Urban realities: the contribution of residential gardens to the conservation of urban forest remnants

Urbanization has destroyed and fragmented previously large areas of habitat. Small remnants that still exist in numerous cities will be unable to sustain many viable wild plant populations if they do not expand into the surrounding urban matrix. Residential gardens form a significant component of urban green space in many cities and therefore could play a role in redressing this problem. Our ecological and social scientific study examined factors influencing the dispersal and regeneration of 12 bird-dispersed native woody species from Riccarton Bush, a 7.8 ha urban forest remnant, into surrounding residential properties in Christchurch, New Zealand. Over 125 years, the reported number of native vascular plant species in the Bush has declined by a third. Some species, particularly Dacrycarpus dacrydioides, the dominant woody species in the Bush, are being dispersed by birds and establishing in residential gardens predominantly within 250 m of the forest margin. These juveniles are not reaching maturity as most gardeners tend to remove all non-planted woody species. This suggests natural potential for regeneration exists but is insufficient without active human intervention. Our survey results show people are supportive of native plants in general but lack knowledge of the species. They are willing to plant locally appropriate woody species if provided with plants, information, and, most importantly, control over the location of plantings. Residential gardens consequently have the potential to play a major role in the conservation of urban biodiversity especially for species suited to the functions and size of gardens.