As they expand, many of the world’s fast-growing cities end up building over floodplains, forests, and wetlands that could absorb rising waters during a storm or hold reservoirs of water during a drought.

for more than three-quarters of the world’s economy. As they expand, many of the world’s fast-growing cities end up building over floodplains, forests, and wetlands that could absorb rising waters during a storm or hold reservoirs of water during a drought.

In this group of chapters on decline and regeneration, I intend to dwell on several powerful forces that can influence, for good or for ill, the growth of diversity and vitality in cities, once an area is not crippled by lack of one or more of the four conditions necessary for generating diversity. These forces, in the form that they work for ill,