High Heterogeneity in Canopy Temperature Among Co‐occurring Tree Species in a Temperate Forest

Abstract

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 ΔT (=T c − T a) and ΔVPD (=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.

Imaging canopy temperature: shedding (thermal) light on ecosystem processes

“…Though these interactions are relatively straightforward to estimate in isolated leaves, they are much more challenging to model and measure at the canopy scale. Critically, many of these properties can vary across heterogeneous canopies as a function of canopy position, species composition, and even within species and individual crowns (Leuzinger & K€ orner, 2007;Aubrecht et al, 2016;Yi et al, 2020). Forecasting climate change impacts requires a firm understanding of how and why T can varies with these factors across canopy types and landscape positions.…”

“…The advent of relatively inexpensive and robust thermal cameras promises to transform our understanding of T can regimes (Costa et al ., 2013; Seidel et al ., 2016; Smigaj et al ., 2017; Lapidot et al ., 2019; Still et al ., 2019). Thermal cameras mounted on above‐canopy towers enable remote measurements over large areas and long time periods (Aubrecht et al ., 2016; Kim et al ., 2016; Yi et al ., 2020). Although the images can be influenced by mid and lower canopy elements, they typically capture upper canopy branches and leaves that are directly in the camera’s field of view.…”

Multi‐Sensor Approach for High Space and Time Resolution Land Surface Temperature

“…It is a consequence of the difference in the net radiative energy budget of the surface and rate of heat conduction into the ground. LST can vary greatly over short distances (Yi et al., 2020), as anyone who has walked across wet and dry sand on a beach during a sunny summer day can attest. For LST observation systems, then, the challenge becomes how to integrate that variation at space and time scales relevant to land‐atmosphere interactions.…”

“…Continuous high time and space resolution LST, including the diel cycle, is of high value for a number of scientific investigations (e.g., Kröniger et al., 2019). LST can vary by tens of degrees K over meters and change within seconds to hours, for example, due to shadows, wind, passing of clouds (Yi et al., 2020), or irrigation. These changes in LST then influence the heating of the soil, vegetation, and atmosphere over the course of the day (Dirmeyer et al., 2012; Taylor et al., 2012), and the dynamics that ensue as a result.…”

Utilidad de la termografía para evaluar cambios fisiológicos en árboles de pomelo regados con agua regenerada y riego deficitario combinado

“…Though these interactions are relatively straightforward to estimate in isolated leaves, they are much more challenging to model and measure at the canopy scale. Critically, many of these properties can vary across non-homogeneous canopies as a function of canopy position, and even within species and individual crowns [18]. Several techniques can be found to measure the Tc.…”