Conifer Forest Dynamics, Climate, and Fuel Management

At the regional scale, tree-ring analyses across more than a thousand sites in the continental U.S. demonstrated that southwestern forests are unusually sensitive to drought and heat, and that growth declines and mortality from bark beetles and wildfire accelerated after the mid-1980s (Williams et al., 2010). A parallel paper used these tree-ring chronologies to project that warming and drying will substantially reduce growth across most southwestern populations through the twenty-first century (Williams et al., 2010). Local sapling studies reinforced the picture: young subalpine fir grew more slowly under the earlier snowmelt of 1999–2003 than under the cooler, snowier 1993–1997 period (Lavorel, 2004), while young lodgepole pine showed the opposite response, growing faster with earlier snowmelt (Lambrecht, 2005).

Key findings

A consistent theme is that climate sensitivity varies sharply by species. Lodgepole pine tends to benefit, at least in the short term, from warmer temperatures and earlier snowmelt, whereas Engelmann spruce shows little response and subalpine fir is often negatively affected (Kueppers & Harte, 2005). Across the southwestern United States more broadly, Douglas-fir and ponderosa pine are among the most vulnerable to warming, with measurable declines in tree growth and increases in mortality since the 1980s linked to drought, bark beetles, and wildfire (Williams et al., 2010). Subalpine fir mortality has risen across Colorado in association with both drought stress and biotic agents such as the western balsam bark beetle and root pathogens (Lalande et al., 2019).

Forest carbon and water budgets are also shifting. Warmer conditions accelerate decay of dead wood at low elevations and depress total ecosystem carbon storage, but the response depends on which species dominate the canopy (Kueppers et al., 2004); (Kueppers & Harte, 2005). In the upper East River watershed, transpiration differs substantially among species, with spruce and fir running warmer canopies and transpiring less than lodgepole pine, and environmental factors such as snow persistence and slope explaining more variability than stand structure alone (Golla, 2023). Recent work in the Gothic townsite found that total conifer volume declined by nearly 48,000 cubic meters between 2021 and 2023, with topographic wetness and snowpack duration emerging as the strongest predictors of growth (Hernandez, 2023).

Management-oriented findings round out the picture. Silvicultural thinning can raise individual tree vigor and reduce bark beetle susceptibility, while complex multilayered stands favor defoliating insects and simpler even-aged stands favor bark beetles (Waring & Bucholz, 2023). Fuel surveys at the Willey Conservation Easement near Gothic documented heavy accumulations of duff, litter, and downed wood on densely treed slopes, along with fire-scarred Douglas-firs that record a history of low-severity surface fires before twentieth-century suppression (Philips, 2022). For aspen, which often shares the landscape with conifers, fire suppression since the late 1880s has been implicated in decline, although heterogeneity in stands and fire regimes makes broad generalizations difficult (Rosenblum, 2015).

Current frontier

Early work in the 1990s and 2000s leaned on tree rings, plot-based carbon measurements, and elevation gradients. Research since 2020 has shifted toward higher-resolution, technology-driven approaches and a sharper focus on water. Drone-based remote sensing now allows researchers to link DBH measurements to canopy volume across whole stands, and emerging analyses suggest a lagged relationship in which canopy growth in one year predicts stem growth the next (Luedtke, 2024). Remote sensing workflows developed in the Gothic townsite are also being used to detect stand-level declines and to identify which environmental drivers — wetness, snow duration, slope — matter most at the scale of individual stands (Hernandez, 2023).

Other recent threads are extending the questions outward. Snow drought has become a focus as warm winters increasingly deliver rain instead of snow, and tree-ring proxies are being developed to distinguish warm from dry snow droughts over the past century and a half (Lundquist, 2022). Studies of subalpine tree communities in the West Elk Mountains are tracking how growth, mortality, and recruitment differ by species along elevation gradients, with mortality rising in the 2010s relative to the 2000s (Budoff-Corujo, 2023). New work on the conifer needle microbiome shows that both host species and site shape bacterial communities and their capacity to break down conifer terpenes, opening a microbial dimension to forest health (Bowers et al., 2025). Treeline studies in the Elk Mountains, meanwhile, show that despite warming, the elevational limit of trees has not advanced upslope during the twentieth century (Elliott, 2016).

Open questions

Many of the most pressing questions concern thresholds and feedbacks. How much warming, drying, or snow loss can each conifer species tolerate before mortality outpaces recruitment? Why does treeline appear to lag the climate signal, and what limits seedling establishment at the upper edge of the forest? How will shifting fire regimes interact with fuel loads built up under a century of suppression, and which silvicultural treatments — thinning, prescribed fire, or species-specific interventions — will best maintain resilience in the Gunnison Basin? The role of belowground processes, including root turnover and root-soil interactions, remains poorly quantified at RMBL, as does the contribution of needle and soil microbiomes to drought and pest resistance. Finally, scaling drone-based measurements of growth, transpiration, and mortality into watershed-level forecasts of carbon and water yield is a methodological frontier with direct relevance to land managers across the region.

References

Bowers, R. and colleagues (2025). Host species and geographic location shape microbial diversity and functional potential in the conifer needle microbiome. Microbiome. →

Budoff-Corujo (2023). Effects of Altitude on the Growth, Mortality, and Recruitment of Subalpine Tree Species in the West Elk Mountains of Colorado. →

Elliott (2016). Reconstruction and spatial analysis of alpine treeline in the Elk Mountains, Colorado, USA. →

Golla (2023). The Influence of Forest Structure and Composition on Transpiration Rates Among Drought-Stressed Conifer Species in the Upper East River Watershed. →

Hernandez (2023). Analysis of growth patterns in Conifer stands present in Gothic town. →

Kueppers, L. M. and Harte, J. (2005). Subalpine forest carbon cycling: Short- and long-term influence of climate and species. Ecological Applications. →

Kueppers, L. M., Southon, J., Baer, P., and Harte, J. (2004). Dead wood biomass and turnover time, measured by radiocarbon, along a subalpine elevation gradient. Oecologia. →

Lalande and colleagues (2019). Abiotic and biotic factors influencing western United States coniferous forests. Colorado State University. →

Lambrecht (2005). Effects of climate change on growth and seedling establishment of young lodgepole pine. →

Lavorel (2004). The effect of climate change on the germination and growth rates of young subalpine fir (Abies lasiocarpa). →

Luedtke (2024). Stem and canopy growth analysis in Picea Engelmannii with UAVs and field measurements. →

Lundquist (2022). An Extreme Number of Sensors in One Spot. Mt. Views Chronicle. →

Philips (2022). Forest Fuels and Management Considerations at the Willey Conservation Easement, Colorado. →

Rosenblum (2015). Altered Fire Regimes and the Persistence of Quaking Aspen in the Rocky Mountains: A Literature Review. Open Journal of Forestry. →

Waring, K. and Bucholz, E. (2023). Silviculture. →

Williams, A. P., Allen, C. D., Millar, C. I., Swetnam, T. W., Michaelsen, J., Still, C. J., and Leavitt, S. W. (2010). Forest responses to increasing aridity and warmth in the southwestern United States. PNAS. →

Williams, A. P., Michaelsen, J., Leavitt, S. W., and Still, C. J. (2010). Using tree rings to predict the response of tree growth to climate change in the continental United States during the twenty-first century. Earth Interactions. →

Pseudotsuga

Altered Fire Regimes and the Persistence of Quaking Aspen in the Rocky Mountains: A Literature Review