Plants of the Marsh
The dominant species of plant is the narrowleaf cattail, a plant more common to salty water. This plant typically develops its characteristic flower spike by June and releases seeds in the fall. Other species include arrowhead, arrow arum, pickerelweed, sweetflag, spatterdock and wild rice.
Unfortunately, many non-native plant species have been introduced into the area, plants that often outcompete beneficial native species. Examples are porcelainberry, Japanese honeysuckle, multi-flora rose and Asian bittersweet.
Saturday Morning Plant Walk in Dyke Marsh
On a hazy Saturday morning on July 26, 2014, about 30 FODM members and friends turned out for a plant walk led by Dr. Elizabeth Wells (“Call me Beth”), Associate Professor Emerita of Botany at The George Washington University. Dr. Wells’s walks are always engaging and informative, and this one was no exception: the enthusiastic group observed a number of colorful and interesting plants. FODM President Glenda Booth provided the accompanying photos with essay by Pat Salamone.
The tropical-looking blossoms of the swamp rose mallow (Hibiscus moscheutos) are among the largest flowers produced by any perennial that is winter-hardy in our area.
The native wild grape vine (Vitus L.) bears drooping clusters of fruit in the familiar bunch-of-grapes form.
Smooth sumac (Rhus glabra) has compound pinnate (feather-like) leaves that turn red and orange in the fall, and bears clusters of small round red fruits that serve as winter food for wildlife.
The tubers of the groundnut vine (Apios americana) were an important food source for many Native American tribes and some early European colonists. The vine bears clusters of beautiful reddish purple sweet-pea-like flowers.
The tall coneflower or cutleaf coneflower (Rudbeckia laciniata) is recognized by pollination ecologists as attracting large numbers of native bees, according to The Xerces Society for Invertebrate Conservation.
Dyke Marsh is home to two plants known as swamp dogwood, Cornus amomum and Cornus foemina, which are very similar in appearance. The blue berries of the swamp dogwood are eaten by several species of birds.
Swamp milkweed (Asclepias incarnata) serves as a host plant for monarch butterfly caterpillars.
The purple flower spikes of pickerelweed (Pontederia cordata) are pollinator magnets.
Although a member of the carrot family (Apiacieae) and looks similar to Queen Anne’s Lace, water hemlock (Cicuta maculata) is highly poisonous.
Trying to Save Pumpkin Ash Trees
FODM is partnering with the National Park Service (NPS) on a project to try to save some of the preserve's pumpkin ash trees (Fraxinus profunda) from destruction by the emerald ash borer (EAB) (Agrilus planipennis), an invasive insect that was found in Fairfax County in 2003 and has been documented in Great Falls and Turkey Run Parks. "An EAB infestation is always fatal to ash trees," says the U.S. Department of Agriculture (USDA) website. The insect could kill all of the pumpkin ash trees in Dyke Marsh in 20 years without action.
Dyke Marsh has over 1,000 pumpkin ash trees. These trees thrive in wet areas like swamps, floodplains and bottom lands, can reach 130 feet in height and have a 68-inch diameter. The pumpkin name comes from the trees' usually swollen or pumpkin-shaped butt or base.
Ensuring a Breeding Stock
FODM's goal is to help NPS maintain a small, healthy breeding stock of these trees. In the spring of 2015, we contracted with Bartlett Tree Experts to conduct an insecticide treatment called Tree-age into the root flares of nine selected trees (Joshua Darkow applies treatment, photo left) in hopes that the treatment will kill any emerald ash borers infesting the trees. NPS chose a small group of trees located close together because ash trees have both male and female flowers and are air pollinated. NPS also tagged and wrapped the trees with beaver-resistant netting. Bartlett's Joshua Darkow injected the trees on May 13. If the treated trees remain healthy for two years, we hope to repeat treatments until the EAB infestation has passed through our area. There is no guarantee that the treatment will be successful.
In September, four North Carolina Botanic Garden staff members, with the assistance of Peter McCallum and Brent Steury from NPS and Robert Smith from FODM, collected pumpkin ash seeds in Dyke Marsh for preservation. They met their goal of 10,000 or more seeds from 25 or more trees. These seeds will be available in the future to help in the marsh's restoration and to replace trees expected to be lost to the EAB.
On May 16, 2016, with support from FODM and NPS, Bartlett Tree Experts treated another four pumpkin ash trees for the emerald ash borer. At that time, there were many dead trees, presumably because of this non-native insect. “Significant numbers of ash trees along the George Washington Memorial Parkway and in Dyke Marsh have failed to leaf out this spring,” said FODM project manager Robert Smith, “presumably due to the emerald ash borer. However, the nine trees we treated last spring are all in good shape.” He added, “Adding these trees to the initial group will greatly enhance the chances that we will be able to maintain a healthy set of pumpkin ash trees in the marsh. Hopefully, they will be able to both propagate themselves and provide seeds for use in the restoration.”
Referring to the trees treated in 2015, NPS Biologist Brent Steury said,” The first nine trees were obviously much healthier than any other ash trees in the area except the four I selected for treatment in this round.”
“Most of the surrounding ash trees are dead with one notable exception and that is a female at the far southeastern edge of the copse that also produced plenty of seeds. Of the study trees, three showed some significant bare areas ranging from approximately 25 percent to 40 percent of the branch area, but this does not indicate a fatal emerald ash borer infestation. Two of these trees were added in 2017 and showed some bare areas at the time of treatment but were determined worth trying to save.”
On September 25, 2017, five FODMers and Brent Steury with the National Park Service surveyed the treated trees in Dyke Marsh. Project leader Robert Smith wrote, “It was very encouraging to see that all of these trees had leafed out this season and that all six of the females had produced plenty of seeds. Six of the trees were originally treated in 2015, four more were treated in 2016 thanks to a dedicated donation, and six more were added by NPS in 2017 and all 16 were treated this spring with NPS funding (mitigation for three that were accidentally removed last year).
On April 11, 2019, FODM and National Park Service (NPS) employees revisited the pumpkin ash preservation site. FODM will finance the treatment of two more trees in May 2019.
In preparation for the treatment, Brent Steury, NPS Natural Resources Manager, Stephen Fagin, NPS Horticulturist, and Robert Smith, FODM Project Manager, surveyed the 16 study trees. They also wrapped trees with wire mesh to prevent beavers from chewing them down and tagged two trees for probable addition to this year’s treatment program. They took diameter measurements, put fresh orange ribbons on the study trees and did some minor clearing of invasive plants.
The success of this project is unknown. The emerald ash borer usually kills the trees it infects. It is too early in the year and in the study to draw any firm conclusions about the treatment’s effect or the health of the trees.
"It is painful to imagine Dyke Marsh without its expanse of ash trees so we are doing what we can to ensure that they will revive after an attack," said Robert Smith, FODM project manager. Photos courtesy of Glenda Booth.
