Status of Invasive Plants in New Hampshire

Invasive Plants by Category

• Aquatic - 6 species, 48 records
• Conifer Trees - 2 species, 11 records
• Forbs/Herbs - 196 species, 7032 records
• Grass or Grasslike - 45 species, 523 records
• Hardwood Trees - 30 species, 4442 records
• Shrub or Subshrub - 40 species, 3900 records
• Vines - 23 species, 2253 records

Top Ten Abundant Invasive Plants (by number of reports)

1. Japanese knotweed - 2670 reports
2. autumn-olive - 2349 reports
3. glossy buckthorn - 2049 reports
4. oriental bittersweet - 2038 reports
5. purple loosestrife - 2012 reports
6. castor aralia - 1035 reports
7. Norway maple - 1026 reports
8. Japanese barberry - 283 reports
9. winged burning bush - 280 reports
10. multiflora rose - 214 reports

Top Ten Widespread Invasive Plants (by number of positive counties)

1. Japanese barberry - 10/10 (100%)
2. oriental bittersweet - 10/10 (100%)
3. Canada thistle - 10/10 (100%)
4. ground ivy - 10/10 (100%)
5. purple loosestrife - 10/10 (100%)
6. multiflora rose - 10/10 (100%)
7. common mullein - 10/10 (100%)
8. cypress spurge - 10/10 (100%)
9. Japanese knotweed - 10/10 (100%)
10. common St. Johnswort - 10/10 (100%)

Counties with the most invasive species reported

1. Strafford County - 285 species
2. Coos County - 264 species
3. Rockingham County - 247 species
4. Hillsborough County - 243 species
5. Cheshire County - 241 species
6. Grafton County - 224 species
7. Carroll County - 215 species
8. Merrimack County - 172 species
9. Sullivan County - 171 species
10. Belknap County - 151 species

Counties with the least invasive species reported

1. Belknap County - 151 species
2. Sullivan County - 171 species
3. Merrimack County - 172 species
4. Carroll County - 215 species
5. Grafton County - 224 species
6. Cheshire County - 241 species
7. Hillsborough County - 243 species
8. Rockingham County - 247 species
9. Coos County - 264 species
10. Strafford County - 285 species