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S02 Tropical Open Rock Vegetation Subclass

The U.S. National
Vegetation Classification
Type Concept Sentence: Tropical rock habitats (such as cliffs, talus, scree, pavement, cobbles, lava, or boulderfields) at low elevations from approximately 23°N to 23°S latitude (typically frost-free) from the equator characterized by nonvascular plant growth forms that have structural adaptations for living on stable rock surfaces or in unstable rocky substrates. A sparse cover of various mesomorphic vascular growth forms, including woody plants, may be present.
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Common (Translated Scientific) Name: Tropical Open Rock Vegetation Subclass
Colloquial Name: Tropical Open Rock Vegetation
Hierarchy Level: Subclass
Type Concept: Tropical Open Rock Vegetation is found on rocky habitats (such as cliffs, talus, scree, pavement, cobbles, lava, or boulderfields) in the tropical regional around the globe. Stands typically contain a covering of crustose lichens and/or sparse covering of vascular plants. Vascular and nonvascular plant cover, especially bryophytes, lichens, algae, or ferns, is >1%; vascular plant cover, including bromeliad growth forms, is largely determined by the rock fissures and is typically <10%, with irregular horizontal spacing. Stable rock surfaces (e.g., outcrops) prevent vascular plant roots from penetrating, and their presence is largely determined by the rock fissures. On unstable rocky surfaces (e.g., talus), the presence of vascular plants is largely determined by a degree of permanence. Vascular woody growth forms of either evergreen broad-leaved or drought-deciduous woody plants, including lianas, may be present. Tropical climates, where daily temperate changes are greater than the seasonal changes, are various and often less determinative than presence of open rock surfaces. Substrates are typically dry to moist, but occasionally wet, and typically lack soil development of any kind.
Diagnostic Characteristics: Rocky or rocklike substrates dominated by lithomorphic growth forms, including lichen (especially foliose and crustose lichens), bryophyte, and alga, with cover >1%; vascular vegetation (including clubmosses, etc.), bromeliads, and crevice-dwelling (rupicolous) vascular plants is typically <10% cover. Vascular cover may include either evergreen broad-leaved or drought-deciduous trees and shrubs or evergreen herbs. Vegetation structure may be patchy across the rocky surfaces.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: There is little information that has been comprehensively evaluated across the globe, making it difficult to describe the type concept. We suggest that cliff and slope sites with hardpacked sedimentary rocks and clays be included in this class. More work is needed to clarify the distinctions between Open Rock Vegetation and other sparsely vegetated habitats where rocky substrates are dominant and lichen vegetation is absent. For example, many rocky river and lake shoreline types may be placed in 2.A.3. Tropical Scrub & Herb Coastal Vegetation Formation (F024) where vegetation is patchy but may exceed 10%.

Currently all vascular plant cover is treated together. But cover of ferns (non-woody, including clubmosses, etc.), bromeliads, and crevice-dwelling (rupicolous) vascular plants may need to be considered separately from other vascular cover when deciding on cover thresholds for this class.

Further review may suggest that this subclass can be improved by distinguishing the less "rocklike" vegetation (including vegetation on scree, badlands, and pavement) from the true lithomorphic (solid rock) vegetation (C. Lea pers. comm. 2012).
Similar NVC Types:
S04 Temperate & Boreal Open Rock Vegetation, note: Warm-temperate cliffs contain subtropical-like cliff features.
Physiognomy and Structure: Stands typically contain a covering of crustose lichens and/or sparse covering of vascular plants. Vascular and nonvascular plant cover, especially bryophytes, lichens, algae, or ferns, is >1%; vascular plant cover, including bromeliad growth forms, is largely determined by the rock fissures and is typically <10%, with irregular horizontal spacing. Vascular woody growth forms of either evergreen broad-leaved or drought-deciduous woody plants, including lianas, may be present.
Floristics:
Dynamics: No Data Available
Environmental Description: Stable rock surfaces (e.g., outcrops) prevent vascular plant roots from penetrating, and their presence is largely determined by the rock fissures. On unstable rocky surfaces (e.g., talus), the presence of vascular plants is largely determined by a degree of permanence. Tropical climates, where daily temperate changes are greater than the seasonal changes, are various and often less determinative than presence of open rock surfaces. Substrates are typically dry to moist, but occasionally wet, and typically lack soil development of any kind.
Geographic Range: Tropical Open Rock Vegetation is found in localized areas throughout the tropical latitudes, where frost is essentially absent, approximately from 23°N to S around the equator.
Nations: US
States/Provinces:
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Greasons:
Name:Database Code:Classification Code:
Class 6 Open Rock Vegetation C06 6
Subclass 6.A Tropical Open Rock Vegetation S02 6.A
Formation 6.A.1 Tropical Cliff, Scree & Other Rock Vegetation F011 6.A.1
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy:
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: D. Faber-Langendoen and J. Sawyer
Acknowledgements:
Version Date: 17Oct2014
References:
  • Faber-Langendoen, D., T. Keeler-Wolf, D. Meidinger, C. Josse, A. Weakley, D. Tart, G. Navarro, B. Hoagland, S. Ponomarenko, J.-P. Saucier, G. Fults, and E. Helmer. 2015c. Classification and description of world formation types. General Technical Report RMRS-GTR-000. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO.
  • Lea, Chris. Personal communication. Ecologist, formerly with National Park Service, USGS / NPS Vegetation Mapping Program, Denver, CO.