American marten (Martes americana), also known as pine marten or the American sable, belong to the weasel family and are closely related to fisher and mink. Marten, like other mustelids (weasels), are inquisitive animals, spending most of their time on the forest floor feeding on small mammals such as red backed voles and even snowshoe hare. Other common food sources include berries, nuts and carrion.
Marten require large areas of relatively intact forest and are sensitive to forest fragmentation, yet can adapt to a wide range of forest types within their territories. They are considered an “umbrella” species—one that requires areas large enough to maintain viable populations of other wide-ranging (and not-so-wide-ranging) species. Marten are often used to help evaluate landscape effects of forest harvesting, and can aid in long-term forest planning. They are listed as a Species of Greatest Conservation Need in one or more states in BCR 14.
Marten have traditionally been associated with mature coniferous forests. Yet over the past 20 years, research has documented that marten occupy a variety of forest types in the Northeast. Regional variations likely exist because marten select structure rather than forest type. Marten prefer wetter or mesic forest as indicated by their use of riparian zones and common avoidance of dry or xeric forests. Preferred structure such as dead woody material (DWM), snags and cavity trees are more likely to be found in mesic forests.
In Maine, for example, forest structure (used for den and resting sites and subnivean access) required by marten is fulfilled by a variety of forest types, and deciduous trees can enhance this type of structure. Marten in an industrial forest selected deciduous stands disproportionately to that available on the landscape, as these stands had high stem-densities with abundant leaf litter, and prey-abundance was higher in deciduous and mixed stands. Marten use of habitat in second growth and mixed stands that had been partially harvested is often less than in stands with greater basal areas and more complex structure suggesting that marten use may be more associated with structure that increase prey densities rather than forest type specifically.
Snow depth and frequency affects marten habitat use. Marten with their smaller body size are specifically adapted as subnivean hunters and will use pockets created by DWM to access areas beneath the snow. Although soft, deep snow can be energetically costly for both marten and fisher, snow cover can also act as a thermal insulator by creating subnivean air pockets that produce midwinter temperatures warmer than the above-snow conditions. Because of specific adaptations as subnivean hunters, marten densities may be higher than fisher in areas with greater amounts of soft snow occurring more frequently. Marten adaptations also pertain on top of the snow. Due to their smaller body size, and disproportionately large feet to disperse their weight, marten can walk on top of snow more readily than fisher. For these reasons, it is suspected that prolonged periods of deep snow would be more stressful to fishers than martens.
Habitat management for marten is separated into two scales—the landscape and the stand scale.
Marten prefer landscapes that are less than 25 percent in non-forest cover and less than 30 to 40 percent of the forested landscape in early successional or young forest stages.
At the stand-scale, marten prefer:
- 30 to 50 percent canopy closure
- 60 to 80 square feet per acre of basal area
- Trees greater than 30 feet tall and greater than 3 inches DBH
- Snags greater than 18 inches DBH
- An abundance of down woody material.
- Maintain an average of seven marten habitat units (and no less than two) per 26,000 acres. A marten habitat unit:
- Is an area greater than 1,250 acres and preferably over 2,000 acres to account for years with lower food abundance.
- Has 75 percent of the stands greater than 40 feet tall with a basal area greater than 80 square feet per acre.
- Has greater than 30 percent winter canopy closure.
- Includes at least one large, intact patch of 700 to 1,000 acres that meets the height and density requirements above.
- Maintain a basal area greater than 100 square feet per acre in at least ½ of the suitable stands.
- Retain 20 percent of the forest in a mature state at all times, as possible
- Maintain 8 to10 square feet per acre of dead trees, plus logs, root mounds, and other structural features as denning sites and cover for small mammals
- Use even-aged or uneven-aged management, while meeting basal area, height, and snag and deadwood goals.
- Regenerate using a shelterwood-with-reserves system in conifer and mixed stands to promote softwood regeneration and prey, especially snowshoe hare, while maintaining canopy cover.
- Retain large conifers when possible to provide extra winter canopy closure.
- Maintain slash to promote small mammal abundance.
- Promote soft mast production.
- In deciduous stands, promote and retain DWM, cavities and snags.
- Maintain habitat patch connectivity by managing riparian buffers.
Bryan, R. R. 2007. Focus Species Forestry: A Guide to Integrating Timber and Diversity Management in Maine. Maine Audubon. 98pp.
Kelly, J.R. 2005. Recent distribution and population characteristics of American marten in New Hampshire and potential limiting factors affecting their occurrence. M.S. Thesis, University of Massachusetts, Amherst, Massachusetts, USA.
Siren, A. 2011. Population Ecology of American marten in New Hampshire: Impact of Wind Farm Development in High Elevation Spruce-Fir Habitat Research Proposal. University of New Hampshire. 56 pp.