SKELLEFTEA, Sweden — Construction of one of the tallest timber buildings in the world — the Sara Cultural Center here — began with a pine seedling planted almost a century ago. …the tree grew to become part of a grand experiment in sustainable architecture — one that seeks to reduce greenhouse gas emissions and store carbon in revolutionary “mass timber” structures going up around the world. Constructing shelter from logs — Abe Lincoln-style — is old-school … wood has been humanity’s go-to building material for low-rise dwellings for thousands of years. …But, now, building codes are being rewritten in Europe and the United States to accommodate big wooden structures. And trailblazing architects and engineers — and their early-adopter clients — are in a proof-of-concept race to erect ever-taller timber towers. …Advocates want to show that the buildings will not fall over. That they are not firetraps. That they can be built quickly — at competitive prices.