Common (Translated Scientific) Name: Temperate & Boreal Open Rock Vegetation Subclass

Colloquial Name: Temperate & Boreal Open Rock Vegetation

Hierarchy Level:  Subclass

Type Concept: Temperate & Boreal Open Rock Vegetation is found on rocky habitats (such as cliffs, talus, recent lava flows, or rock outcrops) in the Mediterranean, temperate and boreal regions around the globe. Stands typically contain a covering of saxicolous foliose and/or crustose lichens growing directly on rock surfaces and/or sparse covering of vascular plants growing in soil pockets. Vascular and nonvascular plant cover is >1%; vascular plant cover is typically <10%, with irregular horizontal spacing, and is typically exceeded by nonvascular cover, especially lichens, bryophytes, and/or algae. On stable rock surfaces (e.g., outcrops), vascular plant roots are prevented from penetrating most of the substrate, and their presence is largely determined by the rock fissures, where minimal soil development and more moisture occurs. On less stable rocky surfaces (e.g., talus), the presence of vascular plants is largely determined by a degree of permanence and depth to soil under the boulders. A sparse cover of vascular mesomorphic growth forms, including evergreen needle-leaved or cold-deciduous broad-leaved woody plants, may be present. Herbs are often seasonally green. Low-elevation temperate and boreal climates are various, often less determinative than presence of open rock surfaces. Substrates are typically very dry to moist, but occasionally wet and typically lack soil development of any kind. The climate is cool and warm-temperate, Mediterranean, and to boreal, and even subarctic, where frosts occur regularly (except in part of the Mediterranean region), snow is not permanent, and there are strong daily and seasonal temperature changes.

Diagnostic Characteristics: Rocky or rocklike substrates dominated by lithomorphic or lithophilic plant species, including lichens (especially foliose and crustose lichens), bryophytes, algae, and rupicolous vascular plants, often with a strong component of ferns and other pteridophytes. Vascular vegetation is typically <10% cover, and may include either evergreen needle-leaved or cold-deciduous broad-leaved trees or shrubs. Vegetation structure may be patchy across the rocky surfaces.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: There is little information that has been comprehensively evaluated across the globe, making it difficult to describe the type concept. We tentatively include cliff and slope sites with hardpacked sedimentary rocks and clays (badlands) within this class. More work is needed to clarify the distinctions between rock vegetation and other sparsely vegetated habitats where rocky substrates are dominant and lichen vegetation is absent, such as scree or volcanic cinders. For example, many rocky river and lake shoreline types may be placed in 2.B.4 ~Temperate to Polar Scrub & Herb Coastal Vegetation Formation (F005)$$ where vegetation is patchy but may exceed 10%.

Further review may suggest that this subclass can be improved by distinguishing the less "rocklike" vegetation (including vegetation on scree, badlands, pavement) from the true lithomorphic (solid rock) vegetation (C. Lea pers. comm. 2012). Scree and other loose rocky substrates (volcanic cinders), where the median particle size is >10 cm in diameter, typically have enough soil development to support a dominant layer of disturbance-adapted, facultative mesomorphic shrubs and/or herbs (e.g., in the United States, Ribes spp., Prunus virginiana, and other forest, woodland, or shrubland shrubs in the central Rockies), and true lithomorphs (saxicolous lichens) are quite sparse, if present at all. Although the surface may be "rocky," the driving ecological factor is the availability of soil in quantity under the relatively shallow rock armoring and the absence of large, stable substrates for true lithomorphs (saxicolous lichens) to establish. Cobbles along rivers and streams may also not typically support lithomorphic growth forms, and may best be treated as sometimes sparse flooded types within mesomorphic formations. Badlands (hard clays) and desert pavements also tend to support facultative vascular species, as opposed to lithomorphs or lithophiles, and could be considered for the xeromorphic class. Given this narrower definition of lithomorphic, a requirement for <10% vascular cover and nonvascular cover greater than vascular cover would be more appropriate for distinguishing the "true" lithomorphic types, and separate out sparse or occasionally sparse types (scree, volcanic cinders) in which vascular layers are clearly dominant and lithomorphic nonvascular is insignificant (C. Lea pers. comm. 2012).

Similar NVC Types: No Data Available

note: No Data Available