Climate change and logging contribute to the disappearance of Pacific salmon

The aggravated effects of climate change and logging are contributing to habitat degradation for Pacific salmon, experts say, adding that a re-evaluation of logging practices and watershed restoration will be key to helping distressed fish populations. .

Younes Alila, a professor in the department of forest resources management at the University of British Columbia, said decades of logging in BC have disrupted the landscape’s natural mechanisms to mitigate floods and landslides.

Such events, along with heat waves, wildfires, droughts and so-called atmospheric rivers of heavy rainfall are becoming more frequent and severe, which could have significant consequences for freshwater salmon habitat, Alila said in an interview.

Before logging, the forest canopy helps collect rain and shade the snow cover, slowing down spring thaw, Alila said. Trees also pump moisture out of the soil, increasing the soil’s ability to absorb runoff, he said.

The felling or felling of everything in a given cut block dominated the province’s forestry industry in the second half of the 20th century and is commonly practiced in combination with different approaches that leave more trees standing.

Alila said her research over the past 15 years has consistently shown that logging increases the size and frequency of floods for all return periods, referring to the estimated years between floods of a similar size or intensity. What would have been 10-, 20-, 50- or 100-year floods are all recurring more frequently after logging, he said.

“That’s a huge increase in flood risk in downstream communities,” Alila said.

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It is also a risk to salmon, which need certain conditions to spawn, including gravel to protect delicate eggs and fry. The swell of the waters can wash away the gravel, wash the eggs from the river bed or smother them with sediment, he said.

With some British Columbia salmon populations declining to record lows, the provincial and federal governments have allocated hundreds of millions of dollars for recovery efforts in recent years, including grant programs aimed at habitat restoration.

Like floods, logging and forest service roads also increase the severity and frequency of landslides, Alila said. The slides carry debris and sediment which, in turn, can make the habitat unsuitable for spawning and raising juvenile fish.

Slopes become unstable without tree roots as anchors, he said, while logging roads alone increase risk as ditches and culverts divert underground runoff to the surface, pushing more water, sediment and river debris. down at a faster rate.

Alila said she is conducting research in a watershed in interior British Columbia that is 8,000 square kilometers in size with more than 18,000 kilometers of forest service roads.

“That density of the road network is all over British Columbia. This basin is no exception,” he said.

It takes decades for forests to regain their full hydrological functionality after being cut down and replanted, Alila added.

The effects of logging are exacerbated by climate change, which is fueling increasingly intense forest fires that leave “hydrophobic” or water-repellent soil, he said. Charred soil gradually regains its ability to absorb moisture, but the years after a severe wildfire are especially risky of flooding and landslides, he said.

At the same time, Alila said that climate change will bring more frequent and severe atmospheric rivers that will push heavy rains into the wildfire-worn interior of British Columbia.

Forests also provide shade and algae keep streams cool, while logging in riparian areas can raise water temperatures above the 18-20 C that salmon can generally withstand, especially when combined with the effects of change. said Jonathan Moore, a professor of biological sciences. at Simon Fraser University.

“The more logging that occurs, the less climate change it can withstand,” said Moore, whose work focuses on aquatic ecosystems. “Reciprocally, the more watersheds that are protected, the more resilient they are to climate change.”

Moore points to a 2017 study published in the Journal of Environmental Management that examined how stream temperatures in two river basins in Oregon might respond to restoration of vegetation and “channel morphology,” or the interaction between the force of the river. water and the stability of a river. river bed and bank.

The researchers found that a combination of channel narrowing and riparian area restoration could reduce maximum summer water temperatures by 1.8 and 3.5 C in neighboring river basins, offsetting the projected impacts of climate change.

Their model predicted that colder temperatures as a result of the entire basin restoration would lead to an increase in the abundance of juvenile Chinook salmon, even when climate change projections for the 2080s were taken into account.

Trees, branches and woody debris that fall naturally into streams also provide nutrients and shelter for migratory and juvenile salmon, Moore noted.

A recent study by Moore and his colleagues found that a combination of changes in ocean and freshwater habitats had led to sharp declines in five salmonid populations over 40 years in a river on the northeastern tip of Vancouver Island.

In freshwater habitat, “the strongest signal was forestry,” he said.

Alila said she hopes the government will recognize that forestry practices must change significantly, and not just through “tinkering” with existing legislation, to protect both salmon habitat and communities from flooding and landslides.

“If the government doesn’t do it voluntarily, they will be forced to do it when we experience … more of the same flooding that we experienced this fall,” he said.

A series of atmospheric rivers brought record rains to southwestern British Columbia in November, causing destructive landslides and flooding that cut off key transportation routes and inundated a prime agricultural area east of Vancouver.

The British Columbia government made amendments to existing forest law earlier this fall, promising to reshape forest management with a focus on sustainability.

With the proposed changes, a new 10-year forest landscape planning system developed with First Nations, local communities and other stakeholders would prioritize forest health, replacing management plans developed largely by industry, he said. Forestry Minister Katrine Conroy at a press conference at the time. .

Past policies “left too much control of forestry operations in the hands of the private sector” and limited the province’s ability to combat climate change, protect primary forests and share the benefits with local and indigenous communities, he said.

The British Columbia Forest Industries Council supports “modernizing and strengthening forest policy to ensure that we have a strong, sustainable and competitive forest sector,” President Susan Yurkovich said in a statement when the amendments were announced.

John Betts, executive director of the Western Forestry Contractor’s Association, said in a statement provided by the province at the time the announcement was made that the changes would allow the government to better manage forest resources for both climate change and cumulative effects. of the resources. developing.

“For our reforestation sector, it means that we will manage stands and implement forestry practices that are more sensitive to the complexities and dynamics of how our forest and grassland ecosystems connect across landscape and time.”

This Canadian Press report was first published on January 3, 2021.