Widespread drought-induced leaf shedding and legacy effects on productivity in European deciduous forests,Remote Sensing in Ecology and Conservation

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Widespread drought-induced leaf shedding and legacy effects on productivity in European deciduous forests
Remote Sensing in Ecology and Conservation ( IF 3.9 ) Pub Date : 2022-08-08 , DOI: 10.1002/rse2.296
Adrià Descals _{1,

2} , Aleixandre Verger _{1,

3} , Gaofei Yin ₄ , Iolanda Filella _{1,

2} , Josep Peñuelas _{1,

2}

Affiliation

Heatwaves and droughts are becoming more common and severe in Europe, causing changes in tree phenology, disrupting the sequestration of carbon and causing tree mortality on a continental scale. The responses of leaf shedding to heatwaves and droughts remain uncertain, although temperate deciduous forests may shed their leaves if exposed to extreme heat and water stress. Little information, however, is available about the extent and recurrence of early leaf shedding induced by drought, likely because it occurs in small forest patches and can be discriminated only during a few weeks. We used highly spatiotemporal Sentinel-2 data as evidence of widespread drought-induced early leaf shedding in Europe during 2017–2021. We estimated the timing of leaf shedding from NDVI time series and a threshold-based method that extracts the end of the growing season. Then, we evaluated the heatwave and drought impacts at the end of season by analysing the z-score of Landsat-7 and -8 land surface temperature and the ERA5-Land air temperature and aridity index. The 10-m resolution Sentinel-2 data identified early leaf shedding not detected by the low-resolution (250 m) MODIS sensor. Early leaf shedding was observed across Europe during the entire study period and its occurrence was linked to preceding anomalously high temperatures and arid conditions. Our results also indicated that mean summer NDVI decreased significantly in the years following early leaf shedding, suggesting a legacy decline in vegetation productivity. Our study demonstrates that decametric satellite data can be used to monitor the responses of forests to extreme climate events at the canopy level and indicates that early leaf shedding associated with heatwaves and droughts is more widespread and frequent across the continent than previously thought.

中文翻译：

广泛干旱引起的落叶和对欧洲落叶林生产力的遗留影响

热浪和干旱在欧洲变得越来越普遍和严重，导致树木物候发生变化，破坏碳固存并导致大陆范围内的树木死亡。叶子脱落对热浪和干旱的反应仍然不确定，尽管温带落叶林如果暴露在极端高温和水分胁迫下可能会脱落叶子。然而，关于干旱引起的早期落叶的程度和复发的信息很少，这可能是因为它发生在小片森林中，并且只能在几周内被辨别出来。我们使用高度时空的 Sentinel-2 数据作为 2017-2021 年欧洲广泛干旱引起的早期落叶的证据。我们根据 NDVI 时间序列和提取生长季节结束的基于阈值的方法估计了落叶时间。然后，我们通过分析 Landsat-7 和 -8 地表温度的 z 得分以及 ERA5-Land 气温和干旱指数，评估了季节末的热浪和干旱影响。10 米分辨率的 Sentinel-2 数据识别出低分辨率（250 米）MODIS 传感器未检测到的早期叶片脱落。在整个研究期间，整个欧洲都观察到早期落叶现象，其发生与之前的异常高温和干旱条件有关。我们的结果还表明，在早期落叶后的几年中，平均夏季 NDVI 显着下降，表明植被生产力的遗留下降。

更新日期：2022-08-08

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