Perfect storm: Wet, windy winter could be last straw for drought-stressed trees

And so it begins.

A falling tree hits a power line in North Saanich, knocking out power to the Swartz Bay ferry terminal.

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B.C. Ferries is unable to lift its loading ramps. ­Several sailings are cancelled. The lineups snake for a kilometre and the plans for thousands of people are thrown into disarray. Frustrations mount.

Power-outage season is underway … early.

And B.C. Hydro says we can expect more darkness, colder homes and other inconveniences associated with outages as we head into a La Niña fall and winter that is forecast to bring more wind, rain and colder ­temperatures.

Trees are weakened from an extraordinary summer of blistering heat and extended dry spells, which means more trees will be blown down onto power lines.

There are telltale signs of drought damage. ­Scientists say several species are showing dead or drooping branches, browning foliage, sudden limb loss and ­compromised root systems.

Forest ecologist Andy MacKinnon says he has ­spotted dying Western red cedar trees in Metchosin near his home. At a wedding in August, he experienced falling branches firsthand.

“About 15 minutes before the ­ceremony, a huge limb fell off [a Garry oak] on a table piled with glassware.”

While that can happen with healthy oaks, where limbs are sometimes bigger than the trunk and fall victim to gravity, MacKinnon said he expects to see it a lot more with stressed trees.

Peter Constabel, chair of the biology department at the University of Victoria, said extended periods of little precipitation can cause severe stress to trees. These long dry spells — including a 53-day stretch in Victoria this summer — can make trees more susceptible to fungi and insects, said Constabel.

A study by the National Science Foundation in the U.S. indicates some tree deaths occur because of carbon ­starvation.

During drought, trees close their stomata — the ­minute openings in the epidermis of leaves — ­essentially starving themselves by blocking the entry of carbon needed for photosynthesis.

Trees then have to rely on stored starches and sugars until the drought ends.

The study said if a tree loses too much water too quickly, an air bubble forms, resulting in “hydraulic failure,” because it can’t transport water from the roots to the leaves, causing it to dry out and die.

The scientists found that hydraulic failure is always a death knell for a tree, while carbon starvation is a contributing factor about half the time.

Contrary to popular belief, the so-called rainy west coast isn’t that wet in the summer, at least not in Greater Victoria, Nanaimo and the southern Gulf Islands. Records compiled by weather analyst Steve Murray show Victoria is the driest city in Canada during the summer months, and Nanaimo gets less rainfall than typically arid areas around Kamloops and the southern Okanagan.

Murray says the 30-year average for rainfall from June to August is 54.4 mm, far less than Kamloops (92.5mm), Nanaimo (97.2), Penticton (103.3) and Kelowna (115.2). Vancouver, by contrast, gets 126 mm.

Drought has hit native species such as arbutus, Garry oak and Western red cedar hardest, said Dan Sharp, an arborist with Davey Tree Service.

While arbutus and Garry oak have adapted to lower precipitation in the summer months, they still show signs of extreme stress, says MacKinnon. Others like cedars that rely on moisture are suffering.

The Western red cedar — B.C.’s provincial tree — struggles in dry conditions, showing signs of “flagging,” or browning of its foliage, says MacKinnon. Over the years, large stands have died off on the east coast of the Island, although it does much better on the Island’s west coast.

“Climatically, the [south Island] is the edge for Western red cedar,” says MacKinnon. “As drought and temperatures increase, it becomes a less hospitable place. It’s very likely with climate change that we won’t see any more Western red cedars on the south Island.”

Sharp concurred, saying cedars have struggled after several successive years of hot dry summers: “Really, they are rainforest trees.” He added grand firs are also hard hit by the drought and attacks of bark beetles, and by veiled polypore fungus, which follows the beetles.

MacKinnon said the Western red cedar is often called the Tree of Life because of its cultural and economic importance. It’s not only a significant cash product for the lumber industry and B.C.’s economy, but an integral part of First Nations history and culture.

“It’s a cradle-to-grave tree for First Nations, providing [everything from] cradles and diapers to ceremonial death poles,” says MacKinnon. “It has provided housing, transportation in the form of canoes, clothing and forms of art.”

It’s raining acorns

The Garry oak is built for dry conditions, but even these majestic, gnarly trees are feeling the effects of prolonged drought as their systems are weakened by increased exposure to insects and fungi that can weaken limbs.

Sharp said Garry oak trees have had a difficult time retaining their leaves, with many dropping early or turning a crispy brown long before normal.

They’ve also suffered the additional stresses of pests and pathogens. An outbreak of winter moths defoliated many oaks and the trees had to dip into energy reserves to grow new canopies. “When they’re stressed, oaks tend to be attacked by opportunistic pests and pathogens,” said Sharp.

Root rot is another common problem, and he’s seen the heavy oaks uproot or drop limbs on a calm day without the help of the wind.

In addition, Garry oaks are producing an exceptional amount of acorns this fall , something that happens every so often in what botanists call “a mast year,” says MacKinnon.

Scientists haven’t figured out the timing — it usually happens every five years — but it is something in their genetics that ensures the species’ survival.

Each year, birds and rodents feed on fallen acorns, sometimes taking them all. But in a mast year, when there are more acorns that any predator can consume, at least some will be left untouched, fall into a crevice or sprout from a bird’s forgotten stash to grow to seedlings and future oaks, says MacKinnon.

Mast years prove costly to the trees, however, as experts suggest the extreme production of nuts can stunt their growth cycle. It’s not known what the effect of a mast year and drought could have on the trees.

Arbutus battle back

The Island’s arbutus trees have been struggling with fungal leaf blights and successive seasons of drought.

The problem is widespread and some areas are harder hit than others. Several of the majestic trees have been stricken, from the south Island to its northern-most ranges around Parksville and even Campbell River.

Last spring, the arbutus were being hammered by blight, a species of fungus that attacks the leaf.

MacKinnon said drought and changes in climate have left the arbutus stressed and unable to fight the fungus, and some of the trees are dying.

The arbutus has been dealing with fungal leaf blight for hundreds of years, MacKinnon said. While the organisms haven’t changed, the trees are less hardy and more susceptible to defoliation due to eroding soils, dry summers and stress from human disturbances. “Five years ago, we had a similar experience and we ended up with a lot of dead arbutus.”

Experts are monitoring trees to determine if the afflicted arbutus are mainly those growing in shallow soils, where moisture isn’t easily maintained.

Meanwhile, Sharp said home and property owners should water during periods of drought to help maintain the health of trees. He suggests watering every two weeks “throughout the entire spread of the branches, called the drip line.” Water enough to soak at least a foot into the soil, said Sharp.

“Frequent shallow watering for flowers and grass can cause tree roots to grow shallow because that’s where the water is … shallow rooting can contribute to tree failure.”

Brace for power outages

Weakened trees and La Niña conditions will bring a “perfect storm,” B.C. Hydro has warned.

During La Niña events, trade winds along the equator are stronger than usual, pushing more warm water toward Asia. Off the west coast of North America, upwelling increases, bringing cold water to the surface that push the jet stream northward. This tends to lead to heavy rains, wind and cooler temperatures in the Pacific Northwest.

During El Niña years, everything is reversed, resulting in dryer, warmer conditions here.

B.C. Hydro says the province has some of the highest densities of trees per kilometre of power line in North America. And falling trees and branches are the single biggest cause of power outages.

Dry soil is more rigid and less of a shock absorber when the wind hits, the utility says, while dry wood is brittle and has less ability to bend or stretch as the wind passes through.

Even a small-scale windstorm can cause numerous tree failures and associated power outages.

B.C. Hydro said it has seen a 117% increase in storms that it has responded to over the past several years, rising from 52 in 2014 to an average of 113 a year over the past three years. Storm-related damage has caused more than one million outages on average annually over the past few years, it said.

In August 2015, after four dry months, a summer storm with wind speeds reaching 89 km/h blew drought-damaged trees to their limit, resulting in more than 710,000 customers without power at its peak.

This fall, conditions are slightly worse than they were in 2015, says B.C. Hydro. The utility’s meteorologists warn storm conditions could be especially challenging for the south coast, where much of the vegetation is not adjusted to desert-like conditions.

Unusually heavy rainfall contributed to loosening soil and weakened trees falling on power lines during the 2018 windstorm – the worst in Hydro’s history – that left 750,000 customers without power. Some of the worst hit areas during the storm were Vancouver Island and the Lower Mainland.

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Garry oak

Garry oak was named by botanist and explorer David Douglas for Nicholas Garry of the Hudson’s Bay Company. Quercus is the Latin name for oak.

The Garry oak has thick, grooved, scaly, greyish-black bark and a round spreading crown, and grows up to 20 metres tall.

Deeply lobed leaves are bright green and glossy above and paler with red to yellow hairs underneath. The leaves turn brown in the fall. Leaves often have bumps caused by gall wasps.

It grows in southeastern Vancouver Island and the Gulf Islands, with some isolated groups of trees in the lower Fraser Valley, where some experts say acorns might have been traded with Island First Nation groups.

Garry oak wood was used by coastal peoples for combs and digging sticks as well as for fuel. They also ate the acorns either roasted, steamed or ground into meal. They managed the Garry oak ecosystem by underburning in order to cultivate a supply of camas bulbs. Camas was an important food source for many coastal groups.

Garry oak forms open parkland and meadows that are scattered with Douglas-fir and a lush spring display of camas, Easter lilies, western buttercups, and shootingstars. These meadows are threatened by urban development.

Arbutus

Arbutus is the only native broadleaf evergreen tree in Canada. Growing up to 30 metres tall, it has crooked and leaning trunks and divides into several twisting upright branches.

Another common name is madrone, a Spanish word for the strawberry tree, a close relative to arbutus.

Scottish botanist Archibald Menzies first collected specimens in 1792 and described it as the oriental strawberry tree.

Arbutus is restricted to a narrow band along the south coast and generally occurs within eight kilometres of the ocean, often found on exposed rocky bluffs.

It has thick, leathery leaves, producing white flowers with a honey smell attractive to bees and berry-like fruit savoured by robins and waxwings.

Arbutus bark is thin, smooth and reddish brown, peeling in thin flakes to expose younger bark. It has been used in the hide-tanning process, and the hard and heavy wood is now only used for woodworking.

Western red cedar

The western red cedar is British Columbia’s official tree. The name plicata comes from a Greek word meaning “folded in plaits,” in reference to the arrangement of the leaves. It is sometimes called arbor-vitae, Latin for “tree of life.”

It grows up to 60 metres tall when mature, with drooping branches and a trunk that often spreads out widely at the base.

The leaves are scale-like, opposite pairs, in four rows, folded in one pair but not in the other and overlapping like shingles. They are arranged on the twigs in flat, fan-like sprays. It has a very strong aroma.

Seed cones are egg-shaped, one centimetre long, with several pairs of scales. Pollen cones are small and reddish.

It typically occurs at low to mid-elevations along the coast and in the wet belt of the Interior, where the climate is cool, mild and moist. It grows best in moist to wet soils, with lots of nutrients. It is tolerant of shade and long-lived, sometimes over 1,000 years.

Western red cedar frequently grows with western hemlock and Douglas fir. On the north coast, it also grows with amabilis fir and spruces. These forests usually have a lush layer of ferns, huckleberries and Devil’s club, with a thick carpet of mosses on the forest floor.

— B.C. Tree Index, Province of British Columbia

dkloster@timescolonist.com

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