Pushing floating islands
A floating island attacks parking lot

Sometimes what appear to be islands rising out of the water are actually drifting masses of peat, mud, and plants. In extreme cases, these "islands", which range in size from a few feet across to hundreds of acres, can contain trees more than 50 feet tall and 8-12 inches in diameter. Though this page pertains to tussocks and floating islands found in Florida, these phenomena are in fact world-wide, witnessed in such places as Argentina, Australia, Finland, India, Japan, Kenya and Papua New Guinea.

Aquatic plant managers refer to these islands as tussocks, floating islands or floating forests. In this section, we will discuss the origins, impacts, utilization, and management of these phenomena which can be extremely expensive, costing the Bureau of Invasive Plant Management $8.6 million in the 2004-2005 fiscal year.

Tussocks and floating islands are a product of the aging process of water bodies and probably have always been a part of Florida’s shallow lakes. Historically, their numbers and magnitude were altered by periodic drought and fire that controlled them within lake margins, or occasional floods that deposited them high in the uplands or in downstream marshes.

Nowadays, water levels in most of Florida’s public lakes are manipulated by some sort of human-made structures, such as weirs, dams, or levees. This manipulation eliminates the extreme high and low water events that historically suppressed tussock and floating island formation. For example, the Kissimmee Chain of Lakes that once had a water level fluctuation range of more than 10 feet now is permitted to vary only a few feet each year.

Additionally, people who have moved near lakeshores don’t particularly cherish the arrival of tussocks and floating islands.

Tussocks and floating islands aren't all bad, though. They do provide habitat for animals like marsh rabbits, alligators and rookeries for birds. They are usually comprised of native plants so resource managers, who are charged with controlling invasive exotic plants, are reluctant to remove them unless they pose imminent economic or public safety hazards, or damage to beneficial plant and animal habitat.

So how do these seemingly benign rafts of plants and organic material affect people? Lake-side residents, fish camp owners and other water users have a few stories to tell!

Hurricane Jeanne pushed floating forest onto residential shoreline of Lake Pierce

Tussocks covering most of the water surface in Lake Davis

Imagine the dismay after having just installed that new dock or just placed those emergent plants for fish and wildlife habitat, and a two-acre mass of 10-feet tall floating cattail washes up next to your property and re-attaches to the lake bottom. Or the shock of walking into your back yard after Hurricane Frances passed over Lake Pierce and seeing 18 acres of floating island "forest" with trees to 50 feet tall - a forest that used to bother no one when it was attached to the unpopulated eastern shore of the lake? Or the bewilderment of waiting four years for the drought to end and water levels to return to Davis Lake only to see nearly 40% of the 250-acre bottom pull loose and float to the surface in 12 feet of water?

Freely drifting tussocks and floating islands are not only aggravating to waterfront homeowners. What if you were one of six fish camp operators on Orange Lake who also waited for the water levels to recover from years of exceptional drought only to have your customers’ boat trail access to the main body of the lake blocked by some of the 3,500 acres of tussocks drifting in that lake? Or what if you were one of these customers whose safe return was cut off by a drifting tussock that blocked the boat trail while you were fishing in the lake? And what if you are the emergency preparedness manager responsible for flood control in the Kissimmee Chain of Lakes or Lake Hancock and hundreds of acres of tussocks are drifting toward the outfall structures that regulate water levels in these flood control reservoirs?

Tussocks drifting toward Highway 60 Bridge and flood control structure on Lake Kissimmee	Shredder and tussocks caught in flood control structure on Lake Hancock

The occurrence of tussocks and floating islands may not be new, but the need for their large-scale management is. Ten years ago, the Florida Department of Environmental Protection’s Bureau of Invasive Plant Management (BIPM) spent an average of $300,000 annually to manage all native plants including tussocks and floating islands.

In fiscal year 04-05, the BIPM spent more than $8 million strictly for controlling tussocks and floating islands.

This unprecedented level of problems has put a stress on available funding, technology, and equipment to control tussocks and especially floating islands, and draws into question, Which agency or agencies are responsible for managing them?

Historically, if tussocks drift and if they block access, flood control, or navigation in established boat trails, they are managed under contract through the BIPM under Priority Level 2 of the Cooperative Aquatic Plant Control Program. Previously, tussocks were controlled under priority Level 6 if they were simply drifting or floating in a lake. Funding for tussock control or any plant control in Priority Level 6 was usually insufficient. The Florida Fish and Wildlife Conservation Commission (FWCC) has restoration funds to remove organic deposit build-up, tussocks, or floating islands when they cover or degrade fish and wildlife habitat in high priority waters. The 2003-2004 outbreaks of tussocks and floating islands taxed both agencies’ budgets, causing them to redirect funds from other important projects. For example, any tussock control funded through the BIPM diverts funds from invasive plant control, especially hydrilla management. Tussock management funded through the FWCC diverts funds from de watering and muck scraping restoration efforts planned years in advance of the current tussock and floating island problems.

OF TUSSOCKS AND FLOATING ISLANDS

It is important to define them if we are to understand how and why tussocks and floating islands are managed.

Because the numbers and magnitude of these floating masses are unprecedented, at least during the past 30 years, the terminology to define them is still evolving. Managers have borrowed from terrestrial terminology and jargon. Until recently, any floating mass of vegetation that was not a true floating plant like water hyacinth and water lettuce was termed a tussock. Webster defines a tussock as a tuft of grass. So when mats of grass or other emergent plants were drifting in a lake, calling them tussocks seemed a natural fit, especially since they can be managed using traditional herbaceous plant control methods – most notably, aquatic-registered herbicides.

But how do you characterize a floating mass of mud, peat and trees, whose herbaceous plants are susceptible to herbicides, but which will nonetheless continue to float and colonize new herbaceous plants. How do you manage such a floating mass? Clearly new terminology was needed.

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Tussocks
Tussocks are rafts of herbaceous plants that form in a number of ways. They can be controlled using herbicides that kill the plants, and the entire mass will soon after sink to the bottom.

1) Floating invasive plants like water hyacinth and water lettuce and even native floating plants like frog’s bit, if not managed, can form large rafts, acting as substrate for emergent plants to colonize. The emergent plants like primrose willow tie the rafts together below the surface with their roots and above the surface with stems and branches.

2) Native emergent species such as pennywort and smartweed grow from the shoreline forming mats across the water surface. If the mats become large enough, wind and wave action can tear them loose generating floating vegetation tussocks. One of the most prolific plants at generating floating tussocks is another native species, Scirpus cubensis. This grass-like sedge sends long runners among and over other emergent plants and can eventually crowd them out forming a floating mat in their place consisting exclusively of Scirpus cubensis.

3) As water levels increase after draw downs or droughts, masses of spongy-tissue plants like cattail and pickerelweed that colonized shallow mud flats during low water occasionally pull loose if the sediments are soft and flocculent, or "woolly". In 2003-2004, thousands of acres of tussocks generated in this fashion were drifting in Orange Lake, and Lakes Hancock and Apopka.

Cattail tussock on shore of Lake Hancock	Cattail tussock plugging entrance to Apopka-Beauclair Canal

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Floating islands
Floating islands are comprised of aquatic and sometimes upland plants; herbaceous as well as woody plants, and most importantly, they are characterized by suspended masses of organic deposits like peat and mud from a few inches to a few feet thick. Simply killing the vegetation on these floating masses will not eliminate their presence. The mud, peat and woody material will continue to float and the cycle will repeat. The nature of floating island formation dictates that they must be dismantled if they are in an area where they must be controlled.

Hundreds of acres of tussocks that popped to the surface of Todd and Dodd Lakes

1) Floating islands can form in the same manner as tussocks that pull loose from sediments upon re-flooding of lakes. In some cases the sediments are compact or fibrous enough that the emergent plants, whose roots are interwoven into the sediments pull as many as a several feet of organics with them to the surface as lakes re-fill. This is the case with hundreds of acres of floating islands drifting in Hernando Pool of the Tsala Apopka lake / marsh system, as well as Lakes Okahumpka and Runnymeade.

2) Occasionally, wind from storms rips up vegetation; for example in Lake Istokpoga during the 1993 Storm of the Century, or rapid water level increases and wave action tear plants loose and shred them; for example in 1994 on Lake Okeechobee. Although the vegetation is dead, it is so compacted, often several feet thick and substantial enough to walk on, that it continues to float. As decomposition occurs at the surface, this soil supports a new crop of aquatic and wetland plants whose roots help to hold the mats together. In the case of Lake Okeechobee, a subsequent drought lowered the water level and the ~15-mile long x several hundred feet wide floating island settled to the bottom forming a berm that hinders water exchange between the main body of the lake and the adjacent marsh.

Peat mat that floated to the surface in Croft Lake

Close-up of floating peat mat showing thickness of sediments

3)In lakes with high organic content in the sediments, gasses can build up to the extent that they lift small patches of decomposing fibrous material and peat to the surface. These patches coalesce along shorelines or emergent vegetation boundaries and are eventually colonized by wetland and even upland plant species.

4)When lake bottoms with high organic (especially peat) deposits are exposed for prolonged periods, the sediments thoroughly dry. If the water level increases rapidly, before the sediments can re-saturate, several feet of the sediment layer, especially highly buoyant peat, can rise to the surface bringing with it overlying aquatic, wetland, and upland plants.

Standing on floating forest drifting in 8 feet of water on Lake Pierce

5)In extreme cases, a rapid water level increase combined with severe wind and wave action can break loose wetland and upland vegetation that had been growing on floating mats for years attached to the shoreline. Examples are the floating forests with trees up to 50 feet tall drifting in Lakes Pierce, Marion, and Apopka resulting after the series of hurricanes that crossed central Florida in 2004.

Tussock control
In the case of tussocks, management is fairly straightforward. Most tussock control is achieved using herbicides registered with the USEPA and the Florida Department of Agriculture and Consumer Services.

Tussock management using herbicides costs $100-200 per acre (2006).

The most appropriate herbicide is chosen to control the target tussock plants as well as provide the greatest measure of protection for adjacent beneficial rooted plants. For examples:

- 2,4-D is applied to control Scirpus cubensis mats or rafts of pennywort
- glyphosate is used to control rafts of para grass
- mixtures of 2,4-D and glyphosate are applied to wild taro or frog’s bit mats
- imazapyr or triclopyr are used to control tussocks with mixed vegetation including woody species like water primrose and willow.
(For more information about herbicidal control of aquatic plants, go to this page of this web site.)

Much of the tussock controlled with herbicides decomposes at the surface. Some of the material falls to the bottom to break down further. Although some organic material is thus deposited on the lake bottom, the amount is less than what would rain down through the years if the tussock were not controlled. By removing long-existing tussocks, wave action, oxygen, and light, cut off by the tussock, can once again penetrate to the sediments to further break down accumulated organic deposits and stimulate regeneration of rooted submersed and emersed plants. Preemptive control of tussocks as they begin to form usually results in a one-time or short-term deposition of small amounts of organics that do not significantly impact the lake bottom.

Shredding floating forest in Marion Creek to clear bridge after Hurricane Charlie

Occasionally, tussocks must be immediately controlled, for example when they are lodge against bridge pilings or flood control structures, such as can occur during a hurricane. In these cases, much more labor intensive and expensive methods like shredders, harvesters, barge-mounted track hoes, or draglines are employed. Since these methods are usually applied for floating island control, they will be discussed in more detail in that section below.

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Floating island control
The greatest difference between tussock and floating island management is that tussocks can be cheaply controlled with herbicides whereas floating islands must be dismantled and/or removed from the area using machines.

Floating island control using machines costs from about $3,000 to $15,000 or more per acre (2006).

Cost is another reason managers are reluctant to control floating islands unless their removal is absolutely necessary.

There is enormous variability among floating islands, from the composition and thickness of suspended sediments to the type and amount of vegetation growing at the surface. Plants range from soft tissue herbaceous plants to trees up to 12 inches in diameter and 50 feet tall. This variability requires the use of a wide array of machinery, imagination, and innovation to resolve floating island problems.

Floating island control is messy business and it is important to understand that all floating island control has some level of negative impact. Remember, removing the island itself means removing plant and animal habitat.

The DEP-BIPM looks for the most cost-effective control program that is compatible with other uses and functions of the water body. The FWCC is consulted when developing all floating island control projects. Other agencies including Water Management Districts and the US Army Corps of Engineers are contacted where appropriate. In developing control plans, managers ask two very important questions:
- Will any of the potential control options cause undue harm to the uses or functions of the lake? If so, then those strategies are eliminated.
- Will one potential control strategy significantly enhance the uses and functions of the lake over another method? If the answer is no, then the most cost-effective strategies are selected.

Below are the general methods and strategies available to control floating islands.

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Shredding floating islands on Tsala Apopka

Shredders
Shredders are machines with rotating blades that shred and grind suspended organic sediment material, herbaceous and woody plants, as well as trees up to 12 inches in diameter. Several variations and prototypes have been tested. All units operating in Florida lakes function with two bow-mounted counter-rotating blades that are thrust into the floating island. Shredders need about two or more feet of water depth to be most effective. Depending on vegetation and sediment density and composition, shredders can dismantle up to 10 acres of floating islands each day.

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Harvester lifting part of a peat and vegetation island out of a lake

Harvester removes water hyacinth from Caloosahatchee River in 1939

Harvesters
Harvesters are machines that can lift floating island material, including sediments and small trees, out of the water via a conveyor belt that extends from below the water surface to a storage area on the barge. Material is then transferred to a transport barge or hauled within the shredder to an in-lake or shoreline disposal site. Harvesters have operated in Florida since at least the 1930s and have evolved into specialized machines that range in width from 5 to 10 feet and in carrying capacity from 4-15 tons. High capacity harvesters can remove up to about an acre of dense floating islands each day.
(For more information about mechanical controls, go to this page of this web site.)

Loading harvested floating island material into trucks at Tsala Apopka

When harvesting is the method chosen for tussock and floating island control, harvesting is just the beginning of the removal process. Harvesting, especially floating islands, means hundreds of tons of material to haul and dispose, either in the lake, which has further environmental implications, or taken out of the lake. Removing harvested material from the lake requires conveyors, elevators or loaders to transfer material to trucks. If trucks drive on the road, they must be sealed. Disposal sites must be secured prior to harvesting and may require tipping fees at dumps or additional costs to purchase land or spread material out if dumped on private property or public lands.

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Track hoes and draglines
Track hoes and draglines are used when floating islands are accessible from shorelines or rights-of-way leading to flood control structures, such as when floating islands drift onto boat ramps, public beaches or against bridges or dams. Prior to 2004, track hoes were seldom mounted on barges to go into lakes to remove floating islands. Before 2004, floating islands away from shore access were generally small enough to be controlled with shredders or harvesters or both.

However, strong winds during hurricanes Charlie, Frances, and Jeanne dislodged floating islands that had been attached to shorelines perhaps for decades in several lakes, especially Pierce, Marion, and Apopka. Trees on these drifting juggernauts are too tall for conventional harvesters and too thick for most shredders alone to dismantle. Trees are secured to the track hoe boom; chain sawed off at the base, stacked on the barge and hauled to a disposal site. Track hoes or clam shells then scoop out the stump, root, and sediment mass before harvesters and shredders control the remaining contents of the floating island.

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