Given the dangerous, precipitous global decline in biodiversity, coupled with rapid urbanization, cities have a key role to play in protecting biodiversity. In fact, cities already do harbor a large share of biodiversity. This may be due to the fact that cities are often situated in places of large inherent biodiversity (along rivers, for example), and/or because of large numbers of introduced species and landscape heterogeneity in cities. Furthermore, surrounding agricultural areas are often simplified landscapes with limited biodiversity while many forests are degraded, and thus less biodiverse, due to timber harvest regimes, roads, etc. Thus, contrary to what might be assumed, rural areas are not necessarily more biodiverse than cities.
The author stresses the importance of managing cities to increase biodiversity. This process should begin with a city-wide tree inventory to identify tree species, locations and health. Management should focus on increasing biodiversity among street trees, and in parks, woodlots, abandoned lots, and back/front yards, while also fostering public awareness and appreciation for ecological principles. Planting efforts should prioritize native species, which are better adapted to local conditions, are non-invasive, and whose protection contributes to global biodiversity conservation. (While great numbers of introduced species may increase local biodiversity, it has a homogenizing effect on global biodiversity.) Furthermore, natural regeneration of parks and woodlots should be encouraged through less intensive management, whereby seeds of native (or at least non-invasive) species are allowed to germinate and establish where they fall, instead of being fastidiously mowed or weeded.
Alvey, Alexis A., 2006, Promoting and preserving biodiversity in the urban forest, Urban Forestry & Urban Greening 5, https://www.sciencedirect.com/science/article/abs/pii/S1618866706000732.