The Colorado River had been a ghost of its former self. For generations during the height of human civilization just five percent of the water that once flowed through the Colorado Delta actually made it to the sea. Even this water was almost entirely agricultural waste. The delta itself, once a lush green marshland of extreme ecological value, was reduced to mostly dried mud flats.
One day, however, a stream of fresh clear water begins to flow again. The flow increases over the coming weeks until the thirsty delta is once again filled with clean water from half a continent away. Many species have been lost forever in the last century, but those that remain quickly bounce back to recreate the lush habitat that once was.
Some 300 miles to the northwest, the suburbs of Los Angeles are vibrant with life. Rabbits and deer chew on the grass growing between cracks on the freeways, and the abundant shrubs in former lawns. Former housecats stalk the former pet rabbits, to in turn be chased by dogs. Native bobcats, coyotes and cougars prowl the bounty as well.
Birds flutter in and out of holes in roofs, and in the evening bats stream out of the shattered windows of houses to be silhouetted against the monolithic hulks of skyscrapers. Possums trundle among the calcified human skeletons in the shrubbery, searching for tasty snails to snack on.
I recently read World War Z and The Zombie Survival Guide, both by Max Brooks. They were a fun read, but I had a major complaint with one aspect of his vision of the coming zombie apocalypse (Don't worry I don't think this is a critical spoiler) -- with humans being overrun by zombies he describes complete environmental destruction. The environment is completely devastated somehow by the upheaval of human civilization in his books.
I think this is a fair bit daft since one of the greatest "extinction events" in history is the very existence of humans. There's even a word for it -- the holocene extinction event. It's estimated 140,000 species a year are currently becoming extinct, with possibly a loss of half of all species by 2100.
Even if you suppose the collapse of civilization entailed nuclear meltdowns, well, see this quote from wikipedia about the Zone of Exclusion around Chernobyl --
There have been reports that wildlife has flourished due to significant reduction of human impact. For this reason, the zone is considered by some as a classic example of an involuntary park. Populations of traditional Polesian animals (like wolves, wild boar and Roe Deer), red deer, moose, and beaver have multiplied enormously and begun expanding outside the zone. The area also houses flocks of European wisent and Przewalski's Horses released there after the accident. Even extremely rare lynx have appeared, and there are reports of tracks from brown bear, an animal not seen in the area for several centuries.
Basically, most animals simply don't live long enough for the lingering effects of a nuclear event to significantly effect them. Or at least, a nuclear holocaust is not as bad for wildlife as the regular activities of people are.
I think I may need to write my own zombie apocalypse book, where the zombie apocalypse actually returns the world's environments to equilibrium.
Several houses on the end of a suburban cul-de-sac have had the fences between them removed and around them reinforced to create a modern hunter-gatherer village out of decaying upper-middle-class homes. Around 100 people live inside the complex. They hunt for food and cook it on a fire pit that once was a jacuzzi. They still have guns to hunt with and clothing that was made of durable synthetic fabrics during the high point of human civilization, but in time they'll run out of bullets, and their denim and gortex will wear out, and they will have to re-learn how to make their own tools and clothing. Already they have a younger generation among them that will never know facebook, wikipedia, and blogging.
The evening sun sparkles off the remaining windows of the skyscrapers of Los Angeles to the north. Sadly, the sunset actually isn't as beautiful as it once was when the air was full of colourful pollutants.
A villager looks up at the distant tower and regards it as a solemn reminder of the beauty of how advanced civilization once had been. He then returns to a life that has much more in common with the way humans lived for most of the 200,000 years they've been on this Earth.