The conservation value of mesic gullies in dry forest landscapes: avian assemblages in the box-ironbark ecosystem of southern Australia

Drainage lines and shallow gullies generally have different microclimates a nd hence flora to surrounding upland ridges and slopes (abbreviated through out as 'ridges'). Gullies often have mesic, or at least less xeric, conditi ons compared with surrounding ridges. Gullies are frequently subjected to g reater human impacts, such as clearance for agriculture, logging, grazing-d amage and mining for alluvial deposits. We tested the hypothesis that mesic gullies in the generally dry (400-700 mm precipitation p. a.) box-ironbark forests of central Victoria, Australia, harbour a richer and different avi fauna to surrounding ridges. Ten pairs of adjacent gullies and ridge sites were surveyed eight times over 1 year. Species richness was one-third great er in gullies than in ridges, while mean total densities of birds were almo st twice as great. Assemblage composition also differed significantly, whic h reflected: (1) significantly different densities of those species common to both gullies and ridges (several more abundant in gullies, some more abu ndant in ridges); and (2) differences in composition wherein some species o ccurred only in one or the other habitat, even though pairs of gullies/ridg es were only 400-1900 m apart. These results indicate that avian assemblage s within gullies are distinct from those in ridges and slopes, and that int egrated management is required to conserve the entire avifauna of these dry forests and woodlands. The depletion of gully habitats through human distu rbance makes prescriptive management of gullies the highest priority at pre sent. (C) 2000 Elsevier Science Ltd. All rights reserved.