Natural Community Systems -- Photo Guide

Hemlock - hardwood - pine forest system

Hemlock - hardwood - pine forest system in Hollis (photo by Ben Kimball for the NH Natural Heritage Bureau)
Hemlock - hardwood - pine forest system in Hollis (photo by Ben Kimball)

 

DescriptionThis is a transitional forest region or “tension zone” in New Hampshire that is positioned latitudinally and elevationally between northern hardwood - conifer forests to the north and higher elevations (mostly >1,400 ft.) and oak - pine (Appalachian or central hardwood) forests to the south and lower elevations (mostly <900 ft.).  This transitional forest lacks most boreal species and central hardwood species that characterize these other forests, but has many Alleghanian species such as Pinus strobus (white pine) and Tsuga canadensis (hemlock).  Many of the other species of this system are common throughout the eastern United States.  Hemlock - hardwood - pine forests are found throughout the state from the White Mountains south below about 1,500 feet.  Dry-mesic to mesic glacial till soils are most abundant, but this system also occupies river terraces, sand plains, and stabilized talus areas covered by a forest canopy.  It includes dry, sandy soils with red oak and white pine that have not been burned on an historically frequent enough interval to support a pitch pine sand plain system.  These areas are likely to be successional to hemlock and/or beech over the long term without the return of fire.

The main matrix forest community that defines this system is hemlock - beech - oak - pine forest. Hemlock and beech are the primary late-successional trees in this community, with maximum ages of about 500 and 300 years, respectively.  Quercus rubra (red oak) and Pinus strobus (white pine) are also typically abundant, in contrast to their absence or low abundance in northern hardwood – conifer forest systems.  Most of the old-field white pine stands in central NH are successional examples of this system.  Acer saccharum (sugar maple) and Betula alleghaniensis (yellow birch) are occasional but of less importance than in northern hardwood – conifer forests.  They are most frequent in mesic areas such as concavities and along drainages where Fraxinus americana (white ash) is frequent, or locally abundant in patches of semi-rich sugar maple forests.  Picea rubens (red spruce) and Abies balsamea (balsam fir) are generally sparse or absent, but are occasional on the lower slopes of some mountains south of the White Mountains (i.e., Ossipee Mountains, Mt. Monadnock).  Central hardwood/Appalachian species are essentially absent, including hickories (Carya spp.), oaks (Quercus spp.) other than red oak, dogwoods, and southern herbs (see oak – pine forest description).  These more southern species do appear in occasional outposts as the more definitive oak – pine forests to the south are approached.  

Differences in soil type or landscape position within this system explains much of the variation in component community composition.  Hemlock forests often occur in ravines or extremely rocky sites; beech forests occur on coarse washed till soils; semi-rich mesic sugar maple forests occur in colluvial landscape positions or associated with bedrock or till with greater base-cation contributions to the soil; hemlock - beech - northern hardwood forest occurs in more mesic settings or at higher elevations near the transition to northern hardwood - conifer forests; dry red oak - white pine forests occur on sandy or rocky soils that may perpetuate oak and pine dominance locally with repeated disturbance.



Diagnostic natural communities:

      • Hemlock - beech - oak - pine forest (S5) – matrix forest type

      • Hemlock forest (S4)

      • Beech forest (S4)

      • Hemlock - white pine forest (S4)

      • Dry red oak - white pine forest (S3S4)

      • Semi-rich mesic sugar maple forest (S3S4)

Peripheral or occasional natural communities:

      • Hemlock - oak - northern hardwood forest (S4)


Landscape settings: high to low hills, mountain valleys, lowland flats

Soils: loose and firm glacial till, glacio-fluvial soils (e.g., river and kame terraces, outwash), occasionally on stabilized talus

Spatial pattern: matrix (<10–1,000+ acres); irregular and linear zonation of component communities

Physiognomy: forest

Distribution:  below 1,500 ft. elevation in central and southern NH, extending into low elevations of White Mountains.


Characteristic species:
Characteristic tree species of the hemlock – hardwood – pine forest system:
      
Tsuga canadensis (hemlock)
      Fagus grandifolia (American beech)
      Quercus rubra (red oak) 
      Pinus strobus (white pine)
      Acer rubrum (red maple)
      Betula papyrifera (paper birch)
      Fraxinus americana (white ash)
      Betula lenta (black birch)
      Betula populifolia (gray birch)
      Prunus serotina (black cherry)

Shrubs mostly absent from northern hardwood - conifer forests:
      
Hamamelis virginiana (witch hazel)
      Viburnum acerifolium (maple-leaved viburnum)
      Gaultheria procumbens (wintergreen)

Herbs common to communities of both systems:
      Dryopteris intermedia (intermediate wood fern)
      Aralia nudicaulis (wild sarsaparilla)
      Trientalis borealis (starflower)
      Uvularia sessilifolia (sessile-leaved bellwort)
      Epifagus virginiana (beechdrops)

      Maianthemum canadense (Canada mayflower)
      Mitchella repens (partridgeberry)
      Monotropa uniflora (Indian pipes)

Understory species mostly absent in hemlock – hardwood – pine forests:
   
Herbs 
      Clintonia borealis (bluebead lily)
      Huperzia lucidula (shining clubmoss)
      Dryopteris campyloptera (mountain wood fern)
      Oxalis montana (northern wood sorrel)
      Aster acuminatus (whorled aster)
      Streptopus lanceolatus (rose twisted stalk)

   
Shrubs & dwarf shrubs
      Acer spicatum (mountain maple)
      Viburnum lantanoides (hobblebush)
      Cornus canadensis (bunchberry)
      Coptis trifolia (goldthread)
      Lonicera canadensis (Canadian honeysuckle)
      Polystichum braunii (Braun’s holly fern)


Associated natural community systems Hemlock - hardwood - pine forest systems transition upslope and northward to northern hardwood - conifer forest systems.  To the south and sometimes lower elevations or onto rocky, dry or frequent-fire landscapes this system transitions to oak - pine forest, Appalachian oak rocky ridge, or pitch pine sand plain systems.

Plants that tend to be more prominent in hemlock - hardwood - pine forests than in northern hardwood - conifer forests include Hamamelis virginiana (witch hazel), Betula lenta (black birch), Prunus serotina (black cherry), Ostrya virginiana (ironwood), Viburnum acerifolium (maple-leaved viburnum), Gaultheria procumbens (wintergreen), and Gaylussacia baccata (black huckleberry).


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