Dr. Benjamin Blonder from University of California at Berkeley presents his last publication ‘Low predictability of energy balance traits and leaf temperature metrics in desert, montane, and alpine plant communities‘, one of his first steps in the world of thermal ecology. He shares his experience about how little actually we know about how plants manage leaf temperature and the hard but very rewarding fieldwork at Rocky Mountains.

About the paper

What’s your paper about?

 The study’s main focus is on the predictability of leaf temperature metrics – both in terms of the difference between leaf and air temperature, as well as the rate of increase in leaf temperature for a unit increase in air temperature. Knowing these metrics is potentially important for understanding carbon and water fluxes and for predicting other thermally dependent aspects of plant performance. We therefore wanted to find out whether these metrics varied across environments or times of day, or among species within communities. We also wanted to find out whether these metrics could be easily predicted by common functional traits, as solving the energy balance equations directly for leaf temperature is usually not practical. The hope was that these metrics would be predictable by some of these factors, thus enabling easier integration of thermal ecology ideas into community ecology.

What is the background behind your paper?

I was fascinated by the idea that leaf and air temperatures might differ strongly from each other – I had always imagined plants as passive participants in the environment.

 I first got interested in thermal ecology when Sean Michaletz and I were both working with Brian Enquist at the University of Arizona. Sean had been doing some exciting work on homeothermy in plants, a topic I knew very little about. I was fascinated by the idea that leaf and air temperatures might differ strongly from each other – I had always imagined plants as passive participants in the environment.

Over the next two years I started getting more curious about plant energy balances in the context of community ecology, and did some exploratory work with thermocouples and a borrowed thermal camera, and also wrote a theory paper with Sean on thermal decoupling. I finally then got to buy my own camera via a postdoctoral fellowship, and decided to use it to ask some questions about thermal ecology in Rocky Mountain plant communities.  

How did you come up with the idea for it?

 Sean and I wanted to do a study of thermal ecology along environmental gradients. We were both working in southwestern Colorado at the Rocky Mountain Biological Laboratory, where large elevation gradients are easily accessed. Brian Enquist was kind enough to let us use some of his long-term sites, and then I augmented with an additional alpine site of my own. That summer I was the mentor for a summer Research Experience for Undergraduates student, Sabastian Escobar (co-author on this study). Sabastian was also interested in thermal ecology, and was up for a project involving a lot of heavy equipment up and down mountains – he had recently been serving in the US Army. We agreed on the research questions, and he, Sean, myself, and Rozália E. Kapás (technician and co-author on the study) figured out how to do the work over the course of the summer.

What are the key messages of your article?

We found unfortunately that the predictability of leaf temperature metrics was low, challenging our future ability to predict such metrics via easy proxies like environment, species, or common functional traits. High heterogeneity among species and environments was very common. While other studies have demonstrated similar heterogeneity, our study is unique in collecting such data for a large number of co-occurring species, and also for doing it in deserts and subalpine meadows. Our study is also useful in that it contributes a large code base for logging data from FLIR cameras, for doing accurate temperature reconstructions from radiometric data (i.e. taking into account various atmospheric phenomena), as well as for analyzing thermal videos and extracting information from them. A lot of the code to do this already exists but is hidden in proprietary manufacturer code. I hope that our open source software will democratize access to thermal imagery.

Does this article raise any new research questions?  

The high heterogeneity in leaf temperature metrics that we documented seems very likely to have implications for plant performance and perhaps for community assembly. We weren’t able to directly assess these questions, but I think there will be an increasing role for thermal ecology in community ecology soon, as well as an opportunity to better consider the consequences of thermal ecology for plant water use models. My postdoc recently published a study showing that temperature variation may have large impacts on water use, but the modelling followups remains to be done.

About the research

Did you have any problems setting up the experiment/gathering your data?

Aside from carrying ladders, cameras, batteries, and all manner of other heavy equipment up steep mountains, and the occasional lightning storm… we also had some adventures getting to our sites. I was living in the UK at the time of the study so did not have a field vehicle available during the project. I was able to borrow an old Ford Explorer that David Inouye (faculty at University of Maryland at the time) was kindly willing to lend me. It was great – except for the overheating radiator and the time the muffler fell off! We had a lot of fun adventures making the logistics for this project work out.

What is the next step in this field going to be?

I think there is a big potential for making repeated measurements of plant canopies with thermal imagers, then assessing their impact for resource fluxes and community dynamics. Drones will continue to have battery lives that are too short for very effective time-series work, but I think balloons will be promising for small-scale imagery – and NASA’s ECOSTRESS instrument is looking very exciting at larger scales.

About the Author

How did you get involved in ecology?

I started out in physics but rapidly discovered that I preferred being outdoors to being in a laboratory. I was fortunate to get work surveying fish and salamander habitat, then teaching environmental science… and shortly thereafter was tempted into going to graduate school for ecology. I haven’t looked back since.

What are you currently working on?

I have a research project focusing on quaking aspen forest mortality in the Rocky Mountains. We are trying to see whether some genotypes are more at risk than others, and if those genotypes can be remotely sensed from satellite imagery. I’m also working more on plant water use models, thinking about how thermal ecology may influence classic predictions for how carbon gain and water loss are coupled. Stay tuned!

One piece of advice for someone in your field…

Don’t be afraid to try out your ambitious ideas – and make sure to invest in good people that can help make your dreams reality!

Read Low predictability of energy balance traits and leaf temperature metrics in desert, montane, and alpine plant communities here!