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High Heterogeneity in Canopy Temperature Among Co‐occurring Tree Species in a Temperate Forest
Author(s) -
Yi Koong,
Smith Jake W.,
Jablonski Andrew D.,
Tatham Elizabeth A.,
Scanlon Todd M.,
Lerdau Manuel T.,
Novick Kimberly A.,
Yang Xi
Publication year - 2020
Publication title -
journal of geophysical research: biogeosciences
Language(s) - English
Resource type - Journals
eISSN - 2169-8961
pISSN - 2169-8953
DOI - 10.1029/2020jg005892
Subject(s) - vapour pressure deficit , canopy , atmospheric sciences , transpiration , environmental science , stomatal conductance , tree canopy , botany , horticulture , biology , physics , photosynthesis
Trees regulate canopy temperature ( T c ) via transpiration to maintain an optimal temperature range. In diverse forests such as those of the eastern United States, the sensitivity of T c to changing environmental conditions may differ across species, reflecting wide variability in hydraulic traits. However, these links are not well understood in mature forests, where T c data have historically been difficult to obtain. Recent advancement of thermal imaging cameras (TICs) enables T c measurement of previously inaccessible tall trees. By leveraging TIC and sap flux measurements, we investigated how co‐occurring trees ( Quercus alba , Q. falcata , and Pinus virginiana ) change their T c and vapor pressure deficit near the canopy surface (VPD c ) in response to changing air temperature ( T a ) and atmospheric VPD (VPD a ). We found a weaker cooling effect for the species that most strongly regulates stomatal function during dry conditions (isohydric; P. virginiana ). Specifically, the pine had higher T c (up to 1.3°C) and VPD c (up to 0.3 kPa) in the afternoon and smaller sensitivity of both ∆ T (= T c − T a ) and ∆ VPD (=VPD c − VPD a ) to changing conditions. Furthermore, significant differences in T c and VPD c between sunlit and shaded portions of a canopy implied a non‐evaporative effect on T c regulation. Specifically, T c was more homogeneous within the pine canopy, reflecting differences in leaf morphology that allow higher canopy transmittance of solar radiation. The variability of T c among species (up to 1.3°C) was comparable to the previously reported differences in surface temperature across land cover types (1°C to 2°C), implying the potential for significant impact of species composition change on local/regional surface temperature.