Temporal changes in the foliar chemical composition of forest trees after fire

Food is essential for animal survival, but wildfire can influence the availability and quality of food resources. However, even in fire-prone regions, we often lack a detailed understanding of how fire alters the nutritional landscape and how plant chemical composition varies over time since fire. In Australian forests, many eucalypts exhibit a key fire adaptation: the ability to resprout epicormically, producing new shoots from aerial stems shortly after fire. Little is known about the nutritional quality of epicormic foliage or how it supports the survival and recovery of endangered arboreal folivores such as the koala (Phascolarctos cinereus) and the greater gliders (Petauroides spp.). This gap in knowledge is particularly urgent to address as wildfires increase in frequency and severity due to anthropogenic climate change. The aim of this study was to measure how the nutrient and plant secondary metabolite (PSM) concentrations of post-fire epicormic growth changed over 1 year in six eucalypt species known to be browsed by arboreal marsupials. For comparison, we also sampled adult phase foliage from the same species in a nearby unburnt area, and in the burnt landscape where it was available. Total nitrogen concentrations were higher in epicormic foliage than in adult phase foliage from unburnt areas for all six eucalypt species, and declined over time in four of the six species. The available nitrogen concentration (a measure of the concentration of N liberated by mammalian digestion) was only higher in epicormic foliage for four of the six species, also decreasing over time. Concentrations of formylated phloroglucinol compounds, a type of PSM known to deter feeding by marsupial folivores, were generally higher in epicormic foliage. In contrast, unsubstituted B-ring flavanone concentrations, another class of PSMs, were generally lower in epicormic foliage. Synthesis. This study shows that fire changes the leaf chemistry of a critical food resource for arboreal folivores. This could conceivably influence diet selection and quality after fire by altering trade-offs between nutrient acquisition and plant defence. This has implications for our understanding of the habitat requirements for threatened folivores, since the tree species normally associated with their diet may differ in quality in burnt and unburnt landscapes.