Finding the Mother Tree: Uncovering the Wisdom and Intelligence of the Forest

by Suzanne Simard

imagining a birch leaf photosynthesizing—converting light energy to chemical energy (sugar) by combining carbon dioxide from the air with water from the soil. Because of their ability to photosynthesize, the leaves were the source of chemical energy, the engines of life. The sugar—carbon rings bonded with hydrogen and oxygen—would accumulate in the cells of the leaves and the sap then load into the leaf veins like blood being pumped into arteries. From the leaves, the sugar would travel into the conducting cells of the phloem—the blanket of tissue encircling the birch trunk under the bark and forming a pathway from leaves to the root tips. Once the sweet sap was in the uppermost sieve cells of the phloem, an osmotic gradient would develop between them and adjacent phloem cells. Water taken up by the roots from the soil would travel up the xylem—the innermost vascular tissue linking roots to foliage—and be loaded into the top sieve cells of the phloem by osmosis, diluting the solution to balance the concentration with the interlinking sieve cells. The increase in pressure in the cells—turgor pressure—would force the photosynthate downward through the smooth chain of sieve cells, eventually reaching the roots. The roots, as with the aboveground parts of the tree such as buds and seeds, need energy and are sinks for this sugary burst. (While leaves are the source of photosynthate, roots are sinks.) The root cells would quickly metabolize the sugar and move some into adjacent ...