cypress-tupelo swamps structure, and location relative to the i remained almost storm’s path. The zone of heaviest unaffected by Hurricane damage to the forest extended 20 km Andrew, bottomland (12 mi) east from the hurricane eyepath hardwood forests lost in the southern portion of the basin almost one third of their and 10 km (6 mi) east of the eyepath frees. in the northern part. Sites exposed to wind speeds less than 120 kph (75 mph) experienced lower levels of damage. (Figure 13) Most of the initial loss in tree den- sity and canopy cover was restricted to the bottomland hardwood forests. These stands lost 10 percent of their 8 Even though there were many fallen trees (about 10 percent of the forest Table 1. How Hurricane Andrew Damaged Specific Types of Trees in volume, basinwide) overall tree mor- Bottomland Hardwood Forests tality was initially low because, despite severe damage, many of the downed Most damaged Moderately damaged Least damaged trees resprouted. Surveys conducted two years after Hurricane Andrew, Sandbar willow Red mulberry Pumpkin ash however, revealed that there was a Swamp cottonwood Boxelder Deciduous holly considerable amount of delayed mor- Black willow Swamp red maple Water hickory tality among certain tree species. Mortality for persimmon, swamp cot- Waxmyrtle Swamp privet Baldcypress tonwood, and sandbar willow increased Chinese tallow Hackberry Water elm from 5 to 7 percent during the first year Sycamore Various oaks Buttonbush to 25-61 percent the next year. Swamp dogwood Various hawthorns Despite the widespread destruction in the Atchafalaya Basin, not all tree species responded in the same manner to the catastrophic winds. (Figure 15) Some species were resistant to wind and lost only individual limbs; others were susceptible to windthrown or snapped tree trunks and died. Tree species that were susceptible to wind- throw are prolific sprouters and have survived. Species that initially survived and sprouted, however, appear to be highly susceptible to delayed death. A significant impact of the storm was the amount of plant material

Figure 15-One tree shows the haphazard damage a hurricane can cause. NATIONAL BIOLCIGICAL SERVICE

Figure l&Landsat Thematic Mapper image of Atchafalaya Basin; red areas indicate green vegetation. Same area through Advanced Very High Resolution Radiometer at three different times in 1992. Normally, the area outlined would appear white or similar to the area above it. The pink-purple areas indicate new leaf cover just a few months after the storm. NATIONAL BIOLOGICAL SERVICE

stripped and broken off the trees by amount of organic material falling the winds. This phenomenon was so into the swamp in a short period led widespread that it showed up on to extremely low levels of oxygen in satellite imagery of the study area. the water column in the Atchafalaya Widespread defoliation (leaf removal) Basin and a large die-off of fish. An caused up to 41 percent of the normal estimated 182 million game and com- seasonal leaf fall to occur in a single mercial fish died, an economic loss of day. The decomposition of this large $160 million. (Figure 16) Can we predict how the forest will Various climate change models Basin will be at greater risk of dam- recover from such catastrophic distur- suggest that under global warming, age, and intensive land management bance? Forest recovery and the forma- tropical storm intensity might may be required to direct the devel- tion of a new canopy are accomplished increase as much as 50 percent. If so, oping forest toward more desirable in several ways. Defoliation of living then the forests of the Atchafalaya forest cover. (Figure 18) trees by Hurricane Andrew, for instance, caused a surge of new leaf growth in the fall of 1992. Furthermore, many understory trees and saplings were unaffected by the hurricane despite the loss of the canopy trees. These survivors will grow rapidly and form the new canopy. In other cases, seeds and new tree seedlings will become established and eventually form the new forest. (Figure 17) Initial surveys suggested that heavy- seeded species such as oaks were underrepresented in the ground layer, while other species such as Chinese tallow tree and water elm were more common. It is disturbing that an exotic species such as the Chinese tallow tree has such a high representation in the understory, while the more valuable oak species commonly found in bot- Figure 17-Resprouting in bottomland hardwood forest eight months after the storm. tomland hardwood forest sites are NATlONAL BlOLOGlCAL SER”lCE underrepresented. This suggests that exotic species may play more of a role in recovery from disturbance than they have historically and can alter the nature and function of these forests. Hurricanes are an important agent of forest disturbance in coastal wet forests. The recovery of the forest will depend on the previous forest cover, the type of damage, and the specific environmental conditions affecting regeneration. The harvest of the virgin cypress swamps and the building of levees earlier this century caused widespread change in the forests of the Atchafalaya Basin. Increased sedimentation has resulted in the dominance of willow stands in the southwest portion of the basin, an area that was most heavily damaged by the hurricane because of the willow’s susceptibility Figure I8-Ground view of damage in bottomland hardwood forest six months after the storm. to hurricane-force winds. NATlONAL BlOLclGlCAL SER”lCE

10 x Wildlife

Figure 19--White tail deer.

The northern parula, a Neotropical warbler, was one bird directly affected by the storm. This bird uses Spanish moss to build its nest. In addition to the number of warblers lost during the storm, there was a continuing loss afterward, probably because the moss needed for new nests was blown off the trees and scattered throughout the basin, making it difficult for the birds to find. This bird also uses the canopy of trees as a feeding ground, and lack of canopy for forage could also explain a decrease in the number of birds. (Figure 20) Other studies have shown some improvement of bird habitat in the Atchafalaya Basin. Birds that nest in t is certain that a storm with cypress-tupelo swamps, provided tree cavities, for instance, did not lose winds of 225 kph (140 mph) will more forage opportunities for deer their nests because the winds rarely immediately kill some fish, birds, after the hurricane. Over time, how- completely toppled trees. The trunks and other animals as it passes through ever, this increased forage will decrease remained standing, so the nest sites their habitat. Surprisingly, however, as mature canopy trees become were not lost, even if a tree was heavily studies have shown that the passing reestablished and shade out the understory. Further research will show if damaged. In fact, more nests were of Hurricane Andrew actually provided alternative management, such as provided for cavity-nesting birds by benefits to some wildlife species while clearing debris in these forests after a the trees that were not toppled barely affecting others. Sweeping hurricane, would enhance the habitat through the Atchafalaya Basin, the of white-tailed deer in years following winds of the storm cleared much of Figure 20-Northern parula. storms. (Figure 19) 0”IREO. ACADEMY OF NATURAL SCIENCES. PHlLADELPHlA the canopy in the bottomland hard- Birds in the Atchafalaya Basin wood forest. This disturbance allowed were affected more significantly by more sunlight and other nutrients for Hurricane Andrew. Numbers of resi- a greater variety and number of plants dent birds-those that live in an area to grow and, ultimately, provided year-round- dropped immediately small mammals like white-footed deer after the hurricane, as individuals, mice, and amphibians, and reptiles their nesting places, and habitat were with more food. battered by the high winds. But studies Populations and growth of larger have shown that any actual mortality mammals in the Atchafalaya Basin, caused by the hurricane was not a such as the white-tailed deer, seemed negative factor for long; surviving not to be affected at all by the hurri- residents and birds from the sur- cane. The mixed hardwood forest, rounding forest soon began repopu- sustaining more damage than the lating the empty areas. because new cavities were made when Andrew. Scientists developed maps Figure 21-Distribution of animals in areas branches broke off. estimating damage to these forests of Iberia, St. Martin, and St. Mary parishes affected by Hurricane Andrew. While the number of resident birds and used a powerful computer tool THE NATURE CONSER”ANCY dropped immediately after the storm, known as a geographic information the broken forests provided some system to compare damaged areas attraction for migrating birds like with the known positions of bald eagle Neotropical warblers. These traveling nests, colonial wading bird colonies, songbirds visit the Louisiana forests and the range of the Louisiana black on their migration through North bear. This analysis demonstrates the America, but their new attraction to importance of maintaining multiple sites they usually ignored increased nesting sites and habitat for larger bird diversity in the basin right after birds and mammals, though site or the storm. nest abandonment may result from In Iberia, St. Martin, and St. Mary other factors. (Figure 21) parishes, large areas of forest that provide important habitat for many species were affected by Hurricane / Hurricanes Are Inevitable

e are only just beginning to

appreciate the significance of ‘BERMUDA hurricane effects on our biological resources. As we learn more from scientists about the frequency with which hurricanes can occur, the systems they affect, and how they inter- act with the evolution of our coastal ecosystems, we can better prepare ourselves and our environment for their onslaught. Hurricanes have long affected the Atlantic and gulf coasts of North America. We can find chronicles of these storms in the New World expe- riences of Christopher Columbus and Figure 22-Tracks of cyclones in the Gulf of Mexico this century. throughout the period of colonial set- tlement. Evidence is also imbedded in the growth rings of trees and in coastal activity and a tendency toward living in coastal areas much more so geologic deposits, and it tells us that stronger storms as we approach the than in the past, and these areas are these storms have struck our coast- new century. the ones hit hardest by hurricanes. lines with regularity. (Figure 22) Statistics compiled from storms Over half the nation lives and works For instance, return times-how this century indicate that while the in coastal counties, which represent frequently hurricanes strike an area- number of deaths per hurricane only about 10 percent of the U.S. land along the northern gulf coast can decreased over time (Table 2), the costs mass. At the same time, however, the average from five to 20 years, of hurricane damage increased. In advent of aerial reconnaissance and depending on location. Before 1995, 1992, Hurricane Andrew was listed as satellite imagery has warned people the deadly nature of these storms had the costliest natural disaster to occur about the approach of such storms, on U.S. soil; total damage assessment faded from the public consciousness leading to prompt evacuations and a for the storm was about $27.2 billion, reduction in deaths. But we still have because, even though Louisiana had but only 60 lives were lost. much to learn before we can under- been hit by other recent storms, the How is it that the cost of storms stand whether human activities in the previous 25 years had been relatively has increased over the years while coastal zone are making these ecosys- inactive. The inactivity, however, their deadliness has decreased? One tems more vulnerable to hurricane seems to be changing. reason is that people are building and effects. $ Recent studies of hurricane activity and global weather patterns seem to indicate that hurricane activity comes Table 2. Hurricanes Affecting Coastal Louisiana Earlier This Century (Data From the U.S. in cycles of roughly 20 years. Army Corps of Engineers) Meteorologists predicted 1995 to be one Year Effect of the most active years for tropical storms in the last 50 years, and indeed 1909 $6 million in damage; 353 deaths; winds 200 kmh (124 mph); 5-m (16-ft) storm surge by mid-October, a near-record 18 1915 $13 million in damage; 275 deaths; flooding in New Orleans 0.3-2 m (l-8 ft) deep; tropical storms and hurricanes had 3-m (10 ft) storm surge covered Grand Isle been named and tracked. Although 1947 $100 million in damage; 34 deaths; flooding in New Orleans 0.3-2 m (l-8 ft) deep these storms missed Louisiana that 1957 Hurricane Audrey: $150 million in damage; 500 deaths; 4-m (12-ft) storm surge year, future storms will inevitably come 1965 Hurricane Betsy: $1.4 billion in damage; 81 deaths; 3-m (I0-ft) storm surge covered this way. Most climatic computer Grand Isle models suggest a period of increased

13 “*““./” --- - ,*

Value of Louisiana’s Coastal Barrier Islands and Wetland Systems

t is estimated that every 1 km coastal wetlands are also at risk. The resources for a $1-billion-per-year fish (0.6 mi) of barrier island shoreline current rate of wetland loss in and shellfish industry. The fisheries protects 30 km* (12 mi’) of wetland- Louisiana averages some 65.6 km2 industry in southern Louisiana relies estuarine habitat. The islands that (25 mi’) each year. Since the 1930s, an on coastal marshes for crucial nursery fringe the coastal wetlands can limit estimated 3,950 km2 (1,525 mi’) of habitat. A powerful hurricane damages the height of hurricane storm surges, coastal wetlands and barrier islands the livelihoods of people who rely on reduce wave energy, reduce the have been lost. Subsidence, human fisheries. After Hurricane Andrew, for potential for erosion of landward impacts, and erosion caused by storms example, $15 million was granted to wetlands, and retard saltwater intru- have all been implicated in these high the gulf commercial fishing industry sion. The continued degradation of rates of loss. A hurricane such as to help recover from those losses. these islands, however, has dimin- Hurricane Andrew can result in a Farther inland, forested wetlands pro- ished their ability to protect the wet- year’s worth of loss in a single day. vide crucial habitat for wildlife and a lands, bays, and estuaries that sup- Besides offering great protection to renewable resource for the timber and port Louisiana’s coastal fisheries. cities and upland areas, Louisiana’s paper industries. The Atchafalaya Coastal wetlands offer an impor- coastal and forested wetlands also Basin holds the largest single parcel tant buffer from flooding and salinity have an important impact on the of forested wetland left in the United intrusion associated with the hurricane’s state’s economy. The state’s coastal States, about 1.5 million acres. ( storm surge. However, Louisiana’s ecosystems provide the natural

Monitoring, Protecting, and Restoring Coastal Louisiana

hough many natural habitats wetlands of the Atchafalaya Basin make note of which species are present were devastated by the hurri- will probably be as resilient as the as well as establish permanent study cane, research is showing that most of coastal wetlands despite damage and plots that can be followed over time. these systems will recover in time. loss to the canopy trees. Despite initial Without continued research into how Physical destruction was limited to an losses, wildlife populations have gen- both nature and humans affect area near the path of the storm, but erally recovered. Louisiana’s coast, we may one day the secondary effects of Hurricane Our conclusions must be tempered arrive at a point where we find that Andrew were noticed at sites quite with the realization that these coastal willful winds are agents of total distant from its path. Some of the ecosystems are increasingly at risk destruction. Hurricane Andrew‘s barrier islands were severely eroded. from various natural and human- damage was tempered by its part in Hurricanes such as Andrew can only caused factors. The forested wetlands the continued evolution of the coast, accelerate a trend towards their are being rapidly reduced in area and but that may change with future, disappearance, although efforts to are experiencing changes in the com- fiercer storms and continued degra- restore those islands are already see- position of their woody species. Over dation of our coastal resources. ( ing some success. time, Louisiana has lost nearly 60 per- Vegetation has recovered in cent of its forested wetlands. Barrier Louisiana’s coastal wetlands, but in islands are eroding at alarming rates, certain areas wetland loss was accel- and Louisiana leads the nation in erated and distinct physical changes- wetland loss. such as the compression of coastal We must continue to monitor the marshes-resulted. The forested long-term effects of hurricanes and

14 Pieces of trees and sediment, care- folds in marshes pushed together by made by people who actually use the fully extracted and preserved, provide winds, and the defoliation and break- coastal marshes: trappers, hunters, and a historical view of the environment. ing of trees in bottomland forests. camp lessees. They provided detailed Analytical techniques carry names Comparisons of aerial photographs information about damage to sites that like dendrochronological (dendro=tree, taken before the storm, classification they were most familiar with, and chrono=time) and cryogenic (cryo=frost, of damage type and entry of these almost all of them knew within a week genic=generation) core sampling. Tree classifications into digital data bases, of the storm exactly what had happened samples reveal the impacts of past and the use of geographic information in their areas. The information also hurricanes on tree growth, as do sedi- systems allowed researchers to gener- helped land managers in setting pri- ment samples of the life of a marsh, ate color maps that clearly showed orities for repairing storm damage. both offering valuable information damage that the human eye can miss. More information about past storms about the present environment. Furthermore, similar delineation of will presumably be provided by the Wetland scientists have made use images taken from satellites allowed compilation of oral histories of the of these technological advances to the same kind of damage assessment Atchafalaya Basin. To balance technol- develop tools that assist their research and will help lead to large-scale analy- ogy and tradition is fitting because, efforts and offer more detailed infor- ses of land cover trends. (Figure 23) ultimately, it is the tie between the mation about the resources to be With field data and digital data people and the land hurricanes affect managed. In the studies undertaken bases, scientists can develop computer that will teach us the most about the after Hurricane Andrew, these tools models that simulate the effects of willful winds. 5 were used to assess the damage to the different types of hurricanes on dif- coastal environment and predict the ferent habitats. Models developed can long-term effects on valuable coastal actually use historical data on wind resources. strength and direction of past hurri- For instance, data loggers for the canes to predict the probability of continuous recording of water eleva- hurricane return frequency, as well as tion, wind speed, and other informa- the intensity of the winds at remote tion had been placed at various locations. marsh sites prior to the hurricane to But these hurricane studies were evaluate marsh management methods. also aided by some old-fashioned These computers recorded the hurri- techniques. Site-specific damage sur- cane as it passed over the sites. They veys throughout the coastal zone were showed that, on August 26, Jug Lake, Louisiana, received wind gusts of Figure 23-Louisiana depicted through 162 kph (101 mph) that were respon- Advanced Very High Resolution Radiometer sible for the extensive tearing of the at three different times in 1992. Normally, the brackish marsh and its conversion to area outlined would appear white or similar open water, which is specific, on-the- to the area above it. The pink-purple areas spot information scientists would not indicate new leaf cover just a few months after the storm. have had otherwise. NATIONAL BIOLOGICAL SERVICE Aerial photographs, satellite imagery, and predictive models are also techniques used in studying natural resources. Aerial photographs, taken from airplanes right after the storm, showed immediate loss of spits on barrier islands, the accordion Atlantic Hurricanes. G.E Dunn and B.I. History of Hurricane Occurrences Along Restless Ribbons of Sand: Atlantic and Miller. 1960. Louisiana State University Coastal Louisiana. 1972. U.S. Army Corp Gulf Coast Barriers. J.T. Wells and C.H. Press, Baton Rouge, LA. 326 pp. of Engineers, New Orleans, LA. 43 pp. Peterson. 1986. U.S. Fish and Wildlife Service and Louisiana Sea Grant College Early American Hurricanes 1492-1870. Hurricane Force: A Coastal Perspective. Program, Baton Rouge, LA. 20 pp. D.M. Ludlum. 1963. American 1994. Department of the Interior, U.S. Meteorological Society. Boston, MA. Geological Survey. 28-minute video. Tropical Cyclones of the North Atlantic 191 pp. Ocean, 1871-1992. C.J. Neumann, B.R. Hurricanes, Their Nature and History. Jarvinen, C.J. McAdie, J.D. Elms. Florida Hurricanes and Tropical Storms, 1959. I.R. Tannehill. 1959. Princeton 1993. National Climatic Data Center, 1871-1993, An Historical Survey. University Press, Princeton, NJ. 308 pp. Asheville, NC, 193 pp. F. Doehring, I.W. Duedall, and J.M. Williams. 1994. Florida Sea Grant Journal of Coastal Research, Special World Wide Web homepage for the College Program, Gainesville, FL. 118 pp. Issue 21. Impacts of Hurricane Andrew USA National Hurricane Center. on the Coastal Zones of Florida and Http://www.nhc.noaa.gov/ The Fragile Fringe: Coastal Wetlands of Louisiana: 22-26 August 1992. the Continental United States. 1992. Louisiana Sea Grant College Program, U.S. Fish and Wildlife Service, and National Oceanic and Atmospheric Administration. 16 pp.

Dal Chappell, Bill Jones, Steve Laine, Sue Lauritzen, and Jim Lynch prepared figures for this publication. Gaye Farris, Lee Foote, Lori Huckaby, Janet Keough, Bob Stewart, and Kristie Weeks reviewed the entire manuscript; Don Cahoon, Tom Doyle, and Clint Jeske provided technical reviews. Elizabeth Coleman edited the text. Karen Short designed the publication.

We are especially grateful to the individuals who led the projects reported here: Wylie Barrow, Pete Bourgeois, Don Cahoon, Robert Chabreck, TomDoyle, Darryl Felder, Debbie Fuller, James Grace, Glenn Guntenspergen, Larry Bob Keeland, Paul Leberg, Greg Linscomb, Ted Leininger, Graeme Lock; Irv Mendelssohn, Elijah Ramsey, Mark Swan, and Joe Truett.