Charlotte de Keyzer can usually be found in a park somewhere, staring at trees — particularly the eastern redbud. But she’s not so much interested in admiring the tree’s flowers as in the bees that feast on its pollen and leaves. The tree is relatively new to Toronto, and de Keyzer, a PhD student at U of T, is studying how native pollinators interact with it.
“A hundred years ago you couldn't have planted a redbud in Toronto, it never would have survived. Now you can plant them,” de Keyzer says. “We have 15 different species of bee that visit the flower, and we're going to try and figure out how many species of leafcutter bees visit the leaves.”
De Keyzer is running a citizen science project to gather information about the tree, including when it flowers and which bees visit it (with a particular focus leafcutter sightings). Her study — the Urban Redbud project — will provide insight into how new plant species interact with native pollinators, mapping the trees in Toronto and beyond to find out how effectively they establish themselves in the region.
Research like de Keyzer’s is becoming more important as the climate continues to change. Aided by changing temperatures and precipitation patterns, plants are taking root in new territory year after year: a 2014 paper in the journal BioScience reported that the growing area for 62 tree species moved north an average of 57 kilometres between the periods from 1931 to 1960 and 1981 to 2010. (Many climate researchers study 30-year periods to get big-picture information.)
“What we do in this kind of modelling work is we can look at where things grow, we can generate a climatic profile from that and we can map that profile,” says Dan McKenney, one of the authors of the BioScience paper and a research scientist with the Canadian Forest Service.
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The eastern redbud’s migration is just one of many massive changes coming to Canadian forests as a result of global warming. The species is a welcome guest in Toronto to both pollinators and people, but it has had a lot of help establishing itself here: gardeners have planted it, and so has the city. Other species may not get as much assistance.
“As the climate in Canada begins to warm … potentially 50 years from now that same climate could be the same in northern Ontario [as it is in Toronto], however trees can't move that fast,” says Anthony Taylor, a forest ecologist with the Canadian Forest Service.
Trees that can’t keep up may start to die off. For example, the Boreal forest’s southern boundary stretches across northern Ontario from Thunder Bay to Timmins. Trees above that line are able to survive in cold conditions, but the warming climate will push that border northward.
“Those trees that are adapted to these cooler conditions are no longer going to be able to grow as well as they did,” Taylor says. “Species farther to the south, which have been constrained by colder temperatures, are going to be able to be more competitive than these Boreal species. It's a phenomenon that we'll see across the continent for all sorts of tree species.”
But it’s not just temperature that limits a tree’s range. Rainfall, soil conditions, sunlight hours, and frost cycles all play a role in the survival of a species.
“Part of understanding how species shift with climate change is trying to understand why they have a range limit historically,” de Keyzer says. “There's always going to be something that limits it. It could be cold, but it could also be that pollinators don't visit it.”
A 2007 BioScience analysis of 130 North American tree species projected that if greenhouse gas emissions remain high the climate habitat for all species will, on average, move northward 700 kilometres by 2100.
“What the big issue is is that the climate will potentially warm and change at a faster rate than a lot of plants and tree species can move,” Taylor says. “They can't necessarily move with the climate.”
Photo courtesy of John Hayes and licensed for commercial use under a Creative Commons licence. (See the uncropped version.)
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