Scaling individual tree transpiration with thermal cameras reveals interspecies differences to drought vulnerability

Authors: JAVADIAN, M. - Northern Arizona University; AUBRECHT, D.M. - Harvard University; FISHER, J.B. - Chapman University; Scott, Russell; BURNS, S.P. - University Of Colorado; DIEHL, J.L. - Northern Arizona University; MUNGER, J.W. - Harvard University; RICHARDSON, A.D. - Northern Arizona University

Submitted to: Geophysical Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2024
Publication Date: 10/12/2024
Citation: Javadian, M., Aubrecht, D., Fisher, J., Scott, R.L., Burns, S., Diehl, J., Munger, J., Richardson, A. 2024. Scaling individual tree transpiration with thermal cameras reveals interspecies differences to drought vulnerability. Geophysical Research Letters. 51(20). Article e2024GL111479. https://doi.org/10.1029/2024GL111479.
DOI: https://doi.org/10.1029/2024GL111479

Interpretive Summary: Understanding how forests use water, especially during droughts, is crucial for a changing climate. We developed a method using thermal cameras to estimate individual tree water loss (transpiration), something traditional methods lack. These cameras capture temperature data from the tree crown, which is then used to estimate transpiration rates. Tests in two forests showed this method aligns well with other water use measurements. The study also revealed fascinating differences in how species handle drought. For instance, lodgepole pine outperformed Engelmann spruce in one forest, while red oak proved more resistant than red maple in the other. This suggests some trees are naturally more resistant to drier conditions. This thermal camera technique has the potential to become a valuable tool for monitoring forest health as our climate evolves.

Technical Abstract: Understanding tree transpiration variability is vital for assessing ecosystem water-use efficiency and forest health amid climate change, yet most landscape-level measurements do not differentiate individual trees. Using canopy temperature data from thermal cameras, we estimated the transpiration rates of individual trees at Harvard Forest and Niwot Ridge. PT-JPL model was used to derive latent heat flux from thermal images at the canopy-level, showing strong agreement with tower measurements (R2 = 0.70–0.96 at Niwot, 0.59–0.78 at Harvard at half-hourly to monthly scales) and daily RMSE of 33.5 W/m2 (Niwot) and 52.8 W/m2 (Harvard). Tree-level analysis revealed species-specific responses to drought, with lodgepole pine exhibiting greater tolerance than Engelmann spruce at Niwot and red oak showing heightened resistance than red maple at Harvard. These findings show how ecophysiological differences between species result in varying responses to drought and demonstrate that these responses can be characterized by deriving transpiration from crown temperature measurements.