Suppose a chemical was accidentally released into the air and killed all the plants in a city. Would it matter? Would the city look slightly different, or fundamentally different? Would almost everyone leave?

Or perhaps only certain types of plants died – trees, flowers, or native species. Or, in only certain habitats – lawns, street trees, or woodlands. Or, it prevented flower formation, seed germination, or shrub growth. Or it cut biodiversity by 90%, or tripled the number of species. Or vegetation change slowed, or accelerated, tenfold. Or areas were hit at different intensity, reconfiguring the vegetation patterns of the urban landscape. While these are extreme examples, they point to many of the key patterns, processes, and changes to be explored in this chapter.