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Disentangling the Role of Forest Structure and Functional Traits for the Thermal Balance in the Mediterranean-Temperate Ecotone
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  • Adria Barbeta,
  • Diego G. Miralles,
  • Teresa E. Gimeno,
  • Leire Mendiola,
  • Santiago Sabaté,
  • Jofre Carnicer
Adria Barbeta
Universitat de Barcelona

Corresponding Author:adria.barbeta.margarit@gmail.com

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Diego G. Miralles
Ghent University
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Teresa E. Gimeno
Basque Center for Climate Change (BC3)
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Leire Mendiola
Basque Centre for Climate Change (BC3)
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Santiago Sabaté
Universitat de Barcelona
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Jofre Carnicer
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The thermal balance of forests regulates land-atmosphere feedbacks. Forests dominated by different plant functional types have contrasting energy balances, but little is known about the influence of forest structure and functional traits. By combining spaceborne measurements of land surface temperature from ECOSTRESS with ground-based meteorological data, we estimate the thermal balance at the surface (∆Tcan-air) during four summers in a region located at the Mediterranean-temperate ecotone in the NE Iberian Peninsula. We then analyze the spatiotemporal drivers of ∆Tcan-air by quantifying the effects of meteorology, forest structure (e.g. basal area, tree height) and ecophysiology (hydraulic traits, water use efficiency), during normal days and hot spells. Canopy temperatures fluctuate according to changes in air temperature but are on average 3.2˚K warmer than the near-surface air. During hot spells, ∆Tcan-air is smaller than normal periods because the advection of hot and dry air masses from the Sahara region results in a sudden increase in air temperature relative to the canopy temperature. Vapor pressure deficit (VPD) is negatively correlated to ∆Tcan-air, since the highest VPD values coincide with peaks in heat advection. Still canopy temperatures increase with VPD due to decreased transpiration and stomatal conductance and transpiration. Meanwhile, soil water availability is shown to enhance evaporative cooling. Importantly, we demonstrate that plot-scale forest structural and hydraulic traits are key determinants for the forest thermal balance. The integration of functional traits and forest structure over relevant spatial scales could improve our ability to understand and model land-atmosphere feedbacks in forested regions.