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This article was published 19/8/2011 (1866 days ago), so information in it may no longer be current.
OUR enviable urban forest — the collection of trees that line our streets, shade our lawns and populate our parks — faces constant challenges. It’s hard enough to find big shade trees that grow well here, and when we do find them, we put them in a killer environment: our trees absorb our cars’ exhaust, many of our roads don’t allow for proper root growth, in summer trees swelter under the heat-island effect that makes the city up to 10 degrees hotter than surrounding areas, and in winter the salt and sand from our roads corrodes them. Aside from our ill-treatment of them, bugs and disease lurk that can kill off the entire population of a tree species if left unchecked.
They take that so we can enjoy the way they cut the wind in winter and shade us in summer, and we can all sense a necessity to have some connection to nature within the boundaries of any city.
What we put them through is asking a lot, and we don’t give enough back to keep them in the best shape. Certainly, we don’t maintain them well enough, and we don’t remove diseased ones soon enough.
Under constant pressure, the trees persist, stubbornly coping with a host of challenges we make them face. Yet, they will fail without vigilant help from us. They suffer for us, under attack all the time, and we neglect them; the least we owe them is more than we give.
The city can put a dollar value on part of our urban forest, pegging the worth of 160,000 city-owned elms on boulevards and in parks at $594 million. That amount comes from applying a formula devised by U.S.-based Council of Tree and Landscape Appraisers, a formula that accounts for qualities such as height and trunk diameter, as well as condition and species. But that value doesn’t count the approximately 60 per cent of city-owned trees other than elms. Nor does it count the vast majority of the estimated eight million trees that grow within the perimeter, owned by the city, the province and individuals. All told, our collection of trees in Winnipeg could be worth billions. But we know enough to value our trees for more than the money they represent.
Tim McLachlan, a landscape architecture professor at the University of Manitoba, calls trees in the city "urban sponges" that pull pollutants and dust out of the air, while they absorb the elements of weather. "During winter and summer the trees act as a buffer between us and the extreme temperatures, either reducing wind chill in the winter or blocking us from heat in the summer," he says. "But besides helping us cool and heat our homes, a plentiful tree population makes it more likely that people can interact with their environment. I hear the term ‘nature deficit disorder’ used a lot lately, and the trees in an urban forest allow us to keep a connection to the greater world. They’re biological, something to relate to, more like us than buildings, concrete and asphalt."
Wendy Land can tell you about the depth of potential connections between people and trees. "I’m planning to have a wake for it, a sort of goodbye party," she says, sitting in the porch of her Wolseley area home, talking about the dying 150-year-old elm on her front lawn, one of the first trees planted on her street, at the moment still towering above Land’s two-storey house. But the orange dot spray-painted on the trunk identifies the tree as having Dutch elm disease, its water-conducting vascular system choking on the Ophiostoma ulmi fungus. Land expects a city removal crew to cut it down by the end of summer.
"It’s been like a family member," she says, telling of her family’s desperate attempts to save the big elm since it showed signs of the disease. Despite thousands of dollars in arborists’ bills for fungicide injections and aggressive pruning, though, "they said it couldn’t take any more loss of branches without making the canopy too small for the tree to survive even without the disease."
Land insists she had a healthy tree. You can see a slight indent in the tree’s bark, around the trunk, where Land and her family have for years placed Tanglefoot bands, which help prevent the wingless canker worm moth from climbing up to eat all the leaves in a tree. The resulting defoliation weakens a tree, leaving it attractive to the fungus-carrying elm bark beetle. Land says she also treated the tree to pruning about every four years, to remove dead wood the beetles prefer for summer breeding.
Nevertheless, the fungus can also spread through grafts that commonly form between the root systems of mature nearby trees. When arborists Land consulted last year heard a city crew had removed a fungus-infected boulevard elm from in front of Land’s house in 2009, they figured her tree got sick via root graft transmission of fungus from that boulevard tree.
"This is a result of something the city hasn’t done," says Land, blaming her tree’s impending death on an inadequate pruning cycle for city-owned trees that left the previous boulevard tree weak and susceptible to disease. "These trees haven’t been pruned in at least 15 years," she says, indicating boulevard trees on her block that have numerous dead branches, each one ready to provide a site for beetles to breed. Moreover, she says, most marked elms stand for up to a year after being identified, all the while threatening nearby trees.
Land makes points about pruning and rapid removal no forester could argue with, but the forestry branch can only afford to do an inadequate job. City forester Martha Barwinsky says civic funding supporting the urban forest has remained "relatively steady" over the last four years, allowing for a pruning cycle of once every 13 years (she would prefer it every eight) and a replant rate of 0.75 to one.
Land’s main concern is for the city’s elm trees, many of which populate her neighborhood so densely, but in other parts of the city, ash trees have come to dominate the neighbourhood flora. Prior to 1975, the city planted almost nothing but hardy elms. When the threat against them arose, the city focused on ash trees, with not many other shade trees to choose from. By 2005, then city forester Dave Domke had established a "25 per cent rule" that now calls for planting 25 per cent each of ash, elm and linden and 25 per cent of other species. Nevertheless, our reliance on ash as a compliment to the elms has given us an ash population of about 280,000, more than twice that of elms. Anytime now, the emerald ash borer will appear here to threaten every one of them.
The voracious emerald ash borer kills trees directly, taking a tree’s nutrients for itself. Enough of them feeding under the bark will starve an ash to death in as little as two years. It first appeared in Detroit in 2002 (native to Asia, probably traveling by shipping crate) and has since killed tens of millions of ash trees through the American midwest and in parts of Ontario and Quebec. Loss rates of ash trees in affected areas range around 20 per cent a year. Compare that to our Dutch elm loss rate, which city officials say is about two per cent a year.
Canadian efforts to contain the emerald ash borer have proven relatively successful. To the east, it only ranges as close as southern Ontario. To the south, though, it appeared in St. Paul, Minn. in the spring of 2009. Barwinsky believes its arrival here is inevitable. "The elm bark beetle was brought in by humans, and the emerald ash borer will be brought in by humans," she says. "We spread the diseases around."
"At this point, the emerald ash borer will be much worse than the threat of Dutch elm disease," says Domke, who now works as division manager of the city’s parks and open space division. "At least with DED we have controls we can use," he says. In fact, the City of Toronto, rather than fighting the bug, decided this year to start culling its entire 860,000-strong ash population, replacing them with other species at an estimated cost of $68 million. As the Toronto city website explains: "Thus far, infestations elsewhere in North America have increased and spread despite significant control measures attempted. Once established, EAB has proven impossible to control." The Canada Food Inspection Agency twice a year monitors bright green traps they’ve set up in selected Winnipeg ash trees. At last check in late July, the bug hadn’t appeared.
Yet, while we wait for the borer, the forestry branch continues to plant varieties of the ash species, as it still plants varieties of elm. "We are trying to replant with other species to alleviate the mistake of monoculture," says Barwinsky, "but there are very few trees available to grow in our climate." For example, the other category of trees can include delta hackberry, bur oak and Ohio buckeye, but the selection varies each year, depending on tree availability at nurseries. With confidence that seems based on faith, Barwinsky wants to avoid an ash cull here and looks to our remaining elms as a hopeful example for the ash population. "We’re going to learn a lot from others who got the borer first," she says, "the way it happened with Dutch elm disease."
Allen echoes Barwinsky with a list of trees tried here that are failed or failing. The Swedish aspen? It gets bronze leaf disease. Schubert choke cherry? Once on the list of potential other trees, many of them are dying from black knot disease, which looks like burned marshmallow wrapped around the branches. Native oaks feel urban stresses harder than most trees, often falling prey to the two-line chestnut borer. Weeping birches get killed by the bronze birch borer, and Allen also recently noticed the dying of green ash, succumbing to a disease called ash anthracnose. "The trees live complicated lives," he says. "It’s dynamic, changing every day in some form or another."
Efforts to discover a greater selection of Prairie-ready shade trees are scarce, according to tree developer Rick Durand. He says once-promising work at Agriculture and Agri-food Canada Morden Research Station has decreased gradually over the past five years or so, until the station ceased its last "woody ornamentals" program this spring. Now, Durand is among a group of Prairie tree nurseries and developers aiming to produce a longer list of trees for us to plant.
The Prairie TRUST project, started by the Western Nursery Growers’ Group, has 750 trees comprising 150 varieties, planted at four nurseries in Manitoba, Saskatchewan and Alberta. The trial, which started in 2008, needed particular varieties of two-year-old trees, not all available on a yearly basis from developers, so the group spread their schedule out, planting the last trees this year. Many of the test subjects in this five-year program will grow to be seven years old, tested along the way for size, disease and insect habitation. Severe winter damage already took a maple cultivar called Autumn Fantasy out of the trial, but Durand sees promising results so far in other cultivars of maple, along with a few tree lilacs and lindens.
The project’s website says trees found acceptable at the end of the trials will be labelled "Prairie tested," which represents "a tree that has shown to be Prairie hardy and has high resistance to insects, disease and environmental factors." Durand admits, though, resistance at seven years old doesn’t mean resistance at 35. "Our main focus is on hardiness," he says. Barwinsky, already wary of resistance claims, says she’s glad just for the chance to find a wider variety of trees to plant. "We need them out there for 20 years or so, before we can trust any claim of disease resistance," she says, adding most trees exhibit natural "juvenile resistance" to disease for about 20 years.
Even without the constant threat of Dutch elm disease and the coming threat of the emerald ash borer, our trees suffer daily. The urban environment gives them compacted roadbeds to restrict their root growth, while pollution and heat reflected off buildings and roads test their resilience more than a natural setting could. In winter and spring, de-icing salt splashed from sloppy roads kills branches, resulting in a "witch’s broom" effect. The city currently plans only limited replanting of boulevard trees along busy regional streets, such as Pembina Highway and Grant Avenue.
"We will not replant trees on regional streets under their current condition," says Barwinsky. Instead, trees removed from boulevards of busy feeder routes will only be replaced "under conditions we’ve outlined in the forestry department’s guidelines." Those conditions include necessary space for the tree to avoid salt spray and to enjoy adequate soil volume. The guidelines also suggest the use of technologies such as the Silva Cells system and tree vaults for trees in stressful and crowded places.
Silva cells (in use along Broadway, as well as along King Street by Old Market Square) make a framework under sidewalks and roads that supports concrete and asphalt, while allowing tree roots to spread more naturally and helping to control storm water runoff; tree vaults (in use by trees on the Main Street centre median near Pantages theatre) are essentially giant plant holders that can be raised above grade if necessary. Barwinsky says these "enhanced planting sites" seem to be doing well. Though the city has none on hand for current use, Barwinsky says engineers in the public works department know about them as an option to write into the budget of any road or sidewalk rehabilitation projects coming up.
Asked for three wishes for the forestry department, Barwinsky gives one. Her department has a set of principles and guidelines, but she wants an urban forest management plan for the city. Banff, Kingston, Vancouver and Toronto are among the places with plans for their trees that set definite goals, instead of suggesting them. A plan for Winnipeg would likely set marks for pruning and replanting and of course it would address treatment of diseases and where they are planted. But it might also include rules about tree protection on private property and soil quality in new housing developments (something that especially bothers her). To that end, the department began collecting data for a tree inventory, including counts of the trees in parks and on boulevards, reports on their condition and a list of potential spaces for new trees. Barwinsky plans on it being completed next year.
"You have to think of trees as infrastructure," says Barwinsky, "and as infrastructure, they’re the only one that actually accrues value with time." The older roads and utility lines get, the weaker they become. But for every year trees grow bigger, they take out more pollutants from the air and absorb more heat. All along, they help us keep an essential connection to life beyond the hardness of the city. A University of Illinois study of a Chicago housing project showed apartment blocks surrounded by trees had fewer reports of violence than blocks on barren lots.
Barwinsky notes, too, the biggest trees in the city all got big under less stress than they face now. And, reluctantly, she concedes it’s entirely possible our urban forest 50 years from now will be much thinner and shorter. Winnipeggers will live in a city that is even hotter, windier and less pleasant to look at. Let’s face it, this place would be dreadful without them. They need our attention and care and a proper gauge of their worth, in terms of money and spirit. Barwinsky admits "but the potential is there if we find the best ones to plant and treat them in the best way we can."
The greatest trees
In late July, Martha Barwinsky and city naturalist Rodney Penner went to McBeth Park to inspect a cottonwood that would remind anyone of how awesome a tree can be. About 150 years old, it stands 27 metres tall and has a tree hollow at the base big enough to stand in. Long ago, some physiological stress caused a small cavern on the then-smaller tree that persisted and grew into this. Barwinsky and Penner say they try to see the tree once a year or so just to make sure it’s still standing. The cavern makes it less strong than its scattered neighbors, tall and short, in this river bottom forest.
The cavern also makes the tree popular with some number of tree-hating partiers with lighters. Burn marks line the inside the cavern, and outside the charring continues up stretches of heartwood, left exposed by flames from fires set inside the tree. Barwinsky notices new cracks in the trunk, filled in with callous as the tree tries in vain to repair itself.
"This is one of the greatest trees in the city," says Penner, explaining the path running by it is a recent addition from a nearby suburb, put there in the hope of deterring firebugs. "I hope people don’t set it on fire anymore," he adds, as Barwinsky points out the expected failure points.
"It’ll buckle up there and crack down around here. And it will take those with it," she says, waving at about half a dozen smaller but impressive trees nearby. "We may never see trees of this size in Winnipeg again."
With hope at least someone might see trees this big again, Penner has about 20 cuttings, from this and other cottonwoods around the park, at the city nursery and is trying to root them. "We wanted to try it out, to see if we can get them going," says Penner, smiling at the old cottonwood. "This is such a great example of a river bottom forest tree. If it works out, maybe people will see these in parks. Some of the cuttings have taken root, and we want to take more while we can."
No more remediation for sick elms
Until mid-July this year the forestry branch allowed some Dutch elm disease-infected trees on private property to go on a remedial therapy list. Entry on the list gave a tree’s owner a year to to try and save a tree by pruning infected branches or injecting fungicides to halt the disease. Martha Barwinsky says the efforts have saved trees but not often enough and not soon enough. "We won’t approve remedial therapy any longer," she says. "For the past three years, it has only been 60 to 80 per cent effective, but even at 80 per cent effective, it’s too much risk because the tree spreads infection while it’s being treated."
The tree removal process
Martha Barwinsky says removal time varies, depending on the tree. A younger tree on a boulevard is easy, compared to an old backyard tree, tall and hanging over a garage or with branches threaded through overhead wires. Hydro clearance may be needed, along with climbing and rigging among the canopy. "Sometimes we can remove 10 trees in a day and other times it might take three days to remove one tree."
Big gear for a typical removal includes a bucket truck to lift a technician up to canopy level, a wood chipper for the branches coming off and a loader to put bigger tree pieces in the back of a pickup. From the raised bucket, a technician pares the branches down to leave the main trunk remaining. The bare tall pedestal is then dropped with a cut through the base. A big enough tree will shake the sidewalks and the road nearby when it hits the ground.
Stump removal comes next, with workers grinding the stump to about six inches below ground level. Homeowners have the option to pay to have the stump removed further, in order to plant a tree in the same place. Otherwise, a city crew finishes up by filling the hole with soil and laying grass seed.