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ANR responds to massive tree mortality in the Sierra Nevada using field-based research

The Issue

The California drought from 2012 to 2015 included historic dryness and warmth. This drought generated widespread water stress in trees across California and instigated a massive wave of tree mortality in the Sierra Nevada. U.S. Forest Service aerial surveys detected over 127 million newly dead trees due to the drought and other disturbance agents such as bark beetles. This unprecedented tree die-off is transforming California at the stand-to-landscape level and reveals the vulnerability of large portions of California’s forests to novel conditions.

What Has ANR Done?

A field-based project by UC ANR academics captured on-the-ground measurements of tree mortality and forest characteristics in 2017. The newly established network of monitoring sites provides insights on changing forest conditions, including tree mortality, live tree biomass, and surface fuel loads. Linking local efforts in a Sierra Nevada-wide network has produced both general and specific insights to inform management for resilience in California forests. UC ANR led a multi-institution knowledge sharing collaborative between scientists and stakeholders. On March 12th, 2018, project leaders hosted a Tree Mortality Data Network Workshop to share results from the 2017 field season and solicit input from partners on useful data and summary products. Participants from state and federal agencies, local governments, and communities heard the results from the assembled scientists. The material presented at this workshop, including detailed site summaries, can be found at http://ucanr.edu/treemortalitynetwork.

The Payoff

Stakeholders gain critical field-based answers to California’s tree die-off

Feedback during the workshop’s open forum indicated that participants valued the opportunity for in-person communication and suggested further in-person events. In addition, they valued the broad scale overview of tree mortality patterns and mechanisms. They suggested using local fine scale data to project mortality in the near term at the county level, within the context of the overall health and structure of the local forest before the drought. Project stakeholders wanted more information on live forest conditions; estimates of how quickly dead trees would fall; regeneration rates, especially where tree regeneration is unlikely without management intervention; and areas with low mortality where thinning should be prioritized. They also suggested the collection of social data on the impact of tree mortality on small landowners, land tenure, land value, and availability of insurance. The UC ANR project will continue to monitor the plot network to provide needed information on stand conditions, tree fall rates, as well as if regeneration is occurring and, if so, for what species. Extension on project results and implications for small landowners will also continue. Through this project, UC ANR answers critical questions on the resilience of Sierran mixed conifer forests and the management challenges posed by massive tree mortality, emerging as a leader in pursuing a field-based understanding of this tree mortality event.


Supporting Unit: ESPM - Ecosystem Sciences

Jodi N Axelson, Ph.D., Assistant Cooperative Extension Specialist - Forest Health, jodi.axelson@berkeley.edu