When is Being Green Not Sustainable?

Invasive plant species in the U.S. were in many cases brought here for the very same landscape and garden qualities that allow them to outcompete native varieties. Often, they have shorter maturation periods, and can produce prolific flowers,fruits, or seeds. Some of them exhibit allelopathy, the release of chemical compounds from their root systems, that suppress the growth of nearby plants. Many of these species leaf out earlier than natives in the spring, and hold those green leaves longer into the fall, a characteristic becoming noticeable this time of year. 

One common woody invasive species that is visible now is Autumn olive (Elaeagnus umbellata) Autumn olive, a 6-8’ tall shrub whose leaves, twigs and red fruits are scattered with silvery scales so that the entire plant seems to glisten in sunlight, is common along roadsides, woodland edges and even deep in forested areas. It holds its leaves well into the fall.  Its edible fruits are widely spread by birds and animals, and its longer growing season allows it to outcompete native plants.  Japanese honeysuckle vine (Lonicera japonica), and Morrow’s honeysuckle shrub (Lonicera morrowii) similarly have longer active periods of green than many natives. Shrub honeysuckle has been sold for landscape plantings, but rapidly spreads from gardens into natural areas.  The red pigments in honeysuckle berries reportedly contribute to darker orange tail feathers of cedar waxwing birds. Such changes in coloration could impact these birds’ fitness for mate selection and reproduction.

Japanese barberry (Berberis thunbergii) a thorny shrub native to Asia has been widely planted in the U.S. as an ornamental.  It is now considered invasive, as it is widespread  throughout Maryland in places it was not planted. Barberry grows 3-5 feet tall and can form dense thickets that crowd out native understory plants. It spreads both by seed and by propagation from root creepers and rooting of branch tips. 

Japanese barberry leaves raise the pH of normally acidic forest soil and change the production of nitrates in the soil, facilitating conditions for more barberry invasion and non-native earthworm invasion. Earthworm activity then changes the profile of natural forest soil layers, thinning the layer of detritus that protects forest soils through the winter. Before leafing out the spring, barberry blooms in clusters of 3 to 5 small yellow flowers hanging along its upper branches. It produces red, oblong berries about 1/3 inch in length in late summer. Although barberry fruit is not preferred wildlife food, birds and small mammals will eat the fruit late in winter when other food is not present. After the first hard frosts in our area, deciduous native trees and shrubs will lose their leaves and most other native plants will have died back and turned brown.  Late fall is a good opportunity to identify invasive species for control work — if it’s still green late in the fall, a plant has a good chance of being from somewhere else in the world than here.

Article by Tom Anderson, Frederik County Forestry Board

November 2026 Nature Note