"The tree population in Scandinavia's capitals isn't very diverse - Tilia is the most common genus in Stockholm, Oslo and Helsinki," he said. "Does it matter? People like the symmetry and neatness of trees of the same species and age, but the time for this is probably gone. The threat of exotic pests means it's not a question of if we change, but when."
He added: "We should get away from the paralysing fixation on native species. Cities are not natural environments - we are creating novel ecosystems. The palette could be much wider. What kind of trees do our immigrant populations relate to? We need to raise awareness of this issue among politicians and our customers, as they are already doing in Australia. Landscape architects have a big role to play."
Also speaking at the conference, Bicton College head of sustainable land use Kevin Frediani echoed the call. "There is a huge shift required in urban tree populations if they are to remain resilient," he said. "Botanic gardens such as ours at Bicton Park can inform on candidate trees for greater biodiversity."
Head of Royal Botanic Gardens, Kew's arboretum Tony Kirkham added: "In the next 10 years we will see significant changes in climate that will impact on all of us. At Kew we have already seen huge changes over the last 30 years in what we can grow."