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Koalas continue to occupy their previous home-ranges after selective logging in Callitris-Eucalyptus forest

Kavanagh, RP, Stanton, MA, & Brassil, TE 2007, Wildlife Research, vol. 34, pp- 94-107.

Tree logging is one of the many processes that contribute to habitat loss for a variety of arboreal marsupials; however, sensitivity to logging may vary amongst different species. Koalas, for instance, do not require old trees for breeding or nesting as other arboreal marsupials do, but require certain tree species for food. The authors of this study investigated how selective logging affects the koalas in the Pilliga forests in north-western New South Wales, and found that tree preferences, home range sizes, home range overlap between individuals, movements, fidelity, fecundity and mortality of the koalas did not differ between logged and unlogged sites. These results suggest that selective logging does not necessarily adversely impact the conservation of koalas in the Pilliga forests.

  The Pilliga forests consist mainly of the commercially exploited white cypress pine (Callitris glaucophylla), several Eucalyptus species, rough-barked apple (Angophora floribunda) and bull oak (Allocasuarine luehmannii).  During the one-year study period, white cypress pine in the study area was reduced by 34-40.5% in basal area as a result of selective logging, while the other tree species remained mostly undisturbed as they were not targeted for commercial exploitation.  It was observed that the koalas in the study area utilised trees of all sizes and preferred Eucalyptus species over the other species regardless of the logging status of the sites. The only occasions where koalas were seen utilising other species, such as white cypress pines and rough-barked apple, were during hot summer days as these tree species provided shade opportunities for koalas. There was no difference in koala mortality between logged and unlogged sites; within the logged sites, only one out of eight deaths was found to be a possible consequence of logging activities, where the koala might have been displaced by tree-felling and later found by predators. Together, these findings revealed that selective logging in the study areas within the Pilliga forests did not lead to any significant changes in the movements, home-range sizes and overlaps, fidelity, fecundity, and mortality of the koala. This was likely because logging did not remove koalas’ preferred food trees, the Eucalyptus species, but instead only targeted white cypress pine, which the koalas do not rely heavily upon for their day-to-day survival.

  The Pilliga forests contribute significantly to the conservation of koalas in New South Wales; therefore, it is important to safeguard these habitats.  The authors of this study suggest that conservation management within these forests should focus on connecting the larger koala population within the Pilliga with surrounding smaller populations and protecting vegetation along waterways and drainage lines, as well as realising the role of white cypress pine as shade and shelter for koalas in hotter summer months. Thus, although not primary habitat for koalas, it is recommended that the over-exploitation of this commercially valuable tree is avoided.

 

Summarised by Cherie Chan

 

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