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Montana Field Guide

Montana Field Guides

Rocky Mountain Wooded Vernal Pool

Provisional State Rank: S4

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General Description

In northwestern Montana, wooded vernal pools occur from valley bottoms to montane elevations ranging from 866-1,585 meters (2,840-5,200 feet). Wooded vernal pools are small, shallow, circumneutral freshwater wetlands of glacial origin that partially or totally dry up as the growing season progresses. Pools are generally found on valley bottoms, lower benches, toe slopes, and flat sites. This system is well represented in the Seeley-Swan Valley in northwestern Montana. Depending on annual patterns of temperature and precipitation, the drying of the pond may be complete or partial by the fall. These sites are usually shallow and less than 1 meter in depth, but can be as much as 2 meters deep. The pool substrate is a poorly drained, often clayey layer with shallow organic sediments. Wooded vernal pools have a ring of trees surrounding the ponds that provide shade and influence their hydrology. The surrounding forest generally includes grand fir (Abies grandis), subalpine fir (Abies lasiocarpa), western larch (Larix occidentalis), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta), Douglas-fir (Pseudotsuga menziesii), black cottonwood (Populus balsamifera ssp. trichocarpa), and, to a lesser extent, quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera). In Montana, water howellia (Howellia aquatilis), a federally threatened species, is found only in wooded vernal pools. Other common species include water starwort (Callitriche heterophylla), inflated sedge (Carex vesicaria), common spikerush (Eleocharis palustris), and reed canarygrass (Phalaris arundinacea).

Diagnostic Characteristics
Depressional isolated wetland

This system occurs in northern Idaho and western Montana. West of the Continental Divide, in the Seeley-Swan Valley, there is a large concentration of pools and ponds occurring within forested environments. East of the Continental Divide, glaciated pools and ponds occur at elevations up to 1585 m (5,200 feet), particularly in the forested foothill and montane zones of the glaciated pothole region.

Ecological System Distribution
Approximately 3 square kilometers are classified as Rocky Mountain Wooded Vernal Pool in the 2016 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.

Montana Counties of Occurrence
Carbon, Cascade, Deer Lodge, Flathead, Gallatin, Glacier, Granite, Lewis and Clark, Lincoln, Meagher, Missoula, Park, Pondera, Powell, Stillwater, Sweet Grass, Teton, Wheatland

Spatial Pattern


In northwestern Montana, these ponds and pools occur in forested environments. Occurrences are found from valley bottoms to montane elevations ranging from 866 to 1,585 m (2,840-5,200 feet) (Mincemoyer, 2005). This system is well represented in the Seeley-Swan valley in northwestern Montana. Pools are generally found on valley bottoms, lower benches, toeslopes, and flat sites, often in glaciated kettleholes that vary in size and depth.

Depending on annual patterns of temperature and precipitation, the drying of the pond may be complete or partial by the fall or during drought years. However, many of these ponds remain at fairly constant water levels throughout the growing season. These sites can be shallow and less than 1 meter (3.3 feet) in depth, but can be as much as 2 meters (6 feet) deep. The pool substrate is a poorly drained, often clayey layer with shallow organic sediments. Parent materials are typically clay alluvium or clay colluvium (Mincemoyer, 2005). These freshwater ponds have pH ranges from 6.2 to 7.8 with most measurements between 6.5 and 7.5. The size of the pools/ponds can range from .4 to 4 hectares (1-10 acres) in size.


The overstory surrounding vernal wooded pools is typically a mixed coniferous forest consisting of grand fir,, subalpine fir, western larch, Engelmannspruce,lodgepolepine, Douglas-fir, and deciduous trees like black cottonwood and, to a lesser extent, quaking aspen and paper birch. Western red cedar (Thuja plicata) often borders the ponds, especially in the northern Swan Valley. Common shrubs occurring in the forest edges surrounding the pools include thinleaf alder (Alnus incana), redoiser dogwood (Cornus sericea), buckthorn alder (Rhamnus alnifolia), and willows (Salix spp.).

The herbaceous component is dominated by graminoids such as shortawn foxtail (Alopecurus aequalis), water sedge(Carex aquatilis), beaked sedge (Carex utriculata), inflated sedge, common spikerush, and rushes (Juncus spp.). Other characteristic species include woolyfruit sedge (Carex lasiocarpa), awned sedge (Carex atherodes), and wooly sedge (Carex pellita). Reed canarygrass is invasive in this system.

Water starwort (Callitriche species), pondweeds (Potamogeton spp.), burr reed (Sparganium spp.), white water crowfoot (Ranunculus aquatilis), common mare’s tail (Hippuris vulgaris), bladderworts (Utricularia spp.), field mint (Mentha arvensis), and yellowcress (Rorippa spp.) are common herbaceous plant associates. Horsetails (Equisetum spp.) are often present. In Lake and Missoula counties, wooded vernal pools are habitat for water howellia, a federally threatened species. This annual aquatic may undergo dramatic yearly fluctuations in population size.

Dynamic Processes
Many of the pools in the Swan Valley remain at a fairly constant water level year round. In some cases, these pools can partially or completely dry down, depending on temperature, precipitation patterns and pool depth, by late fall. Prolonged drought caused by changing climatic patterns will impact the populations of species such as water howellia occurring within these pools.

Adjacent land uses surrounding wooded vernal pool can potentially alter their hydrology, including grazing and timber harvest. Due to the lack of genetic variability in sampled water howellia populations, multiple pond clusters of inhabited and potential water howellia pools should be protected (Lesica et al., 1988.)

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 (common or occasional) 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 2012, 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 observation 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 listed as associated with 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 listed as 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.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific 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 assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    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: 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.  2012.  Mammals of Montana.  Second edition.  Mountain Press Publishing, Missoula, Montana.  429 pp.
    • 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
Natureserve Western Ecology Group

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

Version Date

  • Classification and Map Identifiers

    Cowardin Wetland Classification:
    System Palustrine
    Class Emergent
    Water Regime Seasonally flooded, semipermanently flooded
    Geographically Isolated Wetland Strictly isolated

    NatureServe Identifiers:
    Element Global ID
    System Code CES304.060, Northern Rocky Mountain Wooded Vernal Pool

    National Land Cover Dataset:
    90: Woody Wetlands

    9162: Northern Rocky Mountain Wooded Vernal Pool

  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Hansen, P. L., R. D. Pfister, K. Boggs, B. J. Cook, J. Joy, and D. K. Hinckley. 1995. Classification and management of Montana's riparian and wetland sites. Montana Forest and Conservation Experiment Station, School of Forestry, University of Montana, Miscellaneous Publication No. 54. 646 pp. + posters.
    • Lesica, P., R.F. Leary, F.W. Allendorf, and D.E. Bilderback. 1988. Lack of genetic diversity within and among populations of an endangered plant, Howellia aquatilis. Conservation Biology 2: 275-282.
    • Mincemoyer, S. 2005. Range-wide status assessment of Howellia aquatilis (water howellia). Prepared for the U.S. Fish and Wildlife Service. Montana Natural Heritage Program, Helena, MT. 21 pp. + appendices.
    • 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 Wooded Vernal Pool — Northern Rocky Mountain Wooded Vernal Pool.  Montana Field Guide.  Retrieved on , from