Effects of partial logging systems on bird assemblages in Tasmania

Abstract

The effects on bird assemblages of several partial logging systems were examined in dry eucalypt forests in Tasmania. Densities and species composition of birds in partially logged areas were compared with those in adjacent mature forest, with clearfelled areas sometimes also being sampled. In the first study, the effects of advanced growth retention logging, which involves retaining all young trees with good growth potential, were compared with those of 17-year-old regeneration resulting from clearfelling. Densities of most bird species were lower in areas of advanced growth retention than in mature forest but there was no evidence of any species being excluded from the advanced growth retention. The relative use of the three forest types varied over the seasons. The differences were most marked in spring and winter. Two species (superb fairywren and brown thornbill) were most abundant in areas of advanced growth retention in autumn. Two species (strong-billed honeyeater and flame robin) that were common in mature forest and advanced growth retention were not recorded in the clearfell regeneration. In the second study, the effects of overstorey removal logging, which involves the removal of older trees and the retention of an even-aged stratum of younger trees, was examined with 3-year-old clearfell also sampled. Most species were more abundant in mature forest than in overstorey removal with canopy and mid-layer birds being more adversely affected than birds which predominately utilised the lower layers or the ground. One species, the superb fairy-wren, appeared to be advantaged by logging. Species diversity and abundance of birds were much lower in 3-year-old clearfell than in both mature forest and overstorey removal. In the third study, the effects of shelterwood logging, which involves the retention of 30–50% of the canopy to provide protection for young regeneration from climatic extremes, were examined. Many species were more abundant in mature forest than in shelterwood with the differences being most pronounced for canopy and mid-layer birds. In winter one species, black-headed honeyeater, was more abundant in shelterwood than in mature forest. Satin flycatchers appeared to be unable to utilise the logged forest. Partial logging is increasingly being used in preference to clearfelling in the dry forests in Tasmania. Partial logging systems have a much lower impact on birds than does clearfelling. Thus, retention of older trees can amellorate the impacts of logging. Densities of birds are reduced after partial logging but numbers of species present are comparable with mature forest. A few species increase in abundance after partial logging. However, on some sites retention of a large component of the mature canopy will still lead to the disappearance of one or two species.