The distribution and abundance of an unusual resource for koalas (Phascolarctos cinereus) in a sodium-poor environment

PLoS One. 2020 Jun 11;15(6):e0234515. doi: 10.1371/journal.pone.0234515. eCollection 2020.


Environmentally available sodium tends to decrease with increasing elevation, and sodium resources in these sodium-poor environments are critical for the survival of herbivores. Eucalypt leaves in the subalpine Monaro region of NSW, Australia contain much less sodium than eucalypt leaves at lower elevations, and subalpine koalas obtain this much needed resource by eating the bark from some Eucalyptus mannifera trees. To better understand the availability of salty-barked trees, we searched for evidence of koala bark chewing at 100 randomly generated locations in the region. We found 318 E. mannifera trees with koala chew marks. We also analysed sodium concentrations in the bark of three unchewed E. mannifera trees from each site to determine whether there were trees with high bark sodium content that had not yet been utilized by koalas. Although 90% of unchewed trees had sodium concentrations less than 225.4 DM, some unchewed trees contained high sodium concentrations (up to 1213.1 DM). From the random survey, we can extrapolate that 11% of trees in this area have bark sodium above 300 DM, which is based on the concentration of bark sodium observed in at least moderately chewed trees. We would expect to find 0.24 of these trees per 200 m2, or 720,000 salty-barked trees in the 30 km by 20 km study area. Bark chewing by koalas is widespread in the area, and trees with salty bark are more common than initially thought. We discuss correlations with the occurrence of salty-barked trees and other landscape attributes; however, questions remain about why some E. mannifera trees have much more bark sodium than others. Studies such as this one should be expanded to identify sodium resources and their availability for other herbivorous species, since many are predicted to move to higher elevations in response to climate change.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Altitude
  • Animals
  • Australia
  • Climate Change
  • Eucalyptus / chemistry*
  • Herbivory / physiology*
  • Micronutrients / analysis*
  • Phascolarctidae / physiology*
  • Plant Bark / chemistry
  • Plant Leaves / chemistry
  • Population Density
  • Sodium / analysis*


  • Micronutrients
  • Sodium

Grants and funding

KNY received funding to support this work from the New South Wales (NSW) Office of Environment and Heritage (OEH). This came from a grant to NSW OEH from the Australian Government Biodiversity Fund (Grant number LSP-945029-1202). WJF received financial support from the Australian National University, Research School of Biology. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.