...Overworld

After the Fall, the planet was left barren.  A few areas remained viable for plantlife, such as the river basins of the Mississippi, Nike, and Amazon, along with other large sources of fresh water.  Many plants evolved root and leaf systems which leeched water from the soil, filtering out the poisons that couldnt be neutralized or adapted to.  Mountainous regions retained some vegetation, though vast forests no longer stand.  Where plants are able to grow, the density is sparse and the root systems are spread out.  The rainforests delicate ecologies were unsustainable.  Rugged plains and deserts have taken their places on the globe.  The majority of oxygen is generated by oceanic ecosystems, where the massive kills of sea creatures allowed kelp, plankton and algae to run rampant.  Bodies of water such as the Great Lakes, Mediterranean Sea and the Gulf of Nevada have developed separate kelp bogs hundreds of square miles apiece.

                Animal life underwent mutations, as well.  Herbivores, such as deer, elk, and cattle, increased in size and mass.  Many of these species became somewhat predatory in nature, adding insects and small reptiles to their diet, some resorting to the cannibalism of the weaker members of the herd when other food becomes too scarce.  Their bodies developed systems to store food and water for long periods of time without having to digest their own muscle or organ tissues.  Because the prey grew larger, the predators grew smaller.  They learned to hunt in larger packs, and use strategies to bring down the game.  Most predators are about the size of medium-sized dogs, while cattle (for example) can grow to ten feet tall at the shoulder, weighing over 5000 pounds.  Reptiles flourished in the deserts and wastelands, while amphibians were drawn to the vast kelp bogs.  Insects became more diverse, though fundamentally unchanged.  These inhabit more of the planet than humans.

                Like most of the remaining life, birds have found habitable places near water sources, where food is plentiful.  Carrion feeders enjoyed a brief population explosion after the Fall, until their sheer numbers drove many of their species close to extinction through disease, starvation and direct competition for food sources.

                Within the high domes of the CorpStates, hydroponics is widely used for growing food for the population of the consumer-associates who live and work for UNICorp there.  Trade with specialized CorpState farms, and with the Off-World colonies also supplies a variety of foodstuffs.

                Overworlders (those who live outside of the domed CorpStates) hunt, fish, and gather vegetation where possible, and supplement their food stocks by raiding the UNICorp shipping network.

                Subearthers have developed their own forms of hydroponics and sunless farming.  It is rumored that they also trade with the CorpStates and some of the larger Overworld factions.