Effect of soil treatment on the growth and foliage chemistry of three Eucalyptus species grown in a plantation as a food source for koalas

Abstract

Koalas in captivity are often provided with food from purpose-grown eucalypt plantations. In this study the growth/establishment of a long-term koala food plantation and the foliage chemistry of three Eucalyptus species (Eucalyptus microcorys, E. propinqua and E. tereticornis) that had applications of soil treatments (Terracottem™, mycorrhiza or a combination of both, and a control) at the time of planting were investigated. As well as tree growth, the foliage chemistry measured included total nitrogen (N), available N, ash, and moisture contents, and dry matter digestibility. Shortly after planting, the soil treatments had significant effects on tree growth but after approximately 2.5 years, they did not impact either tree growth or foliage chemistry. However, foliage age affected foliage chemistry, with new foliage having higher moisture and total N concentrations and lower ash contents than mature foliage. There were significant differences in tree growth and foliage chemistry between replicate blocks, which may have been related to environmental or geographical variables. This research provided critical information concerning the establishment of a suitable feed source for captive koalas and, more generally, furthered knowledge of Eucalyptus foliage chemistry. Future studies should investigate impacts of soil treatments on plant secondary metabolites including formylated phloroglucinol compounds. Understanding dietary selection is an important consideration when selecting species and managing food plantations for koalas. Providing captive koalas with a variety of different Eucalyptus species and foliage maturity ensures that they can select species and nutrients that they require.