When considering the rarity of a species, it is important to consider the status of a species both in New Hampshire and across its total range. Some species, such as the wildflower Jesup's milk-vetch (Astragalus robbinsii var. jesupii), are critically imperiled both globally and in New Hampshire. Jesup's milk-vetch has three known populations on the planet, all on a 16-mile stretch of the Connecticut River. Other species, such as small yellow lady's-slipper (Cypripedium parviflorum), are very rare in New Hampshire but quite common in other parts of their range.
NH Heritage considers the rarity of a natural community or a species both within New Hampshire and across its total range. We identify the degree of rarity within New Hampshire with a "State Rank" and throughout its range with a "Global Rank." Ranks are on a scale of 1 to 5, with a 1 indicating critical imperilment, a 3 indicating that the species or natural community is uncommon, and a 5 indicating that the species or natural community is common and demonstrably secure (see Explanation of Global and State Rank Codes below). Species and natural communities considered to be "globally rare" or "state rare" are those designated G1-G3 or S1-S3, respectively. Some species are rare both globally and in New Hampshire (e.g., G2 S1), while others are common elsewhere but rare in New Hampshire (e.g., G5 S1). Many natural communities have not been assigned global ranks at this time, pending a comprehensive review of their status and distribution range-wide.
In addition to considering the rarity of a natural community or species as a whole, NH Heritage ranks the quality of individual natural community occurrences and rare species populations. These ranks are valuable for setting conservation priorities and help us distinguish between, for example, a rare plant population with two stems versus one with 1,000 stems, or a population in an extensive forest versus one between two buildings.
We refer to a plant species as "globally rare" if it has fewer than 20 populations anywhere in the world, or if it has more populations but few reproducing individuals. "State rare" species are those that may be common elsewhere, but have few populations or total individuals in New Hampshire.
Most of New Hampshire's rare plants are listed as "threatened" or "endangered" under the NH Native Plant Protection Act of 1987 Four of these species are also listed under the federal Endangered Species Act of 1973 (42 USCA §§ 4321-4370c). Listing represents a political recognition of rarity, so some species that are biologically rare (and therefore included in the list) may not be listed as "threatened" or "endangered." Under the NH Native Plant Protection Act, "endangered" species are those in danger of being extirpated from the state, while "threatened" species face the possibility of becoming "endangered."
In addition to the state and global scales, NH Heritage contributed to the development of Flora Conservanda, a regional list of rare plants recently developed for New England (Brumback and Mehrhoff 1996). Flora Conservanda is based on a review by scientists (including state Natural Heritage botanists) of current information on rare plant populations from Natural Heritage databases in the six New England states. Plants were assigned to five divisions indicating the degree of rarity, current understanding of taxonomy and nomenclature, and their status in the wild.
The rankings for wildlife are based more on the degree of imperilment than on the number of occurrences in the state, although abundance certainly plays a role in assessing a species' long-term viability in New Hampshire. Some species, such as the fish crow (Corvus ossifragus) have only a few occurrences in New Hampshire but, since they are expanding northward into the state, they are not considered imperiled. Blanding's turtles (Emydoidea blandingii), on the other hand, appear to be distributed fairly broadly across the state, but populations are extremely small and vulnerable to habitat loss, so they are considered at risk.
A portion of New Hampshire's rare animals are listed as "threatened" or "endangered" under the NH Endangered Species Conservation Act of 1979 (NH RSA 212-A). Five of these species are also listed under the federal Endangered Species Act of 1973 (42 USCA §§ 4321-4370c). As with plants, listing represents a political recognition of rarity, so some species that are biologically rare (and therefore included in the list) may not be listed as "threatened" or "endangered." Under the NH Endangered Species Conservation Act, "endangered" species are those in danger of being extirpated from the state, while "threatened" species face the possibility of becoming "endangered."
Rare wildlife in New Hampshire are under the jurisdiction of the Nongame & Endangered Wildlife Program in the NH Fish & Game Department.
Quality ranks are based on the size, condition, and landscape context of a natural community occurrence or rare species population. These terms collectively refer to the integrity of natural processes or the degree of human disturbances that may sustain or threaten long-term survival. There are four quality ranks.
- Excellent Occurrence: An A-ranked natural community is a large example nearly undisturbed by humans or which has nearly recovered from early human disturbance and will continue to remain viable if protected. An A-ranked rare species occurrence is large in both area and number of individuals, is stable, exhibits good reproduction, exists in a natural habitat, and is not subject to unmanageable threats.
- Good Occurrence: A B-ranked community is still recovering from early disturbance or recent light disturbance by humans and/or is too small in size to be an A-ranked occurrence. A B-ranked population of a rare species occurrence is stable or expanding, grows in a minimally human-disturbed habitat, and is of moderate size and number.
- Fair Occurrence: A C-ranked natural community is in an early stage of recovery from disturbance by humans and/or is a small sized representative of the particular type of community. A C-ranked population of a rare species is in a clearly human-disturbed habitat and/or small in size and possibly declining.
- Poor Occurrence: A D-ranked natural community is severely disturbed by humans, its structure and composition are greatly altered, and recovery is unlikely. A D-ranked occurrence of a rare species is very small, has a high likelihood of dying out or being destroyed, and/or exists in a highly human-disturbed and vulnerable habitat.
For example, consider a population of a rare orchid growing in a bog that has a highway running along one border. The population may be large and apparently healthy (large size and intact condition), but the long-term threats posed by disturbance at the bog's edge – its low-quality landscape context (pollution from cars and roads, road-fill, garbage, altered hydrology, reduced seed dispersal, etc.) – may reduce the population's long-term viability. Such a population of orchids would receive a lower rank than a population of equal size and condition in a bog completely surrounded by a forest (i.e., with a higher quality landscape context).
There are some exceptions to the rank standards. The Ossipee Pine Barrens (in Freedom, Madison, Ossipee, and Tamworth), for example, contains the globally rare pitch pine/scrub oak barrens natural community and habitat for a variety of rare species. This system is naturally dynamic, requiring periodic disturbances (historically wildfires) to maintain its distinctive characteristics. Evidence indicates that human-caused fires and logging have profoundly influenced the current structure of the Ossipee Pine Barrens. As such, the system cannot be considered to be nearly undisturbed by humans. However, the pitch pine/scrub oak barrens has been assigned a very high quality rank because most of the historical human activities were compatible with the underlying ecological processes.
Steeply-sloped hemlock forest in Pawtuckaway State Park (photo by Ben Kimball)