Global climate change increases uncertainty in sustained functioning of forest ecosystems. Forest canopies are a key link between terrestrial ecosystems, the atmosphere, and climate. Here, we introduce research presented at the 66th meeting of the Ecological Society of Japan in the symposium “Structure and function of forest canopies under climate change.” Old‐growth forest carbon stores are the largest and may be the most vulnerable to climate change as the balance between sequestration and emission could easily be tipped. Detailed structural analysis of individual large, old trees shows they are allocating wood to the trunk and crown in patterns that cannot be deduced from ground, thus can be used to more accurately quantify total forest carbon and sequestration. Slowly migrating species sensitive to novel climatic conditions will have to acclimate at the individual level. Accounting for physiological responses of trees to climate change will improve predictions of future species distributions and subsequent functioning of forest ecosystems. Field experiments manipulating temperature and precipitation show how trees compensate physiologically to mitigate for higher temperatures and drought. However, it is difficult to measure acclimation responses over long timeframes. Intraindividual trait variation is proposed as an indicator of acclimation potential of trees to future conditions and suggests that acclimation potential may vary among regional populations within a species. Integrating whole‐tree structural data with physiological data offers a promising avenue for understanding how trees will respond to climatic shifts.

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We compared acclimation potential of three native, evergreen tree species to wind-exposure in an 6 urban green-roof environment. One year after planting on the green roof, Machilus thumbergii 7 retained all leaves and produced new leaves. In contrast, Fraxinus griffithii, and Quercus 8 myrsinifolia shed all leaves but produced more new leaves than the previous year. After two years, 9 current-year leaves of all three species had acclimated hydraulically (lower osmotic potentials at 10 saturation and turgor loss) to wind-induced water stress and leaf number increased to four to eight 11 times the initial amount. When trees were exposed to simulated winds in a greenhouse experiment, 12 osmotic adjustment was observed for current-year leaves of M. thumbergii, whereas leaves of F.13 griffithii and Q. myrsinifolia had hydraulic traits more vulnerable to wind-induced water stress 14 (higher osmotic potential and relative water content at turgor loss). We inferred that, M.15 thumbergii invests in hydraulic acclimation to retain current-year leaves in response to increased 16 wind, whereas F. griffithii and Q. myrsinifolia allocate resources to new leaf production. Our 17 results suggest both strategies achieve tree-level acclimation to wind exposure.

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