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!)
I’m surprised there is no mention of toxic pollution potential from runoff for this spraying effort. Why is this not a consideration? We can’t keep allowing unnatural toxins and byproducts to wash away into our oceans. (Please consider only studies that are not funded by manufacturers of the herbicide.)
Hi Leah, and thank you for your comment. The CREW project team certainly appreciates your concern. Land and wildlife management is always a challenge. Whether it’s controlling invasive species, doing prescribed burns, or restoring hydrology, the goal at CREW is always to maintain or restore functioning ecosystems that protect the water, land, and wildlife within the watershed. Many factors are always considered before choosing a particular management strategy or technique, including time of year, resources available, and potential impacts of the technique – both good and bad. The willows are a major threat to both the wildlife habitat and the functioning of the marsh to store water and recharge the aquifers, the reason it was purchased in the first place. Other means of control have been tried – burning, mechanical roller-chopping, etc. But these methods are limited by access and often are very expensive. A test patch of herbicide spraying a few years ago proved to be the most effective method to control the invasive willows. Your concern about the toxicity of the herbicide is understandable. No one wants to add pollution to our waterways, especially not the CREW team, which works so hard to protect this precious water resource for southwest Florida. Be assured that the formula of herbicide being used here at CREW is specially designed for use in aquatic environments and is used at the lowest concentration/ratios that should effectively kill the willows. It is a contact herbicide which attaches to the leaves of the plants sprayed in a fine mist. In addition, the willows are so thick (even the helicopter pilot couldn’t believe how thick they are) and the spraying done so very skillfully using GPS coordinates that it is unlikely that much of the herbicide even gets to the water in the areas where spraying is occurring. Thank you for voicing your concerns and giving us the chance to add to the conversation. CREW (and all the waters of SW Florida) needs good friends and active, involved citizens to keep our environment healthy.
I forgot to mention the birds, butterflies, bees, wasps, flies and other wildlife that will be poisoned by aerial spraying such a “contact herbicide” (valuable predators such as bats will be eating toxic prey, thus being poisoned in turn). Even hand spraying would be better. We need to break ourselves of this habit of relying on remedies that damage ecosystems as much as the problem we’re trying to solve. Man caused this hydrology problem in the first place so we should pay for a much safer remedy no matter what the price (such as hiring low wage manual labor to remove the willows physically, repetitively if necessary?). “First do no harm” with remedies.