UNDERSTANDING TRAJECTORIES OF LANDSCAPE CHANGE: THE RESPONSES OF A ROCKY MOUNTAIN FOREST-SAGGEBRUSH-GRASSLAND LANDSCAPE TO FIRE SUPPRESSION, LIVESTOCK GRAZIN, AND CLIMATE

Open Access
- Author:
- Lauvaux, Catherine Tasarla
- Graduate Program:
- Geography
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 16, 2018
- Committee Members:
- Alan H Taylor, Dissertation Advisor/Co-Advisor
Alan H Taylor, Committee Chair/Co-Chair
Andrew Mark Carleton, Committee Member
Erica A H Smithwick, Committee Member
Margot Wilkinson Kaye, Outside Member - Keywords:
- fire suppression
fire history
Rocky mountains
Sawtooth National Forest
Soldier mountains
Douglas-fir
whitebark pine
sagebrush
subalpine fir
livestock grazing
tree enchroachment
vegetation dynamics
tree mortality
fire severity - Abstract:
- Naturally functioning forest ecosystems have been called gemstones of the Rocky Mountain landscape, and yet, since Euro-American settlement, these forests have been altered by land-use, fire suppression, extreme wildfires, and climate change. Understanding the changes is limited by lack of information about historical conditions. Knowledge of pre-settlement vegetation patterns and disturbance processes may also be useful in predicting and mitigating future ecological impacts. This study uses repeat aerial photography, fire-scar dendrochronology, tree population age structure, and grazing reports to determine fire history and land-use history and the characteristics, timing, and drivers of vegetation change in a forest-sagebrush-grassland mosaic in the Soldier Mountains, Idaho. Fire frequency before 1900 was greater in low-elevation Douglas-fir forests than high elevation whitebark pine forests (mean interval of 31(±28.8) years vs 66 (±34.4) years). Climate was a driver of widespread fires as evidenced by fires burning across multiple forest types during extremely dry years. Pre-settlement fires created a heterogeneous forest structure of even-aged, high severity stands and uneven-aged, low to moderate severity stands across the landscape. Livestock grazing, climate variation, and recent fires have altered vegetation patterns in several ways. In sagebrush-grasslands, tree encroachment peaked in the 1960s following a steep decline in sheep grazing and a period with cool, wet summers. In whitebark pine forests, regeneration declined after fire suppression in the early 1900s. Then, in the late 2000s, many whitebark succumbed to combined drought related stress and beetle attack. In contrast to pre settlement patterns of mixed severity fire effects, a 2013 wildfire had predominately high severity effects in Douglas-fir forests, potentially erasing heterogeneity in the forest and indicating that restoring the historical forest structure may be time sensitive.