Most winters, the Nooksack River rises threateningly to flood stage — or above, as it did last year with devastating results.

In summer, river levels have been dropping on average 5% each year over the last decade, jeopardizing salmon and farming.

Proposed solutions to these disruptions and tragedies range from dredging the river to building reservoirs and relocating houses. 

The Nooksack Basin covers 832 square miles, 41% of which is forested. What if among the solutions pursued is a forest management system that can be key to the river system’s health?

Older forests make a difference

“Since at least two-thirds of our county is forested, we cannot minimize the role and significance that forest ecosystems have on everything, whether that’s watershed health, or resiliency to natural disasters or hazards such as wildfires,” said Chris Elder, senior planner with Whatcom County’s Natural Resources division.

Studies show that forests play a bigger part in regulating streamflows, as older trees retain water, distribute it progressively, retain soil moisture and regulate stream temperatures in heat events. 

A 2020 study in Oregon on the long-term effects of forest harvesting on streamflows showed that streamflows in the summer were 50% lower near a 40-year-old plantation forest than near a 110-year-old one.

Michael Maudlin, forest and fish specialist and restoration geomorphologist for the Nooksack Tribe’s Natural and Cultural Resources Department, said the age of trees makes a difference in how they release moisture.

“Initially, with young rapidly growing forests you’ll see an increase in overall water use and through time, that recovers as stands grow older,” Maudlin said. “They get back to more of an old-growth level of transpiration.”

Maudlin said it is not certain when that effect of hydrologic recovery comes in, as it most probably depends on the species, elevation, soil characteristics and what happens around stands.

Protecting legacy forests

Of the county’s forested land, 14% is owned by commercial timber companies, 12% is state forest and 68% is either federal or private lands, said Natalie Johnson, Forest Practices Communications Manager for the state Department of Natural Resources.

DNR manages approximately 85,000 acres of forests in Whatcom County, with nearly 41,000 of those acres managed for conservation. 

Johnson said that generally 12% of DNR-managed lands throughout the state are considered old-growth. It is difficult to quantify the exact amount of forests that could be considered old-growth within the county given the different types of ownerships.

Restoring the legacy

Legacy forests that naturally regenerated before 1945 are the most promising for restoring or regaining old-growth habitat characteristics that have pretty much all but disappeared on state lands, contends Center for Responsible Forestry media and communications coordinator Brel Froebe. CRF is a Whatcom County-based organization with the mission of protecting legacy forests.

“These forests are really effective at increasing water quality and quantity in the watersheds,” Froebe said. Watershed support, wildfire resiliency, biodiversity and carbon sequestration are the most important roles that these older forests play.

“The things that forests do are so numerous and so easily overlooked,” said Paul Kearsley, an instructor at Western Washington University. “So much attention in recent years has been given to wetlands as sort of super-important ecosystems and there’s so much in terms of regulation, as far as development goes.”

But for mature forests, Kearsley said, legal protections are very minimal.

“A really big important thing that we struggle with in our Western culture is understanding that the wetland is charged and sort of maintained by the forest on the slopes above,” Kearsley said. Logging these trees increases runoff and sediment loads and really disturbs the watershed and its ecosystem, he said. 

With major flooding as last November in mind, land management practices in the county look to the role of forests in regulating flow levels and retaining water in the soil. 

Interconnected to wetlands and the Nooksack

The Nooksack Indian Tribe Natural Resources Department completed a pilot study of the South Fork Nooksack River to quantify hydrologic effects of potential forest management strategies and give “a starting point for including summer streamflow within a larger consideration of watershed management and climate change resilience.” 

The study indicates that young trees transpire at a rate that is up to three times higher than older trees. At a larger scale, the study found that the presence of continuous, young forest decreases summer base flow by up to 50% as compared to older forests. 

The study showed that forest management practices “influence the amount and duration of snow and soil water storage on the landscape, and spring and summer streamflow.”

Logging forests in the highlands above streams can exacerbate the severity of floods, said Kearsley. “Forests retain water, they sink it, they store it, and they slowly distribute it over the course of weeks during a large event versus getting it off site within a matter of hours.”

Maudlin noted that this study really looked at end-member scenarios, like fully managing the watershed as an old-growth forest or harvesting everything on really rapid rotations.

“It didn’t really capture all of the complexities of how current forests are managed,” Maudlin said. “Going forward, what we want to figure out is what kind of realistic things we can do and how might those affect flow.”

Maudlin thinks it is possible for forests to be a tool in increasing water quantity and streamflows in watersheds but we need to figure out to which extent.

“I don’t think we have a good feel for that yet,” Maudlin said. “I think the research shows that manipulating forests can improve flow conditions.”

Maudlin said this approach has been taken in Colorado forests for snow retention but it hasn’t happened in the Pacific Northwest yet and “with the changing climate it’s going to become more and more critical that we get creative about our management.”

Mimicking older forests

Froebe thinks it would be beneficial to look at ways to manage forest lands so as to mimic the ecosystems of older forests. 

“That could look like planting different species of trees that grow at different rates, so that we have an uneven, structurally complex forest, rather than an even-age mono crop,” Froebe said.

The South Fork study examined how engineering forest gaps for snow retention and spreading cut rotations could improve summer streamflow in the Nooksack River and buffer some of the effects of climate change.

According to Johnson, cut rotations established on state trust lands by the DNR always range between 60 to 80 years to maximize functions of the forests like carbon sequestration.

“The longer rotation helps us meet our management objectives as far as habitat conservation and it minimizes impact to soil and understory plants by limiting the amount of disturbance,” Johnson said.

According to Froebe, by taking the diversity and complexity of mature forests into account and managing them more sustainably, streamflows could be increased and watershed issues could be addressed.

“If our community is reaching a crisis for the amount of water and the quality of water in our watersheds, protecting forests, especially older forests, and changing how we manage them within our county, has tangible impacts,” Froebe said. “I just really want people to start thinking more about the interconnectedness between how we manage forests and the health of our watershed.”

Elder said the question in Whatcom County is figuring out how to develop programs where forest practices can benefit the timber industry and maintain larger riparian buffers or maintain forest ecosystems on key upland watershed features, wetlands and headwater contribution zones. 

Whatcom County does not have development regulations or land requirements for developing lands that take into account key ecological functions and maintain what can be called “green infrastructure,” he said. County rules mostly pertain to wetlands so residents and developers have no requirements to maintain ecological functions such as wildlife corridors.

Moving forward, Maudlin said more modeling needs to be done on management strategies like thinning that aim to get dense forests on quicker trajectories to old-growth conditions.

“How does thinning affect flow?” Maudlin said. “That’s something we didn’t look at with the modeling the first time, it is something that is widely applied as a treatment and we would like to know more; for example, how that could affect flow.”

He said it’s important to understand the trade-offs of different approaches, whether its length of time for rotations, thinning, varying species compositions and accounting for geological and elevation differences.

Testing the waters with a community forest

On Stewart Mountain, a collaborative group of stakeholders is in the process of establishing a 6,000-acre community forest and has just acquired the first 500 acres to pilot some of the different forest management practices being considered, Elder said. The goal is to begin a project that can address the needs of Whatcom County in multiple ways. 

The Stewart Mountain Community Forest Initiative aims to “enhance watershed resilience by restricting harvest on old-growth stands, extending harvest rotations to 80 years or more, selectively thinning dense stands and limiting harvest on steep slopes, near streams, in forested wetlands, and in headwater areas.”

But the project also wants to give the local timber industry a more sustainable and long-term vision to support jobs and forest health. The land is also intended to become an educational and recreational space for the community.

“In order for us to have a sustainable future, we need to manage for both economic needs, climate needs, watershed resiliency needs and biodiversity needs,” Froebe said. “Multiple needs need to be taken into account when we think about how we manage these lands.”

Because nurturing a space into what could be considered an older, mature forest takes time, Kearsley said it is possible to adapt land uses over time to bring them to what could be a complex, diverse ecosystem that would have the same functions as an old-growth forest.

Johnson said the state lands conservation plan’s goal is to protect wildlife habitat and aquatic species while also sustainably managing the forests. “We want the lands to be as healthy as possible but that’s a management practice rather than the forest practices law regulations that all landowners have to follow.”

Forest Practices Rules have requirements regarding clean water and meeting the federal Clean Water Act but they don’t specifically require any related to streamflow and the amount of water, Johnson said.

Forest management and a holistic approach to land management could become tools to avoid conflict while restoring the health of the river to its people through a more comprehensive approach to watershed management.

— Reported by Clifford Heberden

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