This may be an odd question, but it dawned on my the other day that you never really hear anything ever mentioned about large European wildlfe. I assume there is some, but was wondering if the effect of two large scale wars in the span of 30 years had a major ecological impact on native European fuana, or if this is something that has even been studied.
By the turn of the 20th century, the wisent (or European Bison) was already endangered and it's range severely limited. Hunting by German officers further decreased the population in Białowieża Forest (today a border region between Poland and Belarus), although the last of this population was killed after the war in 1919. Today's wisent population there goes back to zoo animals that have been re-introduced into the wild.
There is a newspaper article from 1917 that surfaces on reddit from time to time about an outright war between the Russian and German armies on one side and a large number of wolves on the other. Given that the article does not even cite the vaguest of sources, I wouldn't give it much credit though.
Slightly off topic, but the Atlantic cod stocks which had been on the decline for decades had their biggest recovery period to date during WWII due in part to the difficulties off large scale commercial fishing by the major powers, mainly Norway and the UK. This however only stalled the eventual collapse of the fisheries.
Source: Mark Kurlansky