{"slug": "rapid-loss-of-the-sierra-nevada-s-largest-trees-driven-by-fire", "title": "Rapid Loss of the Sierra Nevada's Largest Trees Driven by Fire", "summary": "A deep learning model called U-Net-ID mapped 6,515,705 large trees across roughly 78.7% of the Sierra Nevada Floristic Province using 2020 sub-meter aerial imagery, according to a study published on arXiv (2609.17925v1). Wildfires, estimated from CAL FIRE fire perimeters, killed 10% of all large trees in the region, with mortality concentrated in the extreme 2020-2021 fire seasons. The model, trained on more than 3.3 million synthetic tree crowns, achieved a median Intersection over Union of 0.602 against an independent dataset of 20,273 crowns.", "body_md": "arXiv:2609.17925v1 Announce Type: new \nAbstract: 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.", "url": "https://wpnews.pro/news/rapid-loss-of-the-sierra-nevada-s-largest-trees-driven-by-fire", "canonical_source": "https://arxiv.org/abs/2609.17925", "published_at": "2026-09-17 04:00:00+00:00", "updated_at": "2026-09-17 04:26:54.164813+00:00", "lang": "en", "topics": ["machine-learning", "computer-vision", "ai-research"], "entities": ["Sierra Nevada Floristic Province", "U-Net-ID", "CAL FIRE", "Sentinel-2", "arXiv", "BFAST"], "alternates": {"html": "https://wpnews.pro/news/rapid-loss-of-the-sierra-nevada-s-largest-trees-driven-by-fire", "markdown": "https://wpnews.pro/news/rapid-loss-of-the-sierra-nevada-s-largest-trees-driven-by-fire.md", "text": "https://wpnews.pro/news/rapid-loss-of-the-sierra-nevada-s-largest-trees-driven-by-fire.txt", "jsonld": "https://wpnews.pro/news/rapid-loss-of-the-sierra-nevada-s-largest-trees-driven-by-fire.jsonld"}}