Thermal sensitivity across forest vertical profiles: patterns, mechanisms, and ecological implications

Abstract

Rising temperatures are influencing forests on many scales, with potentially strong variation vertically across forest strata. Using published research and new analyses, we evaluate how microclimate and leaf temperatures, traits, and gas exchange vary vertically in forests, shaping tree, and ecosystem ecology. In closed-canopy forests, upper canopy leaves are exposed to the highest solar radiation and evaporative demand, which can elevate leaf temperature (T leaf ), particularly when transpirational cooling is curtailed by limited stomatal conductance. However, foliar traits also vary across height or light gradients, partially mitigating and protecting against the elevation of upper canopy T leaf . Leaf metabolism generally increases with height across the vertical gradient, yet differences in thermal sensitivity across the gradient appear modest. Scaling from leaves to trees, canopy trees have higher absolute metabolic capacity and growth, yet are more vulnerable to drought and damaging T leaf than their smaller counterparts, particularly under climate change. By contrast, understory trees experience fewer extreme high T leaf 's but have fewer cooling mechanisms and thus may be strongly impacted by warming under some conditions, particularly when exposed to a harsher microenvironment through canopy disturbance. As the climate changes, integrating the patterns and mechanisms reviewed here into models will be critical to forecasting forest-climate feedback.

Does acclimation in distinct light conditions determine differences in the photosynthetic heat tolerance of coffee plants?

“…Coffee plants cultivated under HS and LS had differences in leaf traits similar to those expected in sun and shade leaves (Vinod et al 2022), and previously reported for coffee (Matos et al 2009;Moraes et al 2010). Generally, coffee leaves from plants grown in LS had a larger LA, SLA, and a lower na st (Table 1).…”

“…Acclimation to full sunlight promotes leaf traits that reduce leaf temperature, while shade acclimation promotes traits that maximize light capture (Vinod et al 2022). Sun leaves are generally smaller in size and thicker, with higher leaf mass to area (LMA), (or lower specific leaf area -SLA), and higher stomatal density to meet demand for cooling, whereas shade leaves have the opposite traits (Zwieniecki et al 2004;Vinod et al 2022). For coffee, these leaf traits significantly differ in plants growing under shade or in full sunlight (Matos et al 2009;Moraes et al 2010).…”

High Productivity at High Latitudes? Photosynthesis and Leaf Ecophysiology in Arctic Forests of the Eocene

“…For a tree canopy model, it is necessary to consider that assimilation and transpiration rates vary within the crown (Lalic et al., 2013; Lalic & Mihailovic, 2004; Vinod et al., 2022). This variation is caused by two factors: (a) leaves are not uniformly distributed within the crown, (b) the solar radiation becomes attenuated on its way through the crown because the leaves shade each other.…”

Feedback loops between 3D vegetation structure and ecological functions of animals

“…For example, moose seek taller and denser vegetation to avoid high summer temperatures (Melin et al, 2014), and arboreal animals track their thermal niche by moving vertically through vegetation, often seeking out tree cavities or denser vegetation during the hottest hours of the day (Scheffers et al, 2017; Scheffers & Williams, 2018). Microclimates vary by ecosystem type, with open woodlands yielding greater diurnal variation in temperature and tall, closed canopy forests reducing temperature extremes below the canopy (De Frenne et al, 2019, 2021; Jucker et al, 2018; Vinod et al, 2023). Canopy gap openings (e.g.…”