Download Invasive Exotic Plant Management at the Arthur R. Marshall

Invasive Exotic Plant Management at the Arthur R. Marshall Loxahatchee
National Wildlife Refuge, an Integrated Approach
Allison G. Snow
U.S. Geological Survey Center for Water and Restoration Studies, Miami, FL
William Thomas, Jr. and Laura A. Brandt
U.S. Fish and Wildlife Service – A.R.M. Loxahatchee NWR, Boynton Beach, FL
Invasive exotic plants pose a severe threat to natural ecosystems worldwide
including South Florida’s unique and imperiled Everglades ecosystem. The subtropical climate, international commerce, and ornamental plant trade industry are
factors, which significantly increase the susceptibility of Florida’s habitats to
invasion. The Everglades are already threatened by human encroachment,
rampant development, and fragmentation of adjacent buffer lands. The Arthur R.
Marshall Loxahatchee National Wildlife Refuge (the refuge) represents a unique
remnant of the northern Everglades ecosystem, whose native species and
ecological integrity are slowly yielding to the influx of invasive exotic plants.
Old World climbing fern (Lygodium microphyllum) is decimating tree islands by
smothering native vegetation, toppling trees, altering fire ecology, creating
tangled mats capable of ensnaring wildlife, and preventing native species
establishment. Melaleuca quinquenervia forms dense stands that are
impenetrable to wildlife, alter hydrologic patterns, fire ecology, and native plant
communities. In addition, other Florida Exotic Pest Plant Council Category I and
II plant species occur with associated detrimental impacts to native plant
communities and wildlife. In response to this threat, the refuge has developed a
multi-faceted program incorporating detection, control, monitoring, and research,
while working closely with other government and private organizations; a truly
integrated pest plant management approach. The primary goals of this program
are to reduce invasive plant populations to controllable levels where impacts to
native plant communities and wildlife are minimized and to further understand the
underlying causes and consequences of exotic plant invasions to native plant
communities and wildlife.
To address the increasing populations of invasive exotic plants, a detection and
treatment program was implemented. The refuge conducts Surveillance and
Reconnaissance Flights (SRF) as the primary mode of detecting visible
infestations of invasive exotic plants. These surveys are coordinated with the
South Florida Water Management District (SFWMD) and the National Park
Service (NPS) to ensure a consistent data set, providing complete coverage of
invasive exotic plant infestations on the refuge as well as infestations on a
regional level for all of South Florida. These SRF results are used to direct field
operations by both private contractors who concentrate on heavier infestations
over large acreages and refuge crews who concentrate on isolated populations and
outliers. The preferred management strategy is to contain and treat small and/or
outlier populations. The most effective method to date for the most problematic
species remains herbicides, which are applied using a variety of techniques.
Refuge crews and volunteers deal with ancillary exotics on an individual basis.
Along with conventional control methods, refuge staff are also active on the
biological control front, working closely with the United States Department of
Agriculture (USDA) to coordinate the release of insects such as the Melaleuca
psyllid, a potential biocontrol agent for Melaleuca quinquenervia, and by
implementing vegetation studies on L. microphyllum infested tree islands in
collaboration with private parties such as the Institute for Regional Conservation
(IRC) to provide baseline information on the impacts of L. microphyllum for
future biological control releases. To combat aquatic invasive plants such as
water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes), the
refuge collaborates with the SFWMD to ensure waterways are clear and navigable
to maintain effective water flow and drainage and to ensure public recreational
activities such as fishing and canoeing are not adversely impacted.
Areas that have undergone eradication efforts are monitored to document impact
to and re-growth of the targeted invasive plant species and of surrounding native
vegetation. These two parameters are then used to gauge the effectiveness of the
treatment programs, improve efficiency, and provide modifications for future
treatment protocols. This monitoring program includes establishing plots on
islands where Melaleuca and Lygodium have been treated via ground-based
herbicide applications. Though ground applications appear to be effective when
performed correctly, they may not be cost efficient due to the severe infestations
now occurring within all refuge habitats. To evaluate an alternative control
technique refuge staff, in cooperation with the SFWMD and University of Florida
(UF) scientists, are also examining the effectiveness of aerial application of two
herbicides at two concentrations on two strand tree islands severely infested with
L. microphyllum. In addition to monitoring post-treatment efforts, the refuge
supports and facilitates several research projects on invasive plant species through
cooperative efforts as well as through the issuance of Special Use Permits.
Keeping with one of the primary functions of the National Wildlife Refuge
system, refuge staff are examining an often-overlooked impact of invasive plant
species; the toll these plants take on the wildlife. By studying the relationship
between L. microphyllum infestations and vegetation and wildlife diversity,
biologists hope to provide insight into the interactions between invasive exotic
plants, native plant communities, and wildlife populations.
Research is also underway to develop tools to aid land managers in effective
detection of invasive plant species as an alternative to the SRF. The SFWMD is
conducting research to determine the feasibility of using IKONOS (satellite) data
to detect infestations of L. microphyllum. Another crucial question for effective
management is the ability to determine those areas at high risk of invasion as a
result of exposure to an invasive seed/spore source. To address this concern,
refuge staff are collaborating on yet another project to examine the distance L.
microphyllum spores can be dispersed from existing infestations. By determining
areas of highest spore deposition, refuge staff can concentrate their detection,
control, and eradication efforts in areas most prone to invasion. This data set will
have a dual function, also being integrated into a larger project conducted by
USGS and the University of Tennessee (UT). This venture will incorporate
current distribution maps, life history attributes of L. microphyllum, dispersal
data, control mechanisms, and hydrology to develop a computer simulation
model. This program will allow land managers to input parameters (current
infestation coverage, funding for control, control method, and hydrological
limitations) and view the potential outcome of different scenarios, thereby
facilitating managerial decisions on the appropriate resources needed for efficient
treatment and the type and location of treatments needed to achieve the most
effective control to limit spread and invasion to new areas.
Early detection, treatment, and monitoring are critical components of a successful
exotic plant management program. The refuge is aggressively addressing this
problem, and is taking the necessary steps to monitor and reduce populations of
invasive plants on the refuge while strengthening its efforts by collaborating with
other private, local, and federal and state agencies including the SFWMD, USDA,
Florida Department of Environmental Protection, UF, UT, USGS, Florida
Atlantic University, and the IRC. Collaboration is essential; a variety of agencies
throughout South Florida are battling invasive plants on a landscape level,
encompassing a plethora of federal, state, local, and private buffer lands. By
working together and with the help of volunteers, refuge staff are helping ensure
the reduction of current exotic plant populations across South Florida.
Contact: Allison G. Snow, U.S. Geological Survey, A.R.M. Loxahatchee NWR,
10216 Lee Road, Boynton Beach, FL, 33437, Phone: 561-732-3684, Fax: 561369-7190, Email: [email protected]