Common (Translated Scientific) Name: Thuja occidentalis - Pinus strobus - Tsuga canadensis / Bristleleaf Sedge Slope Woodland

Colloquial Name: Central Appalachian Northern White-cedar Slope Forest

Hierarchy Level:  Association

Type Concept: This is essentially a mixed coniferous-deciduous forest of the Southern and Central Appalachians, with each component contributing approximately 50% of the canopy cover. Thuja occidentalis and Pinus strobus are codominant in these samples, with Tsuga canadensis a less abundant associate. A variety of hardwoods co-occur, the most constant and abundant of which are Liriodendron tulipifera, Quercus alba, and Quercus rubra. Habitats are on gentle to steep west-northwest-facing slopes at relatively low elevation. Sites include colluvial slopes situated in stream and river valleys and adjacent residual landforms. Bedrock parent materials include limestones of Devonian and Ordovician ages and interbedded limestone and sandstone of Silurian age. Soils have a neutral pH and high levels of calcium. The soil moisture regime tends toward the submesic class. This community type is extremely rare in Virginia, where it is known only from several plot-sampled stands and two putative locations in Montgomery and Russell counties, all in the Ridge and Valley province. Two plots from West Virginia were attributed to this association in 2020 and at least two other WV stands represent occurrences of this association. Patches of this vegetation are very small (0.1-1.0 ha), and additional occurrences are likely in suitable habitats. Young reproduction of all three conifers (Thuja occidentalis, Pinus strobus, and Tsuga canadensis) is present in the understory layers; in Viginia, Sassafras albidum is also a constant understory tree, and Amelanchier arborea codominates in one plot. Shrubs include Hamamelis virginiana, Ostrya virginiana, Dirca palustris, Viburnum acerifolium, and Paxistima canbyi. Tree height is variable from occurrence to occurrence. Herbaceous growth is sparse (mean stratum cover = 24%) and patchy. Many herbaceous species and woody seedlings occur at low cover. The most important herbaceous species include Carex eburnea, Eurybia divaricata, Brachyelytrum erectum, Chamaelirium luteum, Collinsonia canadensis, Dioscorea quaternata, Hepatica nobilis var. obtusa, Piptatherum racemosum, Solidago arguta, Solidago curtisii, and Uvularia perfoliata.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This community is extremely rare in Virginia, where it is known only from three plot-sampled stands and two putative locations in Montgomery and Russell counties, all in the Ridge and Valley province. Patches of this vegetation are very small (0.1-1.0 ha), and additional occurrences are likely in suitable western Virginia habitats. The type may also occur in adjacent states. Similar mixed forests of Thuja occidentalis with Tsuga canadensis and/or Pinus strobus were described qualitatively by Walker (1987) from the Eastern Highland Rim, Ridge and Valley, and low Blue Ridge provinces of Tennessee. This type is based primarily on three plot samples from Giles and Rockbridge counties, Virginia. In the Ridge and Valley of Virginia, Thuja occidentalis communities occur in two situations; on rocky bluffs with admixtures of hardwood species (classified elsewhere) and on mesic slopes with Tsuga canadensis and Pinus strobus (Fleming 1999) (placed in this association). Southern Thuja stands are more genetically diverse than northern populations (Walker 1987). This association is now recognized as distinct from open-canopy Thuja communities of the Central Appalachians because of excellent documentation provided by Fleming (1999). Additional assessment of Thuja stands in adjacent areas will be needed to understand their relationship to documented stands that are the basis for this community type.

~Thuja occidentalis - Pinus strobus - Tsuga canadensis / Carex eburnea Cliff Woodland (CEGL008426)$$ is readily distinguished from all other calcareous forests in Virginia by its strong coniferous component, particularly Thuja occidentalis. It is distinguished from ~Thuja occidentalis / Carex eburnea - Pellaea atropurpurea Cliff Woodland (CEGL002596)$$ by its occurrence on relatively mesic slopes with few rock outcrops (vs. shrubland or sparse woodland physiognomy and occurrence on exposed, xeric cliffs and outcrops). Despite having sparse herbaceous cover, this community type has a mean species richness (n=60) comparable to other units in the Dry and Dry-Mesic Calcareous Forests. Both sampled plots contain interesting mixtures of calcium-demanding plants and plants more characteristically associated with acidic habitats. It is possible that bedrock melanges and abundant needle litter from the three dominant conifers contribute to microtopographic variation in the soil environments of these areas. Noteworthy calciphiles include Berberis canadensis, Cystopteris bulbifera, Galium boreale, Hepatica nobilis var. acuta, Veratrum hybridum, Paxistima canbyi, Piptatherum racemosum, Polygala senega, Quercus muehlenbergii, Thuja occidentalis, and Viola walteri; species with stronger affiliation to acidic soils include Gaultheria procumbens, Hexastylis virginica, Oxydendrum arboreum, Polygala paucifolia, Quercus coccinea, Rhododendron maximum, and Spiraea corymbosa. This community type needs additional inventory, and its classification must be considered provisional pending additional plot sampling and analysis. The two tentatively assigned stands in Montgomery and Russell counties have somewhat different compositions than the plots documented here. The Montgomery County occurrence, dominated by Thuja, Pinus strobus, Quercus muehlenbergii, Hamamelis virginiana, and Cornus florida, occupies a somewhat drier dolomitic habitat and approaches woodland physiognomy. The Russell County stand is a closed-canopy, mesic Thuja forest with scattered Tsuga canadensis. Similar mixed forests of Thuja occidentalis with Tsuga canadensis and / or Pinus strobus were described qualitatively by Walker (1987) from the Eastern Highland Rim, Ridge and Valley, and low Blue Ridge provinces of Tennessee. West Virginia stands are closed canopy forests codominated by Thuja, Tsuga, and Pinus strobus, associated with hardwood species.

Similar NVC Types: No Data Available

note: No Data Available