Aspen Restoration
Why Quaking Aspen Matter
Quaking aspen stands provide ecosystem services such as enhanced landscape-scale fire resilience, improved water quality, and increased water retention. Despite comprising less than 1% of forests in the Sierra Nevada, aspen habitat bring outsized biodiversity benefits by adding complexity to the landscape and offering high-quality forage for a variety of species.
Aspen have been in decline on the western slope of the Sierra Nevada due to fire suppression, climate change, intensive grazing practices, hydrologic changes, and increased infrastructure. Restoration can be used to promote aspen regeneration to prevent further decline and loss. Aspen stands provide high elevation habitat for aquatic species, migratory birds, and terrestrial wildlife with a wetted landscape and high quality forage. With increasing periods of drought, aspen stand restoration is imperative to increasing resilience to climate change.
Aspen Physiology
Quaking aspen (Populus tremuloides) are distinct on the landscape due to their white bark and shaking leaves. The ‘quaking’ of aspen is caused by flattened bases of the leaves that flutter in the wind and cool the leaf surface. The white bark acts as a sun protectant, and becomes more green in the winter as the aspen photosynthesize through their bark for additional energy once they lose their leaves.
Aspen often grow clonally through a shared root system within each aspen stand. The younger ‘suckers’ grow from roots of the mature aspen stems, and use the older aspen for resources until they can produce enough food for themselves. Aspen can reproduce sexually, but this is rare when compared to clonal reproduction.
Regeneration of aspen stands are stimulated by natural disturbance events, such as a fire, that removes the competition from other slower growing trees, such as coniferous species. The unique physiology of aspen dictates restoration actions. Instead of planting new individual aspen seedlings, most restoration projects aim to stimulate regeneration of existing stands.
Aspen and Disturbance
Aspen on the western slope of the Sierra Nevada are considered to be a ‘pioneer’ or ‘seral’ species, meaning that after a disturbance event—which could be as small as a tree falling creating an opening in the canopy or as large as a landscape-level wildfire—aspen will be among the first trees to respond. Due to historic fire suppression in US forests, there has been little to no reset in the succession of aspen stands converting to conifer forests in over 100 years. Therefore, we are adapting our management approach to use restoration actions as a way to reintroduce disturbance events within and around aspen to stimulate regeneration of remaining stands.
SYRCL works closely with the Tahoe National Forest, researchers, and other aspen restoration specialists to restore and monitor aspen within the Yuba River watershed. Aspen stands can be restored by stimulating regeneration and increasing the availability of suitable habitat through the removal of competing conifers and the application of low-intensity fire. Ungulate exclusion is sometimes used to reduce grazing pressure. Restoration actions are selected based on stand characteristics and the surrounding landscape.
Restoration Action
Conifer Removal
Encroaching conifers are primarily removed via mechanical and hand thinning. High elevation conifer species such as white fir, red fir, lodgepole pine, Jeffery pine, and incense cedar are shade-tolerant. The seedlings will establish within an aspen stand and slowly grow, creating drier stand conditions and will eventually outcompete aspen for sunlight. By removing the conifers, aspen are able to receive light, and the solar radiation of the soil will increase, triggering regeneration.
Ungulate Exclusion
Ungulates, such as domestic sheep and cattle or wild deer and elk, will forage on young aspen suckers . Aspen are an excellent food source for large herbivores, and provide hidden cover from predators for young fawns. However, excess herbivory inhibits the aspen’s ability to grow to a height above the browse level of ungulates. Ungulate exclusion fencing is often used to protect aspen stands temporarily from concentrated livestock. The stand may also be ‘reset’ by changing the location of domestic herbivores.
Reintroduction of Fire
Fire has been a part of our landscape for millennia, from natural ignitions through lightening strikes to cultural burns by Indigenous Peoples. Fire is a disturbance event the aspen on the western slope of the Sierra Nevada rely on to remove conifer competition, reduce litter, and increase radiation on the roots to simulate regeneration. Reducing standing and surface fuels first (via removal of ladder fuels) and then reintroducing fire to the landscape is imperative to promote a low intensity fire that will not damage aspen roots. Pile and broadcast burning in and around aspen stands can promote aspen regeneration and forest health.
Learn More about SYRCL’s Aspen Restoration projects:
Yuba Headwaters Aspen Assessment and Planning
In 2020, the Wildlife Conservation Board awarded SYRCL a planning grant to conduct a watershed-wide aspen assessment. This effort cataloged the location, health, and size of aspen stands. In total, the assessment surveyed 123 aspen stands covering 490 acres on Tahoe National Forest (TNF) land within the Yuba River watershed. SYRCL’s aspen assessment paired on-the-ground stand evaluations with the development of a quantitative prioritization tool to select high priority aspen stands for restoration. The prioritization tool utilized three suitability models to perform a landscape level analysis: Access, Habitat Quality, and Stand Health.
Salmon & Packer Creek Aspen Restoration Project
In 2023, SYRCL and the Tahoe National Forest (TNF) transitioned into focused planning efforts for the Salmon and Packer Creek Aspen Restoration Project. This Project is within the Lost Sierra and Gold Lakes Highway region near scenic Highway 49 in the Sierra Nevada.
The expected outcomes and benefits of this Project are to promote aspen regeneration, improve forest health, increase riparian habitat and improve riparian health, and reduce fire risk. Restoration of aspen will increase the availability of aspen habitat, increase water retention and improve water quality, reduce high severity fire risk in the area, and increase the aesthetics of a large aspen stand.
SYRCL’s Former Aspen Restoration Projects
SYRCL has a long history of aspen restoration in the Yuba River Watershed. Beginning in 2011, SYRCL collaborated with the Tahoe National Forest (TNF) to remove conifers and create barriers to domestic ungulates with volunteer hand crews at Rucker Lake and Loney Meadow Complex (LMC). SYRCL continued this work with volunteer aspen regeneration workdays at LMC and the organization explored their first combined meadow and aspen restoration project at this site.
Aspen restoration at LMC includes conifer removal, cattle exclusion fencing, and restoration of the hydrology at the meadow. Since 2015, SYRCL has collected monitoring data of the aspen to understand the impact of the restoration activities. This work is often done with local high school students through the Youth Outdoor Leadership Opportunity (YOLO) expedition.