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Designing food and habitat trees for urban koalas: identifying short ecotypes of Corymbia intermedia

Trueman, SJ, McMahon, TV, Grant, EL, Walton, DA, Elliott, BB & Wallace, HM 2017, Australian Journal of Botany, vol. 65, no. 1, pp. 384-388.

A short variety of a preferred koala food tree, Corymbia intermedia or ‘pink bloodwood’, may provide suitable food and shelter for koalas in urban and peri-urban areas where taller eucalypts present unacceptable risks to people and infrastructure.

  Short ecotypes of C. intermedia grow on the exposed headlands of Australia’s subtropical eastern coast. In this study, seed was collected from these coastal populations and cultivated externally. The long-term survival rate of these short ecotype seedlings was 50-85%, which suggests their suitability for cultivation in horticultural plantings beyond their natural distribution. In cultivation, the short ecotype C. intermedia trees were 22 – 43% shorter than tall ecotype C. intermedia from a nearby population, with heights of 5 – 7m tall and 8 – 12m tall respectively. Although tree height can be affected by environmental conditions, the finding that short ecotype C. intermedia seedlings retained short height in cultivation suggests that the trait is genetic. The selection pressures that favour this trait at the exposed headlands may include reduced susceptibility to soil salinity, strong winds and salt spray. The short ecotype C. intermedia trees in cultivation reached a mature height of up to 7m after eight years. When the foliage of these cultivated trees was offered to a captive Queensland koala population, it was consumed as readily as that of tall ecotype C. intermedia.

  Given the ongoing threat of habitat loss to declining koala populations, the revegetation of urban areas with Eucalyptus species has been recognised by local councils as a potential strategy for enhancing food and shelter availability and habitat connectivity for the animals. Although most food and shelter tree species utilised by koalas are tall, such trees can pose threats to residents and infrastructure where they drop branches. If koalas are to survive in urban areas, however, the presence of mature eucalypts is essential.

  Short ecotype C. intermedia trees have been found here to grow well in environments outside of their natural distribution, reach mature heights that make them suitable for planting in urban areas, and provide a valuable food source for koalas. Planting these short ecotype eucalypts in areas where the growth of taller species is prohibited may be a valuable tool for koala conservation in Australia’s highly populated regions.

 

Summarised by Joanna Horsfall

 

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