Carbon negative seems like a misnomer, since all of the carbon that a tree absorbs literally becomes a part of its mass. Since mass is conserved (mass can't com

Carbon negative seems like a misnomer, since all of the carbon that a tree absorbs literally becomes a part of its mass. Since mass is conserved (mass can't come from nowhere, and it can't be destroyed), how is it possible for the trees to store more carbon than what is required to produce them?