G229 Pinus ponderosa / Festuca spp. - Muhlenbergia spp. Southern Rocky Mountain Open Woodland Group
Type Concept Sentence: This group includes savanna-like woodlands with widely spaced (<25% tree canopy cover) Pinus ponderosa (primarily var. scopulorum and var. brachyptera) (>150 years old) as the predominant conifer. The understory vegetation is predominantly fire-resistant grasses and forbs that resprout following surface fires. These occur at the lower treeline/ecotone between grassland or shrubland and more mesic coniferous forests typically in warm, dry, exposed sites and are found predominantly in the Colorado Plateau region, west into scattered locations in the Great Basin, and north along the eastern front of the southern Rocky Mountains into southeastern Wyoming.
Common (Translated Scientific) Name: Ponderosa Pine / Fescue species - Muhly species Southern Rocky Mountain Open Woodland Group
Colloquial Name: Southern Rocky Mountain Ponderosa Pine Open Woodland
Hierarchy Level: Group
Type Concept: This group is found predominantly in the Colorado Plateau region, west into scattered locations in the Great Basin, and north along the eastern front of the southern Rocky Mountains into southeastern Wyoming. These savannas occur at the lower treeline/ecotone between grassland or shrubland and more mesic coniferous forests typically in warm, dry, exposed sites. Elevations range from less than 1900 m in central and northern Wyoming to 2800 m in the New Mexico mountains to well over 2700 m on the higher plateaus of the Southwest. It is found on rolling plains, plateaus, or dry slopes usually on more southerly aspects. This group is best described as a savanna that has widely spaced (<25% tree canopy cover) (>150 years old) Pinus ponderosa (primarily var. scopulorum and var. brachyptera) as the predominant conifer. It is maintained by a fire regime of frequent, low-intensity surface fires. A healthy occurrence often consists of open and parklike stands dominated by Pinus ponderosa. Understory vegetation in the true savanna occurrences is predominantly fire-resistant grasses and forbs that resprout following surface fires; shrubs, understory trees and downed logs are uncommon. Important species include Festuca arizonica, Muhlenbergia straminea, Pseudoroegneria spicata, Andropogon gerardii, Schizachyrium scoparium, Festuca idahoensis, Piptatheropsis micrantha, and Bouteloua gracilis. A century of anthropogenic disturbance and fire suppression has resulted in a higher density of Pinus ponderosa trees, altering the fire regime and species composition.
Diagnostic Characteristics: This group is dominated by well-spaced Pinus ponderosa. The understory is predominantly fire-resistant grasses such as Festuca arizonica, Muhlenbergia straminea, Pseudoroegneria spicata, Andropogon gerardii, Schizachyrium scoparium, Festuca idahoensis, Piptatheropsis micrantha, and Bouteloua gracilis. This group will have floristic affinities to adjacent grasslands, especially when it occurs in the ecotone between foothill woodlands and grasslands.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: The Pine Escarpment regions of northwestern and central Nebraska are not included within this group; they have been lumped into ~Black Hills-Northwestern Great Plains Ponderosa Pine Forest & Woodland Group (G216)$$. This group was created to account for the new concept of ponderosa pine savannas in the southern Rocky Mountains. Presently, many stands contain understories of more shade-tolerant species, such as Pseudotsuga menziesii and/or Abies spp., as well as younger cohorts of Pinus ponderosa. ~Central Rocky Mountain Ponderosa Pine Open Woodland Group (G213)$$ in the eastern Cascades, Okanogan, and Northern Rockies regions receives winter and spring rains, and thus has a greater spring "green-up" than the drier woodlands in the Central Rockies.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: This group is characterized by widely spaced conifers forming open savannas (<25% cover) and a parklike understory strongly dominated by fire-resistant graminoids. Shrubs are few or absent from communities within this group. There may be a mid-level canopy of shrubs, copses of oaks, or even an occasional oak tree, but these are minor vegetation components.
Floristics: This group is dominated by well-spaced Pinus ponderosa with other conifers such as Pseudotsuga menziesii and Abies spp. sometimes present as canopy associates. Small trees and shrubs are poorly represented but can include scattered Juniperus spp., Quercus gambelii, Artemisia tridentata, and Chrysothamnus depressus. The understory is predominantly graminoid-dominated with species including Festuca arizonica, Muhlenbergia straminea (= Muhlenbergia virescens), Pseudoroegneria spicata, Andropogon gerardii, Carex rossii, Elymus elymoides, Koeleria macrantha, Poa fendleriana, Schizachyrium scoparium, Festuca idahoensis, Piptatheropsis micrantha (= Piptatherum micranthum), and Bouteloua gracilis.
Dynamics: Fire is a key factor in maintaining the open canopies characteristic of these savannas. Historically, surface fires and drought were influential in maintaining open-canopy conditions in these savannas. With settlement and subsequent fire suppression, stands have become more dense. Presently, many contain understories of more shade-tolerant species, such as Pseudotsuga menziesii and/or Abies spp., as well as younger cohorts of Pinus ponderosa. These altered stand structures have affected fuel loads and altered fire regimes. Presettlement fire regimes were primarily frequent (5- to 15-year return intervals), low-intensity surface fires triggered by lightning strikes or deliberately set by Native Americans. With fire suppression and increased fuel loads, fires are now less frequent and often become intense crown fires which can kill mature Pinus ponderosa. Establishment is erratic and believed to be linked to periods of adequate soil moisture and good seed crops, as well as fire frequencies which allow seedlings to reach sapling size. Longer fire intervals have resulted in many stands having dense subcanopies of overstocked and unhealthy young Pinus ponderosa. Savage and Swetnam (1990) suggest that continuity of understory fuels, especially the grass layer, maintained high frequencies of low-intensity, surface fires along the entire gradient from ponderosa pine woodlands to spruce-fir forests. This hypothesis is supported by evidence that forests with grassy understories were once extensive and continuous over a large elevational range (Savage and Swetnam 1990, Moir et al. 1997). Descriptions of forests around the turn of the century noted open, large areas not confined to ponderosa pine forests. Most ecologists agree that hot, crown fires were not extensive in these open ponderosa pine savannas, although small thickets would have been destroyed by spot crown fires.
Environmental Description: Elevations range from less than 1900 m in central Wyoming to 2800 m in the New Mexico mountains to well over 2700 m on the higher plateaus of the Southwest. It is found on a variety of landforms including rolling plains, plateaus, or cinder cones, bottomlands, mesas, and dry slopes usually on all aspects. Climate: Where precipitation is greater than about 480 mm, blue grama is absent or minor and ponderosa pine occurs with understory bunchgrass species, mainly Festuca arizonica, Muhlenbergia montana, and/or Muhlenbergia straminea. Fires, either lightning- or human-caused, are frequent in these dry forests.
Geographic Range: This group is found predominantly in the Colorado Plateau region, west into scattered locations of the Great Basin, and north along the eastern front of the Rocky Mountains of Colorado and Wyoming.
States/Provinces: AZ, CO, MT, NE, NM, NV, OK, SD, TX, UT, WY
Confidence Level: Moderate
Confidence Level Comments: No Data Available
Greasons: No Data Available
|Type||Name||Database Code||Classification Code|
|Class||1 Forest & Woodland Class||C01||1|
|Subclass||1.B Temperate & Boreal Forest & Woodland Subclass||S15||1.B|
|Formation||1.B.2 Cool Temperate Forest & Woodland Formation||F008||1.B.2|
|Division||1.B.2.Nb Rocky Mountain Forest & Woodland Division||D194||1.B.2.Nb|
|Macrogroup||1.B.2.Nb.1 White Fir - Douglas-fir - Blue Spruce Forest Macrogroup||M022||1.B.2.Nb.1|
|Group||1.B.2.Nb.1.a Ponderosa Pine / Fescue species - Muhly species Southern Rocky Mountain Open Woodland Group||G229||1.B.2.Nb.1.a|
|Alliance||A3419 Ponderosa Pine / Grass Understory Southern Rocky Mountain Open Woodland Alliance||A3419||1.B.2.Nb.1.a|
Concept Lineage: No Data Available
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: < Interior Ponderosa Pine: 237 (Eyre 1980)
- Eyre, F. H., editor. 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, DC. 148 pp.
- Faber-Langendoen, D., J. Drake, S. Gawler, M. Hall, C. Josse, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, L. Sneddon, K. Schulz, J. Teague, M. Russo, K. Snow, and P. Comer, editors. 2010-2019a. Divisions, Macrogroups and Groups for the Revised U.S. National Vegetation Classification. NatureServe, Arlington, VA. plus appendices. [in preparation]
- Harrington, M. G., and S. S. Sackett. 1992. Past and present fire influences on southwestern ponderosa pine old growth. Pages 44-50 in: M. R. Kaufmann, W. H. Moir, and R. L. Bassett. Old-growth forests in the southwest and Rocky Mountain regions. Proceedings of a workshop, March 9-13, 1992, Portal, AZ. General Technical Report RM-213. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.
- Johansen, A. D., and R. G. Latta. 2003. Mitochondrial haplotype distribution, seed dispersal and patterns of post glacial expansion of ponderosa pine. Molecular Ecology 12:293-298.
- Mehl, M. S. 1992. Old-growth descriptions for the major forest cover types in the Rocky Mountain Region. Pages 106-120 in: M. R. Kaufmann, W. H. Moir, and R. L. Bassett. Old-growth forests in the southwest and Rocky Mountain regions. Proceedings of the old-growth forests in the Rocky Mountains and Southwest conference, Portal, AZ. March 9-13, 1992. General Technical Report RM-213. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO.
- Moir, W. H., B. Geils, M. A. Benoit, and D. Scurlock. 1997. Ecology of southwestern ponderosa pine forests. Pages 3-27 in: W. M. Block and D. M. Finch, technical editors. Songbird ecology in southwestern ponderosa pine forests: A literature review. General Technical Report RM-GTR-292. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO. 152 pp.
- Moir, W. H., and J. H. Dieterich. 1988. Old-growth ponderosa pine from succession on pine-bunchgrass habitat types in Arizona and New Mexico. Natural Areas Journal 8:17-24.
- Savage, M., and T. W. Swetnam. 1990. Early 19th-century fire decline following sheep pasturing in a Navajo ponderosa pine forest. Ecology 71(6)2374-2378.