Fragmented landscapes: direct measurement of species loss and implications for conservation and landscape restoration

A project undertaken at the School of Ecology and Environment, Deakin University, Burwood, Victoria, and supervised by A Bennett.

Great changes have occurred to Australian landscapes since European settlement.  One of the most profound changes for the native flora and fauna has been the clearing and fragmentation of natural habitats and the consequent fragmentation of populations for species that depend on natural environments.  Some species have declined to the point of local extinction, and there is concern that many others may follow this pathway.  There is now a growing scientific understanding of the distribution of species in relation to fragments of habitat that remain in developed landscapes today.  However, a major gap in our knowledge is an understanding of how landscapes and the native biota change through time. 

More than twenty years ago, extensive surveys of native mammals were undertaken in a large number of forest fragments in the Naringal area, south-western Victoria (between Warrnambool and Terang).  In this study, we are revisiting these sites to survey the status of the native mammal fauna today, to assess whether there has been long-term changes to the fauna in this fragmented environment.  The study provides a unique opportunity to address three issues of direct relevance to the conservation and restoration in rural environments:

  • is there a long-term loss of species in the decades following fragmentation of habitats and, if so, what is the extent of species loss?
  • which types of species are most vulnerable to long-term decline and loss?
  • what are the characteristics of remnant habitats that favour the maintenance of native species in these landscapes?

To answer these questions, surveys of native mammals are being carried out in the same forest fragments that were first surveyed in 1979-80.  Care is taken to use the same survey techniques (e.g. trapping, spotlight observations, daytime observations of mammals or their tracks and signs) and at the same intensity as the original survey.

Aerial photos have been used to map and measure the changes in native vegetation in the study area.  In the early 1940s, approximately 51% of this 190 km2 study area remained forested with large continuous tracts of forest.  By 1966 clearing had reduced forest cover to 22% of the area and by 1980 to 12%, with the remaining forest patches becoming increasingly smaller and isolated by cleared farmland.  Over the subsequent 20 years forest cover has remained relatively constant, with 11.3% forest cover in 2002.  All remaining forest fragments are smaller than 100 ha (most <10 ha) but a notable feature is the connecting network of forested vegetation along roadsides and creeks. 

A total of 33 species of native mammals, including 11 species of bats, are known from the study area.  Of these, six species have become locally extinct since settlement in the late 1800s (Tiger Quoll, Eastern Quoll, Dingo, Common Wombat, Koala, Eastern Pygmy-possum) although the Koala has been re-introduced.  Our current research will determine the extent of change that may have occurred over the last 22 years, whether an increase or decrease in status or local extinction.  Species predicted to be most vulnerable to decline include the Long-nosed Potoroo, Southern Brown Bandicoot and Long-nosed Bandicoot.

References for historical surveys

Bennett, A.F., 1987. Conservation of mammals within a fragmented forest environment: the contributions of insular biogeography and autecology.  pp. 41-52 in Nature Conservation: The Role of Remnants of Native Vegetation. (Eds. D.A.Saunders, G.W.Arnold, A.A.Burbidge and A.J.M.Hopkins) (Surrey Beatty: Sydney).

Bennett, A.F. 1988. Roadside vegetation: a habitat for mammals at Naringal, south-western Victoria.  Victorian Naturalist 105, 106-13.

Bennett, A.F., 1990.  Land use, forest fragmentation and the mammalian fauna at Naringal, south-western Victoria. Australian Wildlife Research 17, 325-47.

Bennett, A.F., 1990. Habitat corridors and the conservation of small mammals in a fragmented forest environment. Landscape Ecology 4, 109-22.

 

Aerial view of the study area showing remnant forest vegetation amongst farmland

Roadside vegetation links many forest patches, contributing to a connected network of forest habitat across the district

The Long-nosed Potoroo Potorous tridactylus, a notable species of mammal in this study area