Estimating changes in fire behavior and forest structure through a comparison of pre-fire suppression and contemporary forest conditions in the Lake Tahoe Basin, CA.

Open Access
Author:
Vandervlugt, Anna Maria
Graduate Program:
Geography
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Alan Taylor, Thesis Advisor
Keywords:
  • human-induced ecosystem change
  • ecosystem management
  • fuel structure
  • fire behavior
  • presettlement conditions
  • old-growth forests
  • Lake Tahoe CA
Abstract:
Reconstructions of forest conditions before Euro-American settlement and fire suppression policies have been used to understand structure and composition changes over time, and to establish reference points for ecosystem management. However, this approach has rarely quantified the changes in fuel structure caused by fire suppression that affect potential fire behavior. This study: (1) Compares forest and fuel structure between reconstructed pre-suppression old-growth forests and contemporary mixed conifer forests in the Lake Tahoe Basin, California (2) Estimates changes in potential fire behavior between pre-suppression and contemporary forests in 12 stands that occur across a range of site conditions. Results include a net increase in density and fuel loading from 1873 to the present and a concomitant increased risk of high-intensity crown fire. Mean plot densities increased from 161 stems/ha in 1873 to 503 stems/ha in 2010, with fire intolerant white fir contributing the most to the increase. Mean basal area also increased with time, from 30 m2/ha to 59 m2/ha. Forest structure and species composition shifted from open stands with relatively even distributions of species in different size classes to dense stands dominated by small white fir. The major potential fire type changed from surface fires in 1873 to passive and active crown fires in 2010. All potential fire variables measured—including flame length, scorch height, and crowning index—were significantly more severe in 2010. The results of this study will inform managers charged with reducing fire hazard and restoring natural conditions to highly altered forests by providing an understanding of how and where human activity alters disturbance regimes. The forest reconstructions can provide a range of conditions to strive towards when implementing prescribed fire or other fuel treatments in the Basin to reduce risk of severe fire.