Invasive species in New Hampshire

Many conservationists consider invasive plant and animal species the second-most critical threat to the persistence of native biodiversity (habitat loss is first). A non-native species is one that exists outside its native range, having arrived into a new region as a result of either intentional or unintentional human-related activities. Intentional introductions of non-natives include those chosen for use in horticulture or landscaping; plants and animals that “hitchhike” on packing crates or other imported products are examples of unintentional introductions.

Invasive plants are a subset of non-native species whose introduction to an ecosystem has the potential to cause environmental harm. Once established, invasive plants produce many viable seeds or other propagules that travel by wind and water, animal transport, or inadvertently through human activity. Disturbed areas, both human and natural, are especially susceptible to the establishment and spread of invasive species. In riparian areas, combinations of frequent ice and water scour, rich floodplain soils, increased sunlight, and water transport dispersal opportunities provide excellent conditions for these invaders to establish, grow, and spread.

In New Hampshire, some of the more troubling invasive plant species occurring within riparian zones include Japanese knotweed, glossy buckthorn, and Asian bittersweet. These species shade-out natives, lower native plant diversity, and reduce habitat value. In upland habitats, invasive species of concern include honeysuckle, glossy buckthorn, autumn olive, and multiflora rose.

The threat of invasive species is considerable in New Hampshire. Best management practices require multiple approaches including inventory and mapping, control at the most ecologically important or vulnerable sites, policy and legislation, and regional partnerships.

For much more information on invasive species in New Hampshire, please visit the USDA's National Invasive Species Information Center website, and the NH Department of Agriculture's website. See also the NH Guide to Upland Invasive Species.

  (photo by Ben Kimball) 
Japanese knotweed (Fallopia japonica) along the Baker River in Wentworth 
(photo by Ben Kimball)

Japanese barberry (Berberis thunbergii) at Pawtuckaway State Park in Nottingham (photo by Ben Kimball)
Japanese barberry (Berberis thunbergii) at Pawtuckaway State Park in Nottingham 
(photo by Ben Kimball) 

purple loosestrife (Lythrum salicaria) at Blow-Me-Down Pond in Cornish (photo by Ben Kimball)
purple loosestrife (Lythrum salicaria) at Blow-Me-Down Pond in Cornish 
(photo by Ben Kimball)