Peter has written:
“While most people have a negative view of spontaneous urban plants, they are actually performing many of the same ecological functions that native species perform in nonurban areas. ..absorbing excess nutrients that accumulate in wetlands; reducing heat buildup in heavily paved areas; controlling erosion along rivers and streams; mitigating soil, water, and air pollution; providing food and habitat for wildlife; and converting the carbon dioxide produced by the burning of fossil fuels into biomass.
The typical urban plant is well adapted to soils that are relatively fertile, dry, unshaded, and alkaline. Through a twist of evolutionary fate, many of these species have evolved life-history traits in their native habitats that are ‘pre-adapted’ them to flourish in cities.
Marble or brick buildings, for example, are analogous to naturally occurring limestone cliffs. Similarly, the increased use of deicing salts along walkways and highways has resulted in the development of high-pH microhabitats that are often colonized by either grassland species adapted to limestone soils or salt-loving plants from coastal habitats. Finally, the hotter, drier conditions one finds in cities favor species that come from exposed, sunny habitats in nature.
Preadaptation is a useful idea for understanding the emergent ecology of cities because it helps to explain that some plants and not others grow on piles of construction rubble, chain-link fence lines, highway median strips, pavement cracks, and compacted turf.
While most biologists view invasive plants as a serious biological problem, the fact remains that their initial introduction and distribution were usually the result of deliberate decisions that reflected the economic, ornamental, or conservation values of the day. Between the 1930s and the 1960s, various federal, state, and local agencies encouraged— and often subsidized— the cultivation of plants such as kudzu, multiflora rose, and autumn olive for erosion control and wildlife habitat purposes. It should come as no surprise that they became major problems forty years later, after millions of them had been planted. Indeed, the spread of nonnative species across the landscape is as much a cultural as a biological phenomenon, a fact often overlooked by advocates of strict ecological restoration.”