In contrast to humans, trees undergo uninterrupted expansion over their lifespan. Precisely, one can determine a tree’s age by gauging the count of growth rings through the scientific technique of dendrochronology. Among these, the loftiest tree, a coast redwood (Sequoia sempervirens), achieves a mean yearly growth of 25 cm (9.84 inches). Notably, the most towering verified example stands at a remarkable 115.55 meters (379.7 feet), and hitherto, no tree surpassing 120 meters (393.7 feet) in height has come to light.
Tree Height: The Taller It Is, the Higher the Risk of Embolism
In order to convey water and essential nutrients from the roots to the leaves, the tree employs a duo of mechanisms: evapotranspiration, a process that draws water molecules up to the leaves, and capillarity. The unrefined sap courses through tracheids, lifeless cells endowed with valves that facilitate the upward movement of water. Nevertheless, as the tree’s height increases, the pressure inside these tracheids diminishes due to gravitational effects. As this pressure plummets, the tree contends with a phenomenon known as “xylem embolism,” wherein air bubbles form in the vessels, obstructing the flow of sap.
To counteract this potential cavitation, the tree diminishes the dimensions of tracheids in the upper segments to augment pressure within the cells. However, this constriction comes at a price: a decreased volume of water arrives at the leaves, resulting in a reduction of photosynthesis, growth, and evapotranspiration. Beyond a certain threshold, the cells become so narrow that even water droplets fail to reach the branches, precipitating their desiccation and demise.
The Tallest Trees
A study published in the journal Nature in 2004 estimated that the maximum height of a giant sequoia is limited to 122 or 130 meters (400 or 427 feet). Another study from 2008 published in PNAS focused on the Douglas fir, another conifer that can reach record heights; it reaches a theoretical maximum height of 138 meters (453 feet) (between 131 meters and 145 meters, accounting for the margin of error). The tallest known Douglas fir, located in Coos County, Oregon (USA), currently measures 99.7 meters (327 feet) in height. The Centurion, in the Arve Valley, Australia, is the tallest living eucalyptus and stands at 99.8 meters (327 feet) in height.