Stem functional traits vary among co-occurring tree species and forest vulnerability to drought

Context Stem functional traits are critical for tree hydraulic infrastructure and have important consequences for forest function, particularly concerning vulnerability to drought. Methods. Three stem traits, sapwood area, heartwood area, and bark area, were measured in two co-dominant forest species, Eucalyptus marginata Donn. Ex. Sm. and Corymbia calophylla (Lindl.) K.D.Hill & L.A.S.Johnson, in forest patches with low and high vulnerabilities to drought in south-western Australia. Patches of high drought vulnerability experienced die-off during a heatwave and drought in 2011, while patches of low vulnerability were largely not affected. Key results. Sapwood area was significantly higher in C. calophylla than in E marginata, and C. calophylla maintained more sapwood per unit DBH than did E. marginata, especially in larger trees. There was a 29% smaller sapwood area in high drought-vulnerability patches than in low drought-vulnerability patches (including both species). The relationship between sapwood area and DBH varied by tree size. Small trees had a greater sapwood area in high drought-vulnerable patches, whereas larger trees had more sapwood in low drought-vulnerable patches. It is unclear whether sapwood area relationships reflect differences in leaf area or tree age. Conclusions. Implications. Observed differences in sapwood between species may help explain their differential tolerance to drought, whereas differences between drought-vulnerability sites may suggest adaptation in the studied species. Understanding the traits associated with drought vulnerability will increase our prediction of forest response to drying and warming. Strong relationships between stem traits and DBH, developed here, may help future efforts to model water-use in the Northern Jarrah Forest.