Hi there, military historian (PhD Candidate specializing in the history of war's effects on society and the environment). World War One had a few effects on wildlife and the environment more generally.
While combatants and observers remembered the battlefields as destroyed wastelands, environmental historian Tail Keller argues that eh war's negative effects on Europe's flora and fauna were short-lived while wildlife populations elsewhere suffered much more. "Flora quickly recovered and fauna soon returned. Paradoxically, longer-termed environmental transformations occurred behind the lines, away from the killing fields. Comparing the fate of the fighting fronts to timber harvesting around the world, tin mining in Malaysia, oil extraction in Mexico, and wheat farming in the United States and Canada reveals a far more complicated picture of the war's environmental legacy than what photographs of No Man's Land suggest."[See https://encyclopedia.1914-1918-online.net/article/destruction_of_the_ecosystem]
Soldiers in the Eastern Front hunted and dined on European bison and nearly exterminated the species; however the species population was already reduced to only 400 animals by aristocratic hunting parties before the war.
Submarine warfare and a decline in the size of European fishing fleets led to an increase in the population of oceanic fish. Ironically, the war accelerated the development and deployment of more powerful and efficient fishing technologies, which increased the number of fish taken after the war, greatly reducing the viability of North Sea fishery populations.
The war also marked the "militarization" of the French forestry profession (with help of the US fores service) which greatly increased logging in France and adversely effected wildlife populations throughout the country. The war also undermined what a previously emerging international wildlife conservation movement.
Changes in martial technology marked the emergence of petroleum as the most important source of wartime fuel. It was initially used to complement the use of coal, but it quickly became the critical source of energy. It's effects are probably more drawn out than your looking for, but it's a key fact to keep in mind if you're interested in the environmental effects of the war.
Hope this helps!