Invasive Species

Invasive Aristocrat pear trees lining a Lexington street

Invasive plants are non-natives that escape from the spaces where they were originally planted to colonize natural environments. Their seeds are dropped by birds, or sometimes by the wind, in places that can be at a good distance from the mother plant. As they establish themselves they form a monoculture and suppress existing vegetation by depriving it of nutrients, space, and above all light.

In our Bluegrass region, the two most devastating invasive plants are bush honeysuckle and winter creeper. Like many such plants bush honeysuckle was imported from east Asia: the early emergence of its leaves, its many pretty white flowers, its abundant red berries, its rapid growth all seemed to recommend it as an attractive ornamental plant for gardens and parks. But these are precisely the characteristics that create havoc in nature: its berries, sugary though not particularly nutritious, are eagerly sought out by birds who disperse the encapsuled seeds far and wide. Once established in our woodlands, the early leaf cover deprives native vegetation of the light it needs to germinate or grow. Anybody who walks in one of our nature sanctuaries, like Raven Run, along a path that divides an area of honeysuckle thicket from another area where the honeysuckle has been removed immediately understands the ruin this plant inflicts. One side is devoid of ground vegetation due to excessive and early spring shade, while a richly diverse forest floor with wildflowers, ferns, and the seedlings of native trees and shrubs reemerges on the side to which the life-giving spring sun light has been restored.

Two invasive Miscanthus grasses

Winter creeper, shockingly and unethically, is still sold in some Lexington garden centers. Like English ivy, also considered an invasive though less aggressive, it rapidly covers the ground and prevents germination of other plants. When it encounters a wall, fence, or tree, it climbs upward and produces flowers and seeds which are dispersed by birds. While bush honeysuckle responds to herbicide treatments and has, with considerable effort and expense, been successfully eradicated from some woodlands, winter creeper is largely immune to currently available herbicides. Removal, if attempted at all, is usually done manually.

Sadly, many other favorite garden plants are exhibiting the characteristics of invasive plants, i.e. they establish themselves in natural areas where they begin to out-compete our native vegetation. All ornamental pear trees are now on Lexington's "do-not-plant" list. Concerned gardners and landscapers no longer plant burning bush, butterfly bush or Miscanthus grass, the latter having penetrated deep into Red River Gorge from the Mountain Parkway where it had been used as an ornamental by the Highway Department. The Kentucky chapter of EPPC (Environmental Pest Plant Council) monitors the plants that show invasive characteristics in our region and publishes a list that divides such plants into 4 categories, depending on the degree of threat they pose.

A 5- or 10- or even 20-year observation of a plant newly introduced to a region is not enough to determine whether it will escape and suppress biodiversity. Many plants now considered invasive lived peacefully in gardens for decades before becoming thugs and manifesting their destructive characteristics. The ecological issues raised by invasive plants provide vigorous support for choosing native plants for our ornamental gardens. Not only do such choices give a lifeline to plants threatened by invasives that have penetrated natural areas, they also avoid the risk of unwittingly spreading unwanted vegetation and causing ecological havoc.