MADISON, Wis. — What limits the height of trees? Is it the fraction of their photosynthetic energy they devote to productive new leaves? Or is it their ability to hoist water hundreds of feet into the air, supplying the green, solar-powered sugar factories in those leaves?
Both factors — resource allocation and hydraulic limitation — might play a role, and a scientific debate has arisen as to which factor (or what combination) actually sets maximum tree height, and how their relative importance varies in different parts of the world.