The Limits to Tree Height: Why Redwoods Don’t Grow 500 Feet Tall


To a large extent, the ultimate height of a tree is determined by its genes. Most of the remaining influence comes from the quality of the site in which the tree is growing. In other words, an oak tree may be genetically predisposed to reach about 60 feet in height, but the amount of sunlight and rain it receives determines if it will be a 40-foot-tall runt or an 80-foot-tall behemoth.

However, even trees with great genes and ample resources are still constrained by physical factors, such as gravity and the surface tension of water. It appears that these physical constraints create a cap on the ultimate growth of trees. Accordingly, even California’s tallest redwoods (Sequoia sempervirens), British Columbia’s tallest Douglas firs (Pseudotsuga menziesii) or Australia’s tallest eucalyptus trees (Eucalyptus regnans) are unable to grow much taller than they already do.

How Trees Drink

First, a review of some basic tree physiology:

  • Water enters a tree via the roots, and then travels throughout the trunk, branches and twigs, via an assortment of vascular tissues, until if finally reaches the leaves.
  • Water escapes the leaves (a process called transpiration) via small holes in the leaf surface, called stomata. The individual stoma open and close to alter the rate of this process, which varies over the course of the day.
  • The leaves use a very small percentage of the water reaching them for basic cellular processes and photosynthesis, but most escapes into the atmosphere.

Passive Pumping

The movement of water through a tree is not an active process. Trees do not “suck” water from the ground, nor do they “pump” water up their trunks. Instead, trees rely on the surface tension of water and something called capillary action to draw water up through the tree. The process works because of both the attractive forces between individual water molecules and the attractive forces that occur between water molecules and other molecules.

Surface tension is produced by the cohesion of individual water molecules – this is why water forms droplets instead of spreading out. Capillary action is exhibited when liquid is placed in a narrow tube. The water molecules are attracted to the molecules in the tube (adhesion); but normally, gravity pulls harder on the water than the tube does. However, if the tube is narrow enough, the adhesive forces can overcome gravity.

Sponges illustrate this principle well: If you place a sponge (which is full of tiny capillaries) half-way into a glass of water, it will draw some of the water up into the sponge via the same mechanisms that trees use.

The water transpiring from the leaves creates a void, which cohesion and adhesion work to fill. This creates tension that further helps to draw the water up the tree. The rate at which water transpires from the tree influences the tension placed on the water column. The faster the water exits the tree the greater the tension on the water column.

Tree Height Limits

As you can imagine, it takes far more tension to raise water to the top of a 400-foot tall tree than it does a 40-foot-tall tree. Ultimately, some trees reach heights where the tension necessary to draw up the water becomes too great. When this happens, the column of water breaks down and bubbles may form in the capillaries – these bubbles break the surface tension of the water and leave voids in the system. The voids cause the capillaries to stop functioning properly, and become useless. This leads to a reduction in vigor, and prevents the tree from growing any taller.

In 2004, George Koch and three colleagues examined this mechanism in order to determine the theoretical maximum height of trees. By studying some of the tallest trees in the world (including California’s own “Hyperion,” which is the world’s tallest documented tree), the team concluded that the tallest possible trees may be able to reach about 425 feet, but not much more. Were trees to grow taller than this, the tension would simply be too great. (George W. Koch, 2004)

Problems with Climate Change

The method by which trees drink not only limits their ultimate height; it also limits their ability to survive climate change.

The tension on the water column is dependent on many factors aside from the height of the tree. These factors include air temperature, solar radiation, groundwater availability and wind speed. Generally speaking, when the air gets warmer, drier or windier, the water evaporates from the leaves more quickly. This increases the tension on the water column, and as we have seen, excessive tensions can cause permanent harm.

A 2012 study by Brendan Choat and 23 other researchers showed that the threshold at which these sorts of problems occur is remarkably close to the tensions trees normally produce. This held true for a wide range of tree species, across several different habitats. This means that if global temperatures rise relatively little, trees are likely to suffer greatly, as many will begin to transpire at rates that will cause them irreparable harm.  (Brendan Choat, 2012)


Brendan Choat, e. a. (2012). Global convergence in the vulnerability of forests to drought. Nature.

George W. Koch, S. C. (2004). The limits to tree height. Nature.



A Conservation Success Story: Protecting a Rare Albino Chimeric Redwood

Thanks to the efforts of local citizens, historians and conservationists, one of the rarest trees in the world has been granted a reprieve. Now, instead of being cut down to make room for a railway expansion project in Cotati, California, crews will move the tree about 450 feet from its current location, where it will hopefully live for years to come.

The project, which has an estimated price tag of $150,000 according to NBC Bay Area, was deemed appropriate as the “Cotati redwood,” is one of only a handful of albino chimeric redwoods in the world. (Fernandez, 2014) Clad in a patchwork of green and white leaves, the unusual tree intrigues onlookers and tantalizes scientists, who are eager to explore the tree’s hidden secrets.

Why Is This Tree So Special?

The first albino redwoods were likely discovered in 1866, but in the nearly 150 years since then, scientists have only documented about 230 similar trees in the State of California, according to “National Geographic.” (Jaret, 2014)

Most of these albino redwoods are extremely small and frail; unlike their towering relatives that soar 300 feet or more into the air, most albino redwoods are decidedly shrub-like. Yet, the Cotati tree is unlikely to be confused with a shrub. The tallest such mutant ever discovered, the unique redwood stands over 50 feet tall and has a crown that is 30 feet in diameter.

Most albino redwoods are parasites that derive sustenance from the roots of other redwoods. But strangely, this special tree stands alone, isolated from other redwoods. Combined with the tree’s tendency to produce both male and female cones – the only albino chimera documented to do so — terms such as “one of a kind,” are potentially appropriate for this special tree.

treesProblematic Pigment

The term “albino” is a colloquial term that is usually used to describe amelanistic organisms. Plants do not produce melanin, but most produce chlorophyll. Chlorophyll is the pigment that enables plants to conduct photosynthesis and gives them their green color. Therefore, “albino” plants appear white or yellowish, as they fail to produce chlorophyll.

Without chlorophyll, plants cannot convert sunlight into energy; accordingly, most die early in life and are only rarely observed. This is why most albino redwoods are parasitic: They cannot produce their own food. Instead, they survive by stealing nutrients from the roots of other, healthy redwoods. The ability to derive sustenance from the roots of other plants is rare, and explains why redwoods are capable of producing albinos that survive, while most other albino plants die as soon as the energy reserves from their seeds run out.

However, the Cotati redwood does not derive resources from a host tree.

A Tale of Two Trees

The key to the relative success of the redwood in question – and the handful of others like it — lies in its genes. The Cotati tree is a chimera, meaning that it has the DNA of two different trees located in its meristems (areas of rapid cell division in a tree). In essence, this single tree is comprised of two different individuals.

This unique compliment of genes means that some of the tree’s leaves get ordinary genetic instructions. These leaves are green in color and produce food for the tree. The mutant genes supply the code for other leaves, so they fail to produce chlorophyll, and are white in color. The combination of white and green leaves gives the tree its patchy look, and likely provides the explanation for how it survives: The numerous green leaves produce enough energy to support the entire tree, including the white leaves.

Scientists are still in the dark about many details of the phenomenon, which further illustrates the importance of protecting and studying this tree. Fortunately for the world, a local landowner named Pete Tapian planted the unique specimen about 70 years ago, where it still stands today, at least for the time being.

Visiting the Rare Redwoods

The exact location of most albino redwoods is closely guarded to protect their wellbeing. While the Cotati tree is probably farther away from the Los Angeles area than most people would care to travel (approximately 420 miles), there are quite a few normal redwood trees in the greater Los Angeles area. Check out this map to see a few of the closest documented specimens.


Fernandez, L. (2014, July 28). Tallest Albino Redwood Chimera Tree in Wine Country to be Saved, Moved at Cost of $150,000. Retrieved from

Jaret, P. (2014, March 19). Rare “Albino” Redwood May Hold Clues to the Super-Trees’ Longevity. Retrieved from

Lapidos, J. (2009, January 6). How Many Albinos Are in Tanzania? Retrieved from


Trees Don’t Just Save Money, They Save Lives

Most people realize that trees provide a number of environmental and economic benefits, but few realize that trees also provide health benefits for those living near them. However, a recent national study, conducted by the United States Forestry Service and the Davey Institute, is likely to change that. Given that Los Angeles is bathed in the country’s most polluted air, this study is especially important for those of us living and working in Southern California. (BARBOZA, 2014)

The Unique StudyTree with form of human lung

Unlike many other studies, which have concentrated on quantifying the ability of trees to reduce energy costs, sequester carbon or improve water quality, this study sought to quantify the physiological benefits that humans enjoy, thanks to the air-cleaning abilities of trees. As explained in the study, trees not only help to reduce the costs associated with health care, but they actually reduce the rate of illness in the community and actually save lives.

The Results

According to the study, trees reduce national healthcare expenditures by nearly 7 billion dollars each year. More impressively, the study found that trees eliminate nearly 670,000 cases of acute respiratory symptoms. Nevertheless, the most impressive statistic produced by the study showed that trees were responsible for preventing approximately 850 human deaths each year.

How They Help

Trees provide these health benefits (among other ways) by helping to remove pollution from the air. Trees remove particulates in the air, such as soot, easily enough – the pollutants simply stick to the bark, leaves and branches of the trees. Eventually, the particulates fall to the ground or they are washed away with the rain. Trees remove toxic gases, such as carbon monoxide and sulfur dioxide, by drawing the pollutants into small pore-like openings called stomata. Once inside the trees, different species safely quarantine or discard the substances in a variety of ways. Additionally, trees reduce the local air temperature, which reduces the amount of pollutants entering the atmosphere by reducing the rate of the pollution-causing chemical reactions take place.

Geographic Variation

While 34 percent of the continental United States is covered with trees, the amount of coverage varies from one area to the next (as of 2006, 21 percent of Los Angeles was covered by tree canopy). (Million Trees LA, 2006) While some urban environments, particularly those in the southeast and along the Atlantic seaboard, have robust tree populations, most urban areas have fewer trees than rural areas do. Ironically, these urban areas are the ones most in need of the services of trees. While the bulk of the air pollution removed from the air by trees takes place in the relatively unpolluted air of rural areas, the greatest positive health effects (in terms of both reduced illnesses and reduced costs) occurred in urban areas.

You can read the entire study here (PDF).




BARBOZA, T. (2014). L.A., Central Valley have worst air quality, American Lung Assn. says. Retrieved from

David J. Nowak, ,. S. (2014). Tree and forest effects on air quality and human health in the United States. Environmental Pollution.

Million Trees LA. (2006). Tree Canopy Analysis. Retrieved from



The Psychological Benefits of Trees and Natural Areas: Beyond Supposition

Some of the most important benefits that trees provide to humans are psychological or emotional in nature. While countless authors, arborists and philosophers have mused that trees help to clear the mind and invigorate the soul, it is important to realize that these claims are not merely conjecture. Scientists have collected plenty of evidence that supports the notion that trees and natural areas improve one’s mood and provide people with an increased sense of well-being.

boy and girl sittingSimple but Profound

In 1984, Doctor Roger S. Ulrich published a study, which sought to determine if trees (and natural landscapes in general) provided tangible benefits for people recovering from surgery.

Between 1972 and 1981, Ulrich analyzed the recovery details on patients who had recently had their gallbladders removed. Ulrich grouped the patients in pairs, based on criteria such as age, gender and preexisting health conditions. One member of each pair stayed in a recovery room that provided a view of a natural-looking patch of deciduous trees, while the other member recovered in a room that only provided a view of a brick wall.

Ulrich’s results were eye opening, and forever changed the nature of hospital architecture and landscaping. In the study, Ulrich compared the length of the patient’s stay, medications administered, complications and the nurse’s notes regarding patient care. Ulrich found that those patients whose windows faced the trees recovered significantly faster, exhibited fewer complications and required fewer pain-relieving medications, than their brick-wall-facing counterparts did. (RS Ulrich, 1984)

Standing on the Shoulders

In the years following publication of his study, numerous researchers have confirmed and expanded upon Ulrich’s work. One such example was published in a 2001 issue of “Environment and Behavior.” In the study, researcher Rachel Kaplan found that residents of suburban apartments whose windows overlooked natural areas experienced a greater sense of well-being and satisfaction with the neighborhood, than those whose windows overlooked man-made structures and scenes. (KAPLAN, 2001)

In 2007, Richard A. Fuller and his colleagues investigated the relationship between biodiversity and the psychological benefits that higher biodiversity may provide. The results of the study found that the participants (laypersons) were able to discern broad patterns in plant biodiversity. Perhaps unsurprisingly, the higher the biodiversity of the green space, the more benefit the participants derived. (Richard A Fuller, 2007)

Climbing Up the Right Tree

However, none of this should imply that trees and natural areas are only helpful in a passive context – interacting with trees can also produce significant psychological benefits. Take for example, a 2006 study, conducted in Japan and published in the journal “Urban Forestry & Urban Greening.” During the course of the study, researchers administered psychological tests to people who climbed concrete towers and trees. The researchers found that the climbers scored better on a battery of psychological tests after climbing trees than they did after climbing the cement towers, despite the fact that the towers were in the same location and were of equal height. (John Gathrighta, 2006)

Just the Beginning

While it is quite clear that trees and natural spaces provide concrete psychological benefits to the people living near them, scientists still have much to learn about the interrelationship between humans and trees. Nevertheless, this much is clear: Spending time around trees is not only fun, but it is also good for your psyche. If you live in the Los Angeles area, check out this list of local nature centers, which can help you get out of the city and spend some time healing in the company of trees.


John Gathrighta, Y. Y. (2006). Comparison of the physiological and psychological benefits of tree and tower climbing. Urban Forestry & Urban Greening.

KAPLAN, R. (2001). THE NATURE OF THE VIEW FROM HOME. Environment and Behavior .

Richard A Fuller, K. N.-W. (2007). Psychological benefits of greenspace increase with biodiversity. Royal Society Biology Letters.

RS Ulrich, e. a. (1984). View Through a Window May Influence Recovery from Surgery. Science.


Healthy Forests for Healthy Water

small runoff waterThough seemingly unrelated, the health of a forest directly affects the health of the surrounding waterways. While the trees depend on the local water supply for survival, they perform valuable filtering services on this water, which helps to keep the local supply clean. One of the most valuable ways trees help to protect the local water bodies is by reducing the amount of runoff water flowing across the landscape.

Reining in Runoff

While not a type of pollution in the strictest sense, excess runoff water is a serious problem for local watersheds. Excess runoff water can overwhelm creeks and streams, causing widespread flooding. Additionally, it accelerates the rate of erosion, rapidly undermines stream banks, undercuts roads and can cause significant destruction to the local infrastructure.

The sediments collected in the runoff water eventually make their way into streams, making the water cloudy, which can harm many aquatic organisms. In urban areas, runoff water collects numerous pollutants in the form of oils, fuels and debris, which ultimately flow into the rivers, ponds and swamps of the region.

Mechanisms of Mitigation

Trees – and more importantly forests – reduce runoff water and the amount of sediment reaching local streams and creeks in a variety of ways.

  • They reduce the amount of groundwater in the area through the process of transpiration. This allows the soil to absorb more water during the rain, thus reducing the amount of runoff water reaching streams
  • Trees collect water on their surfaces, and release it slowly to the ground, which helps to reduce the amount of runoff water in an area.
  • The growth pattern of tree roots and the activities of the microorganism near their roots encourage increased rates of water infiltration into the soil, which further reduces runoff water.
  • The trees’ roots help retain soil and prevent erosion, which protects yards, roadways and – most importantly – stream banks from collapsing.
  • The canopies of trees protect the soil from the pounding of raindrops, which reduces the amount of sediment that reaches local waterways.

Complicated Considerations

One common way that trees are used to reduce the amount of runoff water flowing across parking lots, driveways and other small paved areas is by planting a small group of trees near the low point of the surface. This can help you reduce the runoff from your property and increase the property’s value at the same time. The trick for those living in the Los Angeles area is to select species that are native to the state – and thus equipped to deal with periodic droughts – yet still able to cope with the periodically saturated soil that they will be exposed to. California laurels (Umbellularia californica), western hemlocks (Tsuga heterophylla) and California buckeye (Aesculus californica) are excellent choices, but if you prefer non-native species, consider black gums (Nyssa sylvatica) or bald cypresses (Taxodium distichum).

Healthy Water through History

Humans have understood that trees affect water quality for hundreds of years. According to, residents of Rio de Janeiro began advocating for the protection of the area’s coastal rainforest to prevent declining water quality in 1658. Later, after a series of droughts reduced the available water in the mid-1800s, reforestation efforts were begun in the region of Tijuca, along the Atlantic Coast. (Messenger, 2010) Today, the Tijuca National Forest is one of the largest urban forests in the world, covering approximately 12 square miles, and helping to provide clean drinking water for Rio’s nearly 12 million residents.


Messenger, S. (2010, August 22). World’s Largest Urban Forest Was Planted by Hand. Retrieved from

Trees in Downtown Chicago

Trees and Healthy People – No Appointment Necessary

Trees, parks, and gardens are not just simply considered beauty in the city but as a matter of improving public health. There is a link between an individual’s socio-economic position and their health is well-established. Epidemiological studies show a positive relationship between longevity and proximity to green space. Fewer people die of asthma and heart disease in Chicago, Los Angeles, and other U.S. cities when trees and other greenery are present. A single tree cleans the air because of a tree’s ability to absorb tiny smog and soot particulates. Trees also provide shade which block ultraviolet rays that contribute to skin cancers. Another health benefit of evergreen trees can be found by patients in hospitals with views of trees and gardens outside their window who recovered faster after surgery.

Brief encounters with nature make people happier, reduce chronic stress that leads to ill health and help both adults and children (including kids with ADD) focus better on mentally taxing tasks. Exposure to green surroundings reduces mental fatigue and irritability. The ability to concentrate is increased by green views, along with the ability and willingness to deal with problems thoughtfully and less aggressively.

A 2011 study in the Amercian Journal of Epidemiology found that vandalism and gun assaults and stress levels decreased in greener environments. In a study conducted in a Chicago public housing development, people who lived in apartment buildings with trees and greenery immediately outside reported fewer aggressive and violent acts than those living in barren but otherwise identical buildings. In addition, the people in greener surroundings reported a smaller range of aggressive tactics during their lifetime.

Microburst Knocks Down Hundreds of Trees

A line of thunderstorms that went through Hopkinton, New Hampshire, in July created a microburst that knocked down several hundred trees in the area. National Weather Service meteorologist Michael Cempa estimated that the winds were blowing at 60 to 80 miles an hour. The storm and the resultant fallen trees knocked out power in the area.

Resident Pauline Meridien was home with her husband when the storm hit. “It’s amazing how huge these trees are. It was just awful. We had a 60-foot blue spruce that came down next to our house,” she said. Meridien also reported that four large pine trees fell around her son’s house, who lives next door, but did not damage the house. A vehicle in Hopkinton was crushed by another fallen tree, but no injuries were reported.

Evergreen Arborists Consultants, Inc. has experience in examining thousands of trees. We evaluate a tree’s signs and symptoms ranging from decay, poor branch structure, poor pruning and maintenance practices, and roots. Tree risk assessment helps minimize the risk of falling trees or branches. Please call us today for a consultation.

Man Arrested After Felling Pine onto Highway

A man was hired by a private property owner to cut down a large pine tree on the property, which bordered the Kaumualii Highway in Hawaii. When the man cut the tree down, the tree fell into the highway and landed on a Dodge pickup truck travelling in the eastbound lane. The tree smashed into the roof and bed of the truck, injuring the driver, who was taken to the hospital with a possible neck injury. Another pickup travelling east hit the fallen tree and sustained front-end damage, but the driver was not injured.

The man who cut down the tree was arrested on suspicion of second-degree reckless endangering. The highway was closed for about an hour and traffic was rerouted while crews cleared the road of debris.


Eucalyptus in Santa Monica

eucalyptus tree

eucalyptus tree

Santa Monica City Hall ordered the removal of a 100-year-old, 100-foot-tall eucalyptus tree after three large limbs fell from the tree within two weeks. The first limb could possibly have been explained as caused by dry weather, but the next two limbs showed signs of fungal decay. One of these limbs weighed 2000 lbs. The tree, located on private property, was examined by a number of arborists to determine if the tree was decaying. A Community Forester and an arborist hired from City Hall determined that the tree was falling apart and that a fungus had infected the upper section of the tree. Independent arborists felt the tree was sound overall and with consistent and careful pruning, the tree could be maintained safely. Walt Warriner, the Community Forester, said after examination, “Once I got into the tree, I was more concerned that the decay had spread further than anticipated. There were other wounds that were entry points for decay fungi. The science points to the fact that the potential is there. There are significant limbs that, if they were to fail, would cause serious damage.”

After the findings, the tree’s owners said they would try to memorialize the tree by using the wood for projects and possibly leave a 10 to 20 foot stump. The tree had been highlighted in two books, “Trees of Santa Monica” and “Exceptional Trees of Los Angeles,” and it had been officially landmarked by the city. It was the largest known specimen of its type in the country.


Hurricane Sandy Downs Historic 400-Year-Old Oak



The city of Shelton, Connecticut, recently lost a historic oak tree believed to be at least 400 years old when Hurricane Sandy blew through the area in early November. It was not only the oldest tree in the city, but the tallest, at approximately 85 feet. Winds first blew off the top branch of the tree, which fell into power lines and cut off power to the neighborhood. John Miller, who lives across the street from the tree, said he heard a loud “crack” at about 6 p.m. “It sounded like thunder,” he said. Twenty minutes later, the entire top of the tree was taken off by another gust of wind.

Residents said that they were saddened by the loss, but not surprised. One resident said that the tree was a little hollowed out, although from outward appearances there was no indication of decay. The tree had been impacted by construction, which may have damaged its roots, and in the 1970s a construction crew planned on cutting it down until they discovered its historic nature.

“It’s sad to see it come down. There should be some kind of tribute for it,” said resident Lin Mulford.

Evergreen Arborists Consultants, Inc. has experience in examining thousands of trees. We evaluate a tree’s signs and symptoms ranging from decay, poor branch structure, poor pruning and maintenance practices, and roots. Please call us today for a consultation.