5 Conclusions
The distribution of street tree assemblage and its associated air
purification benefit can’t be explained by population density theory and
don’t vary along the urban-suburban gradient. That is probably due to
the social characteristic of street trees. Street trees’ installation is
closely related to roads/streets’ construction, and roads/streets’
development is closely related to
economic development. Therefore,
where the government invests more for economic development and
streets/roads, and promote more people to settle down, there would be
more street trees and the associated air purification benefit. From the
ecosystem services perspective, it is a good
phenomenon that where there are more people, there
is more ecosystem services. However, street tree assemblage is just one
of the natural components in cities, we need further researches to
illuminate the distribution patterns and the
affected factors of other natural components and their associated
ecosystem services in cities respectively, then we can modify and
promote green infrastructure installation to meet the need of city
dwellers.
Public policy is a main driver of street trees planting and government
take lead role in promoting street trees installation. Therefore, it is
important for city sustainable development that public policy maker
conceive eco-consciousness when they are making decision and the
environmental decision-making ability of a government should be
strengthened.
Public policy would have a time leg effect on ecosystem services
provided by street trees for trees needing time to grow up. High-quality
heritage trees should be preserved during area redevelopment and city
sprawl.