CASE STUDY 1 - Northern Balds
What is a Northern bald?
Northern bald is a low shrub with scattered flagged trees and trees distorted into a windblown tree growth form by branch breakage due to heavy snow, thick ice, and extreme winds. Northern balds are restricted to large escarpments of volcanic bedrock ridges and are characterized by sparse vegetation, areas of exposed bedrock, and thin, slightly acidic soils.
What kind of soil?
The soils are thin, slightly acid sandy soil over bedrock. Areas of exposed bedrock that lack soil development are common. Thin organic sediments accumulate in joints, cracks, and depressions and are important substrates for vegetation.
The soils are thin, slightly acid sandy soil over bedrock. Areas of exposed bedrock that lack soil development are common. Thin organic sediments accumulate in joints, cracks, and depressions and are important substrates for vegetation.
Natural processes
Extreme winds and ice storms characterize the northern bald community, causing trees in the scattered overstory to become flagged, a condition in which freezing winds kill branches on the windward side of the tree and the upper branches grow mainly from the leeward side of the tree, like a flag blowing from a flagpole. In addition, the harsh conditions result in some trees developing a krummholz form, a stunted, twisted condition common to subarctic or subalpine tree lines. The high winds and lack of soil development result in severe plant desiccation, despite the year-round occurrence of fog off Lake Superior. Although the thin soils promote extremely droughty conditions, the absence of full-grown trees is induced chiefly by the exposed ridge-top position, which promotes winter desiccation, ice and snow abrasion, and breakage by high winds. The lack of soil development and droughty conditions are further maintained on these bedrock ridge tops by rapid runoff following snow melt and rain events. Lastly, portions of the bedrock escarpment regularly slough off, forming talus slopes along the base of cliffs and exposing fresh, bare rock substrates.
Extreme winds and ice storms characterize the northern bald community, causing trees in the scattered overstory to become flagged, a condition in which freezing winds kill branches on the windward side of the tree and the upper branches grow mainly from the leeward side of the tree, like a flag blowing from a flagpole. In addition, the harsh conditions result in some trees developing a krummholz form, a stunted, twisted condition common to subarctic or subalpine tree lines. The high winds and lack of soil development result in severe plant desiccation, despite the year-round occurrence of fog off Lake Superior. Although the thin soils promote extremely droughty conditions, the absence of full-grown trees is induced chiefly by the exposed ridge-top position, which promotes winter desiccation, ice and snow abrasion, and breakage by high winds. The lack of soil development and droughty conditions are further maintained on these bedrock ridge tops by rapid runoff following snow melt and rain events. Lastly, portions of the bedrock escarpment regularly slough off, forming talus slopes along the base of cliffs and exposing fresh, bare rock substrates.
Noteworthy vegetations
Vegetation is scattered with areas of exposed bedrock common.
Dominant tree species include:
Dominant shrubs include:
Fern diversity is high with the most common ferns, which include:
Common ground flora include:
Northern balds may contain several vegetation zones. The ridge top is typically open, with only herbs and shrubs, while at slightly lower elevations, where winds may be less severe, dwarfed trees occur. Many of the ferns and rare plants, such as small blue-eyed Mary (Collinsia parviflora, state threatened), are concentrated along the south edge of escarpments, where there is typically a cliff. Talus slopes form along the base of the cliff. One rare plant, redstem ceanothus (Ceanothus sanguineus, state threatened), grows almost exclusively on the talus.
Vegetation is scattered with areas of exposed bedrock common.
Dominant tree species include:
- white pine (Pinus strobus)
- red oak (Quercus rubra)
- big-toothed aspen (Populus grandidentata)
- Balsam fir (Abies balsamea)
- white spruce (Picea glauca)
- northern white-cedar (Thuja occidentalis)
Dominant shrubs include:
- bearberry (Arctostaphylos uva-ursi)
- common juniper (Juniperus communis)
- staghorn sumac (Rhus typhina)
- low sweet blueberry (Vaccinium angustifolium)
- choke cherry (Prunus virginiana)
- juniper (Juniperus horizontalis)
Fern diversity is high with the most common ferns, which include:
- maidenhair spleenwort (Asplenium trichomanes)
- rusty woodsia (Woodsia ilvensis)
- braun’s holly-fern (Polystichum braunii)
- northern holly-fern (P. lonchitis)
- male fern (Dryopteris filix-mas, state special concern).
Common ground flora include:
- wild strawberry (Fragaria virginiana)
- poverty grass (Danthonia spicata)
- western smartweed (Polygonum douglasii)
- prairie cinquefoil (Drymocallis arguta)
- three-toothed cinquefoil (Sibbaldiopsis tridentata)
- early saxifrage (Saxifraga virginiensis)
- ground cedar (Diphasiastrum tristachyum)
- sand violet (Viola adunca)
- sand club moss (Selaginella rupestris)
Northern balds may contain several vegetation zones. The ridge top is typically open, with only herbs and shrubs, while at slightly lower elevations, where winds may be less severe, dwarfed trees occur. Many of the ferns and rare plants, such as small blue-eyed Mary (Collinsia parviflora, state threatened), are concentrated along the south edge of escarpments, where there is typically a cliff. Talus slopes form along the base of the cliff. One rare plant, redstem ceanothus (Ceanothus sanguineus, state threatened), grows almost exclusively on the talus.
Noteworthy animals
The steep rock ridges associated with northern bald are important habitat for raptors.
Rare animals
Falco columbarius (merlin, state threatened)
Biodiversity Management Considerations
Because of the thin soils, which cause shallow rooting, and harsh conditions, the vegetation of northern balds can be extremely slow to recover or reestablish following excessive trampling. Trails through balds should be minimized or avoided. Roads and trails also provide routes for invasive plants to establish. Invasive plants that threaten the diversity and community structure of northern balds include spotted knapweed (Centaurea stoebe), ox-eye daisy (Leucanthemum vulgare), Canada bluegrass (Poa compressa), sheep sorrel (Rumex acetosella), and hawkweeds (Hieracium spp.). Monitoring and control efforts to detect and remove invasive species are critical to the long-term viability of northern balds. Maintaining a mature, unfragmented forested buffer around balds may help limit the local seed source for invasive species distributed by wind or birds. Use of the escarpments for rock climbing has the potential to degrade vegetation along the cliff edge. Snowmobiling through northern balds also threatens vegetation.