Climate on the Coram Experimental Forest is classified as a modified Pacific maritime-type. Occasional winter, continental-type polar air moves westward over the Continental Divide dropping temperature substantially for a few days. Seasons at Coram are classed broadly as:
- November - March
- April - June
- July - August
- September - October
Annual precipitation ranges from an average of about 890 mm (35 in) at the lowest elevation of 1,006 m (3,300 ft) to 1,270 mm (50 in) at the highest elevation of 1,942 m (6,370 ft), falling mostly as snow. The May through August mean temperature is about 16 °C (61 °F) with highs occasionally exceeding 38 °C (100 °F). Winter temperatures average about -7 °C (20 °F) but rarely drop below -29 °C (-20 °F). Length of growing season (frost-free days) ranges from 81-days near Abbot Creek, to about 160-days on a nearby east-facing slope.
Current and historic precipitation data is available for the nearby Emery Creek SNOTEL site.
A rock layer primarily comprising argillite and quartzite underlies most of the upper slopes. Glacial outwash and till were deposited on the lower areas. A thin layer of volcanic ash covers about half of the forest. Rich loamy soils predominate. Soil depths range from a few centimeters on steep, upper slopes to over 3 m (9 ft) on gentle, lower terrain. Six soils are evident at Coram Experimental Forest:
- Loamy-skeletal soils on materials weathered from impure limestone and argillite
- Loamy-skeletal soils on argillite, siltite, and quartzite
- Loamy-skeletal soils on glacial till
- Loamy-skeletal soils on both alluvium and glacial outwash
- Loamy-skeletal soils on glacial outwash
- Fine and fine-loamy soils on lacustrine deposits
Suitable growing conditions on the Coram Experimental Forest have resulted in a diverse mix of vegetation. Larix occidentalis (western larch) grows almost everywhere at Coram in association with Pseudotsuga menziesii (Douglas-fir), Abies lasiocarpa (subalpine fir) and Picea engelmannii (Engelmann spruce). Hybrids of P. engelmannii and P. glauca (white spruce) grow at lower elevations.
Less common associates are Pinus contorta (lodgepole pine), Pinus monticola (western white pine), Tsuga heterophylla (western hemlock) and Thuja plicata (western red cedar). L. occidentalis and Pinus ponderosa (ponderosa pine) grow together on dry, lower-elevation ridges with shallow soil, the only sites where ponderosa pine is found. At high elevations, larch grows with Pinus albicaulis (whitebark pine), a species nearly eliminated from Coram by Cronatrium ribicola (white pine blister rust). Occasionally, individual Abies grandis (grand fir) trees occur on warm, moist sites. Taxus brevifolia (Pacific yew) and Juniperus communis (common juniper) grow in shrub form.
The only conifers growing within the range of western larch that are not represented on the experimental forest are Larix lyallii (alpine larch) and Tsuga mertensiana (mountain hemlock). Predominant hardwood trees found on the Coram Experimental Forest are Betula papyrifera (paper birch), Populus trichocarpa (black cottonwood) and P. tremuloides (quaking aspen).
Coram has a diverse mix of shrubs including:
- Linnaea borealis (twinflower)
- Physocarpus malvaceus (ninebark)
- Spiraea betulifolia (shiny-leaf spiraea)
- Arctostaphylos uva-ursi (kinnikinnick)
- Alnus sinuata (Sitka alder)
- Salix scouleriana (Scouler's willow)
- Vaccinium globulare (globe huckleberry)
Common forbs are:
- Arnica latifolia (mountain arnica)
- Clintonia uniflora (queencup)
- Epilobium angustifolium (fireweed)
- Trillium ovatum (trillium)
- Fragaria vesca (wild strawberry)
- Cornus canadensis (bunchberry dogwood)
- Disporum hookeri (Hooker fairy-bell)
- Xerophyllum tenax (beargrass)
There are several exotic plant species in the Coram Experimental Forest. Most are on disturbed areas, particularly along roads throughout the forest. Species listed as noxious in Montana include:
- Centaurea maculosa (spotted knapweed)
- Chrysanthemum leucanthemum (oxeye daisy)
- Cirsium arvense (Canada thistle)
- Hieracium aurantaicum (orange hawkweed)
- Hieracium floribundum (meadow hawkweed)
- Hypericum perforatum (St. Johnswort)
- Linaria vulgaris (yellow toadflax)
- Potentilla recta (sulfur cinquefoil)
- Ranunculus acris (tall buttercup)
- Tanacetum vulgare (common tansy)
A comprehensive species list for Coram Experimental Forest is in the appendix of Shearer and Kempf, 1999.