Watching Trees Transpire: Following tree water use across Canada’s North

It is very possible that Christoforos Pappas and I have the best jobs in the world. We are lucky to have research that takes us throughout Canada’s northwestern boreal forest, from the southern edge in Saskatchewan to the northern tree line in the Mackenzie Delta, NWT, where we work with the communities of Fort Simpson, Wrigley, and Inuvik. The southern and northern regions of Canada’s boreal forest are very different from each other but amazingly, tree species like the black spruce are able to survive across these different locations. Trees play an important role in the movement of water by removing it from the soils and releasing it back into the atmosphere, a process known as transpiration. For our research, we want to learn more about the transpiration of tree species across Canada’s northwestern boreal forest and understand the influence of climate change on the movement of water through these forests.

Similar to many researchers in northern Canada, our goal is to better understand how ongoing climate change affects high latitude ecosystems. We know that the global and regional climate systems are changing, and the changes are more pronounced in high latitudes, but we are still learning what those changes mean for different ecosystems and different tree species. We are curious if these changes would affect how tree species contributed to the movement of water through these vulnerable areas. Hopefully, our research will help people learn whether climate change will lead to an increase or a decrease in the amount of water used by boreal tree species and what this means for the overall tree health in these areas.

We spent the summer of 2018 in the field, visiting six sites spread across the northwestern boreal forest. We installed scientific instruments, namely sap flow sensors and dendrometers into the stems of over 200 trees to measure the daily movement of water through tree trunks. The sap flow sensors are small needles that are inserted into the main tree trunk. They measure and record how heat is transferred through tree stems and relates that to the movement of water every minute during the months in which the tree is growing (June to September). We also used stem dendrometers, which are sensors attached around the trunks of trees; they are able to detect very small changes in the width of the tree trunk every minute. These sensors measure how much the main trunk is shrinking and swelling throughout a day, month and year. With these sensors we can learn how much water trees are storing in their stems, how much they are releasing into the atmosphere, and when this storage and release takes place.

While our work was fun, it was not always easy. Black bears and carpenter ants love to chew on our equipment, as a result at four sites that were already up and running, we had to focus on fixing problems caused by these critters. In June, we battled with mosquitoes to set up two brand new sites; Baker Creek, outside of Yellowknife and Smith Creek, near Wrigley, NWT.

Our research is centered on continuous measurements over several years. Over the next few field seasons, we will ensure the sites are running as expected. In the future, we will investigate how the six sites compare to each other. Every site tells us a story about how trees are moving water through boreal ecosystems. With several years of data collection, we will be able to understand the bigger picture of how climate change, and the resulting changes in temperature, precipitation and permafrost are influencing this story across northwestern Canada.

Authors: Nia Perron, PhD Student, Université de Montréal & Christoforos Pappas, PDF, Université de Montréal 

Authors Note

This project is conducted by Christoforos Pappas (postdoctoral fellow; and Nia Perron (PhD student;, from the Université de Montréal and is co-led through the partnership of Jennifer Baltzer (; Wilfrid Laurier), Oliver Sonnentag (; Université de Montréal) and Christoforos Pappas.

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