Montana Field Guide

Forests in this group are dominated by Western Larch (Larix occidentalis), Grand Fir (Abies grandis) and/or Douglas-fir and are common in western Montana. Western Larch and Grand Fir occur west of the Continental Divide while some mesic Douglas-fir stands in this group occur east of the Divide. Most of the forests in this group occur west of the Continental Divide in areas influenced by more maritime, Pacific air masses. Elevations at these sites range from about 2,000 to 5,500ft. East of the Divide, this group is represented by mesic Douglas-fir forests that occur mostly between 5,200 and 6,800 ft (Pfister etal 1977).

Occurrences of this group may be found on all slopes and aspects but grow best on sites with high soil moisture, such as valley bottoms, on benches, mesic slopes and moist ravines. Western Larch may form almost pure stands in some settings, particularly in the decades following a stand-replacing fire. Whereas, Grand fir often occurs in mixed conifer stands with an assortment of other species, including Douglas-fir, Western Larch, Ponderosa Pine, Lodgepole Pine, Western Redcedar and/or Western Hemlock. Which of these species co-occurs with Grand Fir at a site, is largely dependent upon geographic location, successional status and moisture regime. Douglas-fir dominated communities within this group include the most mesic Associations with Douglas-fir as a dominant or co-dominant component. Other dry to mesic Douglas-fir dominated or co-dominated sites are included in groups G210 and G215. Structure of the stands in this group vary widely from open to close-canopied and even-aged (primarily only in the case of Western larch) or multi-aged and multi-storied. Understory vegetation may be largely shrubby or herbaceous-dominated or a mix of the two.

This Group incorporates portions of the Rocky Mountain Mesic Montane Mixed Conifer Forest Ecological System and the Rocky Mountain Dry-Mesic Montane Mixed Conifer Forest Ecological System.

Mesic Conifer Forests; Montane Zone; Inland Pacific Northwest and Rocky Mountains; Mesic Douglas-fir (Pseudotsuga menziesii) Communities; Mixed Severity and Stand Replacing Fires.

Typical Dominants: Grand Fir (Abies grandis), Western Larch (Larix occidentalis), Douglas-fir (Pseudotsuga menziesii)

In Montana, this Group occurs west of the Continental Divide from the southern Bitterroot Valley north to the Canadian border. It may be found in all the major mountain ranges and major river drainages within this area. East of the Divide, it is found in more localized patches in mesic sites at mid-montane elevations in many of the isolated mountain ranges.

In Montana, G211 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), northwestern portion of 17 (Middle Rockies), and 41 (Canadian Rockies).

In Montana, G211 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains; 43B-Central Rocky Mountains, and 44A - Northern Rocky Mountain Valleys.

Large Patch-Matrix

These forests occur primarily west of the Continental Divide in areas influenced by more maritime, Pacific air masses. Elevations at these sites range from about 2,000 to 5,500ft. East of the Divide, this group is represented by mesic Douglas-fir forests that occur mostly between 5,200 and 6,800 ft (Pfister etal 1977). Occurrences may be found on all slopes and aspects but grow best on sites with high soil moisture, such as valley bottoms, on benches, mesic slopes and moist ravines. Annual precipitation occurs as a mix of rain and snow, with snow common from November-March in these habitats.

Forests in this group are dominated by Western Larch (Larix occidentalis), Grand Fir (Abies grandis) and/or Douglas-fir. Western Larch and Grand Fir occur west of the Continental Divide while some mesic Douglas-fir stands in this group occur east of the Divide. Western Larch may form almost pure stands in some settings, particularly in the decades following a stand-replacing fire. Whereas, Grand fir often occurs in mixed conifer stands with an assortment of other species, including Douglas-fir, Western Larch, Ponderosa Pine, Lodgepole Pine, Western Redcedar and/or Western Hemlock. Which of these species co-occurs with Grand Fir at a site, is largely dependent upon geographic location, successional status and moisture regime. Douglas-fir dominated communities within this group include the most mesic Associations with Douglas-fir as a dominant or co-dominant component. On the west side of Glacier National Park, Paper Birch (Betula papyrifera) co-dominates some sites. Structure of the stands vary widely from open to close-canopied and even-aged (primarily only in the case of Western larch) or multi-aged and multi-storied.

Understory vegetation may be largely shrubby or herbaceous-dominated or a mix of the two. Common shrubs include Ninebark (Physocarpus malvaceous), Common Huckleberry (Vaccinium membranaceum), Dwarf Huckleberry (Vaccinium cespitosum), False Huckleberry (Menziesia ferruginea), Serviceberry (Amelanchier alnifolia) Mountain-lover (Paxistima myrsinites) and shrubby-statured Pacific yew (Taxus brevifolia). Forb and subshrub diversity ranges from depauperate to abundant at these sites, and common species include Queencup Beadlily (Clintonia uniflora), Beargrass (Xerophyllum tenax), Bunchberry Dogwood (Cornus canadensis), Twinflower (Linnaea borealis), Arnica (Arnica cordifolia and A. latifola) Western Sweet-cicely (Osmorhiza berteroi) and Cow-parsnip (Heracleum maximum).

Graminoids usually form a very minor component of these stands and may include Bromus vulgaris, Pinegrass (Calamagrostis rubescens) and Elk Sedge (Carex geyeri). Ferns such as Oak Fern (Gymnocarpus dryopteris) may be present in Grand Fir communities. Mosses and lichens may be common in Grand Fir and Douglas-fir communities. Non-native species may be present to abundant in some stands, including both perennial forbs and perennial grasses. A variety of non-native perennial forbs occur at these sites including Canada thistle (Cirsium arvense) and Bull Thistle (Cirsium vulgare). Non-native grasses are more common in some lower elevation Western Larch stands, Common Timothy (Phleum pratense) being one of them.

In Montana, this group is represented by 23 Associations grouped into 2 Alliances, which likely covers the range of vegetation types present in the state within this group.

Historically, fires were an important process within many of these communities. Both stand-replacement fires with 150 to 500-year return intervals, and moderate-severity fire with intervals of 50-100 years were important within this group. Grand Fir forests include many sites dominated by Douglas-fir and Ponderosa Pine which were formerly maintained by wildfire, and may now be dominated by Grand Fir (a fire-sensitive, shade-tolerant species) due to fire exclusion (Lillybridge et al. 1995, Chappell et al. 1997). Pre-European settlement fire regimes were typically of frequent, low-intensity surface fires, maintaining relatively open stands of a mix of fire-resistant species. With the advent of effective fire suppression, longer fire-return intervals are now the rule, and mixed-stature stands with Grand Fir in various size classes now create ladder fuels making these forests more susceptible to high-intensity, stand-replacing fires (Cooper et al. 1987, Lillybridge et al. 1995).

Western Larch is a long-lived species in excess of 700 years in the northern Rocky Mountains. However, the life of Larch-dominated stands probably rarely exceeds 250 years due to various mortality sources and the growth of shade-tolerant species, especially on mesic sites. Western Larch stands are generated by stand-replacing fire, the fire-return interval for which is speculated to be approximately 80 to 200 years (Cooper et al. 1987). These sites may be maintained in a seral status for hundreds of years since Western Larch is a long-lived species and the understory is often dominated by Douglas-fir, which will grow into the upper canopy. The potential dominants, typically Subalpine Fir, Engelmann Spruce, and/or Grand Fir establish and grow on these sites, presenting the distinct probability, given the fire-return intervals for this type, that the "climax" (long-term stable) condition is never attained. It has been noted in northern Idaho that, following disturbance (particularly logging) in some mesic-site occurrences, Western Larch does not necessarily replace itself, the first tree-dominated successional stages being dominated by Douglas-fir, Lodgepole Pine, or less frequently by more shade-tolerant species (Cooper et al. 1987); this response is a consequence of the episodic nature of favorable cone crop years in Western larch.

M.S. Reid, R. Crawford and M. Manning

S. Mincemoyer

12/4/2024