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Andrew is coauthor on a Tansley Review just published in New Phytologist, “Carbon uptake, storage, and allocation patterns contribute to blurring of annual 14C signals in tree rings.” Led by Amy Hessl, a paleoclimatologist at West Virginia University, the paper reviews how trees take up, store and use carbon and how these processes can affect the timing and strength of the radiocarbon “spikes” left behind in the atmosphere by past solar storms, known as Miyake events.  The paper emerged from a new NSF-funded collaboration between Hessl and Prof. Mariah Carbone.

Modeling led by Andrew and Mariah shows how tree biology has a fundamental impact on how faithfully the atmospheric signal is preserved. Andrew noted that “This study has a lot of implications for applications of carbon dating in fields such as archaeology, for example, as well as the use of radiocarbon in tree rings to reconstruct historical patterns of atmospheric radiocarbon.” 

Ecoss visual artist Victor Leshyk contributed a brilliant illustration that captures the underlying processes, reproduced below.

There is a write-up about the paper in the NAU Review.

After meeting up with Andrew and George Koch in Sonoma County earlier this month, Lily Klinek made a visit to NAU to talk more about redwoods and—and to learn more about the dendrometer measurements, supported by Save the Redwoods League, that Andrew and George have been making at sites from Del Norte county to Monterey County. Lily will be including these data in a range-wide synthesis of the timing and environmental sensitivity of redwood tree growth.

Lily had a chance to enjoy multiple social activities and get-togethers, including happy hour at Historic Brewing, a trip to Oscar’s “Blue Chute” pinyon-juniper field site (top photo), a hike into the cinder cone of Red Mountain, and a day trip to the Grand Canyon.

2026 is under way, which means the annual Sevilleta LTER All-hands meeting just took place at the comfortable UNM field station near la Jolla, New Mexico, about an hour south of Albuquerque. As always, exciting dryland science was shared in talks, a field trip, and a poster session; fresh collaborations were sparked, and old friends hand a chance to mingle; and dinners were chile-smothered.

Jacob attended the meeting and presented a poster on a new PhenoCam data processing workflow he is building, which uses the GRIME AI open source software to separate vegetation from bare soil in hundreds of thousands of PhenoCam images from the SEV Mean-Variance Experiment. The questions Jacob is investigating are: 1) does processing images using dynamic masks that separate vegetation and soil improve results compared to static masks that include both vegetation and soil? 2) how well does an AI-based image segmentation model trained on data from one study extrapolate to other study sites?

Jacob’s poster was a hit, and he spent so long answering questions that he almost missed dinner. He is already looking forward to the 2027 All-Hands Meeting!

In the last week of the holiday break, Andrew and George Koch made a trip to visit their field sites in Northern California. Flying into Medford, OR, they then drove to Klamath, CA, where they visited Tree 51 in Redwood Experimental Forest. From there it was on to Save the Redwood League’s (SRL) Harold Richardson Preserve in coastal Sonoma County. After two days spent there (and two nights at Sea Ranch) they drove on to Big Basin Redwoods State Park, just north of Santa Cruz, before flying home out of San Jose.

The purpose of the trip was to conduct site maintenance and download data from Tomst point dendrometers, which had been installed along a vertical profile on one tree at each site. At Harold Richardson, a solar panel had to be re-mounted and some old equipment removed; at Big Basin, a new phenocam had to be installed.

Despite a dismal forecast (a series of atmospheric rivers had drenched the region during the preceding 2 weeks), the hardy arbornauts remained relatively warm and dry the entire trip.

It was a pleasure to meet up with former postdoc Drew Peltier and his student Declan (at Harold Richardson and Big Basin), as well as UC Davis PhD student Lily Klinek and SRL Senior Scientist Laura Lalemand (at Harold Richardson).

The photos show Andrew somewhere in Tree 51, and George playing Tetris with a dozen dendrometers.

In December, lab members Austin, Jen, and Darby attended AGU 2025 in New Orleans, held under the theme “Where Science Connects Us.”

Highlights included a poster presentation by Austin titled “Winter Contributions of Root and Microbial Respiration to the Soil CO2 Flux in Mixed-Conifer and Aspen Forests,” a talk by Jen titled “Is Your Thermal Camera Telling the Truth? Assessing Measurement Accuracy for Ecosystem Science,” and a talk by Darby titled “Increasing Respiration Weakens the Carbon Sink over Two Decades in a Temperate Deciduous Forest.” 

The lab also contributed to two successful scientific sessions. Mostafa and Jen led the session “Advancing Environmental Monitoring Through Near-Surface Remote Sensing: Capabilities, Applications, and Future Directions,” while Darby served as a convener for the session “Quantifying Rates and Coupling of Biogeochemical Cycles in Terrestrial Ecosystems.”

See you at AGU next year! 

Yujie’s paper, “A tale of two towers: comparing NEON and AmeriFlux data streams at Bartlett Experimental Forest,” has just been published in Agricultural and Forest Meteorology. The two towers are separated by less than 100 m, but although meteorology and phenology data show good agreement between AmeriFlux and NEON, and although the agreement is reasonably between measured fluxes of carbon dioxide, latent heat, and sensible heat at the half hourly time scale, Yujie’s analysis shows that the carbon dioxide and latent heat fluxes are in poor agreement at the annual scale. For example, annual C balance differs by over 120 g C m^-2 y^-1 between the two towers, and patterns of inter annual variability are not at all in agreement. 

This paper raises important questions about the representativeness of any one tower in relation to the broader landscape it assumed to represent, and also suggests that we are probably (still) under-estimating uncertainty in annual C budgets derived from eddy covariance measurements, and sometimes we may be reading too much into the interannual variability we measure at individual sites. 

Great job by Yujie and collaborators, including Paul Stoy, Housen Chu, Dave Hollinger, Scott Ollinger, Andy Ouimette, Dave Durden, Cove Sturtevant, and Ben Lucas.

During exam week, Oscar and Andrew joined Cara and Mariah on a field trip to the Mogollon Rim Ranger District of Coconino National Forest. The team was in search of a small ponderosa pine that would provide material for a 14C cellulose standard for some of Cara’s thesis work, and at the same time give Cara her first Christmas tree. With her permit in one hand, and chainsaw in the other, Cara declared the event a success.

It was a lovely day in the woods, and the hike to the top of a small cinder cone provided great views in all directions. Kivi the Wonder Dog enjoyed the outing, too.

Congratulations to Jen on successful PhD defense! On National Stuffing Day (November 21, who knew?), Jen presented her dissertation work on thermal imaging of plant canopies to a large on-campus audience and even larger (and global) virtual audience on Zoom. The event was a “big Diehl” for Jen’s family, as nine Diehls made the long trip to Flagstaff to hear about Jen’s research on this hot topic. Thanks to Jen’s mom and dad for providing some tales from the Diehl family lore (including classics such as “Jen’s Canadian Moose Encounter” and “Jen’s First Day of High School”) that Andrew was able to share with the audience. Later that day, there was a celebration at Mother Road, where lots of Red Bull was consumed.

Jen will officially become Dr. Diehl at graduation on December 12, at which time she will also be awarded the Outstanding Graduate Student award in SICCS. Good luck with all your future endeavors, Jen!

The photo on the left shows Jen in the hot seat, presenting her work, and the picture on the right shows Jen with committee members Andrew, George Koch, and Chris Doughty at the after-party. External committee member Chris Still, at Oregon State, was unable to attend the defense (or celebration) in person, which meant that he missed out on donuts and Red Bull.

As part of the Flagstaff Festival of Science’s In-School Speaker Program, Perry, Jacob, Oscar, and Darby visited six 6^th-grade classrooms at Northland Preparatory Academy in early November. They led hands-on lessons about how PhenoCams are used to track vegetation changes across different ecosystems. Throughout each hour-long session, students remained engaged as they worked with real PhenoCam images. They sorted photos into seasonal sequences based on visual cues from various ecosystems, identified types of environmental disturbances captured by the cameras, and even explored a PhenoCam site independently to determine when the vegetation in that ecosystem was at its greenest and when it was least green. The students also learned how to use metadata from the cameras, such as temperature and time of year, to inform their decisions when arranging the images into the correct seasons. One particularly thought-provoking moment came when they were asked why it’s important to have cameras capturing repeated images from the same location over time. Many correctly concluded that this setup is essential for monitoring long-term changes in vegetation greenness driven by environmental changes, showing a good understanding of the scientific process behind PhenoCam research. By the end of the day, the lesson led to an exciting conversation between students and their teacher about how they might incorporate the PhenoCam into their current unit on ecology.

Great job, Perry, Jacob, Oscar, and Darby!

In late October, members of the lab traveled 4 hours south to Tucson, where the 2025 AmeriFlux meeting was being held at the University of Arizona. Oscar presented his work on near-surface remote sensing in pinyon-juniper woodlands; Yujie presented her analysis of the continuity between paired NEON and AmeriFlux sites, and Andrew gave an update from the AmeriFlux Science Steering Committee and the PhenoCam Network. The meeting included a field trip to the amazing Arizona – Sonora Desert Museum, as well as a delicious conference dinner, and many stimulating talks and posters. It was a great opportunity to catch up with colleagues from across the US, and the Americas more generally.

The pictures below include the standard workshop photo, as well as snapshots from the tours to collaborator Russ Scott’s Santa Rita sites, and the U of A Laboratory of Tree Ring Research. Local host Dave Moore did a fantastic job of keeping meeting participants entertained and well fed (for some, karaoke after the first night’s dinner was a highlight).