Year of Award

2015

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Resource Conservation

Department or School/College

College of Forestry and Conservation

Committee Chair

Cory C. Cleveland

Commitee Members

Solomon Z. Dobrowski, Anna Sala, Michael J. Gundale

Keywords

biogeochemistry, fire suppression, forest restoration, nutrient cycling, Pinus ponderosa, prescribed fire, thinning

Subject Categories

Forest Biology | Forest Management | Plant Sciences | Terrestrial and Aquatic Ecology

Abstract

Decades of fire suppression have left much of the forest in the intermountain western United States exceedingly dense, and forest restoration techniques – including thinning and prescribed fire – are increasingly being used in an attempt to mitigate the potentially disastrous effects of severe wildfire, to enhance tree growth and regeneration, and to stimulate soil nutrient cycling. While many of the short-term effects of forest restoration have been established, the long-term effects on soil biogeochemical and ecosystem processes are largely unknown. In this thesis I present two manuscripts documenting and synthesizing these long-term impacts. The first chapter focuses on the decadal scale impacts of various restoration techniques on soil carbon (C) and nitrogen (N) dynamics. We conducted this study eleven years after the restoration treatments were implemented in a ponderosa pine (Pinus ponderosa var. scopulorum)/Douglas fir (Pseudotsuga menziesii var. glauca) forest at the Lubrecht Fire and Fire Surrogates Study (FFS) site in western Montana. Despite short-term (< 3 y) increases in soil N pools and N cycling rates following prescribed fire, long-term soil N pools and N mineralization rates were not significantly different from values in the experimental controls and have declined significantly over time. Integrated measures such as foliar nutrient concentrations and litter decomposition rates in the experimental plots were not different from control plots, suggesting that nutrient cycles in temperate coniferous forests are resilient to disturbance following long periods of fire suppression. In the second chapter I examined decadal scale impacts of restoration treatments on patterns of tree regeneration density and composition, and examined the factors that drove these patterns. We found all active treatments increased ponderosa pine density and decreased Douglas fir density relative to the control. The thin-and-burn was the only treatment that has created a favorable balance of ponderosa pine to Douglas fir regeneration. Finally, we found that heat load index, overstory basal area, canopy cover and surface fuels were important predictors of regeneration density and composition. Overall, these manuscripts provide scientists, forest managers and policymakers valuable information on long-term ecological effects, efficacy and longevity of various restoration prescriptions.

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© Copyright 2015 Peter Ganzlin