LAKE TAHOE, Calif./Nev. – An annual aerial survey that monitors forest health was significantly reduced in 2025 due to a lack of funding, resulting in many portions of California forests, including the Tahoe area, not being included.
Since 2006, the U.S. Forest Service Pacific Southwest Region’s Aerial Survey Program has flown over California forests every year to observe and document tree mortality, defoliation, and other damage.
These annual estimates capture tree mortality patterns and trends, which researchers and foresters use to monitor ecosystem disturbances often caused by insects and disease. The information is also important for fire behavior forecasting.
While the surveys typically cover large swaths of California landscape and a majority of national forests in California, including the Tahoe National Forest and the Lake Tahoe Basin Management Unit, 2025’s survey was significantly limited to Southern California forests and the far southern Sierra Nevada. The summary report states surveys were conducted in areas where 2025 drought conditions were most severe.
Aerial Survey Program Manager Jeffrey Moore says that a temporary gap like this could create a localized data void and potentially make it harder to identify immediate, fine-grained forest health changes for that year.
However, Moore adds, “The long-term integrity of our forest health monitoring remains strong. Our robust dataset, built over more than three decades, combined with established best practices for data analysis, allow us to track significant trends and understand the broader dynamics of forest health.”
The program does not yet have a finalized budget for the 2026 aerial surveys, but is actively planning to conduct them, including in the Tahoe Basin and surrounding areas, once funding is allocated.
Some general trends observed over the years of monitoring include elevated tree mortality across the region since 2016, when an exceptionally prolonged drought occurred. The program has also observed mortality from another, shorter-duration drought between 2020 and 2022, which is primarily concentrated in the central Sierra Nevada range and the northern interior of the state.
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