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Rock Outcrops, Cliffs, and Talus

This habitat is made up of a suite of communities on exposed bedrock or talus with open to moderately-closed tree canopies and sparse to patchy groundcover.

This habitat has been identified in the Massachusetts State Wildlife Action Plan because it supports a variety of plants and wildlife.

Rock Outcrops, Cliffs and Talus
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Habitat description

Rock outcrop, cliff and talus habitat occurs on either exposed bedrock or talus (rocky debris associated with steep slopes) and features open to moderately closed tree canopies and sparse to patchy groundcover. In general, outcrop communities occur on exposed bedrock on summits and shoulders, cliff communities occur on vertical bedrock exposures, and talus communities occur on exposed boulder fields and scree. Vegetation structure and composition often depends upon slope, bedrock chemistry, orientation and hydrology.

Characteristic natural communities

This habitat type consists of several distinct natural communities that are separated by setting (outcrop, cliff, or talus) and bedrock/soil acidity. These communities often intergrade. Learn more about the natural communities of rock outcrops, cliffs and talus:  

Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled)

Characteristic plants and animals

Circumneutral and calcareous rock cliff communities support several highly specialized regionally rare plants, especially ferns such as fragile rock-brake. Larger occurrences of rock cliff communities are important nesting habitat for peregrine falcons and common ravens. Calcareous summit/outcrop communities support an important suite of rare plants. Acidic summit/outcrop communities, especially those with robust occurrences of lowbush blueberry, support several rare moths such as the orange sallow. Open talus/coarse boulder communities based on circumneutral substrate are important habitat for additional rare plants such as climbing fumitory and purple clematis, and all open talus/coarse boulder communities provide important denning areas for mammals and birds (especially vultures), and in some situations, critical hibernacula for snakes and bats. 

Associated habitats

Rock outcrop, cliff and talus habitats typically have small footprints, fitting into a landscape matrix of surrounding habitats such as northern hardwood and conifer forests or oak forests and woodlands. 

Ecological processes

The vertical nature of rock cliff communities limits the build-up of soil and results in these communities remaining relatively stable. Occasionally, in situations where soil does come established on shelves and in large crevices, sloughing of this material will eventually occur, re-exposing the bare rocky substrate. The harsh environment of summit/outcrop communities limits the rate of succession to generalist vegetation. However, these communities are still disturbance dependent, and in the absence of disturbance may eventually be replaced by generalist species. Periodic fire from lightning strikes and other sources helps to maintain these communities. The open talus/coarse boulder community is generally stable, and micro-disturbances such as tree tip-ups and grazing pressure on woody vegetation from porcupines are important processes that create new sun patches and exposed soil enabling the continued presence of specialized plants. 

Threats

Threats include invasive species (especially open talus/coarse boulder), and human disturbance (e.g., rock climbing, inappropriate trail siting).

Natural systems modification including insufficient natural disturbance can threaten this habitat. For example, fire suppression can lead to forest succession on summits and outcrops.

Climate change may not impact rock cliff communities much, since harsh, exposed conditions are the drivers of these communities. Summit/outcrop communities are also expected to fare well; however, calcareous variants may be more vulnerable to drought since they are slightly more moisture-dependent than the others. The response of the open talus/coarse boulder community to climate change scenarios are difficult to predict. In general, these are stable communities that appear to tolerate a wide range of precipitation and temperature conditions. However, these communities are vulnerable to invasive species, and expanded tree pest activity could impact community composition and structure (e.g., emerald ash borer).

Restoration & management recommendations

Despite a generally small footprint, this habitat is important for statewide and regional biodiversity conservation. These are also relatively stable natural communities, so management commitments of time and resources will generally be low.

  • Rock cliff communities: Generally, require little-to-no management. Smaller occurrences may become shaded by surrounding trees, and if this conflicts with rare plant occurrences, thinning may be considered. Larger occurrences may attract rock-climbers, which will require decisions about whether to allow this activity, and if so, the development of a thoughtful plan to enable continued recreation while minimizing ecological impacts should be undertaken.
  • Summit/outcrop communities: Succession to more generalist vegetation is the primary threat potentially requiring management action. Removing pioneering white pine at degraded sites can be an important undertaking. Sites with many larger white pine trees will require mechanical harvesting, and tree removal is recommended to reduce slash and the addition of organic material to soil and rock surfaces. Care should be taken to protect specialized/rare plants at calcareous and circumneutral sites, and established galleries of low bush blueberry should be protected at acidic sites. Cutting and felling in place may be adequate at sites with smaller pioneering white pine specimens, and girdling may be a solution at sites with only a few large white pines in the community (do not girdle near trails for safety reasons). More mesic calcareous sites can have the potential to develop serious invasive plant issues, and even circumneutral and acidic sites can be impacted by species such as spotted knapweed and swallowwort. As always, an early detection/rapid response approach to new invasive species occurrences in these situations is desirable. Long-term, the introduction of a prescribed fire regime to these communities may help to keep them functioning at a higher level of integrity. Due to their inherent harshness, return rates for prescribed fire in these communities can be quite prolonged (>10-15 years, depending on site conditions). As a final note, many outcrop communities have the potential to be impressive viewscapes (and many historically were), and this provides good opportunities to manage for both recreational and ecological values.
  • Open talus/coarse boulder community: Invasive species are the primary threat to these communities, especially Asiatic bittersweet. Early detection/rapid response to new infestations is the ideal invasives management approach whenever possible, but careful treatment of established occurrences will often be necessary. Stump treatment on larger vines may be needed when the leaves occur primarily in the canopy, but foliar alone can be effective when there is no canopy and vines are lying on the talus. Either way, established occurrences of bittersweet will often take several years to control due to root vigor and the seedbank. 

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