Hacker News new | past | comments | ask | show | jobs | submit login

> the combined cross-sectional areas of a tree’s daughter branches are equal to the cross-sectional area of the mother branch.

Seems so logical, for a flow in the daughter pipes to match the mother pipe... except that the wood of a tree is dead, and the flow happens in the bark... leading to a sum-rule for circumference, proportional to radii and diameter.

However, the point of a tree is structural, to get higher than other trees, higher than herbivores. Is the strength of wood proportional to cross-sectional area (required to resist gravity - the essential problem of height)? If so, that would explain the rule. Similar reasoning to wind in the article.

EDIT it also means the weight per height remains constant through branching... this doesn't seem sustainable; you'd want it to taper.




I like your train of thought. You absolutely want the right amount of taper.

Regarding wood strength being proportional to area: it can't be as simple as that - wood is a strongly anisotropic material, so direction of loading becomes critical to understanding what's going on.

Natural trees have defects, and they "know" it. Limb attachment is messy business - in many species they are frequently defective. Doesn't reduce well to modeling actual limbs as simple beams or whatnot.

Starting to understand thigmomorphogenesis and how trees deal with it in terms of load shedding, compartmentalization, and reaction wood growth was one of my favorite "ahhh ha" moments.


They do taper, the method is to drop branches and limbs over time. Look at an old tree and the first branch is often 10+ feet above the ground, where young trees have many branches much lower.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: