Hemlock - spruce - northern hardwood forest (S3S4)
Hemlock - spruce - northern hardwood forest is generally found on valley bottoms and lower elevation till landscapes in the northern part of the state (below 2,000 ft. elevation). It is primarily a conifer forest, characterized by a canopy of Tsuga canadensis (hemlock) and Picea rubens (red spruce), with a variable component of northern hardwoods including Acer saccharum (sugar maple), Betula alleghaniensis (yellow birch), and Fagus grandifolia (American beech). It is found at moderate elevations between spruce - fir and transition hardwood - conifer forests, ranging from less than 1,000 ft. up to 2,000 ft. It also occurs on river and kame terrace sites where former and current stream channels cut through terraces of different elevations, moisture levels, and sediment textures.
Soils are typically mesic, moderately well to well drained, and generally more nutrient poor than northern hardwoods. They range from wet to dry compact tills or sandy sediments and outwash. This community less frequently occurs on rocky outcrop substrates. Corresponding soil series include Adams, Colton, Au Gres, Salmon, Nicholville, Pillsbury, and Cabot.
Characteristic vegetation: Hemlock (Tsuga canadensis) and red spruce (Picea rubens) are the dominant trees, with occasional balsam fir (Abies balsamea) and white pine (Pinus strobus) in some examples. Sugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), and American beech (Fagus grandifolia) are sometimes present as well. The understory is similar to other
Variants: Four variants are described:
1. Typic variant
Found primarily on somewhat to very compact rocky till soils, and occasionally on river and kame terrace flats. Beech is occasional, though usually not prominent. Good examples occur at the Bartlett Experimental Forest in Bartlett and along Dry Brook in Waterville Valley.
2. Ravine/terrace slope variant
Found in moist ravines and on steep slope faces of river and kame terraces, particularly in the White Mountains. Hemlock and red spruce are the primary canopy and understory dominants. Yellow birch is also usually present. Balsam fir, sugar maple, and beech are sparse or absent. Good examples occur along Snyder Brook on the north slope of the Presidential Range, near Devil's Hopyard in Stark, and along McDonnough Brook in Chatham.
3. Conifer terrace flat variant
Dominant trees may be red spruce, hemlock, and balsam fir. Other native conifers may be present in lesser abundance. Good examples occur along the Swift River in Albany and the Big River in Barnstead.
4. Conifer - hardwood terrace flat variant
Dominated by a mix of conifers, sugar maple, red maple, and yellow, paper, and gray birches, with a common acidic understory flora. A good example occurs along the Peabody River in Gorham.
Hemlock - spruce - northern hardwood forest often occurs as part of a larger northern hardwood - conifer forest system.
Hemlock - spruce - northern hardwood forest (ravine / terrace slope variant)
on the northern slope of the Presidential Range (photo by Ben Kimball)
Hemlock - spuce - northern hardwood forest along Snyder Brook (photo by Ben Kimball)
Hemlock - spuce - northern hardwood forest along the Rattle River (photo by Ben Kimball)