Exotic and Invasive Plant Species
There are many exotic and invasive plants in the Bronx River watershed. Invasive plants can damage wetlands in a variety of ways, but their primary threat is that they out compete and replace native vegetation. This results in the loss of native plant species, which provide habitat for other organisms. Of the invasive species in the Bronx River riparian corridor, the most prevalent are Japanese knotweed (pictured at right), mugwort, Norway maple, Chinese tree of heaven, white mulberry, amur cork-tree, black locust, weeping willow, honeysuckle, multiflora rose, porcelain berry, oriental bittersweet, garlic mustard, mugwort, Japanese hops, smartweed, spotted ladythumb, phragmites and purple loosestrife. NRG's Forestry staff has worked to remove these invasive species using a variety of mechanical, chemical, and bioengineering techniques, as can be seen on the invasive plant management page.
Of the invasive plant species along the Bronx River, two are of special concern. Japanese knotweed (Polygonum cuspidatum) is a shrublike herbaceous plant that can attain heights of up to ten feet. Japanese knotweed spreads quickly and forms dense thickets that outcompete native vegetation. In addition, Japanese knotweed is difficult to control, owing to its substantial rooting system.
Another invasive plant species of concern is phragmites (Phragmites australis). Phragmites is a common reed that forms dense homogenous swaths along riverbanks, excluding native vegetation and degrading available habitat.