National Park Service

Northeast Temperate Network (NETN)

atmospheric deposition and stress


An invasive species is a non-native species (including seeds, eggs, spores, or other propagules) whose introduction causes or is likely to cause economic harm, environmental harm, or harm to human health. Invasive plants are species that have become a "weed" pest - a plant which grows aggressively, spreads, and displaces other plants. Invasive plants tend to appear on disturbed ground, and the most aggressive can actually invade existing ecosystems. Invasive plants are generally undesirable because they are difficult to control, can escape from cultivation, and can dominate whole areas. In short, invasive plant infestations can be extremely expensive to control and environmentally destructive.

A small number of invasives are native plants, meaning they occurred in North America before settlement by Europeans but became aggressive after the landscape was altered. However, most invasive plants arrived from other continents and are often referred to as "exotic," "alien," introduced," or "nonnative" invasives. An aggressive plant freed from the natural/native environmental, pest, and/or disease controls, will often become an invader of other ecosystems.

Characteristics of Invasive Plants

Invasive plants are noted for their ability to grow and spread aggressively. Invasive plants can be trees, shrubs, vines, grasses, or flowers, and they can reproduce rapidly by roots, rhizomes, seeds, or shoots. Invasive plants tend to:
not be native to North America;
spread, reproducing by roots or shoots;
mature quickly;
if spread by seed, produce numerous seeds that disperse and sprout easily;
be generalists that can grow in many different conditions;
and be exploiters and colonizers of disturbed ground.

Impact of Invasive Plants

Second only to habitat loss, invasives are a major factor in the decline of native plants. Plants like Japanese Knotweed, Purple Loosestrife, and Garlic Mustard are displacing native plants and degrading habitat for native insects, birds, and animals. Endangered, rare, and threatened native species of plant and animals are particularly vulnerable/at risk because they often occur in small populations .

Invasive plants, even when grown in a cultivated yard, can spread, escape, and cause environmental problems far from where they were first planted. If you live in an urban or suburban area, there is a good chance that the worst weeds on your property are escaped plants - like Japanese Honeysuckle, Multiflora Rose, Japanese Knotweed, and Oriental Bittersweet. In yards, gardens, fields, and parks these plants are very expensive to control.

Importance & Issues

jefferson salamanderThe presence and extent of invasive exotic species is a critical management concern at all network parks. Parks would greatly benefit from timely identification and removal of new invasive species. Catastrophic consequences to native species (loss of biodiversity and replacement of native flora and fauna) can result if this vital sign is not addressed. Invasive exotic species are a significant and growing stressor with clear ecological relevance to terrestrial systems within the NETN. This vital sign has relatively strong management implications via exotic species control programs. Numerous groups of invasive exotic species are of concern within NETN, including terrestrial and wetland plants. Routine surveys for the presence/absence of particular invasive species should be mandatory at all parks. Lists of non-native species with the potential to invade individual parks already exist in most states and will be integrated into NETN protocols. These lists will identify the types of habitats to examine for invasion.

Preliminary Monitoring Objectives


Ensure the early detection of invasive plants in established forest monitoring plots and alert Park and state managers of any new incidences of invasive species in order to facilitate a rapid response.


Ensure the early detection of aquatic invasive plants in the freshwater resources of NETN parks and alert Park and state managers of any new incidences of aquatic invasive species in order to facilitate a rapid response. 


Detection of non-indigenous species.

Potential Measures

Establish status and monitor for expansion from known limits; exotic species extent and distribution in inter-tidal and wetland communities, time constrained search for indicator species in forest communities, including exotic species; percent cover in forest communities; estimate relative abundance; monitor wetland nutrient level and trend; current spatial distribution, abundance, and/or rate of spread of key invasive exotic shade-tolerant plants including Norway maple, European buckthorn, exotic honeysuckles, Japanese barberry, garlic mustard and Oriental bittersweet.


Last Updated: December 30, 2016 Contact Webmaster