Fire and water crucial to big-tree ecosystem
The stand of about 500 trees was included in the Yosemite Grant that was signed into law on June 30, 1864. This marked the first time the federal government set aside land for protection and is considered to be the genesis of the national park idea. The Mariposa Grove are among the oldest, rarest, and largest living organisms in the world. The trees can live longer than 3,000 years.
About a third of the sequoias in California were cut between the the 1860s and 1950s. Studies suggest that the distribution of the trees is driven by climate, constrained by cold temperatures at upper elevations and limited by the availability of water at low elevations.
In the restoration plan, scientists say restoring natural hydrological and fire cycles is the key to success, since sequoia germination, establishment and persistence are largely driven by fire and hydrology.
Both processes have been profoundly altered in the Mariposa Grove. Tree ring research shows that low-intensity fire was once common, burning every five to eight years on average. Looking at a record going back more than 1,400 years, the longest fire-free period was 15 years.
But the fire suppression policies adopted in the late 1800s led to a 100-year fire-free period, shaping the current forest structure, including the the current number and distribution of younger giant sequoias.
Ensureing germination and recruitment will require frequent surface fires and the maintenance of forest canopy gaps, as well as prescribed fires outside the grove to reduce the risk of a catastrophic fire.
Recent assessments of hydrologic conditions in the Grove indicate that current infrastructure has altered surface flow, water storage and soil conditions in the Mariposa Grove, which is likely to affect the existing and future population of giant sequoias. The ecological restoration of fire and hydrology should be the central focus to ensure success.
The overall goal of the plan is to restore natural processes in the grove, including prime giant sequoia habitat and associated wetlands, which are currently impacted by the parking lot and roads in the lower grove area. Other objectives include improving traffic circulation, visitor parking, and visitor orientation to the grove.
Restoration and improvements to the Mariposa Grove specifically include:
- Restoring giant sequoia and associated wetland habitat
- Constructing a transit hub at the South Entrance which will allow for the relocation of the current parking area from the grove
- Adding shuttle service between the South Entrance and the Lower Grove area during peak use periods
- Building accessible trails through the grove to allow for improved access without impacting the sequoia trees and other sensitive areas.
- Restoring natural hydrology and reducing noise by eliminating commercial tram service through the grove.
- Establishing a new pedestrian trail between South Entrance and the lower grove area, and several new accessible trails within the grove.
Yosemite Conservancy, the park’s philanthropic partner, is contributing significant funding for the landmark project.