If conditions are ideal a tree grows straight up. However, scarce resources may cause trees to grow with a lean, and it turns out that the direction and amount of this lean is affected by where a tree is in the world. Johns et al (2017) focused on a specific tree, Cook Pine, and found that the lean of the tree is dependent on both the hemisphere and the latitude of the tree.
Trees in the northern hemisphere lean south, while trees in the southern hemisphere lean north. And, the higher the latitude (i.e., the more north or south a tree is in its respective hemisphere) the more the tree will lean. Less than 10% of the trees did not follow this pattern.
The researchers don’t have a reason for this yet, but they are hoping that further research may reveal how environmental conditions affect the trees and their lean. I can’t help but wonder if it relates to the angle of the sun, kind of like how we need to angle solar panels to maximize sunlight at different latitudes.
But then, there is my other question, who thought to look at the way trees lean in different hemispheres? This is one of the things that I find fascinating, there are so many questions out there that no single person can think of them all.
Johns, J. W., Yost, J. M., Nicolle, D., Igic, B. & Ritter, M. K. (2017). Worldwide hemisphere-dependent lean in Cook pines. Ecology, 98: 2482–2484. doi:10.1002/ecy.1850