{"ID":22918828,"CreatedAt":"2026-09-17T01:02:08.507062015Z","UpdatedAt":"2026-09-20T18:11:56.143995915Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2609.17925","arxiv_id":"2609.17925","title":"Rapid Loss of the Sierra Nevada's Largest Trees Driven by Fire","abstract":"Large trees disproportionately contribute to biomass storage, habitat structure, and ecosystem functioning. However, their distribution and health dynamics remain poorly quantified at a regional scale. Here, a deep learning model (U-Net-ID) and canopy height models derived from sub-meter aerial imagery from 2020 were used to delineate all individual trees with crown area $\\geq$ 100 m$^2$ across the Sierra Nevada Floristic Province. The model was trained using more than 3.3 million synthetic tree crowns and achieved a median Intersection over Union (IoU) of 0.602 when validated against an independent dataset of 20,273 crowns. A total of 6,515,705 large trees were mapped, occurring across approximately 78.7% of the Sierra Nevada Floristic Province. The spatial distribution of large trees showed associations with elevation, temperature, and precipitation. Using Sentinel-2 time series from 2020 to 2025, tree health dynamics were characterized by extracting spectral trajectories for each crown and applying BFAST breakpoint detection algorithm combined with a disturbance classification framework to identify mortality, disturbance, and recovery trajectories of individual trees. Wildfires, estimated from CAL FIRE fire perimeters, were identified as the dominant driver of large-tree mortality, killing 10% of all large trees in the Sierra Nevada, with mortality strongly concentrated during the extreme 2020-2021 fire seasons.","short_abstract":"Large trees disproportionately contribute to biomass storage, habitat structure, and ecosystem functioning. However, their distribution and health dynamics remain poorly quantified at a regional scale. Here, a deep learning model (U-Net-ID) and canopy height models derived from sub-meter aerial imagery from 2020 were u...","url_abs":"https://arxiv.org/abs/2609.17925","url_pdf":"https://arxiv.org/pdf/2609.17925v1","authors":"[\"Fabien H. Wagner\",\"Dan J. Dixon\",\"Christopher W. Woodall\",\"Mayumi C. M. Hirye\",\"Felipe Saad\",\"Griffin Carter\",\"Ricardo Dalagnol\",\"Lorena Alves\",\"Cynthia Creze\",\"Stephen C. Hagen\",\"Zhihua Liu\",\"Christopher Mihiar\",\"Adugna Mullissa\",\"Le Bienfaiteur Sagang Takougoum\",\"Bryan Shaddy\",\"Yan Yang\",\"Dafeng Zhang\",\"Sassan Saatchi\"]","published":"2026-09-15T23:33:59Z","proceeding":"cs.CV","tasks":"[\"cs.CV\"]","methods":"[]","has_code":false}