I have heard estimates of 100 million trees dead in the Harz. The common refrain is that this was caused by climate change, but also choice of monoculture was a major contributing factor as the area was historically covered by mixed deciduous. Furthermore, choice of forest type will affect soil moisture retention, so reduced rainfall would have been buffered by better choice of forest type.

Loss of those trees was an economic disaster. I’m not sure it’s an environmental disaster yet - especially as replanting seems to be with better reference to the agro-climatic zone.