Forest Vegetation types - TH3

TH3 — Sugar maple – White ash / Christmas fern

Acer saccharum – Fraxinus americana / Polystichum acrostichoides

Lower Springfield, Antigonish County
Lower Springfield, Antigonish County

Concept: This late successional Vegetation Type (VT) has an overstory dominated by sugar maple and white ash with lesser amounts of other shade-tolerant hardwoods. TH3 primarily occurs as rich, seepage patches within larger TH1 and TH2 forests. Plant species richness is among the highest of any upland hardwood ecosystem in the province. Due to the long-lived and shade-tolerant nature of dominant overstory trees, this VT will develop old forest characteristics maintained by gap disturbance. Sugar maple – White ash / Christmas fern is one of several Acadian hardwood VTs found on zonal sites throughout Nova Scotia.

Vegetation: Sugar maple, white ash and yellow birch are the dominant overstory trees accompanied by lesser amounts of red maple, beech and red spruce. Scattered ironwood is typical in the lower canopy or high shrub layer. Although ironwood and sometimes white ash are not dominant in the canopy, their presence is used to distinguish this VT from other sugar maple/yellow birch VTs. The shrub layer is dominated by regenerating hardwood, balsam fir and striped maple, with less prominent amounts of alternate-leaved dogwood, hobblebush and beaked hazelnut. Herb coverage is diverse and may include several rich site indicators including Christmas fern, oak fern, lady fern, shining club-moss and northern beech fern. Spring ephemerals may include spring-beauty, Dutchman's-breeches and dog tooth violet. The bryophyte layer is poorly developed, with moss cover generally restricted to tree trunks, stones and downed woody material.

Environmental Setting: TH3 is mainly found on fresh-moist to moist, nutrient rich soils. These sites often occur in toe slope positions and mid-slope benches, but are sometimes also found on enriched upper slopes. This VT is typically associated with (and found embedded within) larger tracts of TH1 and TH2 matrix forest. TH3 is found throughout the province in the Cobequid Hills, North Mountain and Cape Breton Hills ecodistricts, and on some drumlin sites. It is very rare on Prince Edward Island but abundant and widespread in southern New Brunswick.

Successional Dynamics: TH3 is a late successional, uneven-aged climatic climax VT dominated by shade-tolerant hardwood. Excluding harvesting, stand-level disturbance events are rare, with gaps or small patches usually created by individual tree mortality, wind or ice damage. Although TH3 sites generally maintain themselves through gap replacement, this VT can develop from other early and mid-successional VTs including IH3 (Large-tooth aspen / Christmas fern – New York fern) and IH5 (Trembling aspen – White ash / Beaked hazelnut / Christmas fern).

Ecological Features: This hardwood seepage forest typically occurs in small patches (from less than 1 hectare up to 50 hectares), infrequently scattered as inclusions within broader hardwood matrix forest. Longevity of the overstory tree species increases the potential for old growth development. Vernal pools and moist surface depressions common in this seepage forest provides habitat for red-backed salamanders, yellow-spotted salamanders and wood frogs, while seeds of ash and maple trees may be eaten by evening grosbeaks. Plants that favour moist rich sites are common, including several rare species (e.g. lance-leaved and little grapeferns, foamflower and anise-root). These forests host a variety of spring ephemeral plants, like spring beauty, dog tooth violet and Dutchman's breeches which take advantage of early spring sunlight before tree leaf out. In southwest Nova Scotia this community is home to southern flying squirrels.

TH3 Characteristic Plants


Christmas fern
Christmas fern

Distinguishing Features:
In this rich hardwood forest found on middle to lower slope positions the herb layer is diverse and usually includes Christmas fern, northern beech fern, shining club-moss, lady fern and oak fern. White ash, ironwood and Christmas fern are diagnostic for this forest.

Site Characteristics

Slope Position: Middle4 Lower3 Upper2 Other1

Surface Stoniness:

(Non - Slightly)4 (Moderately)3  (Very - Excessively)3

Bedrock Outcrop: 

(Non-rocky)8 (Slightly - Moderately)2

Elevation Range: 

57 - 237m

Slope Gradient: 

Gentle5 Moderate2 Level1 Steep1 nd1


North2 East3 South3 West2


Moderate5 Mod. exposed3 Mod. sheltered1 Sheltered1


Moderately5 Strongly3 Slightly1 Other1


Moderately well5 Well3 Imperfect2


Soil Characteristics

Soil Type: 

ST83 ST2-L2 ST21 ST91 ST111 ST21 Other1

Parent Material:

Glacial till8 Colluvium1 Till/Bedrock1 nd1

Rooting Depth (cm):

(<30)1 (30-45)4 (>45)4 nd1

Duff Thickness (cm):

(0-5)4 (6-10)4 (11-40)1 nd1

TH3 Map