PS 51-67
Canopy temperature of a ponderosa pine forest: The relationship with environmental drivers and forest metabolism
Leaf temperature reflects biophysical, physiological, and anatomical characteristics of plants that together influence plant function. Measures of canopy temperature can improve our understanding of how environmental changes will affect ecological functions of forests. However, direct measurements of canopy temperature are rarely undertaken. In this study, we continuously monitored canopy radiative skin temperature of a mature ponderosa pine forest in central Oregon using a thermal infrared camera from Sep. 24 to Oct. 29, 2013, a period when trees experience drought stress and draw moisture from deeper soil layers, resulting in reduced carbon and water fluxes. Thermal infrared images were captured every 5 minutes from the top of a 32-m-tall eddy covariance flux tower. Environmental data including air temperature, rainfall, wind speed, humidity, air pressure, and PAR (photosynthetically active radiation) were collected every 10 minutes, and flux data (e.g., carbon and water) were every 30 minutes. We only selected the pixels of the leaves from each image, and means from the pixels were defined as leaf temperature. After averaging the data hourly during the daytime (10:00 and 16:00 hr), we conducted regression analyses to examine the correlation of canopy temperature with environmental data and flux data.
Results/Conclusions
For the first two weeks of the study period, the mean leaf temperature was 7.3ºC (with a range of 0.4 to 20.5ºC), while the mean of air temperatures was 7.8ºC (with a range of 2.2 to 18.3ºC). The mean leaf temperature was significantly correlated with air temperature (r2 = 0.95) and relative humidity (r2 = 0.72), but it was not well with air pressure (r2 = 0.12) and PAR (r2 = 0.11). Our results revealed that leaves in this canopy can be cooler than air temperature, likely due to several interrelated factors including net radiation and latent heat and sensible heat fluxes.