With a changing, hotter climate, three-quarters of the Lower Mainland’s current native and introduced trees might not be able to survive in the future, according an assessment commissioned by Metro Vancouver.
The Urban Forest Climate Adaptation Framework, released recently by Metro Vancouver, identified 42 species commonly planted or naturally occurring in the region — classified into three categories of risk.
Among the trees are hardier versions such as the scarlet oak or shore pine, to somewhat at-risk species like the Japanese cherry or field maple, and to the most restricted trees requiring the most water, such as the kousa dogwood or western red cedar.
Only 10 are identified as “broadly suitable for both the current and future climate.” The medium-risk trees require at least 10 to 11 months per year of moisture, and the most at-risk require year-round fresh water.
Bill Stephen, a City of Vancouver expert on the urban forest strategy team who worked on the report, said on Monday that despite the findings, the risk of planting only hardy trees in anticipation of hotter weather would outweigh a more cautious approach.
“If we over emphasize the threats climate change has in our population by planting only those in the top of the list — most hardy — then that single approach may set us up for other problems,” he said.
“Like not enough diversity of our stock, which means insects and diseases would take out a bigger chunk of our stock in one go.”
A sudden shift to cold weather, he said, could also kill many of those so-called hardier trees intended for hot weather.
Stephen said that about 40 years from now, it’s predicted the Metro Vancouver’s climate would be much like northern California today.
“One of the things that’s working in Vancouver’s favour, and most of the Lower Mainland’s, is for years we have been purchasing trees from growers in the Fraser Valley,” he said.
“Their market for trees, most of them end up back east … to areas which historically have hotter, dryer summers than we have, than we will have with the (future) projections.”
At-risk areas in Vancouver, however, include the southeast False Creek area — around Main and Terminal — where past development has stripped the land of topsoil, he said.
“The whole problem with heat is water loss … having it in better sites or improving the site will extend its resiliency,” Stephen said.