Date of Award

Summer 7-22-2009

Document Type

Thesis

Degree Name

Master of Arts (MA)

Department

Ecology & Evolutionary Biology

First Advisor

Carol Wessman

Second Advisor

Jason Neff

Third Advisor

Timothy Seastedt

Abstract

Disturbance ecology is a growing field within ecology, and while studies of individual and discrete disturbances are increasing in number, there is a paucity of studies on the ecological effects of disturbance interactions. The goal of this project was to analyze how fire, blowdown and logging affect nitrogen cycling and other critical soil properties both independently and when they occur in rapid succession. The study site was located in the Routt National Forest where the forest sustained the largest windthrow ever recorded in the Southern Rocky Mountains in 1997. Of the 10,000 hectares affected by the blowdown, 935 were subsequently salvaged logged from 1998-2001. In 2002, portions of the intact, logged and blowdown were burned by the Hinman fire leaving a matrix of both individually and multiply disturbed sites. From 2005-2009 soil samples were acquired from intact, burned, blowdown, logged, burned logged, and burned blowdown and analyzed for available ammonium and nitrate; nitrification and mineralization potential; total extractable phosphorous; and percent calcium, potassium and magnesium. Multiple analysis of variance was used to evaluate how the different disturbance combinations affected the soil properties evaluated in this study. The main effects of blowdown and logging disturbances showed that the treatment type significantly affected the soil’s total phosphorous, ammonification potential and available nitrate. Evaluation of the effects of burned versus non-burned sites showed that burning significantly affected total extractable phosphorous, bulk density, soil organic matter content, available nitrate and ammonium, and C, N, Ca and Mg content. Analyzing the interaction of the main effects of treatment and burning demonstrated that disturbance interactions do not have a synergistic effect in degrading soil properties. Instead, the reduction of fuel in the logged plots appeared to lower the fire intensity and preserved many soil properties to levels found in the undisturbed sample plots. Continued studies on the effect of disturbance interactions are critical for providing managers with the appropriate tools to manage forest landscapes after disturbances.

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