火灾导致内华达山脉最大树木快速消失
Rapid Loss of the Sierra Nevada's Largest Trees Driven by Fire
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- CTrees
- University of California, Davis（加州大学戴维斯分校）
- University of California, Los Angeles（加州大学洛杉矶分校）
- University of São Paulo（圣保罗大学）
- University of Maryland Baltimore County（马里兰大学巴尔的摩县分校）
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中文总结 AI 辅助
本研究利用深度学习模型和遥感数据绘制内华达山脉大型树木分布，发现野火是导致其快速死亡的主要因素，2020-2021年火灾季造成10%的大型树木死亡。
中文摘要 AI 辅助
大型树木对生物量储存、栖息地结构和生态系统功能具有不成比例的重要贡献。然而，其区域尺度的分布和健康动态仍未得到充分量化。本研究利用深度学习模型（U-Net-ID）以及基于2020年亚米级航空影像生成的树冠高度模型，对内华达山脉植物区系省中所有树冠面积≥100平方米的个体树木进行了 delineation（描绘）。该模型使用超过330万个合成树冠进行训练，并在包含20,273个树冠的独立数据集上验证时，实现了0.602的中位交并比（IoU）。共绘制了6,515,705棵大型树木，覆盖了内华达山脉植物区系省约78.7%的区域。大型树木的空间分布与海拔、温度和降水相关。利用2020年至2025年的Sentinel-2时间序列数据，通过提取每个树冠的光谱轨迹，并应用BFAST断点检测算法结合干扰分类框架，表征了树木健康动态，以识别个体树木的死亡、干扰和恢复轨迹。根据CAL FIRE火灾边界估算的野火被确定为大型树木死亡的主要驱动因素，导致内华达山脉所有大型树木中10%死亡，且死亡率高度集中在2020-2021年极端火灾季节。
英文摘要
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.
