In countless ways, big and small. World War II was by far the biggest ecological impact of any conflict up to that point, a combination of several factors, including technology but also the sheer scope of course. The space that a single soldier commanded in World War II was over 10x larger than in World War I, let alone previous conflicts, with the front per 100,000 soldiers being roughly 3,000 km in the former, and a mere 248 km for the latter. This increases not only how much damage happens in any given area, but also how widespread it can be. 'Obvious' things such as tanks and infantry maneuvering can wreak havoc on a region, and some still haven't really recovered. Deserts especially, being particularly fragile, might never do so, with portions of the Libyan desert where the Desert Rats and the Afrika Korps fought still suffering for it - and similarly even in the US, where evidence of US armor training for deployment to North Africa can still be seen. The 'crusts' of the desert, once broken by the weight of the tanks, can take decades to heal, if they ever do at all, causing an increase both in the frequency and severity of sandstorms for generations.
In similarly perhaps obvious fashion the arrival of thousands of men, animals, and material on previously isolated Pacific islands was hardly conducive to their continued health. Small atolls, transformed into airbases, saw large parts of their land left unable to support the bird populations that had once played host to, while many islands, previously rat free, found themselves now infested by the foreign vermin. Less seen, but no less felt was the introduction of new microbes and diseases which too could be quite harmful. Across the globe, a more famous example of war and disease would perhaps be the outbreak of malaria in Italy during the war, which saw a very noticeable uptick during the Second World War, in part caused by the creation of excellent breeding grounds for the mosquitos in the waterlogged craters and scars of battle, further assisted by the German destruction of the drainage machinery in the Tiber Delta. Curtailing this would be one of the first large scale uses of DDT.
Back, briefly, to the Pacific again though, some islands recovered well enough, but many felt the impact for decades beyond. In more enterprising areas, the transformation could at least be repurposed, such as Ellis Island, where the native population found that although unable to grow coconuts in the coral areas that they once had, the trees took well in the area around the abandoned Japanese airstrip, helped by the fact they had been planted over a massive reservoir of "fertilizer"... the mass gravesites of the Japanese dead. At least in theory the Allies were willing to make things right, but words and practice are not always the same thing. Although congress provided for settling damage claims, Public Law 393 required rather prompt filing of it, with only a year for its statute of limitations, and of course, any damage from enemy action was not covered.
The ecological damage can be far from immediate or obvious though.
One popular anecdote you can find included in several books, not to mention from there propagated out into the interwebs, relates to the displacement of the lupine populations in Eastern Europe. Mark Bellamy uses the story as the opening to his history of the Eastern Front, Absolute War, specifically because of how it illustrates the unexpected, and wide reaching impact that war can have, focusing on the spread of rabies. An outbreak first observed in the red fox population of Poland in 1939-1940 was displaced westward initially due to the conflict and slowly - as little as 20 to 40 kilometers per year - worked its way west, until the late 1960s when it finally had made its way entirely across the continent to the English channel, where it created something of a scare in the UK that it could, despite strict quarantine laws, nevertheless make its way over. Had the war never happened, could the spread still have happened? Perhaps, or perhaps it would have stayed put, or it instead would have been the Soviet Union experiencing the inordinate number of rabies infections in the period.
In another example of how war interacts with the environment that we might not notice immediately, a 2018 study published in Annales Geophysicae was able to isolate and analyze the damage caused on the ionosphere, specifically focusing on the impact of the Allied bombing campaign over Germany in the latter half of the war. If you're interested in the methodology, the article is (I believe) from an open access journal so check out the citation below, but as for the conclusion, they found very clear evidence that the shockwaves from the bombing campaign caused very brief, short-term damage on the ionosphere:
The bomb blasts heated the upper atmosphere, weakening it by reducing the number of electrons. The damage from each raid typically lasted about 24 hours; the impact of the diminished ionosphere at the time isn’t clear, but the research helps explain why Allied airmen reported that their bombers were damaged by shock waves even when they flew above the recommended heights.
In this case, the impact was smaller, or at least what we have so far observed, but it is certainly an interesting illustration of how the war was able to reach to the edge of space.
Some impacts though can be positive, even if unintended. During the conflict, the threat of submarine attack significantly curtailed deep sea fishing, for instance, which in turn gave populations several years to recover, even if only a temporary reprieve.
This is, all in all, a rather varied set of examples, but that is to be sure quite purposeful, as I feel that this rather meandering set of pickings illustrates exactly the core point, that the impact of the war touched everything, from big to small, and from the obvious to the strangely connected.
Sources Cited
Bellamy, Chris. Absolute War: Soviet Russia in the Second World War. Alfred A. Knopf, 2007.
Bennett, Judith A. Natives and Exotics World War II and Environment in the Southern Pacific Honolulu: University of Hawai’i Press, 2009.
Closmann, Charles E. War and the Environment Military Destruction in the Modern Age College Station: Texas A&M University Press, 2009.
Lloyd, H.G. “Wildlife Rabies in Europe and the British Situation.” Transactions of the Royal Society of Tropical Medicine and Hygiene 70, no. 3 (1976): 179–187.
Scott, Christopher J., and Patrick Major. 2018. “The Ionospheric Response over the UK to Major Bombing Raids during World War II.” Annales Geophysicae (09927689) 36 (5): 1243–54. doi:10.5194/angeo-36-1243-2018.
Tripathi, Anil Kumar. Changing Environmental Ideologies. APH Publishing, 1992.
Wiseman, Paul. 2019. “War’s Shock Waves Touched Upper Atmosphere.” World War II 33 (5): 10–11.
The second world war had a very pronounced, if not short lived effect on the fisheries of the North Sea and the Northern Atlantic. During the war, fishing activity in the North Sea was seriously disrupted by ongoing naval conflict, shortages of fuel and equipment, as well as the recruitment of experienced sailors and fishing vessels into the war effort. While the Nordic and Low Countries were able to maintain a modest amount of inshore catch, trawler fishing by British vessels fell to 1/8 of the previous peak during the war and Germany had lost a similar proportion. The need to find alternatives have lead to the exploitation of previously untapped Baltic fisheries by Axis powers and a revival of cod fishing in Newfoundland, possibly contributing to the degradation of these two fisheries in the following decades.
The effect of war on fish population was both immediate and highly tangible, with population growth measured in orders of magnitude as early as 1940. In addition to a general increase in quantity, sudden cessation of fishing caused some interesting reorganization in some fish species. For example, the haddock population in the North Sea saw a general increase similar to other species, however the number of young fish (<1 years old) actually declined by 83% despite a much larger number of sexually mature fish capable of breeding. The exact cause is still not well understood but it's been attributed to a combination of an adverse climate as well as the lack of time for the population to find a new equilibrium.
In any case, most studies agree that any marine biomass accumulated during five years of war was mostly depleted by the end of 1950s as commercial fishing activity plateaued and most traditional fisheries went into long-term decline therafter.
Main reference is a review article titled World War II and the “Great Acceleration” of North Atlantic Fisheries by Prof. Paul Holm. Additional sources are provided inline as hyperlinks.
Cormac Ó Gráda, the famous economic historian, argued that after 1900, famines became more associated with war or political upheaval than with poor harvests. To him, ‘Human action had a greater impact than, or greatly exacerbated, acts of nature’. This is especially true in the case of the Chinese theatre, where a military decision led to natural disaster.
When the Japanese advanced towards Wuhan during 1938, Nationalist leadership decided to blow up the Yellow River dikes to slow the Japanese advance and allow Nationalist forces to beat an ordered retreat. The destruction of the dikes led the river to leave the channel it had followed since 1855, moving southeast to the Huai River at a pace of sixteen kilometers per day. Post-war investigations revealed that the extent of the damage, with the released water swamping the twenty counties of eastern Henan, resulting in the inundation of thirty-two percent of the cultivated land (489,200 hectares) and forty-five percent of the villages. In Henan, 325,000 people died from wartime flooding, 4.8 percent of the pre-war population, while more than 1,172,000 people were displaced. After the river channels had stabilised, both the Chinese and the Japanese tried to utilise the newly inundated area by building dikes and deflection dikes to divert water into the other’s territory, which only exacerbated the situation in Henan.
The ecological change caused by the breaching of the dikes led to other problems in Henan province. In his work The Ecology of War in China: Henan Province, the Yellow River, and Beyond, 1938–1950, Muscolino points to ecological change as the main reason for the Henan famine of 1942-43. The ecological damage brought about by the breaching of the Yellow River dikes meant not only reduced food production but also problems in the circulation of food via transport networks. Short-term climate change in the form of global El Niño Southern Oscillation event which reduced levels of rainfall, as well as locust infestations, meant that food production was even more strained. However, as a frontline region, Henan province had to satisfy the needs of the Nationalist and Japanese armies, the Communists, and the local population, all of whom competed for the meagre harvest. This ‘energy crisis’ resulted in a famine that killed around 1.5 to 2 million people.
The man-made disaster caused by the breaching of the Yellow River dikes not only resulted in substantial ecological change that caused tremendous short-term damage, but also had a long-term ecological effect that resulted in another natural disaster in the form of famine.
Sources:
Lary, Diana, 'Drowned Earth: The Strategic Breaching of the Yellow River Dyke, 1938', War in History 8 (2001), 191-207.
Muscolino, Micah S., The Ecology of War in China: Henan Province, the Yellow River, and Beyond, 1938–1950 (Oxford: Oxford University Press, 2014).
The scars of war: the impact of warfare on modern China, ed. by Diana Lary and Stephen MacKinnon (Vancouver: University of British Columbia, 2001).
Devil's advocate here:
You need to clarify what counts as ecological disruption. Ecologists measure ecologies in many ways, but two stand out: Total Net productivity (basically photosynthesis - decomposition) and species diversity.
You need to distinguish some competing notions:
So for example, a clearcut forestry operation, or major forest fire is a short term ecological disruption. But it is only short term. The introduction of earthworms into the eastern hardwood forests in the U.S. made a huge permanent change those forests. Decomposition on fhe forest floor was *much* faster. The loss of the American Chestnut tree due to chestnut blight was a similar disruption.
One of the answers cited 'zone red' in France where remnants of gas warfare and unexploded ordinance made the region unsafe. I bet there is still a thriving ecology there. Won't be the same as the original farmland or woodland ecology because there is little or no human action.
Another answer cites tank tracks that take decades to recover. Desert ecologies are often water limited. This shows up in the plantless zones between plants. I would expect that the normal response to sterile tracks would be that the plants on either side would be a bit larger, or a bit closer together. When the area covered by tracks is of the same magnitude as the normal empty area between plants, you would start to see changes in the primary ecological measures.