Year of Award

2016

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Department or School/College

College of Forestry and Conservation

Committee Chair

Christopher R. Keyes

Commitee Members

Sharon Hood, Anna Sala

Keywords

ponderosa, biomass, growth, restoration, fuel treatments, wildfire

Subject Categories

Agricultural Science | Botany | Forest Biology | Forest Management | Other Forestry and Forest Sciences | Plant Biology

Abstract

In western North America, many low-elevation, dry forest types historically experienced frequent, low-severity fires. However, European settlement and fire suppression policies have contributed to over a century of fire exclusion, substantially altering forest structure and composition. There is considerable interest in restoring fire resilient characteristics to these forests through fuel reduction treatments. One limitation of current research on the impacts of fuel treatments is treatment longevity, as few studies have been able to quantify long-term responses to commonly applied treatments. This research evaluated tree growth and aboveground biomass responses 23 years after treatment in two silvicultural installations with different underburning prescriptions. Thinning and shelterwood treatments were implemented in 1991 in the Lick Creek drainage of southwestern Montana. Aside from a no-cut control, three post-harvest burning prescriptions were applied in each installation: a no burn, a spring/wet burn, and a fall/dry burn. In 2015 stand density was lower in all treated stands relative to the control, and peak growth of volume accumulation had passed. Stand-level basal area increment was the same across treatments, while tree-level basal area increment was greater in the fuel treatments. In the thinning live tree biomass recovered to pre-harvest levels by 2005 in all three fuel treatments, but was still less than the control. Forest floor biomass was lower in the two burned treatments relative to the two unburned treatments. In the shelterwood, tree biomass had recovered to pre-harvest levels in all fuel treatments by 2015, and was lower in the two burned treatments relative to the two unburned treatments. Forest floor biomass also tended to be lower in the burned treatments. This research suggests that tree biomass in fuel treatments can recover to pre-harvest levels within as little as 10 years while still maintaining reduced stand densities that advance several restoration objectives. Additionally, burning treatments maintain reduced forest floor biomass, even 23 years after treatment, indicating a persistent legacy of burning on this component. However, high regeneration densities indicate that a treatment regime strategies that includes understory treatments are required across treatments to maintain structures conducive to low-severity fire.

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© Copyright 2016 Kate A. Clyatt