Biodiversity Conservation in Urbanising Forested Landscapes

Abstract

Unprecedented human population growth combined with rapid urbanisation of forest ecosystems highlight an urgent need to plan for biodiversity conservation in forested landscapes. To provide scientific evidence to guide management strategies and urban planning, I studied the distribution and/or abundance of amphibians and mammals and vegetation structure in a forest-dominated landscape in south-eastern Australia. In five scientific papers in three sections, I tackled important gaps of knowledge on: (1) the distribution of pond-breeding frogs (Paper I); (2) the distribution and abundance of mammals and vegetation structure across forest-urban interfaces (Papers II-IV); and (3) the fate of mammals under future scenarios of compact versus dispersed urban growth (Paper V).

In the first section, I studied the influence of aquatic and terrestrial variables on species richness and individual species occurrence of pond-breeding frogs in an urbanising landscape. I found the occurrence of common frogs depended on characteristics of the local aquatic habitat. In contrast, the terrestrial habitat was important for rare frogs: rare species richness declined with small increases in road cover as far as 1 km from the breeding habitat. While provision of aquatic habitat within urban areas may increase the occurrence of common species, I identified the need to preserve aquatic habitats within large forest reserves to conserve urban-sensitive amphibians.

In the second section, I studied the distribution and abundance of mammals and vegetation structure across forest-urban interfaces of high and low housing density. For forest-dwelling mammal species, I found low-density housing developments provided suitable habitat, whereas high-density housing developments had low species richness and species abundance. The lower abundance of forest-dwelling mammals in high-density housing developments was likely due to a stronger decline of forest vegetation structures across the forest-urban interface. In addition, I found the distribution of ground-dwelling mammals was better explained by local habitat structure (e.g. understorey cover) than by housing density or distance to an urban boundary. Based on my findings, I argued for the local-scale management of vegetation to improve habitat quality for mammals (e.g. to maintain/provide mature trees and understorey cover). Because a forest-dwelling species reduced its abundance at long distances from urban boundaries, I recommended limiting the amount of forest-urban interfaces when planning for urban development.

In the third section, I quantified the changes in mammal distribution and abundance at a landscape scale under future scenarios of compact (i.e. high-density housing) versus dispersed (i.e. low-density housing) urban growth. Although I previously found that dispersed development maintained biodiversity, I discovered that the occurrence and abundance of urban-sensitive species had a greater decrease under dispersed rather than compact development. I concluded compact urban growth is less damaging in landscapes with urban-sensitive fauna than dispersed development.

Taken together as a connected body of work, my PhD research demonstrates that positive conservation outcomes will be best achieved by integrating: local-scale management of habitat to improve habitat condition for fauna, with land use planning and urban growth policies. Land planning and urban growth policies should aim to limit forest clearing and fragmentation, the amount of forest-urban interfaces, and the sprawl of low-density housing development.