Winter isn’t the ideal season for pruning trees in Upstate New York, but it’s the best time to cut scion or twigs from ash trees in parts of the state where the species has been all but wiped out.

Each strip of wood in Richard Silliboy’s hands started as a year of an ash tree’s life. Silliboy, 79, is a member of the Mi’kmaq tribe and a master basketmaker. His blue eyes are kind and frequently ...