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Research indicates that Douglas firs have the greatest potential height, yet redwoods dominate the list of the tallest trees globally. Explore stunning tree images.
© iStockphoto.com/sassy1902Main Insights
- The height of trees is restricted by their capacity to draw water upward through the trunk, with tracheids being essential for water movement.
- Tracheids, which are pitted dead cells responsible for water transport, narrow in diameter as they ascend the tree, making water delivery more challenging and leading to drought stress in higher regions.
- Taller trees face a higher risk of xylem embolisms, where air bubbles obstruct water flow, thereby restricting height by limiting the supply of water and nutrients.
A 2008 study suggested that the tallest a Douglas fir—one of the planet's tallest trees—can grow is approximately 453 feet (138 meters) [source: Kinver]. But what causes this limitation? Trees are often seen as nature's skyscrapers, seemingly boundless. This ceiling exists because trees can only draw water up their trunks to a certain extent.
The cells responsible for water transport are called tracheids, which are pitted and non-living, facilitating water movement between cells. As you move higher up the tree, the diameter of these critical pits narrows, making water transport more difficult. Eventually, the water supply to the upper leaves and branches diminishes or ceases, causing these sections to suffer from "drought stress." This dehydration leads to their death, effectively setting a natural height limit for the tree.
Scientists believe that the gradual narrowing of tracheids aids tree survival. Height increases the risk of air bubbles. Taller trees are more prone to developing a xylem embolism, where air bubbles obstruct water flow. (Xylem is the tissue forming a tree's vascular system, enabling water and mineral transport from roots to other parts.) A xylem embolism is akin to a human air embolism, where air in the bloodstream can cause serious issues. Tracheids work to prevent air bubbles and handle increased pressure, but this protection reduces water flow and, researchers suggest, limits tree height.
A separate study on tree height, published four years earlier, proposed a maximum tree height of 426.5 feet (130 meters) [source: Amos]. The study focused on coast redwoods, or Sequoia sempervirens, the tallest trees globally, and based its findings on factors like current weather conditions, photosynthesis rates, water flow, and carbon dioxide levels. Predictably, beneficial factors like water flow and photosynthesis decreased in the upper parts of these massive trees, while harmful factors like carbon dioxide increased. Ultimately, as with Douglas firs, xylem plays a decisive role.
These redwoods, like other trees, draw water through their trunks, though they can also absorb moisture from the fog common in their native California and Oregon habitats. Before reaching their maximum height, they grow approximately 9.8 inches (25 centimeters) each year [source: Amos].
Next, we'll explore alternative perspectives on tree size and discuss what might be the largest organism on Earth.
The World's Largest Trees
Currently, General Sherman, a giant sequoia, is recognized as the largest single tree in the world by mass.
© iStockphoto.com/PierGTree size encompasses more than just height. General Sherman, a giant sequoia—one of two redwood species in California, the other being the taller, slimmer coast redwood—is the world's heaviest and most voluminous tree, weighing approximately 6,167 tons (5,595 metric tons) and occupying 52,000 cubic feet (1,487 cubic meters) [sources: Britannica and NPS]. Situated in California's Sequoia National Park, General Sherman stands 274.9 feet (83.8 meters) tall but isn't the tallest tree [source: Britannica]. That title goes to a coast redwood named Hyperion, measuring 379.1 feet (115.5 meters) [source: Leff]. General Sherman's trunk has a circumference of 102.6 feet (31.1 meters), though it’s narrower than El Arbol del Thule in Oaxaca, Mexico, which boasts a circumference of 178 feet (54 meters) [sources: NPS and Barnett].
Tree size can be assessed in various ways, much like determining the largest living organism. Some researchers view massive reefs, such as Australia's Great Barrier Reef, as enormous living entities. Additionally, there are vast fungi, like a 1,500-acre (607-hectare) fungus found in Washington, once regarded as the world's largest organism by area [source: Grant].
However, the world's most massive living organism is likely a cluster of quaking aspen trees in Utah's Wasatch Mountains, known as Pando (Latin for "I spread") [source: Grant]. Pando is considered a single organism because its trees share identical genetic material and a connected root system.
The trees in Pando are essentially clones of each other. New trees form as stems extend up to 100 feet (30 meters) from the parent tree, periodically taking root and producing genetically identical, interconnected trees. This cycle continues with the clone trees, provided weather and other conditions are favorable. This method, called vegetative reproduction, is also used by strawberries and numerous other plants to propagate.
Pando consists of 47,000 trees spread over 106 acres (43 hectares) and is estimated to be up to 80,000 years old [source: Grant]. Despite its vast size, this collection of 47,000 trees weighs approximately 6,600 tons (5,987 metric tons), only slightly more than General Sherman [source: Sugarman].
Quaking aspens, with their slender trunks, can reach heights of up to 100 feet [source: NPS]. Thanks to their reproductive strategy and resilience in challenging environments, quaking aspens are the most widespread tree species in the United States.
Continue reading for additional insights on trees and related links you may find interesting.
