Miller Creek Demonstration Forest demonstrates forest recovery over 55 years

Photo Credit

USDA photos by Peter Stickney (first 5 images) and Adele Underwood (2022 image)

Forest development following clearcutting and prescribed fire (1968) on a south-facing unit in the Miller Creek Demonstration Forest, Flathead National Forest, Montana. The 1968 post-fire image shows common beargrass resprouting through residual duff. Herbs dominated this site 10 years following prescribed fire (1979 image), and considerable herb cover remains 20 years postfire (1987 image). By 37- and 54-years postfire (2005 and 2022 images, respectively), conifers have gradually established dominance and produced a spatially complex forest. 

In many forests, trees grow slowly. It takes decades to understand the slowly unfolding factors influencing vegetation composition, structure, and development after silvicultural treatment or natural disturbance. We studied western larch mixed-conifer forests at Miller Creek Demonstration Forest (MCDF) in western Montana to better understand how site, disturbance, such as clearcutting plus broadcast burning, and a high-severity wildfire, and pre-disturbance vegetation influence current vegetation structure and composition, 55 years later.

The Miller Creek Demonstration Forest is a special management area on the Flathead National Forest set aside to enable co-produced research and active management demonstration. It follows up on a long-term, designed experimental study initiated by Forest Service researchers in 1967, enabling direct comparison of changes in forest structure after alternative silvicultural treatments rather than using modeling or chronosequence approaches to study long-term treatment effects. Color photographs were collected at fixed photopoints on each of the study transect, which provides visual insights into the process of forest change and succession to complement the field data collected at these sites.

We found good forest recovery in this long-term study. Forest regeneration at Miller Creek Demonstration Forest was robust following a variety of high-severity disturbances and across different site types over the past half century. Western larch-dominated moist mixed-conifer forests at Miller Creek Demonstration Forest not only regenerated successfully but progressed through to full site occupancy (or close to) on all sites within five decades.

Broadcast burning after harvesting encourages a diverse early-seral plant community but did not impede the development of flora associated with closed-canopy forests at Miller Creek Demonstration Forest. Variation in broadcast burn intensity interacts with site characteristics to achieve different outcomes and management objectives, producing diverse early-seral habitat before tree regeneration dominates the site.

Western larch is frequently a preferred species because it tolerates fire and is resistant to many diseases. Management actions to keep western larch as a dominant species in mixed-species stands include regeneration harvests that are of moderately high to high intensity, retain some vigorous seedbearing overstory trees, and incorporate post-harvest broadcast burning at high enough intensity to reduce duff but avoid killing residual overstory.

This project helps managers influence the development of western larch forests by identifying the long-term effects of hot versus cool prescribed burns on duff reduction and later conifer recruitment. It also helps managers to quantitatively and visually communicate post-treatment forest development, recovery processes, and timeframes to stakeholders.

For researchers, this work improves the understanding of the pace and drivers of post-disturbance community development, including differences between plant lifeforms. After 55 years, overstory tree composition still reflected the initial disturbance, whereas understory flora had transitioned further toward climax species associated with site, such as aspect, soils, and moisture.

These findings reinforce the value of long-term, site-based, silvicultural research. They improve opportunities for local collaboration, field tours, and experiential learning.