The nutritional quality of post-fire eucalypt regrowth and its consumption by koalas in the New South Wales Southern Tablelands

Abstract

Most forests and woodlands of south-eastern Australia are fire prone. These landscapes are typically dominated by tree species of the genus Eucalyptus, and many of these are proficient epicormic resprouters after fire. Several marsupial folivores rely on Eucalyptus foliage, including the koala. Little is known about the nutritional composition of epicormic leaves and whether folivores can utilise them. Following the 2019–20 megafires, we offered koalas epicormic leaves from eight eucalypt species that occur in the New South Wales Southern Tablelands and measured concentrations of foliar chemical constituents known to influence koala feeding (total and available nitrogen, formylated phloroglucinol compounds (FPCs), and unsubstituted B-ring flavanones (UBFs)). Captive koalas ate epicormic leaves from the four eucalypt species belonging to the subgenus Symphyomyrtus but ate relatively little from the species of the subgenus Eucalyptus. Available nitrogen was significantly higher in symphyomyrtle epicormic regrowth than in monocalypts and differed between species. Concentrations of FPCs and UBFs also differed between eucalypt species. Our results suggest that post-fire epicormic regrowth from symphyomyrtle species may be more readily browsed than that of monocalypts by koalas in the NSW Southern Tablelands. Therefore, some burnt areas are likely to be better quality habitat for koalas than others.