Subalpine Forest Composition Mapped by Imaging Spectroscopy

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Research Primer

Background

Subalpine forests in the Gunnison Basin of western Colorado form a mosaic of quaking aspen (Populus tremuloides), Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), and lodgepole pine (Pinus contorta) that blanket elevations from roughly 2,700 to 3,500 meters. Managing these forests requires knowing not just where trees grow, but which species grow where, at what density, and in what condition. Imaging spectroscopy — high-fidelity remote sensing that captures hundreds of contiguous spectral bands using hyperspectral sensors — has emerged as a tool that allows land managers to map forest composition across entire watersheds at resolutions impossible with traditional field plots. Paired with concepts like self-thinning, root turnover, cover of bare ground, and sampling effort, spectroscopic maps let agencies estimate the utility value of stands for timber, wildlife habitat, watershed protection, and carbon storage.

This matters in the Gunnison Basin because forests here are under pressure from multiple directions at once: bark beetle disturbance is killing conifers in pulses that release needles and reshape biogeochemical cycles; beaver meadows and riparian corridors are shifting as hydrology changes; abandoned underground mines near Mount Emmons continue to influence soils and adjacent vegetation; and macroinvertebrate community composition in streams below forested slopes responds to changes in canopy cover and snowmelt timing. Mapping forest composition with spectroscopy — and validating those maps with ground frequency data on species, herbs, and shrubs — gives managers the baseline they need to track all of these changes.

Historical context

Systematic documentation of subalpine vegetation in the Gunnison Basin grew out of a combination of grazing studies, mining-related environmental assessments, and reclamation research. Early forage work such as the Determination of Annual Forage Production study on Nutras and Chavez Creeks (1954–1955) established baseline methods for quantifying ground cover composition, browse, and the effects of beaver habitat abandonment on montane meadows Determination of Annual Forage Production. In the late 1970s and early 1980s, the proposed molybdenum mine at Mount Emmons triggered some of the most detailed vegetation and wildlife inventories ever produced for the region, including the Vegetation and Wildlife Studies for the Mount Emmons Project (Keammerer & Stoecker, 1980) and its accompanying Vegetation Appendix with herb and shrub layer summaries for Mount Emmons, Alkali Basin, and Antelope Creek Basin Vegetation Appendix Materials.

Parallel efforts focused on how to restore high-elevation lands after disturbance. Technical work by Homestake Mining Company, Western State College, and the Colorado Mined Land Reclamation Board documented hydromulching, revegetation, and overburden management near Gunnison and Marshall Creek 1980 revegetation report, and AMAX-funded studies explored Potential Uses of Abandoned Underground Mines, including underground nursery facilities for high-altitude revegetation stock Potential Uses of Abandoned Underground Mines. Classification efforts culminated in A Classification of the Riparian Vegetation of the Gunnison River Basin (1995), produced with the Colorado Department of Natural Resources and the Environmental Protection Agency, which remains a foundational typology for riparian plant associations adjacent to subalpine forests Riparian Vegetation Classification.

Management actions and stakeholder roles

Forest composition management in the basin involves a layered set of actors. The U.S. Forest Service and the Colorado State Forest Service (CSFS) provide planting stock, reforestation guidance, and soil erosion control recommendations through publications such as Trees for Conservation: A Buyers Guide Trees for Conservation. The Rocky Mountain Biological Laboratory (RMBL) contributes long-term ecological monitoring, including targeted surveys such as the Small Mammal Survey at Acid Fen on Mt. Emmons, which linked habitat composition to vertebrate community structure Small Mammal Survey, Acid Fen. The Agricultural Experiment Station, Western State (now Western Colorado) University, and county and state land boards have historically supported applied research on forage, reclamation, and classification.

Management approaches combine remote sensing with field validation. Imaging spectroscopy products are now being calibrated against stand-level measurements of tree species identity, canopy structure, and understory composition — including common species like Thurber fescue (Festuca thurberi), silvery lupine (Lupinus argenteus), Wood rose (Rosa woodsii), and widespread non-natives such as Kentucky bluegrass (Poa pratensis) and dandelion (Taraxacum officinale). Riparian plant association keys Riparian Vegetation Classification and herb- and shrub-layer inventories from Mount Emmons Vegetation Appendix Materials serve as ground-truth references for spectral classification.

Current challenges and future directions

The most pressing challenges are climate-driven. Warming winters, earlier snowmelt, drought stress, and expanding bark beetle outbreaks are reshaping the relative dominance of aspen versus spruce-fir and lodgepole stands. Recent work at Kebler Pass using terrestrial laser scanning shows that canopy snow interception — a process that can return up to 50 percent of snowfall to the atmosphere via sublimation — differs sharply between deciduous aspen and coniferous species, meaning that shifts in forest composition directly alter watershed water yield (Beutler, 2024). Scaling those findings across the basin depends on accurate spectroscopic maps of which species occupy which slopes.

Future directions include integrating bark beetle disturbance tracking, post-fire regeneration monitoring, and legacy mining-impact assessments into a single compositional framework. Questions about self-thinning trajectories in dense lodgepole stands, root turnover in aspen clones, and expansion of bare ground after disturbance all require repeat spectroscopic surveys paired with plot-based ecology.

Connections to research

Imaging spectroscopy sits at the intersection of RMBL's long traditions in plant ecology, hydrology, and community monitoring. Spectral maps provide spatial context for RMBL's plot-based studies of subalpine meadows, aspen demography, and stream macroinvertebrate communities, while thesis research like Beutler (Beutler, 2024) demonstrates how composition controls the hydrologic function of mountain water towers. As agencies from the Forest Service to Colorado Parks and Wildlife adopt these data, the Gunnison Basin is becoming a testbed for linking hyperspectral forest inventories to decisions about water, wildlife, fire, and mine reclamation.

References

A Classification of the Riparian Vegetation of the Gunnison River Basin, Colorado. →

Beutler, 2024. Forest composition and structural controls on canopy snow interception in a Colorado watershed. →

Determination of Annual Forage Production. →

Homestake/Western State revegetation and hydromulching technical report, 1980. →

Potential Uses of Abandoned Underground Mines. →

Small Mammal Survey, Acid Fen, Mt. Emmons, Gunnison, Colorado. →

Trees for Conservation: A Buyers Guide. →

Vegetation and Wildlife Studies for the Mount Emmons Project. →

Vegetation Appendix Materials for Vegetation and Wildlife Studies for the Mount Emmons Project. →

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