Controlling invasives with biology at CREW

By Allison Vincent

Lygodium Microphyllum

Have you ever been out on the trail, any trail, and that friend that knows a thing or two about invasive species points out a few for you? He or she discusses the threat they pose to the native ecosystem that they’re encroaching on and you wonder, what can we do about it?

One highly successful way of managing invasive species is to employ a biological control agent, using other living organisms to help control invasive and non-native species. It’s a way of reacquainting invasive pests – such as Old World Climbing Fern or Lygodium microphyllum – with their natural enemies to provide natural and sustained population reduction. In the case of Lygodium, the enemy is the brown Lygodium moth (Neomusotima conspurcatalis) which has been successfully used in Florida since 2008.

It’s time-consuming and difficult to get official approval to use biological control agents, but it’s worth the wait. Some agents have proven to be very successful and without unintended consequences. Biological treatment studies often extend for decades before hitting the ground, assuring that there are no negative impacts beyond their intended use.

You may have noticed technicians at the CREW Bird Rookery Swamp trails lately distributing state-approved biological control agents near pockets of a certain species. They hope to limit the expansion of Lygodium from the area – a tall order, as it is one of the worst invasive species, crowding out many native plants and habitats for wildlife. Management of this invasive plant using traditional strategies, such as mechanical and chemical treatments, has proved difficult and expensive, with limited long-term success. Enter biological control agents.

Without natural competition, invasive plants like Lygodium will inevitably wreak havoc on an area not ready for its intense growing cycle. Each fertile leaflet has 133 sori – or the frilly bits on the fern – and each sori has 215 spores! Multiply those numbers to find that each fertile-female leaflet may spread 28,500 spores into the surrounding area (Volin et. al, 2004). It doesn’t stretch the imagination to picture the fern-filled scene should the invasion go untreated. Every invasive plant spreads through different means and in the case of Lygodium, the female portion of the plant with her fertile spores does the work. Other common invasive plants, like Caesar weed, spread by other vectors, such as wildlife and humans. Caesar weed has a particularly sticky bur containing lots of seeds, so be sure to trash those burs that make it home with you after a hike.

Trail camera photo of Florida black bear covered in caesar weed “burs”

But how do the land managers, the South Florida Water Management District (SFWMD) in the case of CREW, go about treating such a powerful invasive plant? Well, they fight fire with fire, sometimes literally, as prescribed fires, after other biological and chemical treatments, have been known to increase the successful die-back – or sustained control of plant spread – both above and below the ground. Many times land management uses a combination of mechanical, chemical and biological control to yield the best results.

In the case of Lygodium, the biggest observable impact in the long-term comes primarily from biological control and, in particular, those brown Lygodium moths. While other species have been introduced and had some success in destroying Lygodium, the brown Lygodium moth has unleashed the biggest disaster for this invasive plant.

Neomusotima conspurcatalis, the brown lygodium moth

It all starts with little caterpillars, who feed on fern leaflets causing browning of leaves and breakdown of entire Lygodium plants. Female moths lay an average of 136 eggs during her short life span – the life cycle of the moth from egg, through caterpillar and pupa to adult, is only about 30 days. Researchers observing the impact of testing sites over 4-6 months found that moth populations increased, and noticeable caterpillar feeding damage in the form of browned-out patches of Lygodium became apparent. Good for us, bad for Lygodium.

Throughout the history of CREW, biological control agents have been used as one element of a three-part approach to treat the invasive Melaleuca quinquenervia tree on the CREW lands. You can still see the process in action in the “Melaleuca graveyard” on the Red trail of CREW Flint Pen Strand where large stands of trees were treated with a combination of mechanical and chemical treatment. Later, biological control agents were added for long-term success – if you look closely you can still see weevils and psyllids, the Melaleuca-loving biological control agent.

We all benefit from the long-term research studies on biological control agents. Through partnerships with leading wildlife agencies and the SFWMD, land managers for the CREW lands hope to see similar results, like the sustained success on throughout the state. There will always be a need for invasive treatment, but with each step we take toward restoring our natural Florida environment, everyone benefits.

CREW Flint Pen Strand lands under preservation for future generations to enjoy!

Early Settlers in CREW

Europeans & Early American Settlers, the history of land use and its effect on our water resources and wildlife in CREW
Lakes of Flint Pen Strand

Water management in Florida today has evolved from the lessons of the past, as well as from changing philosophies about natural resources and the environment. Early Native Americans in Florida altered the land by building settlements, cultivating fields, building mounds, establishing transportation routes, and digging canals and fish ponds. European explorers and settlers arrived in the 1500s, but much of Florida, particularly the central and southern regions, remained relatively undeveloped until the last decades of the 19th century. Significant increases in population and tourism were contemporaneous with new development and developers directly and indirectly caused significant changes to the natural landscape and resources of the state (Purdum et al.).

Europeans & early American settlers:

The history of Florida’s human settlement for most of the past 14,000 years has been shaped by water. When Spanish explorers arrived in Florida in the 1500s, an estimated 350,000 Native Americans were living throughout the state almost exclusively near water filled regions (Bureau of Archaeological Research). At the time of the European contact in the late 16th century, the Spaniards identified the people of Southwest Florida as the Calusa. The Calusa occupied the coastal zone, however their political influence and trade network extended inland to the Lake Okeechobee basin.

Settlement of Lee County really began in the years following the Civil War. Government land surveys seeking out areas for settlement were also completed during this period, although CREW area surveys were left incomplete due to the “impracticable” nature of the swamp. Ultimately, even though people had lived in Florida for thousands of years prior to 1900, their overall impact had been minimal.

Lakes of Flint Pen Strand where majority of research was conducted. Photo by John Lane

Historical & archaeological research at CREW:

Archaeological research on the CREW lands, which includes approximately 60,000 acres, have uncovered no prehistoric or historic artifacts (Halperin et al.). However, archaeologically significant sites were identified adjacent to the CREW lands near Lake Trafford and several potential sites with historical resources were identified within the CREW project. Even though archaeological research uncovered no diagnostic artifacts and given the limited excavation done, it is reasonable to assume CREW would have been used for hunting and gathering activity by prehistoric peoples. Feel free to contact the CREW Trust or the Bureau of Archaeological Research if you discover a possible historical/archaeological site.

The early 1940s aerial photographs show limited cultural activity within the CREW project and by the 1970s, only a partial ditch system was in place. The Flint Pen Strand canals were more recently constructed, as evidenced by the dirt and rubble leftover from excavation. Some time after 1970, 12 to 15 homesteads were established in the slightly higher eastern part of the CREW project. The sites appear to have been selected based on slight elevations and access via the dirt trails. Almost nothing remains of these homesteads except abandoned power poles and a thin scatter of debris (Halperin et al.). 

In 2010, the South Florida Water Management District (SFWMD) began steps to restore hydrologic functions within the CREW Flint Pen Strand area (Blog: History of  Flint Pen Strand: Part Two), just another example of Floridians actively seeking ways to preserve, protect and restore water resources in more recent years.

Environmental choices & change:

Since 1900, Florida has seen substantial changes in land and water use. General consensus viewed Florida as having too much water and as a result, many Floridians were focused on drainage, flood control and navigation (Purdum et al.). Historically, water resources were seen primarily for human use and therefore were controlled and modified to suit our needs. Now, the value and sustainability of our finite water resources are clear. Land managers (SFWMD) today are concerned with water quality protection, water supply and ensuring natural places like the CREW watershed are under protection and preserved for future generations (Purdum et al.). 

Bibliography

Halperin, Christina, et al. “Cultural Resources Survey of the Corkscrew Marsh Tract of the Corkscrew Regional Ecosystem Watershed, Collier County, Florida.” C.A.R.L. Archaeological Survey, vol. Bureau of Archaeological Research, no. June, 2002, p. 42.

Purdum, Elizabeth D., et al. “Florida Waters.” A Water Resources Manual from Florida’s Water Management Districts, vol. Florida Water Management District, no. 1, 2002, p. 120.

CREW Begins Aerial Treatment of Willows in Marsh

written by Deb Hanson and Kathleen Smith

Willows growing in marsh
Willows growing in marsh

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.

Open Water Corkscrew Marsh
Open Water Corkscrew Marsh

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.

Helicopter loading for aerial spraying
Helicopter loading for aerial spraying

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.

Helicopter taking off to go to marsh
Helicopter taking off to go to marsh

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!)

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