The process by which trees absorb sunlight, water and carbon dioxide in order to make oxygen and sugar is know as photosynthesis. Literally, putting together with light. This process is critical because it drives many other major physiological processes within the tree such as transpiration, respiration, absorption and translocation. Through a broad gaze at photosynthesis, arborists can observe many microcosms of specialization in trees.

Leaves are tissues that contain chlorophyll inside cells called chloroplasts. Chlorophyll is the pigment that gives leaves their green color, and it is the primary site of photosynthesis. Leaves by design are perfect absorption panels. They are thin, to allow for thorough penetration of light to reach the chlorophyll (ISA Arborist Certification Study Guide, 5). This thin structure creates a wide platform for specialized cells to spread out and brighten their ability to soak up sun. It is a good representation of solar technology in a sense. Trees will also cater their architecture to give their leaves the best prospect for light accumulation. Trees grow toward light, and their wood is built to support that pursuit. Phototropisms are driven by the tree’s need to photosynthesize. A low, crooked and sweeping limb tells the story of its search for light through time. An ancient and heavy quest. 

Leaves are also regulatory systems, with air and water coming a going like a mico-hydrolic pulse. Because of transpiration and the effect known as ‘transpirational pull’, leaves release water back into the atmosphere as water vapor. Subsoil osmotic transactions produce reactions sometimes hundreds of feet away at the leaf surface: one silent speck of water back into the atmosphere.  An interesting connection is shared here between leaves and roots. Photosynthesis, in this regard, is the entire tree system in symphony. In more regulatory fashion, the thick, waxy coating of the cuticle monitors temperature and prevents unecessary water loss. The stomates, which are openings in the leaf that support the process of gas exchange, open and close as guard cells expand or contract in response to environmental stimuli (ISA ACSG, 5). This cell turgidity is just another way that trees swell with the life that surrounds them.

Much like an assembly line factory conveyor belt, vascular bundles are arranged to immediately carry the by products of photosynthesis (carbohydrate and photosynthate) to other areas of the tree to fund other physiological processes. Allelochemicals, for example, like juglone in walnut are shipped off to the roots from these photosynthetic factories to suppress competition for the sacred rays of sun critical to the tree system. The proof is in the pudding. 

But even for the vast likeness of the structure and process of photosynthesis, each leaf is very unique in its outward appearance: margin, sinus, lobe, apex, petiole, arrangement on the stem, etc. Some leaves have spiny lobes (holly), while others have dusty surfaces (sycamore) or leathery sheens (magnolia). Deciduous trees shed leaves every year as an escape from the heavy loads of ice and snow that their decurrent crowns crinkle underneath. Each tree species lives in part through the house band of photosynthesis, but their defense and structural mechanisms for expression are very eclectic guest appearances. Genetics and environmental stimuli manifest themselves in trees in ways to drive photosynthesis because light builds trees.

Tree parts and processes specialize because the need to carry on photosynthesis is so dire. Respiration continues on, and if energy is not recreated through photosynthesis, it is destroyed after all of the sinks have been sucked dry. Defoliation, drought, and insect infestation can all halt photosynthesis in some way or another. This is what Shigo described as the balance of tree death: the oscillating and reciprocating pumps of tree life slowly settling out to an unmoving equilibrium (Modern Arboriculture). 

The light of the sun reverberates in every tree cell, from xylem to root cap. This vibration is a different sensation than the typical calming touch of the sun upon your neck. Maybe you’ve felt it after a long day aloft bouncing at the ends of limbs: in the kitchen or living room at home you catch yourself still swaying and flexing on solid ground to those loud, dynamic waves of sunlight.

That’s the photosynthesis you feel.