Forest ecosystems provide a variety of ecosystem services, from carbon sequestration to regulating streamflows to modulating energy and water exchanges with the atmosphere. All of these ecosystem services will be affected by rapid climate warming in coming decades leading to climatic extreme like heatwaves. Old growth forests make unique contributions to ecosystem services and biodiversity, and may buffer species against projected climatic changes. In this talk I will focus on forested ecosystems in the Pacific Northwest (PNW) region of the US and discuss an integrative measure of ecological function: surface skin temperature. Although scientists often focus on the critical role of air temperature, organismal skin temperature is actually what determines a wide range of processes and properties. However, until recently direct measurements of plant temperature have been challenging. We have measured temperatures of various forest canopies using thermal cameras and related them to forest type and ecosystem-scale fluxes of carbon, water, and energy measured by eddy covariance. These site-scale measurements can be connected to an extensive satellite record of land surface temperatures (MODIS LST) in order to quantify and assess temporal and spatial variations in forest canopy temperatures.
Results/Conclusions
We assessed the physiological response of an old-growth Doug-fir (Pseudotsuga menziesii) forest canopy and a ponderosa pine (Pinus ponderosa) canopy to multiple heatwaves. Leaf temperatures and net ecosystem exchanges of carbon, as well as latent and sensible heat fluxes, at these forests were compared before, during, and after successive heatwaves in the 2015 growing season. Overall, the wetter Doug-fir forest was more sensitive to heatwaves than the drier ponderosa pine forest, with net carbon uptake early in the growing season reduced by each heatwave for the former forest type. Furthermore, three large heatwaves in June and July caused the Doug-fir forest to become a carbon source, whereas the less biodiverse ponderosa pine forest remained a carbon sink until the final heatwave in late July. The canopy of the pine forest was also always closer to air temperature than Doug-fir as a result of its simpler canopy structure and lower leaf area. By contrast, the understory of forests with more complex canopies experiences distinct conditions that provide microclimate refugia for a wide range of organisms, from epiphytes to birds to arthropods. Analysis of satellite LST data across the PNW highlight connections between this measure of temperature, biodiversity, and ecosystem services.