How Tall Can a Tree Grow, and What Stops It?

How Tall Is the Tallest Known Tree, and Could One Grow Taller?

The tallest known living tree is a coast redwood (Sequoia sempervirens) named Hyperion in Redwood National Park, California. Guinness World Records lists it at 116.07 m (380 ft 9.7 in), measured in 2019, and says it was found on 25 August 2006 by Chris Atkins and Michael Taylor [1]. The National Park Service (NPS) gives “379 feet” (about 115.5 m) for the tallest known tree [2]. The figures differ slightly. Guinness also gives a 2006 measurement, made by climbing the tree and dropping a tape, of 115.55 m, which matches 379 ft [1], but the pages I read do not say how the 2019 figure was measured. A reported height needs a measurement date, because a tree may keep growing or lose its top.

You cannot visit it. The park has built no trail, partly because of the cost of building and maintaining one for a tree that is not expected to stay the tallest, and because visitors pushing through the brush toward it have trampled and killed nearby plants. The park asks people not to seek it out [3].

Could a tree grow even taller? In 2004, Koch, Sillett, Jennings and Davis studied redwoods in northern California, including the tallest tree known at the time, 112.7 m (370 ft). They compared leaf characteristics at different heights and estimated a maximum height of 122 to 130 m (400 to 426 ft), assuming no mechanical damage [4]. That number is a statistical estimate, not a measured wall. So the next question is what could make growing upward harder.

Trees Have No Pump, So Water Is Pulled Up From the Top

A redwood’s roots are underground, and many of its leaves are more than 90 m (300 ft) up. There is no heart. Save the Redwoods League says the water is moved by evaporation and the pull of water through the tree’s tissues [5]. As water evaporates from the leaves, water molecules cling to one another, so the water in the narrow tubes inside the trunk is drawn upward as a connected column.

Gravity works against this. Water is heavy, so every extra meter (3.3 ft) of height needs a little more pull, and for a column of water as tall as a redwood those little amounts add up. The sources I read do not give a number, so the exact pull is left out here. The general point is that the taller the tree, the harder its top leaves must pull.

Redwoods also have a helper: fog. Save the Redwoods League explains that in dry summers fog condenses on the leaves, some of it is absorbed directly, and the rest drips to the ground [5]. The NPS adds that summer fog limits how much water the trees lose [2]. Even so, the pulling problem remains. What does it do to the top leaves?

Even With Wet Soil, the Highest Leaves May Be Short of Water

Koch and colleagues proposed that increasing water stress in the leaves, caused by gravity and by the resistance of the long path the water travels, may ultimately limit how far leaves can expand and how much photosynthesis they can do, even when the soil holds plenty of water [4]. Photosynthesis is how leaves use sunlight to make food. The paper says “may,” so this is a proposal that fits their measurements, not a proven rule.

A simple way to picture it: sipping through an extremely long straw. Even with a full glass, a very long straw makes every sip harder. (That is a picture for understanding, not from the sources; in a tree, the leaves do the pulling and no one is sucking at the bottom.)

This is only one idea. How well does it hold up across many kinds of trees?

Tests Across Many Trees Found the Water Idea Common but Not Universal

The idea that trouble moving water limits tree height is called the hydraulic limitation hypothesis. In 2006, Ryan, Phillips and Bond reviewed 51 studies. According to the abstract, taller trees often had less open leaf pores, less photosynthesis, and a lower ability to carry water to each leaf than shorter trees, but not always. The authors concluded that water-related limits on how leaves take in and give off gases are “common, but not universal”: they happen in many trees, but not in every tree [6].

The redwood estimate has been challenged too. In 2009, Netting argued that some assumptions behind the 122 to 130 m estimate could be questioned and suggested that height may instead be limited by a balance between dieback and growth [7]. Koch and Sillett replied; as far as the reply’s abstract shows, they defended their approach and agreed that how trees divide up the carbon they make needs further study [7].

Redwoods may also have workarounds. The abstract of a 2014 study of tall coast redwoods reports that the ability of leaves to store water rose with height, and that treetop leaves could store more than five times their daily water demand. The authors suggest this stored water may help offset the limits that height creates [8]. I could read only the abstract, so treat this as a tentative finding. So the scientists who study this still disagree about how much each factor matters, and the sources I used cannot settle it.

Broken Tops, Fog, Rain and Sheltered Valleys Also Shape How Tall Redwoods Get

Water supply is not the only thing that can stop a tree from getting taller. The NPS says redwoods frequently lose sections of their crown to wind and lightning during their lifetimes. They try to regrow but may never reach their original height [3]. One famous example is a tree in the park’s Tall Trees Grove. It once measured 367.8 ft (120 m) but lost its top in the 1980s [2].

The NPS also lists conditions that let redwoods live so tall: 60 to 140 in (1.5 to 3.6 m) of yearly rain, summer fog, mild temperatures of roughly 45 to 61°F (7 to 16°C), and neighboring trees that shelter them from strong wind [2]. Some redwoods live up to 2,000 years [2].

Putting it together: a redwood’s height probably reflects several things at once, including how hard it is to lift water, how often a storm snaps a top, and how mild and foggy the place is. The sources here do not say how much each one counts.

Try It Yourself: Compare Low Leaves With High Leaves on a Tree Near You

Find a tall tree in a park or garden (yard). Compare leaves on a low branch you can reach from the ground with leaves high up that you can see by looking up (binoculars help). Are they the same size and shape? Are they as crowded together?

Be careful: do not climb, and do not stand under trees on windy days, since branches can fall. Note that the redwood results came from very tall trees, so an ordinary tree may show no difference. That is still a real result.

To read more, start with the abstract of Koch et al. (2004) [4], the review by Ryan and colleagues [6], and the NPS page about Hyperion [3].

Sources

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