The underside

With the amount of focus on the surface, it's easy to forget that there's an underside to the falling city. And even when you consider it, it can be easy to dismiss it as the barren underside of a dying world. That couldn't be farther from the truth, however. The underside of the falling city has become a paradise for the previously rare cave-dwelling plants living all across the world. The combination of light and darkness needed for these plants was previously only found in cave entrances or caves with holes in the ceilings. Since the world got smaller and, more importantly, thinner, light reaches the underside during the mornings and evenings, while blocking the harsher rays during the day. The thinner ground and lack of flora on the surfaces make it easier for rainwater to get down to the underside, making it a haven for plants previously relying on wet caves to survive. Countless small insects and critters make the underside their home, living off of the plants or each other in a mini-ecosystem. Most insects have a symbiotic relationship with the flora keeping pests away. The plants also serve another important purpose. Used to living hung off of what loose soil they can find, most plants naturally spread their roots far and dense to reinforce the ground they sit in. With the steadily increasing amount of plants, this has had a noticeable effect on keeping the falling city more stable and increased the time it takes before certain parts collapse. Wanting to keep the plants alive and thriving for as long as possible, the city has several drains feeding straight into the ground with any excess water they can't use themselves, keeping the plants well-watered and happy to spread their roots all throughout the ground.