The tree in Stéphane Ouellet’s backyard was ruining a good thing. The yard, once an urban refuge, was now a place where only the tree was thriving. The roots of the 100-year-old poplar were turning the rubber tiles that covered the ground into small hills. There was no level surface for tables and chairs. What’s more, the holes in the rubber tiles were getting clogged with plant matter, impeding drainage and attracting insects because of moisture.