Classification of Vegetation Communities of Maryland: First Iteration

II. WOODLAND
II.A.4.N.b. Conical-crowned temperate or subpolar needle-leaved evergreen woodland
II.A.4.N.b.1. THUJA OCCIDENTALIS WOODLAND ALLIANCE
Northern White-cedar Woodland Alliance

Concept: This alliance contains woodlands (with variable canopy closure) of calcareous bedrock outcrops and limestone cliffs on which Thuja occidentalis is the dominant canopy tree, although associations can include admixtures of deciduous species. The growth form is generally single-stemmed, but trees may be quite stunted. Associated canopy species can include Pinus resinosa, Ostrya virginiana, Quercus rubra, Pinus strobus, Abies balsamea, Betula alleghaniensis, Betula papyrifera, Picea mariana, Picea glauca, Acer saccharum, Fraxinus americana, Tsuga canadensis, Celtis occidentalis, Ulmus rubra, Quercus alba, and Quercus muehlenbergii. Herbaceous species vary with geography but can include Zigadenus elegans ssp. glaucus, Carex eburnea, Cystopteris bulbifera, Pellaea atropurpurea, Pinguicula vulgaris, Primula laurentiana, Saxifraga oppositifolia, Waldsteinia fragarioides, Oligoneuron album (= Solidago ptarmicoides), and Carex pensylvanica, among others. This alliance occurs in Canada, the Great Lakes region, northern New England, New York, and discontinuously in Maryland, West Virginia, Virginia, Kentucky, and Tennessee. In the Southeast it is known mostly from the Ridge and Valley Province, but occurrences are known from the periphery of the Tennessee Blue Ridge.

Comments: This alliance occurs in Maryland, where it lacks Pinguicula, Saxifraga, and Waldsteinia but has Pellaea and Ostrya; it occurs in association with rich forests. It may occur in New York in the Champlain valley and may be in association with alvar communities. Above cliffs of Ohio communities, mixed stands grade into oak or oak-maple stands at short distances from the cliffs. In a comparison of two Thuja occidentalis forests, Kangas (1989) found that a southern glacial relict site in Ohio, which belongs in this alliance, had a stable population of Thuja occidentalis, which was not being replaced by the only subdominant, Ulmus americana.

Range: This alliance is found in Kentucky, Tennessee, Maryland, New Hampshire (?), New York, Pennsylvania, Vermont, Virginia, West Virginia, Michigan, Minnesota, Ohio, Minnesota, and Wisconsin (?), and in Canada, in Ontario.

States/Provinces: KY MD ME MI MN NB NH NY OH ON PA QC? TN VA VT WI WV

TNC Ecoregions: 44:C, 45:C, 46:C, 47:?, 48:C, 50:C, 51:C, 52:C, 59:C, 61:C, 63:C, 64:C

USFS Ecoregions: 212Cb:CCC, 212Ec:CCP, 212Ee:CCC, 212Ha:CCP, 212Hj:CCP, 212Hl:CCP, 212Ja:CP?, 212Jb:CP?, 212Jc:CP?, 212Jl:CPP, 212Jn:CPP, 212Jo:CPP, 212Jr:CPP, 221Al:C??, 221Ba:CPP, 221Db:C??, 222Ea:CCC, 222Eb:CCC, 222Ej:CCC, 222Fd:CCC, 222Ha:CCC, 222Hb:CCC, 222Hc:CCP, 222Ib:CCP, 222Ic:CCP, 222Ie:CCP, 222If:CCP, 222Lc:CCC, 231Ak:CCC, 231Al:CCP, 231Ap:CCP, M212Ac:CCC, M212Ad:CCP, M212Ae:CCC, M212Af:CCC, M212Ba:CCC, M212Ca:CCP, M212Cd:CCP, M212Da:CCP, M212Db:CC?, M212Dc:CCP, M221Aa:CCC, M221Ab:CCC, M221Ac:CCP, M221Bd:CCP, M221Be:CCC, M221Dd:CCC

Federal Lands: NPS (Acadia); USFS (Cherokee, George Washington)

Synonymy: Northern White-Cedar: 37 (Eyre 1980)

References: Braun 1928, Eyre 1980, Faber-Langendoen et al. 1996, Kangas 1989, Walker 1987

Authors: D.J. ALLARD, RW, East Identifier: A.544

Concept: This white-cedar cliff woodland type is found in the Appalachian and Allegheny Plateau region of the United States. The type extends to near the southern limit of Thuja occidentalis, in the southeastern Highland Rim of Kentucky and Tennessee, where it tends to increase its distinctiveness from more northern communities. Stands occur on north-facing bluffs or cliffs of dolomite or limestone, where dip slopes provide slight seepage and maintain humidity higher than the regional average, or provide a cooler-than-normal microclimate. In Ohio it occurs as pure isolated patches on steep calcareous cliffs. It is also found as mixed stands on the uplands above the cliffs. Stands are dominated by coniferous trees but can have a significant amount of deciduous species. The structure of this association can vary from a stunted, very open canopy of Thuja to a mixed conifer-deciduous woodland approaching a forest structure. Canopy species other than Thuja occidentalis vary with geography. The most abundant tree species are Thuja occidentalis, Acer saccharum, Tsuga canadensis, Juniperus virginiana, Quercus alba, Quercus muehlenbergii, and Quercus rubra. Other associates include Celtis occidentalis and Ulmus rubra in more northern stands. Shrub and small tree species include Cercis canadensis, Cornus florida, Hydrangea arborescens, Ostrya virginiana, and Rhus aromatica. Closed-canopy stands have very few vascular species in the lower strata, while stands with broken canopies contain scattered shrubs and a substantial number of herbaceous species. Composition of the herbaceous and shrub strata can also vary due to seepage influence. Composition is quite variable, but some of the most constant herbaceous plants include Asarum canadense, Carex eburnea, Cystopteris bulbifera, and Hepatica nobilis var. acuta (= Hepatica acutiloba). In Kentucky, sites are small (0.1-1 acre), with scattered Thuja occidentalis codominating with Acer saccharum, Fraxinus americana, Ostrya virginiana, and Philadelphus hirsutus. Other associated species include Juniperus virginiana var. virginiana, Cercis canadensis var. canadensis, Pachysandra procumbens, Hamamelis virginiana, Parthenocissus quinquefolia, Solidago flexicaulis, Solidago sphacelata, Symphyotrichum cordifolium (= Aster cordifolius), and Dioscorea quaternata.

Comments: This type is simply defined by the presence of white-cedar or mixed white-cedar - hardwoods, and either forest or woodland canopy; hence all four physiognomic categories fall under this one type. Small-scale occurrences are worth documenting. The relationship between this type and Thuja occidentalis / Carex eburnea Forest (CEGL006021) should be examined and clarified. Stands on lower slopes often grade into swamps, especially those dominated by Thuja occidentalis. There are also many similarities between this vegetation and that in the I.C.3.N.a Thuja occidentalis - Betula alleghaniensis Forest Alliance (A.417). In the Ridge and Valley of Virginia, Thuja occidentalis communities occur in two situations: on rocky bluffs with admixtures of hardwood species and on mesic slopes with Tsuga canadensis and Pinus strobus (G. Fleming pers. comm. 1999). Southern Thuja stands are more genetically diverse than northern populations (Walker 1987). One Tennessee site is a proposed State Natural Area, Window Cliffs. This association is peripheral in the Southern Blue Ridge of Tennessee.

Range: This white-cedar cliff woodland type is found in the Appalachian and Allegheny Plateau region of the United States.

States/Provinces: KY:S?, MD:S?, OH:S2, PA:S?, TN:S?, VA:S?, WV:S?

TNC Ecoregions: 44:C, 45:C, 50:C, 51:C, 52:C, 59:C

USFS Ecoregions: 222Ea:CCC, 222Eb:CCC, 222Ej:CCC, 222Fd:CCC, 222Ha:CCC, 222Hb:CCC, 222Hc:CCP, 231Ak:CCC, M221Aa:CCC, M221Ab:CCC, M221Bd:CC?, M221Be:CCC, M221Dd:CCC

Federal Lands: USFS (Cherokee, George Washington)

Synonymy: Arbor vitae forest (Braun 1928) =, Thuja occidentalis / Carex eburnea - Sedum glaucophyllum Shrubland (Fleming 1999), Thuja occidentalis / Carex eburnea - Sedum glaucophyllum Woodland (Fleming and Coulling 2001)

References: Anderson 1996, Braun 1928, Fleming 1999, Fleming and Coulling 2001, Fleming et al. 2001, Fleming pers. comm., Kangas 1989, Palmer-Ball et al. 1988, Walker 1987

Authors: J. Drake, mod. M. Pyne, mod. G. Fleming and P. Coulling, MCS Confidence: 2 Identifier: CEGL0025

- Maryland Vegetation Classification Subset Report II. Woodland

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