Through winter morning mist, thick fern underbrush and spongy ground, Nooksack Indian Tribe water resources program staffers Chris Trinies and Rich Auguston navigate steep forested slopes to reach a few dispersed trees that look, from a distance, like they have backpacks hugging their trunks.
The packs are storage boxes, holding batteries that power two monitoring devices at each tree. Trinies, a hydrologist, and Auguston, a water resources technician, keep the monitors in working order to record data in this secluded forestland of the Nooksack River watershed.
The tribe is taking the pulse of these particular trees—Douglas firs planted on state Department of Natural Resources land—to better understand how different age classes of commercially managed trees consume different amounts of water, tapping into groundwater supplies important for replenishing streams.
“Streamflow is the big driver,” said Maggie Taylor, the tribe’s water resources program manager. “The goal is to better understand how land uses are impacting Nooksack River flows.”
The team is investigating how tree growth on this forestland near Acme may interact with the hydrology of the South Fork Nooksack River. Their study will quantify how much more water younger, thirstier trees consume compared to more mature trees.
“We want to know specifically, what are these trees here doing in this watershed?” Trinies said.
Previous soil moisture studies in other Northwest forests found that young trees likely use more water than mature trees because they are growing rapidly—and that repeated harvest and regrowth could be taxing on water resources.
“There is a hydrologic cost to that,” Taylor said. “When you’re constantly growing younger, thirsty trees, you are going to be using more water.”
At the study site, Trinies and Auguston visit one set of trees they could easily wrap their arms around and another set of trees too large to encircle in their arm spans. These adjacent groups of trees are about 60 years old and 120 years old, and appear roughly uniform because they are on land where timber harvests have taken place in the past.
Sensors attached to the study trees measure sap flux—the vertical movement of sap inside of a tree that distributes water and nutrients needed for growth. Soil sensors measure water content in the ground.
The information provided by the sensors, combined with information from core samples taken from the trees, will be used to estimate water consumption.
“With this project, we’re measuring how much sap is moving up in the trees, and using that combined with soil moisture levels to quantify how much water they are actually pulling out of the ground,” Trinies said.
Understanding how tree age corresponds to levels of water consumption could inform future forest management and land use priorities in the watershed. Wetlands, for example, bank water naturally and may warrant being prioritized over land uses that siphon water off the landscape.
The study is building off hydrologic modeling the tribe has been working on for over a decade.
“This project fits into a group of projects Nooksack has been doing to explore all of the ways we can retain more water on the landscape, as those resources decrease because of melting glaciers and other impacts of climate change,” Taylor said. “We are seeing drier summers and wetter winters, so the question becomes: how can we retain water so that we have it available when it’s needed?”
The South Fork Nooksack River in particular has low flow issues that are a concern for salmon in the summertime.
Chris Trinies, hydrologist for the Nooksack Indian Tribe, foreground, and Rich Auguston, water quality technician, check a monitoring station attached to a Douglas fir. Photo and story by Kimberly Cauvel.
