2021 featured a diverse season with a late season start while the overshoot precipitation in spring and summer led to a relaxation of the drought-stress since 2018 (high greenness in many parts of German #forests).
Peak season (end of July) NDVI indicates a heterogeneous pattern across Europe. While parts of Central Europe featured a relaxation of the drought of the previous three years due to extensive precipitation, parts of Scandinavia featured low quantiles, possibly due to a relatively warm and dry summer. At the same, parts of the Mediterranean (in particular Italy, Balkan) also featured relatively low NDVI values, reflecting the extraordinary heatwaves of summer 2021 which negatively affected forests.
After the summer break, the forest condition monitor displays a relaxation from the drought of the past three years over large parts of Germany. However, hotspots of forest dieback such as the Harz or Thüringer Wald are yet characterized by very low quantiles and proportions. And despite the relaxation, the drought 2018-2020 has had a significant impact on German and Central European forests as also indicated in the quantiles and proportions of those years.
The greenness of German Forests has in the meantime reached normal to above average values, probably due to a relaxation of the drought in the past three years in course of precipitation surplus and a recovery from the delayed phenology in the extraordinarily cool spring 2021. However, forests in Brandenburg, the Harz and Northrhine-Westphalia yet seem to suffer from drought legacies (NRW) and/or ongoing drought (Harz, BB) in these regions.
The hypothesis from July 1st that high precipitation in spring relaxes the drought situation is supported by increasing shares of high quantiles (blue colors) in the recent update. However, some hotspots of potential forest decline remain in Central Germany (i.e. Northrhine-Westfalia, Hessen, and Brandenburg) matching some of the remaining drought hot-spots early in June 21 as indicated by the German Drought monitor [da gibt’s evtl. ein hash-tag – sind die auf Twitter – falls ja dann gerne verlinken]. The development for these remaining hot-spots of forest decline over the next weeks will be particularly interesting.
The high share of lowest quantiles and low proportions has partly decreased in course of spring greening, supporting the interpretation from June 20th that the low greenness early in spring was caused by a delayed phenology. The development over the next weeks will be particularly interesting since large parts of Germany have received plenty precipitation thereby potentially dampening the soil drought and relaxing the drought-stress of trees.
Large parts of German forests feature extraordinarily low greenness which likely is a combined result of drought legacies from 2018-2020 but also caused by the delayed spring phenology in course of the coldest spring since 1983 (see also these links for temperature anomalies and phenology anomalies).