Red zone study finds urban forest regeneration
Just what would grow in the urban environment if people were not around?
Lincoln University professor of urban ecology Glenn Stewart has been using the unique laboratory of the Christchurch red zone to conduct a pilot study and has found in the absence of human interference a "substantial native-dominated urban forest" would become established there.
His team sampled 100 properties across nine suburbs "with a view to determining the regeneration responses of native and exotic woody tree and shrub species after abandonment".
The regeneration of native species has been rapid "and, in some situations, prolific".
Prof Stewart said the Christchurch earthquakes "provided a unique opportunity to address the impacts of traumas on the urban environment and in particular, identify "resilient" plants.
He said in the absence of garden management we are seeing a "new" vegetation dynamic driven by new substrate availability - like silt from liquefaction - dispersal of seeds by birds, and surviving seed sources.
He said a proposal for the residential "red zone" to be converted into a public park called Avon-Otakaro has the potential to "add to the rich tapestry of natural habitats in the city and become an area of considerable native biodiversity".
The urban environment was often ignored or is an afterthought in planning though it is a key indicator of a nation's adaptability and resilience to catastrophic events such as earthquakes.
"Accessible and diverse green space is regarded as a predictor of human health, happiness, equity, and biodiversity, " he said.
The most common native seedlings in the red zone areas are cabbage trees, pittosporum and poroporo, all of which have fleshy fruits and are dispersed by birds.
There has also been a dramatic increase in seedlings of exotic species as well. Examples included "scotch broom", "elderberry", "buddleja" and gorse.
Substantial planting of native trees and shrubs in city gardens during the past several decades had provided a seed source for this native regeneration.
Prof Stewart said there would have to be "vigorous and intensive on-going management to control exotic species that are both adaptable and aggressive", to maintain a native urban forest. The introduction of other native species which now lack a seed source would increase biodiversity and offer food sources for native birds, lizards and invertebrates.