Graduation Date

Fall 2019

Document Type

Thesis

Program

Master of Science degree with a major in Natural Resources, option Forestry, Watershed, & Wildland Sciences

Committee Chair Name

John-Pascal Berrill

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Martin Ritchie

Second Committee Member Affiliation

Community Member or Outside Professional

Third Committee Member Name

Kevin Boston

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Christa Dagley

Fourth Committee Member Affiliation

HSU Faculty or Staff

Subject Categories

Forestry

Abstract

Quaking aspen (Populus tremuloides) is a valued, minor component on western landscapes. It provides a wide range of ecosystem services, and has been in decline for the last century. This decline may be explained partially by the lack of fire on the landscape as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. Managers are interested in aspen restoration but have a lack of knowledge about their spatial dynamics in response to fire. Improving our understanding of aspen stand spatial changes over time may be important for maintaining their presence on landscapes where their role is unique from neighboring ecotypes. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 54-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized historical (1941, 1993) and current (2017) aerial photos to delineate aspen stand size, location and succession to conifers. We chose aspen stands in areas where wildfires overlapped (twice burned), where only a single wildfire burned, or areas that did not burn within the recent 24-year period. We looked at these same stands within the first period of fire exclusion for comparison (i.e., 1941-1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting aspen recovery and expansion. Stands with less edge:area ratio also expanded more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater changes in area and location (movement), highlighting their vulnerability to loss in the absence of disturbances that provide adequate growing space for aspen over time.

Citation Style

APA

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