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Rocky Mountain Ponderosa Pine Woodland and Savanna

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General Description

This system occurs on warm, dry, exposed sites in the foothills of the Rocky Mountains in west-central and central Montana, at the ecotone between grasslands or shrublands and more mesic coniferous forests. Elevations range from 1,066 to 1,676 meters (3,500-5,500 feet), with higher elevation examples mostly confined to central Montana. Occurrences are found on all slopes and aspects; however, moderately steep to very steep slopes or ridgetops are most common. True savanna types are infrequent; the system is more characteristically an open forest with a grassy understory. In the western part of the state, this system is seen mostly on dry slopes in the rainshadow of the Bitterroot Mountains. East of the Continental Divide, it is most widespread around Helena and Lewistown, although it occurs throughout mountain ranges as far east as the Little Rocky and Bearpaw Mountains. Ponderosa pine (Pinus ponderosa) is the dominant conifer. Douglas-fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) may be present in the tree canopy in the more western areas, but are usually absent. In central Montana, limber pine (Pinus flexilis) and horizontal juniper (Juniperus horizontalis) are frequently components. Although the understory of ponderosa pine forests is often shrubby in other states, in Montana, habitats are mostly dominated by graminoids, although bitterbrush (Purshia tridentata), white snowberry (Symphoricarpos albus), and skunkrush (Rhus trilobata) occur in forests on benchlands and rocky slopes in the central portion of the state. Understory vegetation is more typically grasses and forbs that resprout following low to moderate intensity surface fires. Prolonged drought, beetle kill and exotic invasion are rapidly changing the dynamics of this system.


Diagnostic Characteristics
Ponderosa pine with grass or shrub understory, tree cover from 10 to 50%, shallow, aridic soils with sandy texture, A soil horizon less than 10 cm, intermediate to polycyclic disturbance intervals

Similar Systems

Range
In the western part of the state, this system is seen mostly on dry slopes in the rainshadow of the Bitterroot Mountains. East of the Continental Divide, it is most widespread around Helena and Lewistown, although it occurs throughout mountain ranges as far east as the Little Rocky and Bearpaw Mountains.

Ecological System Distribution
Approximately 2,440 square kilometers are classified as Rocky Mountain Ponderosa Pine Woodland and Savanna in the 2013 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.



Montana Counties of Occurrence
BLAINE, BROADWATER, CARBON, CASCADE, CHOUTEAU, DEER LODGE, FERGUS, FLATHEAD, GALLATIN, GOLDEN VALLEY, GRANITE, HILL, JEFFERSON, JUDITH BASIN, LAKE, LEWIS AND CLARK, LINCOLN, MEAGHER, MINERAL, MISSOULA, MUSSELSHELL, PARK, PHILLIPS, POWELL, RAVALLI, SANDERS, SILVER BOW, STILLWATER, SWEET GRASS, TETON, WHEATLAND

Spatial Pattern
Matrix

Environment

In western and central Montana, this ecosystem forms a belt on warm, dry, exposed sites between grasslands and Douglas-fir (Pseudotsuga menziesii) forests. Elevations range from 1,066 to 1,676 meters (3,500-5,500 feet) (Pfister et al, 1977). This system can occur at higher elevations in central Montana. It is generally found on gravelly soils with good aeration and drainage and a neutral to slightly acidic pH.


Vegetation

Ponderosa pine is the dominant conifer. Douglas-fir and western larch may be present in the tree canopy in the more western areas, but are usually absent. In central Montana, limber pineand horizontal juniperare often components. Although the understory for ponderosa pine forests is often shrubby in other states, in Montana, habitats are mostly dominated by grasses, although antelope bitterbrush, snowberry, serviceberry (Amelanchier alnifolia), bearberry (Arctostaphylos uva-ursi), common juniper (Juniperus communis) and skunkbush occur in forests on benchlands and rocky slopes in the central portion of the state. Understory vegetation is more typically fire-resistant grasses and forbs that resprout following surface fires. High shrub cover, understory trees, and downed logs are uncommon. These more open stands support grasses such as bluebunch wheatgrass (Pseudoroegneria spicata), which is usually dominant, prairie junegrass (Koeleria macrantha) and needle and thread (Hesperostipa comata), as well as dryland sedges likethreadleaf sedge (Carex filifolia) and sun sedge (Carex inops ssp. heliophila). On more mesic sites,bluebunch wheatgrass occurs as the dominant graminoid species with Idaho fescue (Festuca idahoensis) and rough fescue (Festuca campestris). In central Montana, soapweed yucca (Yucca glauca), Pennsylvania sedge (Carex pennsylvanica), grama (Bouteloua spp.) and bluestem (Andropogon spp.) occur on especially dry sites. Common herbaceous forbs include yarrow (Achillea millefolium), pink pussytoes (Antennaria rosea), arrowleaf balsamroot (Balsamorhiza sagittata), Indian blanket flower (Gaillardia aristata), and silky lupine (Lupinus sericeus).


Alliances and Associations
Alliances
  • (A.134) Ponderosa Pine - Douglas-fir Forest Alliance
  • (A.530) Ponderosa Pine Woodland Alliance

Dynamic Processes

Under natural conditions, ponderosa pine woodlands and grasslands are maintained by frequent surface fires (Arno, 1980). The threat of stand-replacing fires is high in areas where periodic fire has been suppressed. A study at the Sawmill Resource Natural Area in the Bitterroot National Forest found an average fire return interval of 13 years prior to the initiation of systematic fire suppression policies. In the absence of fire, forest density increases, and fire-intolerant species like Douglas-fir become more common (Gayton et al., 2006). Grazing by domestic livestock may reduce bunchgrasses, and in cases of intensive overgrazing, cheatgrass (Bromus tectorum) may be dominant in the understory. Wind is not generally an issue, except when trees have been damaged by lightning strikes.


Management

In the absence of natural fire, periodic prescribed burns, selective thinning, and reduction of ladder and basal fuels to prevent crown fires can be used to maintain and restore this system to similar pre-settlement conditions. Thinning understory trees and manually removing ladder fuels and heavy fuels from the base of large trees may be necessary to protect old growth from mortality during prescribed burns.

Periodic burning is used to expose mineral soils, provide nutrient availability, reduce competition, stimulate native grass and forb production, increase basal diameter growth of overstory ponderosa pine, and provide favorable seedbeds. In some cases, especially on sites heavily infested with cheatgrass, frequent prescribed burning at low intensities may stimulate greater cheatgrass cover following fire, especially if the burn did not kill the seed bank. Increasing time between prescribed fires may inhibit cheatgrass by increasing surface fuels (both herbaceous and litter) which directly inhibit establishment, and by creating higher intensity fires capable of killing a much greater fraction of the seed bank. Postfire cheatgrass dominance has been shown to be most strongly controlled by the pre-fire seed bank, soil moisture, fire intensity, soil nitrogen, and duration of direct sunlight (Keeley and McGinnis 2007). Excessive grazing can lead to the loss of the most common perennial grasses and increased abundance of exotic grasses.Cheatgrass establishment in low-elevation ponderosa pine and Douglas-fir forests can be enhanced by disturbance that opens the understory, removes litter, or both (Mack and Pyke 1983). Prolific seed production also contributes to the competitive advantage of this grass over native grasses and associated perennial forbs.

In recent years, prolonged summer drought conditions and milder winters have led to increasingly severe outbreaks of mountain pine beetle (Dendroctonus ponderosae). Ponderosa pine mortality is high in many areas of Montana, especially in the west-central area of the state. Beetle kill is creating conditions for severe, stand replacing fires and is rapidly changing the dynamics and potential recovery of this system.


Restoration Considerations
Post-fire restoration strategies will depend largely on fire severity. Because lightly burned areas recover quite quickly from fire, restoration practices are usually not necessary. In cases where there are severe, stand replacing fires reseeding or replanting efforts may be necessary.

Species Associated with this Ecological System
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (high, medium, or low) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2001, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species’ range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of “observations versus availability of habitat”.
    Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were associated as using an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  High, medium, and low habitat quality was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species in the literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignments of habitat quality.  If you have any questions or comments on species associations with ecological systems, please contact Bryce Maxell at bmaxell@mt.gov or (406) 444-3655.

    Suggested Uses and Limitations
    Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.  These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: http://mtnhp.org/requests/default.asp) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.  Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).  Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species’ known geographic range.

    Literature Cited
    • Adams, R.A.  2003.  Bats of the Rocky Mountain West; natural history, ecology, and conservation.  Boulder, CO: University Press of Colorado.  289 p.
    • Dobkin, D. S.  1992.  Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34.  Missoula, MT.
    • Foresman, K.R.  2001.  The wild mammals of Montana.  Special Publication No. 12.  Lawrence, KS: The American Society of Mammalogists.  278 p.
    • Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998.  Montana atlas of terrestrial vertebrates.  Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT.  1302 p.
    • Hutto, R.L. and J.S. Young.  1999.  Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32.  72 p.
    • Maxell, B.A.  2000.  Management of Montana’s amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species.  Report to U.S. Forest Service Region 1.  Missoula, MT: Wildlife Biology Program, University of Montana.  161 p.
    • Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath.  2004.  Amphibians and reptiles of Montana.  Missoula, MT: Mountain Press Publishing Company. 262 p.

Original Concept Authors
M.S. Reid, mod. C. Chappell and R. Crawford

Montana Version Authors
L.K. Vance, T. Luna

Version Date
2/14/2010

References
  • Classification and Map Identifiers

    Cowardian Wetland Classification: Not applicable

    National Vegetation Classification Standard:
    Class Forest and Woodland
    Subclass Temperate Forest
    Formation Cool Temperate Forest
    Division Western North America Cool Temperate Forest
    Macrogroup Northern Rocky Mountain Lower Montane and Foothill Forest

    NatureServe Identifiers:
    Element Global ID 28445
    System Code CES306.030, Northern Rocky Mountain Ponderosa Pine Woodland and Savanna

    National Land Cover Dataset:
    42: Evergreen Forest

    ReGAP:
    4240: Northern Rocky Mountain Ponderosa Pine Woodland and Savanna


  • Additional ReferencesLegend:   View WorldCat Record   View Online Publication
    Do you know of a citation we're missing?
    • Aguirre, Lucrecia, and Douglas A. Johnson. 1991. "Influence of Temperature and Cheatgrass Competition on Seedling Development of Two Bunchgrasses". Journal of Range Management. 44 (4): 347-354.
    • Arno, S. F. 1980. Forest fire history in the northern Rockies. Journal of Forestry 78(8):460-465.
    • Gayton DV, Weber MH, Harrington M, Heyerdahl DK, Sutherland BB, Hall C, Hartman M, Peterson L, Merrel C. 2006. Fire history of a western Montana ponderosa pine grassland: A pilot study. In: Speer JH, editor. Experiential learning and exploratory research: The 13th annual North American dendroecological fieldweek (NADEF). Prof. Paper Ser. No. 23. Terre Haute, IN: Department of Geography, Geology, and Anthropology, Indiana State University; p 30-6.
    • Keeley, J. E., and T. W. McGinnis. 2007. "Impact of prescribed fire and other factors on cheatgrass persistence in a Sierra Nevada ponderosa pine forest". INTERNATIONAL JOURNAL OF WILDLAND FIRE. 16 (1): 96-106.
    • Mack, Richard N., and David A. Pyke. 1983. "The Demography of Bromus Tectorum: Variation in Time and Space". The Journal of Ecology. 71 (1): 69-93.
    • Pfister, R. D., B. L. Kovalchik, S. F. Arno, and R. C. Presby. 1977. Forest habitat types of Montana. USDA Forest Service. General Technical Report INT-34. Intermountain Forest and Range Experiment Station, Ogden, UT. 174 pp.

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Citation for data on this website:
Rocky Mountain Ponderosa Pine Woodland and Savanna — Northern Rocky Mountain Ponderosa Pine Woodland and Savanna.  Montana Field Guide.  Retrieved on October 31, 2014, from http://FieldGuide.mt.gov/displayES_Detail.aspx?ES=4240
 
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