Dry Tortugas National Park- Loggerhead Key Exotic Plant Management & Island Restoration Figure 1. Dry Tortugas area map Project Figure 2. Fort Jefferson, Garden Key Tony Pernas,1 Brandon Gamble and vided food, and the islands safe harbor- plant and animal communities. The age, to countless mariners who tra- native flora on these islands mainly Thomas V. Armentano versed this popular trading route. Con- consists of plant species typical of sequently, the U.S. Military deemed Caribbean islands including grasses, this area an ideal place for protecting sedges, herbaceous flora, shrubs and and controlling Atlantic-bound Mis- trees. Of the 125 plant species reported sissippi River trade via the Gulf of 81 species (65% of total) are of exotic Mexico. origin; the result of accidental and Military occupancy of the Dry Tor- deliberate introduction by man during tugas during the 1800s paved the way the past century. The smaller islands Carnegie Laboratory, c. 1917 for numerous construction projects (East, Bush, Long, Sand) consist mainly that lasted throughout the century. The of native species, while the larger largest of which was never completed islands (Garden and Loggerhead), with and is the Dry Tortugas’s most famous their long history of human habitation INTRODUCTION structure, Fort Jefferson. and disturbance, have a significantly As the practical use of Fort Jefferson larger abundance of exotic taxa. History waned, protection of the cultural and The islands of the Dry Tortugas have The Dry Tortugas, discovered in historical resources of the area became been the subject of many studies since 1513 by Ponce de Leon are located the priority. In 1934, the Dry Tortugas the 1800s, including detailed vegeta- 70 miles west of Key West, Florida. area was designated Fort Jefferson tion maps and floristic inventories Named for the lack of freshwater National Monument. To assure that the giving the NPS valuable baseline infor- and abundance of sea turtles they natural resources of the area were also mation on historical flora. comprise the western terminus protected, in 1992 the Dry Tortugas of an ancient coral reef tract that was re-designated as a National Park. Loggerhead Key extends 220 miles from Miami (see Dry Tortugas National Park at 100 sq. In the 1840s Loggerhead Key was Fig. 3 ). miles is now the second largest marine- covered with “a large stand of old The biologically rich waters pro- based park in the National Park Ser- white buttonwood trees” that was cut vice, harboring a unique assemblage or burned by the island residents (Stod- of resources unparalleled within the Department of Interior, South Florida dart and Fosberg 1981) resulting in the Natural Resources Center, 1 Florida National Park Service system. first documented impacts to the island Exotic Plant Management Team, Of the total area, only 85 acres is community. Atlanta, GA terrestrial habitat capable of supporting WILDLAND WEEDS 13 The presence of two structures on Loggerhead Key, the U.S. Coast Guard Lighthouse of 1856 and the Carnegie Research Laboratory of 1910 functioned to draw people to the island, increasing the likelihood of plant introductions and habitat modifications. Literature dating back to the early 20th century depicts this area as remark- ably free from common exotic weeds, with the dominant community princi- pally composed of bay cedar, Suriana maritima (Bowman 1918). By 1918, introduced plants were possibly influ- encing the natural ecology of the island by producing shade and conserving water. These introductions include coconut palms (Cocos nucifera), Aus- tralian pine (Casuarina equisetifolia), fig (Ficus elastica), Hymenocalis, oleander (Nerium oleander), sea hibiscus (Hibiscus tiliaceus), mahoe (Thespesia populnea) Figure 3. Bathymetric map of Florida keys region and century plant (Agave spp.). By 1942, the once dominant Surinana (introduced by the director of the these trees will continue to grow and began to be replaced by prickly pear Carnegie Laboratory ca. 1910 (Stod- eventually replace the existing vegeta- cactus (Opuntia stricta), Coastal beach dart and Fosberg, 1981)) had spread tion.” By 1980, the words of Davis sandmat (Chamascyce mesembrianthe- from its original plantings with came to fruition, as nearly all of the mifolia), century plant, as well as others seedlings noted to be growing over native communities were displaced (Davis 1942). At this time, the most many parts of the island. Davis and out competed by two species, prolific exotic was Australian pine states, “It is entirely possible that Australian pine and century plant. Helena Ad 2/c P/U 14 WINTER 2001 North end of Loggerhead North end of Loggerhead Key, circa 1916. Note the Key, circa 1942. Note the Australian pine planted expansion of Australian pine. around the Carnegie < Laboratory. < North end of Loggerhead North end of Loggerhead Key, 2000. Restoration Key, 1995. Dense Australian efforts aim to return the pine covers the island. island to pre-Australian > pine conditions. > Management Activities root systems have hindered the move- The management of exotic pest In 1992, upon the establishment ments and nesting activities of feder- plants on these islands is essential of the Dry Tortugas National Park, ally listed threatened and endangered for maintaining the integrity of the resource managers began to assess sea turtles. In many places, changes natural and physical environments the alterations to the communities in beach morphology, from gentle found at the Dry Tortugas. The of Loggerhead Key with the intent slopes to steep embankments, have establishment and spread of exotic of restoring the island back to pre- accompanied the invasion, further plants can have severe consequences settlement conditions. exasperating the problem of sea turtle for any environment but, due to In 1995, an exotic plant man- habitat disruption. In addition, these the effects of geographic isolation, agement plan was developed and invasive species have altered the com- islands are especially vulnerable. implemented for Dry Tortugas position and structure of the island’s With its long history of human habi- National Park. The plan called for terrestrial plant communities by out- tation, Loggerhead Key has been eradicating Australian pine and competing native plants thus, reducing subjected to substantial human- century plant from Loggerhead Key. species diversity in areas where the influenced impacts, second only to Both genera have altered native exotics were dominant. The natural Garden Key in this respect. The plant communities and reduced the habitats and food sources of native control of the ubiquitous Australian native habitats for island wildlife. animals that use these communities pine and century plant on Log- Where Australian pine occurs on have similarly diminished. gerhead Key is the focal point of the sandy beaches, the trees and their Treatment of Agave sisalana, Loggerhead Key, Bill Snyder (left) and Biddy Simet (right). WILDLAND WEEDS 15 century plants. Vegetative sprouts and involved extending a line between seedlings of Australian pine and century two fixed points and measuring plants in the treatment areas continue the length of occupancy of a spe- to be controlled by hand-pulling and cies along that line, thus depicting application of herbicides. Other inva- the spatial patterns in vegetation sive exotic species on Loggerhead Key cover. (Colubrina asiatica, Scaevola taccada, Transect 1-5, with the exception Prescribed fire treatment and beach Panicum maximum, Thespesia populnea, to the native community along the debris removal, 1995 Terminalia catappa) occur only sporadi- eastern beach strand, are in an area cally and are treated as they appear. which was heavily dominated by The National Park Service has car- exotics. This area was used to moni- vegetation management action ried out treatment and monitoring tor the response to the management within the Dry Tortugas. work. From 1994-2001 the U.S. Forest activities, namely chemical and Treatment of Australian Service and the U.S. Fish and Wildlife mechanical treatment. Transects pine involved the basal-bark Service provided assistance with tree 6-10 represent the native communi- application of Garlon 4 herbi- cutting and prescribed burning. In addi- ties and were used as the target for cide (20% solution diluted in tion, the NPS Southeast Archeological defining restoration success. JLB oil). Century plants not Center conducted an archeological killed by fire were treated with survey of Loggerhead Key in early Vegetation Response a crown applications of Garlon 1998 to determine the effects vegetation During the sampling period 4 at 20%, diluted in JLB oil. management actions may have, if any, 1994-2001, a total of 48 species were Treated Australian pine trees on the island’s cultural resources. identified on Loggerhead Key. Of were left standing; however, Natural areas along the eastern the 48, 17 are considered exotic in trees adjacent to beaches were beach strand were protected from origin, and 31 are native. cut down and treated with her- management activities. These areas Within treatment area we have bicide to prevent their falling were monitored and used as a tool seen reductions in the numbers of and impacting sea turtle nest- to determine if restoration objectives exotics, with a concomitant increase ing habitat. In early 1998, the were being met. in the numbers of native species (Fig. remaining 13.5 acres of Aus- x). Essentially all of the exotic species tralian pine growing on the Monitoring present in the managed areas in 1994 island’s northern half were Monitoring the restoration effort have been removed as of 2001. cut down (no herbicides were was accomplished through a series of used). The felled wood was 10 permanent transects. Transect were Sea Turtle Nesting burned in late 1998, eliminat- established perpendicular to the axis One of the primary environmen- ing not only the Australian of the island. Vegetation along these tal threats to nesting sea turtles in pine slash on the ground but transects were measured utilizing the Dry Tortugas National Park is the also killing a large number of line intercept technique.