Masahito Ueyama is an associate professor of Graduate School of Life and Environmental Sciences at Osaka Prefecture University in Sakai, Japan. He has been a member of both AsiaFlux and AmeriFlux for 15 years, with flux tower sites located both in Japan and Alaska, USA. His research focuses on carbon dioxide and methane exchanges, in both wet and upland ecosystems. We interviewed him to learn how he built his research career that bridged both sides of the Pacific and two of the FLUXNET regional networks.

Masa hiking at Denali National Park.

Please tell us briefly about yourself. How did you first become interested in ecosystem fluxes?

I am an Associate Professor leading the laboratory of ecological meteorology in Osaka Prefecture University. Before I came to Osaka Prefecture University, I worked in the International Arctic Research Center, University of Alaska Fairbanks from 2004 to 2008 where I studied carbon and water fluxes at a boreal forest (US-Uaf) in the interior Alaska as a visiting research scholar under the supervision of Dr. Yoshinobu Harazono.

My major is micrometeorology; I like measuring and modeling the interactions of energy, water, and greenhouse gases between land surfaces and the atmosphere. Currently, our group has conducted micrometeorological measurements at forests, wetlands, and urban landscapes, and has integrated observed data with models and remote sensing data.

I was first introduced to micrometeorology during my undergraduate and master studies under the supervision of Professor Nobutaka Monji, Osaka Prefecture University. Through the studies, I was impressed by how observed physical variables (e.g., wind speed, temperatures, CO2 concentrations, and those fluxes in and above a forest canopy) can be explained by a mechanistic multi-layer model. I was surprised that the coupling between ecosystem and the atmosphere can be explained in a mechanistic and mathematical manner. After graduating from the master’s program, I worked in a software company as a system engineer, but could not forget my enthusiasm for micrometeorology; thus, I decided to pursue my academic career and moved to Fairbanks, Alaska for measuring fluxes.

Maintaining the eddy covariance system at a young birch forest after a forest fire, Alaska (US-Rpf).

What are your most recent studies about? What’s the main take-home message and what is particularly exciting about the studies?

Over the last nine years, I’ve been working on measurements of canopy-scale CH4 fluxes at upland forests including system developments (Ueyama et al., 2013), method comparisons (Ueyama et al., 2014, 2015), and field measurements at various forests (Ueyama et al., 2018). Through a series of studies, I found that some upland forests are to be the annual CH4 source at the canopy scale due to high emissions from hot spots within the flux footprint. The results are unexpected as we learned from past research that upland forests in Japan were considered as a net CH4 sink. I believe that this is a good example of how micrometeorological studies, especially field measurements at remote regions, could help reduce uncertainties in the global change studies.

Please tell us how FLUXNET and the regional networks helped you advance in your career, both in Japan and the United States.

Through the AsiaFlux and FLUXNET, I had many opportunities to make collaborations and write papers; and the collaborations are still growing now. In my earlier career, Dr. Kazuhito Ichii showed me the importance of integrations of flux data to other tools, such as remote sensing and modeling. From him, I learned to integrate multi-site eddy covariance data to process-based models, and to upscale multi-site eddy covariance data with remote sensing data. These study experiences broaden my perspective of the potential applications of utilizing eddy covariance data, beyond merely site-scale analyses. Recently, my collaborations expanded further, by sharing data through AmeriFlux and other research activities in the US (e.g., ABoVE, ADC synthesis, and FLUXNET-CH4).

How has your methane work evolved over the years? In what ways are you participating in AmeriFlux Year of Methane activities?

I am interested in how various landscapes had different controls on CH4 fluxes. I started CH4 flux measurements at upland forests in 2011. I chose the upland forests, because only a few publications were available at that time, and thus it seemed to be a frontier area. To measure the CH4 fluxes, we developed the hyperbolic relaxed eddy accumulation system, automated chamber system, and inverse approach using within/above-canopy concentration profile measurements, and applied the method to three forests. Currently, our group measures CH4 fluxes at three upland forests in Japan, one bog in Japan, two urban landscapes in Japan, and one lowland forest in Alaska. Through my participation in a USGS Powell Synthesis Center workshop on wetland CH4, as part of the FLUXNET-CH4 synthesis activity, I am trying to infer the CH4 processes (e.g., production, oxidation, and transport processes) occurring at global wetlands by optimizing a simple model with eddy covariance data.

What resources or skills would you recommend that early career members of FLUXNET or AsiaFlux should acquire?

For my case, I believe that the most important skills are flexibility, broad interest, and optimism. Flexibility and broad interest has allowed me to build collaborations with scientists from different backgrounds and based in different countries. Since I am not a native English speaker, it is sometimes challenging to communicate and form international collaborations, however, my optimistic personality has helped me jump into joint activities, and I had very good experiences. Through these collaborations, my research interests have expanded from flux measurements to integration with models and remote sensing, and multi-site synthesis.

How can early career members of FLUXNET and/or AsiaFlux benefit or learn from the different network activities?

The big benefits of participating in FLUXNET and AsiaFlux networks are building friendships with international scientists and discussing important topics through those collaborations. As a site PI, I can test and expand the scope of my hypotheses, which were originally restricted to my own sites, to regional, and for, global sites. For example, I gained a better understanding of our sites in Alaska by conducting a synthesis that compared fluxes at multiple ecosystems in Alaska (Ueyama et al., 2013).