Semi-rich mesic sugar maple forest (S3S4)
Semi-rich mesic sugar maple forests are very similar to rich mesic forests, but species diversity and productivity tend to be lower, probably due to a combination of less moisture, organic matter, and/or soil nutrients. American beech (Fagus grandifolia) and yellow birch (Betula alleghaniensis) are frequent in semi-rich mesic forests. Fewer herb and shrub species indicative of rich conditions are found, and those restricted to very rich conditions are absent. Semi-rich site indicator species, besides those also found in rich mesic forests, include Jack-in-the-pulpit (Arisaema triphyllum), baneberries (Actaea spp.), and Christmas fern (Polystichum acrostichoides). Known examples in New Hampshire are all found below 2,600 feet in elevation.
Rich organic matter and sediments often accumulate on or below steep slopes such as those found on talus slopes, in ravines, in drainages, and below cliffs. The forests found in these locations are referred to as rich or semi-rich. Frequently shared tree canopy species in such forest types include sugar maple (Acer saccharum) and white ash (Fraxinus americana). Rich and semi-rich forests often intergrade with one another or are found as small patches within related community types such as northern hardwood forests, talus slope forests, seepage forests, and forest seeps. Rich forests are especially vulnerable to nutrient and species loss when they are disturbed. Some examples of semi-rich mesic sugar maple forests may actually be disturbed examples of former rich mesic forests. Both types are quite uncommon in New Hampshire, and undisturbed examples are rare. Together they harbor many of the state’s rare forest plant species. These natural communities may also be found where mineral-rich bedrock and ample moisture enrich the soil, regardless of the slope or topography. “Sugarbushes” are usually associated with either of these two communities.
Soils are loam or fine sandy loams with a more developed A horizon than that found in most northern hardwoods. Soils have higher nutrient availability, productivity, and base-saturation than acidic northern hardwoods, but less than rich mesic forests. Intermediate or calcium-rich bedrock types such as syenite or diorite can release calcium and other mineral nutrients upon weathering. Enriched soils can also develop on sites prone to colluviation, where organic matter and sediments accumulate in coves and narrow valleys, and at the bases of steep slopes.
Characteristic vegetation: These moderately or somewhat enriched forests are typically dominated by sugar maple and sometimes beech. White ash is occasional and abundant at some sites, but not present in all examples. Basswood (Tilia
Variants: Three variants are described:
1. Typic variant (as described above):
This variant is found on till soils at low to mid elevations (up to 1,600 ft. and locally higher). Herbaceous cover is generally sparse to moderate, or occasionally abundant. This variant is found in most subsections of the state. Good examples are at Langdon Brook North (
2. High-elevation/near-boreal variant:
This variant occurs at higher elevations (1,600-2,600 ft.) in the White Mountains and somewhat lower in the
3. Terrace flat variant:
This variant occurs on loamy river or stream terraces and is dominated by northern hardwoods (sometimes a few softwoods). It may occur in complex mosaics with other river terrace communities. Sugar maple and yellow birch are usually important canopy species, with variable mixes of other hardwoods, including white ash, red maple (Acer rubrum), black cherry (Prunus serotina), and birches (Betula spp.). Understory plants that appear to distinguish this variant from more infertile or drier terraces include beaked hazelnut (Corylus cornuta), alternate-leaved dogwood, Canadian honeysuckle (Lonicera canadensis), Jack-in-the-pulpit, sessile-leaved bellwort, zigzag goldenrod, wakerobin, oak fern (Gymnocarpium dryopteris), and inflated sedge. A potential rare species is pink wintergreen (Pyrola asarifolia). This variant is documented from valley bottom landscapes of the
Good examples of this community occur at Mountain Pond RNA (Chatham),
Semi-rich mesic sugar maple forests often occur as part of larger rich mesic forest systems and hemlock - hardwood - pine forest systems.
Old-growth semi-rich mesic sugar maple forest at Lafayette Brook (photo by Ben Kimball)
Semi-rich mesic sugar maple forest along the Swift River (photos by Ben Kimball)
Christmas fern, seen here at North Mountain in Pawtuckaway State Park, is a common
indicator species of semi-rich mesic sugar maple forest (photo by Ben Kimball) 
Baneberries, seen here at Middle Mountain in Pawtuckaway State Park, are common
indicator species of semi-rich mesic sugar maple forest (photo by Ben Kimball) 
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Two common herbaceous species of this community: 1. Jack-in-the-pulpit. 2. trout lily.
(photos by Ben Kimball) 
Zigzag goldenrod, seen here at Coleman State Park in Stewartstown, is a common
indicator species of semi-rich mesic sugar maple forest (photo by Ben Kimball)
Please see also our fact sheet for rich and semi-rich mesic forests in NH.