Notes from the Field

Boreal Summer

September 12th, 2023 by Fred Huemmrich and Petya Campbell, University of Maryland BalHmore County

Fieldwork notes, July 21-August 3, 2023

Summer fieldwork for our project, “Clarifying Linkages Between Canopy Solar Induced Fluorescence (SIF) and Physiological Function for High Latitude Vegetation,” once again took our team from University of Maryland Baltimore County north to the boreal forests of central Alaska. We visited this area in the spring to collect data during the very start of the growing season, and now we are returning to collect data during the peak of summer.

This project is part of the NASA Terrestrial Ecology program’s Arctic-Boreal Vulnerability Experiment (ABoVE). The goal of ABoVE is to improve our understanding of high latitude ecosystems, how these ecosystems respond to climate change, and how satellite data can provide information to describe ecosystem processes and aid management decisions.

Our study focuses on measuring light emitted by plants called solar induced fluorescence. Green leaves absorb light, and through photosynthesis take in carbon dioxide and water and produce oxygen and sugars. Fluorescence occurs during photosynthesis as some of the absorbed light energy is radiated out from the plant. The amount of light fluoresced is only a very small fraction of what is absorbed, which is why our eyes don’t see plants glowing. In our study, we use sensitive instruments that can detect this fluorescence. Our goal is to better understand the sources of fluoresced light and how to use this information to describe productivity in boreal forests and tundra.

Our study site is at the Caribou Creek flux tower run by the National Science Foundation’s National Ecological Observatory Network (NEON). In spring, we deployed automated instruments at the NEON tower site that continuously collect data. On this trip, we are checking on how they have been working.

In July there was a big change from our previous visit in April. In April, the area had a deep snow cover with temperatures dropping below 0°F, while during this visit the daytime temperatures were in the 80s F and the ground was now all green (images below).

The gated bridge at the entrance to the Caribou-Poker Creeks Research Watershed where we are working in the spring and summer.

The boreal forest landscape in the Caribou creek with a view of the NEON tower in the black spruce forest.

On the top of the tower we have an instrument called a FLoX (Fluorescence Box). The FLoX views a patch of forest from above, and every few minutes during the day it measures the reflected light and solar induced chlorophyll fluorescence. This provides us with a description of plant activity at different times of the day through the growing season (images below).

The boreal forest at our study site (top-left). Looking up at the NEON flux tower, the thin pole extending from the top of the tower is from the FLoX (top-right); looking down from the top of the tower at the pole from the FLoX and the boreal forest below (bottom-right); and Petya and Fred with our safety gear on (bottom-right).

Also at the site we have monitoring PAM (MoniPAM) instruments attached to shoots of the spruce trees. The MoniPAM probes shine pulses of light at individual spruce shoots to measure fluorescence and photosynthetic processes at the leaf level (images below). We put blankets over the probes for a while to dark-adapt the shoots to measure their response when unstressed. In the spring, we put the MoniPAM probes in easy-to-reach places when there was a lot of snow on the ground. On this trip, when we returned to check them in the summer, we found we had to really reach up to get them without the snow to stand on.

MoniPAMs measure fluorescence of individual spruce shoots to describe photosynthetic processes. MoniPAM probe on a spruce tree views the spruce needles inside the clip (left); Bue blankets hang on the trees to cover the MoniPAM probes to dark adapt the shoots during the day (right).

One of the great things about working in the boreal forest in summer is that there are yummy berries to snack on, such as cloudberry (left) and blueberries (right).

From the ground, we collected reflectance and fluorescence measurements (similar to the data collected by the FLoX) of individual plants in the FLoX field of view and a variety of representative plants in the larger area surrounding the tower. These measurements will help us understand the local variability (images below).

A lot of the ground cover was cotton grass (Eriophorum spp.) that forms tussocks, which are tight clumps of grasses. The tussocks made walking through the area difficult, like walking on half-buried basketballs, so it was easy to twist an ankle, especially with a heavy backpack spectrometer on your back.

Measuring reflectance and fluorescence of different types of boreal forest plants. Collecting measurements at the base of the tower in the footprint of the FLoX (top-left); using the STELLA (top-right)—a multiband radiometer you can build yourself; and collecting data from a variety of different plants near the tower site (bottom).

Going into the field, you need to be prepared for pests both large (bear spray, that was never used) and small (mosquito repellent, which was heavily used).

We collected branch samples to make measurements of leaves and needles that we will use to parameterize models of vegetation fluorescence and productivity (images below).

Measuring leaf samples in our hotel room. Measuring photosynthesis rates (top-left); measuring leaf chlorophyll (top-right); measuring leaf level reflectance and fluorescence spectra (bottom-left); and the variety of different species we sampled (bottom-right).

We took a little time off to visit some other places in the area. We saw musk ox, which are animals of the tundra but raised in captivity at the University of Alaska Fairbanks’ Large Animal Research Station. Their thick, shaggy coat keeps them warm through the frigid arctic winters. Under the long guard hairs is a soft wool called qiviut that musk oxen shed in the spring. Qiviut can be spun into a very warm and soft yarn. Small balls of qiviut yarn can sell for over $100.

Musk ox at the University of Alaska Fairbanks Large Animal Research Station.

On our last day in Alaska we visited the Cold Regions Research and Engineering Laboratory (CRREL)  Permafrost Tunnel Research Facility (images below). Permafrost refers to soil that has been frozen continuously for more than two years. The permafrost around Fairbanks, Alaska, is considered ‘warm’ (at a temperature of -0.3oC/-0.4oC) as compared to the permafrost in our other study site in the North Slope of Alaska at Utqiagvik (e.g., a temperature -3oC/-4 oC). This warm permafrost is very sensitive to the changes in soil temperatures that can result from fires, rain events, and other disruptions that can cause permafrost thawing. Thawing permafrost can result in damage to roads and buildings and cause disturbance in forests.

The permafrost tunnel is dug into a hillside through earth that has been frozen for thousands of years. The tunnel reveals bones of extinct ice age animals, plants preserved since the ice age, and large ice wedges that can take hundreds to thousands of years to form. The ice wedges cause the formation of polygonal patterned ground, where the ground surface is covered with a pattern of shapes of slightly higher or lower ground. Our study site in Utqiagvik was in an area of high centered polygons, so it was interesting to be able to actually see the shapes of the underground ice that formed that unique landscape.

Looking down the permafrost tunnel (left) and a large ice wedge exposed in the tunnel (right).

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