The Tree: A Rain Engineer

The pitter-patter of rain may induce you to take dry refuge quickly. Nature wants no such escape. Instead, she collects, funnels, and deposits water in the most innovative ways. Try a tree as your tutor, and you will notice that essentially each tree is a microcosm of an entire watershed, moving water efficiently over its singular, vertically arranged landscape.

Raindrops land on a leaf. Orderly veins or slight cupping in some species’ leaves move the molecules effectively until the moisture reaches the stalk or flexible twigs. Or, rather elegant leaf drip tips or edge serrations serve as tipping points to the next leaf below as the gathered weight of the water spills again and again under the force of gravity.  The leaf does not get wet. Even needles concentrate water and send it on its way to twigs. You are not likely to feel the initial raindrops under a tree, but only the larger concentrated globs that now splatter under the canopy.

Trace the following path of a drop from the leafy headwaters towards the twigs and larger branches. Most trees have branches that ascend or have a rather sinewy pattern, which guides the direction of the liquid downward. You could imagine this as the waterways of first order, second order, and so on, as the sky’s liquid coalesces into streams and rivulets. Check out the evidence from a native sycamore in a city setting. The dark particulate matter captured in an urban environment often gets rearranged and deposited under the large whitish branches. Sometimes you can still trace the water tracks when dry.

Dark V-shaped lines of deposited particulate matter on the underside of a sycamore tree limb show the pattern in which water moves along tree limbs toward the trunk (image credit: Julianne Schieffer, Penn State Extension).

Of course, the trunk connects all those branchy waterway networks. Diamond-shaped funnels or ridges of bark patterns (much like mountains and valleys) increase the flow drip by drip until a larger river goes down the trunk, always following a path of least resistance. Notice that the bark on the trunk does not get wet unless there is a driving wind. Ironically, it too tends to water resistance. The bark sheds or delivers the rain-made cargo to the estuary or base of the tree. There you will find the highest concentrations of roots to absorb the liquid. Perfect placement!

This efficiency especially comes into play when a light sprinkle may not even dampen the soil. By keeping the collected water in its canopy instead of letting the roots pick it up from the soil, the tree again concentrates and gathers the liquid until, by weight and mass, it makes its way to the roots. The tree may expend less energy by design instead of actively using root growth and other processes to gain access to this water.

My hope is that you, too, will want to witness and experience the path the sky's liquid takes across a tree's surface. Let a tree reveal its engineering marvel of moving water during a deluge, and you may never feel the need to make that mad dash to stay dry again!