Another video walk, this time up the Creek with Bec on the other side of the globe, from a dampish occluded dawning in Cork to the end of a day of summer swimming in Tasmania we left our homes together. We show each other small parts of our worlds making connections and noticing differences. There was a seed (called a smokeberry ?) that the Tasmanians use to flavour ice cream, it is bitter sweet and has a strange peachy spiral around it, all the more mysterious for lacking focus, Bec is interesed in brickwork and odd inclusions that occur so I brought her to the Fleishmann residence and showed her the trees growing in the walls often we were talking in parallel as our phones glitched in and out, we both enjoyed getting up close.
Today one of the Glen walkers found a strange object in the river bank – it was a rung of a ladder for a manhole.
I was fascinated by some pale green lichen that managed to hold on to the raindrops/dewdrops while they slid off the other bark, I went back later and this activity was no longer evident, the lichen seemed to have sunk back into a passive role, its colour drained and texture dried and cracking, this made me think about Monday’s scarring on the birch and bustle formations so I began looking at tree skin conditions and healing.
I am preoccupied by my dewy lichen and I go back the next day at the same time, weather conditions are different, milder, and I find no beads of water gathered on the pale green spots. I seek some answers from botanist and author Robin Wall Kimmerer in her book Gathering Moss and I find out about The Boundary Layer:
Mosses inhabit surfaces: the surfaces of rocks, the bark of trees, the surface of a log, that small space where earth and atmosphere first make contact. This meeting ground between air and land is known as the boundary layer. Lying cheek to cheek with rocks and logs, mosses are intimate with the contours and textures of their substrate. Far from being a liability, the size of mosses allows them to take advantage of the unique microenvironment created within the boundary layer.
What is this interface between atmosphere and earth? Every surface, be it as small as a leaf or as large as a hill, possesses a boundary layer.
…I can imagine the pattern of air, flowing smoothly around it until it encounters the surface, where the mosses live. The sun’s warmth gets trapped in the tiny layer of still air. Since the air is nearly motionless, it acts as an insulating layer, much like the dead space in a storm window, which forms a barrier to heat exchange. The spring breeze around me is chilly, but the air right at the surface of the rock is much warmer. Even on a day when the temperature is below freezing, the mosses on a sunlit rock may be bathed in liquid water. By being small, mosses can live in that boundary layer, like a floating greenhouse hovering just above the rock surface.
The boundary layer traps not only heat, but water vapor, as well. Moisture evaporating from the surface of a damp log is captured in the boundary layer, creating a humid zone in which the mosses flourish. Mosses can grow only when they are moist. As soon as they dry out, photosynthesis must cease, and growth is halted. The right conditions for growth can be infrequent, and so mosses grow very slowly. Living within the confines of the boundary layer prolongs the window of opportunity for growth, by keeping the wind from stealing the moisture. Being small enough to live within the boundary layer allows the mosses to experience a warm, moist habitat unknown by the larger plants.
The boundary layer can also hold gases other than water vapor. The chemical composition of the atmosphere in the slim boundary layer of a log differs considerably from that of the surrounding forest. The decaying log is inhabited by a myriad of microorganisms. Fungi and bacteria are constantly at work degrading the log, with an outcome as sure as that of a wrecking ball. The continual work of the decomposers slowly turns the solid log to crumbling humus and releases vapors rich in carbon dioxide, which is also trapped in the boundary layer. The ambient atmosphere has a carbon dioxide concentration of approximately 380 parts per million. But the boundary layer above a log may contain up to ten times that amount. Carbon dioxide is the raw material of photosynthesis, and is readily absorbed into the moist leaves of the mosses. Thus, the boundary layer can provide not only a favorable microclimate for moss growth, but also an enhanced supply of carbon dioxide, the raw material for photosynthesis. Why live anywhere else?