written by Deb Hanson and Kathleen Smith
If you’ve ever stood on the observation tower at the CREW Marsh Trails and looked out over the 5,000-acre marsh, you may have noticed that the sawgrass marsh is being overtaken by coastal plain willow shrubs. While coastal plain willow is a native species, under certain conditions it becomes invasive – out-competing the sawgrass, taking over the landscape and reducing open water habitat for wading birds. The Corkscrew Marsh at CREW has experienced this phenomenon and much of the 5000-acre marsh is now covered with willow.
The invasion of the Corkscrew Marsh by coastal plain willow (Salix caroliniana) has altered the structure of the marsh community. Marshes dominated by coastal plain willow inhibit nutrient cycling and the maintenance of diverse biological communities as well as the use of prescribed fire as a management tool for controlling exotic plants and maintaining open-water habitat for wading birds (Frederick and Spalding 1994). So, the Florida Fish and Wildlife Commission (FWC) and the South Florida Water Management District (SFWMD) jointly applied to the FWC Aquatic Habitat Restoration and Enhancement (AHRE) Sub-section for funds for the treatment of approximately 1,075 acres of willows in CREW. The objective of the project is to decrease coverage of undesirable willow in the marsh to allow herbaceous vegetation to increase in coverage, enhancing fish and wildlife habitat and creating more open-water marsh.
The application was funded, and aerial treatment (via helicopter) began at CREW on August 26th. Three different ratios of Glyphosate and Imazapyr are being used, tested and analyzed to determine which is the most effective treatment and what herbacious vegetation returns to the marsh post-treatment. The goal and performance standard that will be used to assess success of the project is less than 50% coverage of willow within the treatment site two years post-treatment.
The treatment area is in the central eastern and southern parts of the marsh. Aerial photomonitoring at 3-month intervals after initial treatment will be used to evaluate the response of the willow. Georeferencing markers have been established in the marsh to spatially reference aerial photos taken at 3, 6, 9, and 12 months post-treatment (we may also supplement with on the ground photos). This will be a long-term maintenance project with re-treatments and potential native plantings for years to come.
So, when you look out over the marsh during the next couple of years, watch for changes in the plant composition on the horizon to the east. Hopefully it will open the marsh and encourage new native species of plants to grow, providing better habitat for fish and wildlife and water storage and filtration for our drinking water supply.
(Thanks to Kathleen Smith of FWC for providing the photos and facts for this article!)