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Mortality of tree species around the globe is increasingly driven by hotter drought and heat waves. Tree juveniles are at risk, as well as adults, and this will have a negative effect on forest dynamics and structure under climate change. Novel management options are urgently needed to reduce this mortality and positively affect forest dynamics and structure. Potential drought-ameliorating soil amendments such as nanochitosan – a biopolymer upcycled from byproducts of the seafood industry – may provide an additional set of useful tools for reducing juvenile mortality during hotter droughts. Nanochitosan promotes water and nutrient absorption in plants but has not been tested in the context of drought and heat stress. We evaluated factors affecting mortality risk and rate for drylandPinus edulisjuveniles (2–3 years old) in a growth chamber using a factorial experiment that included ambient and +4°C warmer base temperatures, with and without a 10 day +8°C heat wave, and with and without a nanochitosan soil amendment. The nanochitosan treatment reduced the relative risk of mortality, emphasizing a protective function of this soil amendment, reducing the relative risk of mortality by 37%. Importantly, the protective effects of nanochitosan soil amendment in delaying tree mortality under hotter drought and heat waves provides a new, potentially positive management treatment for tree juveniles trying to survive in the climate of the Anthropocene. 

Abstract Tropical ecosystems are undergoing unprecedented rates of degradation from deforestation, fire, and drought disturbances. The collective effects of these disturbances threaten to shift large portions of tropical ecosystems such as Amazon forests into savanna‐like structure via tree loss, functional changes, and the emergence of fire (savannization). Changes from forest states to a more open savanna‐like structure can affect local microclimates, surface energy fluxes, and biosphere–atmosphere interactions. A predominant type of ecosystem state change is the loss of tree cover and structural complexity in disturbed forest. Although important advances have been made contrasting energy fluxes between historically distinct old‐growth forest and savanna systems, the emergence of secondary forests and savanna‐like ecosystems necessitates a reframing to consider gradients of tree structure that span forest to savanna‐like states at multiple scales. In this Innovative Viewpoint, we draw from the literature on forest–grassland continua to develop a framework to assess the consequences of tropical forest degradation on surface energy fluxes and canopy structure. We illustrate this framework for forest sites with contrasting canopy structure that ranges from simple, open, and savanna‐like to complex and closed, representative of tropical wet forest, within two climatically distinct regions in the Amazon. Using a recently developed rapid field assessment approach, we quantify differences in cover, leaf area vertical profiles, surface roughness, albedo, and energy balance partitioning between adjacent sites and compare canopy structure with adjacent old‐growth forest; more structurally simple forests displayed lower net radiation. To address forest–atmosphere feedback, we also consider the effects of canopy structure change on susceptibility to additional future disturbance. We illustrate a converse transition—recovery in structure following disturbance—measuring forest canopy structure 10 yr after the imposition of a 5‐yr drought in the ground‐breaking Seca Floresta experiment. Our approach strategically enables rapid characterization of surface properties relevant to vegetation models following degradation, and advances links between surface properties and canopy structure variables, increasingly available from remote sensing. Concluding, we hypothesize that understanding surface energy balance and microclimate change across degraded tropical forest states not only reveals critical atmospheric forcing, but also critical local‐scale feedbacks from forest sensitivity to additional climate‐linked disturbance.