Inducing whole-assemblage change by experimental manipulation of habitat structure

1. Habitat structure long has been identified as a primary factor influencing local assemblage composition. Most evidence has been in the form of correlations of species occurrence and assemblage composition over a range of habitats, with experimental verification of relationships being relatively uncommon because of the difficulties of enacting precise manipulations of habitat structure. 2. Fallen timber (also known as coarse or large woody debris) is one of the few habitat-structural elements in forests and woodlands that can be manipulated with relatively high precision. We report on manipulations of wood-loads on 30 experimental 1-ha plots in floodplain forests of northern Victoria, Australia, over 4 years (one pre- and three post-manipulation). 3. We show that very high wood-loads (80 Mg ha(-1)) and intermediate wood-loads derived from tree crowns (40 Mg ha(-1)) increase species richness (all species and ground-foraging species) and numbers of birds (all species and ground-foraging species) relative to the control plots. 4. Three bird species consistently increased most following manipulations: white-plumed honeyeater Lichenostomus penicillatus (Gould 1837) (fam. Meliphagidae), brown treecreeper Climacteris picumnus (Temm. & Laug. 1824) (fam. Climacteridae) and yellow rosella Platycercus elegans flaveolus (Gould 1837) (fam. Psittacidae). The honeyeater is not considered as a ground or fallen timber dependent species, while the treecreeper and rosella both are regarded as being dependent on ground-layer structure. 5. Fallen timber management needs to be considered in a landscape and temporal context for improving conservation of avian biodiversity.