Identifying Reference Conditions for Mixed Conifer Forests in Yosemite National Park, California
Andy Scholl
National Park Service policy directs managers to maintain natural environments that evolved with natural processes as opposed to processes that are associated with human action. A major stumbling block for managers implementing this policy is the need to identify a natural reference to both evaluate existing conditions and to identify process and structural goals for restoration to natural conditions. In many cases, the historic natural conditions, referred to as reference conditions, are considered to be those that were present at the time of Euro-American settlement. This time period is used as a reference because of the widespread land use changes that have occurred since Euro-American settlement. In the central Sierra Nevada Mountains, fire is recognized as a major landscape process that was removed from the historic landscape following settlement of the region. This has resulted in major structural and compositional changes in the forests. In Yosemite National Park, fire was removed with the implementation of a policy of fire suppression in the early 20th century.
The overall objective of this project is to identify pre-fire suppression forest structures and fire regimes in two mixed conifer forest dominated landscapes in the Merced and Tuolumne river drainages in the fire suppression management zone of Yosemite National Park. The specific objectives include: 1) Describe the fire regimes (return interval, size, severity, season) for the pre-settlement (pre 1850), settlement (1850-1904), and suppression periods (1905-present) in the Merced and Tuolumne drainage mixed conifer forests; 2) Determine how fire regimes vary along major environmental (topographic) and forest compositional gradients; 3) Determine pre-fire suppression forest characteristics (basal area, density, and size structure) of mixed conifer forests at plot and landscape scales.
This research will provide data to assist the park in the development and implementation of Yosemite National Park’s fire management plan by identifying reference conditions to aid in the management of these areas. In the case of Yosemite National Park, the date of the last fire is considered to be the reference point for the area studied.
Location map and plot locations & fire scar samples in the mixed conifer forests in Big Oak Flat and South Fork Merced, Yosemite National Park, California.
Visual representations of the reference forest landscape and structure in the Big Oak Flat mixed conifer forest in years 1899 (first two images) and 2002 (second two images). The landscape visualizations were developed by placing average forest structure (tree size and density) on the landscape using FVS software.
This project was supported with funding from the National Park Service and the Joint Fire Science Program
