B.C.’s historic floods bring urgency to ecological restoration work

People can help build resilient forests by mimicking nature, says local expert Dave Polster.

A few days after November’s historic flooding, plant ecologist and restoration expert Dave Polster went out into the woods in a local park. He says he didn’t find any standing water or any trace of the torrential rains that a month later continue to make life difficult in many parts of the province.

For Polster, it’s what he expected, because in the forest, unlike roadways and clearcuts, water has places to go. “If you look at a natural forest, it’s lumpy. It’s not smooth.” he says. “That allows the rainfall to soak into the ground as opposed to running across the ground.”

The lumpy ground is the result of trees naturally falling over and decomposing into mounds that get revegetated. In addition, Polster says that plants in the forest also hold and dilute some of the rain, from conifer needles down to sword ferns, salal and mosses that have all adapted to rainy conditions. 

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David Polster collects willow cuttings for a restoration project. Photo by Genevieve Singleton

Understanding how natural processes work is key to bringing disturbed ecosystems back to health, Polster says. The 69-year-old Duncan resident has led ecological restoration projects across North America that try to mimic natural processes, including a method he developed called “rough and loose” to combat soil erosion.

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The devastation caused by last month’s flooding, which he says was exacerbated by forestry practices, is all the more reason why we need to have resilient forests and regain the ecological services they provide. 

Disturbed landscapes exacerbate floods

Polster says that people see the results of a problem, but often not the causes of the problem. For example, the flooding at Russell Farm Market along the highway was very visible, but not the logging upriver that contributed to the Chemainus River running at such high velocity and overflowing its banks.

The relationship between clear cuts and floods is complicated. But it’s clear that more heavily disturbed forests do a worse job holding back heavy rains. “The flooding we recently experienced in the Cowichan Valley is [in part] a result of heavy logging in the forest, in the watershed,” Polster says.

He explains that cut blocks, often situated on steep slopes, don’t hold moisture because repeated logging prevents the buildup of healthy soil. Instead, most of the rainwater, carrying away sediment and gravel, reaches the river. The result is flash flooding, as fast debris flows scour the riverbanks, picking up more sediment and destroying salmon habitat, Polster says. 

He has done ecological restoration projects at sites that have been deforested by human intervention as well as by natural landslides. He says that when forest companies replant a clearcut with a monocrop of conifers, the result isn’t a healthy forest with a diversity of species, especially with logging rotations that aren’t long enough for a mature forest to grow back. Instead, he says the key is to figure out “how you can work with natural systems to create conditions that allow those systems to operate.” 

Polster has studied the revegetation that happens after a forest is disturbed naturally. He says that seeds arrive via birds and the wind. Shrubs and alders start to grow, fixing nitrogen into the soil. These and other species, such as poplars and willows, have evolved to be able to establish themselves in harsh conditions, he says. He adds that research shows that conifers grow better when deciduous trees are around to offer shade.

“This is how natural succession works,” he says. ”Natural succession rebuilds forests.”

To get to the root of the problem, more sustainable forestry practices are needed, says biologist Genevieve Singleton, Polster’s wife. There are many examples of how that can be done, including the Wildwood Ecoforest near Ladysmith, she says. 

The couple has run an environmental consulting firm, Polster Environmental Services, for many years. Polster is now semi-retired, following his recent diagnosis of Alzheimer’s disease.

Making it rough and loose

To accelerate the revegetation process, Polster developed the “rough and loose” method. He says it’s a simple way to control erosion and create the conditions that allow pioneering species to establish themselves. 

Because compacted soil isn’t able to hold necessary water for seedlings to grow, Polster says it’s important to break it up. His method simulates what happens when a tree blows over in the forest and is uprooted.

It involves an excavator digging up holes and piling soil and other materials into mounds between the holes. There should be at least a metre between the top of mounds and the bottom of holes, Polster recommends.

In addition to preventing water from pooling, the rough and loose method creates more places for seeds to fall in, Polster explains. “It starts the process of recovery.”

An example of this is the work Polster did at the Heber Dam site along the Gold River after the dam was decommissioned. He made the site rough and loose and scattered woody debris, as part of restoring the stream bank and the natural flow of the river. “Now it’s a forest,” Polster says. 

Working with nature

One of the simplest ecological restoration methods is live staking, which involves taking cuttings from living trees such as balsam poplar, red osier dogwood and willow and planting at least three-quarters of the cuttings underground. Polster has led successful live-staking projects along Bing’s Creek and Averill Creek, near Duncan, and other sites in the region and throughout western Canada. 

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David Polster leads students from Queen Margaret’s School in a restoration project at Bing’s Creek. Photo by Genevieve Singleton

Wattle fences are another way to stabilize the soil and eventually cover a disturbed area in greenery. The fences are low retaining walls consisting of terraced tree cuttings. The practice is often used on steep slopes as the fences act as a barrier to falling debris, protecting existing vegetation and helping with revegetation. An easily visible example of wattle fencing is a project Polster led along Colquitz Creek in Saanich. 

Live pole drains are another important restoration method, Polster says. It involves bundles of live cuttings placed in shallow trenches in such a way that they intersect and collect moisture. The bundles are partially covered with nearby materials, so that the plants used in the bundles can sprout and grow. The rainwater that the plants don’t need drains out the lower end.  

These techniques are very cost-efficient, Polster says. Making a site rough and loose is less expensive than seeding a large area with grasses and other plants, and live staking costs a fraction of building a concrete retaining wall, Polster says. 

Climate change complicates restoration efforts

Climate change, Singleton says, is making ecological restoration work harder. For one, it’s made it difficult to rely on historical climate data. She says many ecological restoration projects used to happen during late winter and early spring, but the recent long, hot and dry summers made it problematic to keep plantings well-watered. As a result, projects such as live staking now happen in the fall. “Using modeling based on the past, there’s no point.”

The unprecedented nature of extreme weather events is also taking a toll. They led a live staking project at Sandy Pool Regional Park along the Cowichan River seven years ago and another one further upstream at the Stoltz Pool group campsite three years ago. The projects had been doing a good job of stabilizing slopes and ensuring habitat for fish fry, Singleton says, but they couldn’t withstand the torrent of the November flooding. 

But despite the recent setbacks and the challenges of restoring greatly disturbed areas, Polster says the work continues to be rewarding. He says that at the end of a day of restoration work, everyone has a smile on their face. “Even though they’ve worked hard all day with shovels and picks moving dirt, they’re happy.”

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