The late Penni Sharp, botanist, professional wetland scientist, member of the FIConservancy Board and President of the H.L. Ferguson Museum, wrote an overview of invasive plant species, with special attention to plants that dominate the Fishers Island landscape. The following article appeared in the 2003 issue of the Fishers Island Gazette.
By Penni Sharp
The Hurricane of 1938 was a defining moment in the landscape of Fishers Island. Storm winds essentially leveled Island forests, leaving vast areas of disturbed soils that became vulnerable to colonization by aggressive plants.
Bare soil exposed by land clearing has also contributed to the spread of invasive plants. As a result, many plants now common to the Island do not represent native pre-settlement flora. In fact, most, if not all the species that now flourish here are from Europe and Asia.
This problem is not unique to Fishers Island. Biologists across the nation are concerned about the loss in overall biodiversity due to invasive species, which are not limited to plants. Zebra mussel, gypsy moth, European starling, and Japanese green crab are also considered to be invasive.
Connecticut, close enough to Fishers Island to draw comparisons, has approximately 900 non-native out of 2600 plant species growing without cultivation. Of the 900, 90 are listed as either widespread and invasive, restricted and invasive, or potentially invasive.
Man bears responsibility for transporting into new environs many non-native species that otherwise could not have crossed natural barriers such as oceans, deserts and mountains. While the majority of exotic plants introduced by accident or intention are ecologically benign, a small percentage has run rampant.
Many common wildflowers such as Queen Anne’s lace, common buttercup, bouncing bet and red clover, are species that have been introduced from overseas, usually arriving by ship or imported for medicinal purposes. Fortunately, most have not become invasive pests.
An invasive plant species is defined as one that establishes readily, grows aggressively and prolifically, and tends to reproduce in high numbers. It can readily escape from cultivation and is able to persist in the natural landscape without cultivation, crowding out native species. In worst-case scenarios, it not only drives out indigenous species but also radically alters natural ecosystems.
On Fishers Island, one of the only areas that appears to be free of invasives is the Brickyard Woods. Elsewhere, there are invasive species in all plant categories: trees, shrubs, vines, herbs, and forbs.
The Norway maple is our most conspicuous invasive tree and grows on the West End. The most widely planted street tree in North America, it is native from southern Scandinavia to northern Iran and was introduced as an ornamental shade tree in Philadelphia in 1762. It is a problem, because it produces large numbers of seeds that are wind-dispersed and can out-compete and inhibit the regeneration of native trees.
Autumn olive is a small, spiny deciduous shrub that may grow up to 20’ tall. In late May, the Island is permeated with its sweet aroma, so potent that the smell is noticeable from the water as one approaches the Island by boat.
This shrub grows rapidly, often forming dense thickets. A single plant may produce 200,000 seeds each year. Autumn olive is also a nitrogen fixer and can alter nutrient cycling and soil suitability for other species. Its fragrant yellow flowers mature to fleshy fruits, brown at first, and later red (occasionally yellow) with minute silvery dots.
It was introduced to America from Asia for a variety of uses including soil conservation and wildlife habitat enhancement. In Connecticut, Autum olive was widely planted along highways and may very well have been transported to Fishers Island by birds feeding along the I-95 corridor.
Bush honeysuckles are also common on the Island. They are upright, multi-stemmed shrubs that range in height from six to 20 feet and have oval, opposite branching leaves. They can grow in a variety of habitats from open fields, marshes, forest edges, and forests, and are native to Europe, eastern Asia, and Japan. They were introduced as ornamentals during the 1800s.
Morrow’s honeysuckle has downy leaves and white flowers that turn pale yellow with age. The fruits, many-seeded berries, are normally a dark red.
Tatarian honeysuckle, introduced from southern Russia, has smooth, hairless leaves and pink or white flowers. Fruits vary from yellow to dark red.
Bella honeysuckle is a hybrid between Tatarian and Morrow’s. Birds, which readily consume the ripened fruits, are probably responsible for the spread of these shrubs.
Fishers Island has three vine species that are extremely prolific in both open areas and our remaining woodlands. These are: oriental bittersweet (Celastrus orbiculatus), Japanese honeysuckle (Lonicera japonica), and porcelain berry (Ampelopsis brevipedunculata).
Oriental or Asiatic bittersweet
Oriental or Asiatic bittersweet is a deciduous, twining, woody vine that is best recognized during the fall by its three-parted yellow fruits that split to reveal the showy red berries. Many people consider the berries to be attractive and use them in fall decoration. The leaves are roundish to oval and grow alternately on the stem. Vines can be over five inches in diameter and reach lengths of 60 feet or more. They climb up trees twisting around trunks and shading the leaves. When it becomes prolific at treetop levels, it may cause the host tree to become top heavy and subject to wind throw. Asiatic bittersweet may out-compete other plants in its aggressive competition for light, water, and nutrients. Asiatic bittersweet is native to Japan, Korea, and China. It was brought to the U.S. in the mid 1800s, and by the early 1970s had become invasive in 21 states. Its primary means of dispersal are birds and people who use the plant in dried arrangements.
Japanese honeysuckle is rampant on Fishers Island, growing in nearly every habitat. It is a woody vine with very fragrant tubular flowers. The flowers grow in pairs and are white to yellow in color. Its fruits are dark purple to black berries occurring in pairs along the vine. The plant is native to Asia and was brought to New York in 1806 where it was introduced as a landscape plant. It has spread throughout the eastern half of the United States, most likely dispersed by birds that feed upon its fruits. Japanese honeysuckle spreads rapidly. It will overtop and choke out small trees and shrubs. It will also spread like a groundcover, shading out and thereby eliminating native herbaceous plants.
Porcelain berry is also a common vine on the Island. It most likely escaped from garden cultivation, as it was once a popular garden plant used on estates in the East. Today, it is most abundant in the Northeast coastal zone between Boston and Washington D.C. Porcelain berry closely resembles grape and has a similar leaf shape. The flowers are inconspicuous yellow blossoms that appear in late June. The plant is at its most showy during autumn when the berries turn various hues of turquoise blue to purple, sometimes mottled with gray and white.
Once this plant becomes established, it is difficult to eradicate. The plant reproduces readily by seed and vegetatively. The root system is tough and almost impossible to dig out. Porcelain berry will cover the ground, trees and shrubs within woodland edges to the exclusion of other plants. It entwines around trees, making them susceptible to wind damage. Control, but not elimination, can be best achieved by repeated mowings.
No discussion of invasive species on Fishers Island should be undertaken without mention of the notorious kudzu (e). This invasive vine, sometimes referred to as “the plant that ate the South,” is not common in New England. On Fishers Island, it seems to be confined to the West End in the former Fort Wright area. My speculation is that the U.S. Army Corps of Engineers planted it when buildings were torn down and the fort abandoned. The plant was often used for erosion control purposes until its invasive habits became understood.
On the Island, kudzu produces its flowers late in the season. It has deep purple blossoms that smell like grape soda. The blooms are late enough so that the plant does not appear to produce fruits prior to frost. This is probably one of the reasons that its Island presence has remained somewhat stable and confined. Where it does grow, it blankets the ground and clearly demonstrates the fact that no other plants could survive where this prolific vine is present.