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Why Do Trees Topple in a Storm?

The views expressed are those of the author and are not necessarily those of Scientific American.


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Kennebunkport tree, 2010. Photo: Kevin T. Smith

White pine windthrow. “Shoestring” rhizomorphs or mycelial cords of Armillaria found along with dead woody roots. Photo: Kevin T. Smith

For some, an unwanted reminder of Hurricane Sandy that crashed into the East Coast as megastorm of the century is a big tree uprooted, lying across the yard — If lucky, missing the house. From North Carolina to Canada trees toppled or broke off big limbs, killing or injuring people and animals, crashing into homes and cars, blocking roads and ripping down power lines. The intense storm toppled 8,497 trees in New York City alone. But it doesn’t take a hurricane or a megastorm to uproot timber. The nor’easter that hit the upper East Coast Wednesday and Thursday brought down more trees. And storms, of course, hit all parts of the United States and much of the world, downing trees as part of the damage. Yet most trees keep their “feet” firmly planted in the ground.

We Americans have a fondness for trees, often naming streets after them — Oak St., Elm St., Cherry Lane, Willow Tree Lane, Maple Ave., Cypress Blvd., Sycamore Dr., and so many more. I’ve always wanted to live on Maple Ave. It just sounds so homey and safe and friendly. I picture kids riding bicycles down the tree-lined street, touch football and baseball games, neighborhood cookouts and warm, cozy homes. I never picture a maple tree crashing onto a home or a falling branch whacking a kid off his bicycle.

Damage from megastorm Sandy in Franklin Lakes, NJ.. Photo: William de Vos

Damage from megastorm Sandy in Franklin Lakes, NJ. This is a perfect example of endotrophic root growth within the tiny, inadequate “green strip” and the curb and sidewalk. Upon driving by this huge oak (28” - 32” diameter and over 70’ tall), I was shocked at the obvious indication of poor planting and planning. The root ball that pulled up in the tree’s toppling was perhaps 3’-4’ wide by 15’ long, showing the lack of lateral support the tree had. Photo: William de Vos

When I bought my two-story Maryland colonial 12 years ago, it came with trees. My neighborhood was once part of a wooded area that was cleared for development and I am sure the trees on my corner lot are much older than the house which was built in 1937. Some of these big trees are only yards from my library and the upstairs bedrooms, and I can reach out and touch one outside the window of my home office.

So far, only one in the front yard has dropped a sizable limb. But when torrential rain soaks the ground, gusting winds force the branches to sway back and forth, or ice and snow send the limbs sagging, I worry, and run to the center of the house when I hear a loud crack. Who is next? How do we know if our birch, elms, maples, oaks, pines, cedars, willows, hemlocks, and other urban trees that grace our landscape throughout the seasons, will safely co-exist with our families and our homes when the weather rages.

Why do some trees fall in a storm, while most do not? To find out, I asked three experts to explain the science behind falling trees: David R. Foster, Director, Harvard Forest at Harvard University, a Long-Term Ecological Research Site funded by the National Science Foundation; Kevin T. Smith, a plant physiologist with the U.S. Department of Agriculture Forest Service; and William E. de Vos, a registered consulting arborist who is president of Treeworks, a tree preservation company in Montpelier, VT. Be forewarned that Smith admits he’s “been brainwashed by foresters” and says “stem” when he means “trunk” of a tree.

Why do some trees fall during storms and others don’t?

The answer from Smith is not very comforting: “The first thing to know is that all trees have the potential to fail at some level of force from wind, snow, ice, either singly or in combination,” he says. One main reason, all three experts agree, is the phenomenon known as “windthrow” which uproots a tree. “The tree trunk acts as a lever and so the force applied to the roots and trunk increases with height,” says Foster. “Taller trees are more susceptible to windthrow.”

“The roots of trees can extend 1-2.5 times the radius of the branches and many urban areas do not allow this extensive development,” answers de Vos . “The problem lies mostly with trees that have been developed around and had roots cut, crushed or torn in the process. There may be ensuing decay.”

Armillaria fungus on a tree stump. Photo: Kevin T. Smith

Red maple stump with Armillaria mushrooms that previously caused the trunk to snap. Photo: Kevin T. Smith, Northern Research Station, US Forest Service

Smith explains further: “Wood is a very strong and wonderful structural material. Wood, however, is not homogeneous or consistently strong at all places in the stem (trunk). Wood decay caused by fungi can weaken wood structure. However, the mere presence of decayed wood or even a hollow does not mean that the tree is more vulnerable to failure.” What he says next is of some comfort. “Strength comes from the quality and quantity of wood that is present, not what might have been degraded.” An equally big factor in tree falls, he says, is bark between two trunks or between branches and the trunk, and wounds from past injuries which make a tree vulnerable when high winds bend its branches or even cause the trunk to sway.

de Vos adds “generally trees tend to uproot more than break off during wind events, although poor structure in the crown will result in limb breakage, splitting and tearing as well.”

Other risk factors: Large trees growing in shallow soil or in a rocky area and trees that were accustomed to living in a forest. More on that below.

Are some types of trees at more risk than others?

“Well, of course, urban trees in disturbed areas, but some species tend to wind-throw readily,” says de Vos, who regularly visits distressed homeowners after storms and has seen four decades of tree wrecks. “Balsam Fir, sometimes white spruce, willow, white pine, cedar, sometimes hemlock. Most are due to growing in wet areas.”

Red maple. Photo: Kevin T. Smith

Red maple showing failure of a major branch associated with included bark, visible on the wound surface. Photo: Kenneth R. Dudzik, Northern Research Station, US Forest Service

“Trees most at risk are those whose environment has recently changed (say in the last 5 – 10 years),” Smith says. When trees that were living in the midst of a forest lose the protection of a rim of trees and become stand-alones in new housing lots or become the edge trees of the forest, they are made more vulnerable to strong weather elements such as wind.

They also lose the physical protection of surrounding trees that had kept them from bending very far and breaking. Land clearing may wound a tree’s trunk or roots, “providing an opportunity for infection by wood decay fungi. Decay usually proceeds slowly, but can be significant 5-10 years after basal or root injury.” What humans do to the ground around trees — compacting soil, changing gradation and drainage “can kill roots and increase infection,” Smith warns.

Foster explains how the different parts of a tree impact its survival: “Tree species vary in characteristics that influence their susceptibility to breakage and uprooting: the strength of their wood (controls breakage), the depth and strength of their roots (controls uprooting) and the shape of their crowns (branch arrangement, determines how much wind they intercept). The graph below [shows] change in susceptibility with height of the tree. … The susceptibility to wind varies greatly between conifers (pines) and hardwoods (oak, maple, birch). Pines are taller; they concentrate their foliage on the top of the tree sticking up and out above other trees, so catch the wind and act as even larger levers. They are shallow rooted.”

The graphic below “shows the same relationship broken down by tree species. As trees age and get taller they become more susceptible, but that varies greatly by species.” — Foster

Is there any record of what species of trees have toppled most and snapped branches most in wind, snow, and ice storms?

Foster says “One of the best databases was compiled after the 1938 hurricane by [Willett Rowlands], a graduate student at Harvard University. The study was for his thesis completed in 1942, but not published until 1988.

Smith says the U.S. Forest Service is attempting to gather information at a tree-failure database.

From his personal database of visits to downed trees, de Vos says it’s “a pretty sure bet that a willow, white pine and to a lesser extent, Norway maple, Amur maple, will lose branches and sometimes more during an adverse event.”

How many inches of rain makes the soil wet enough that roots can come undone?

“It is possible for trees to topple with little rain or wind if the roots are decayed,” says de Vos. “So I suppose the answer is any amount can cause a tree to fall, given the extenuating underground circumstances. Remember that roughly 90% of a tree’s roots are in the upper 18”- 24″ of soil.”

Regardless of how much rain falls, Smith says that wet soil “is more a function of drainage.” And Foster adds that in “very sandy soils, the rooting firmness may increase with water.” When wetness does cause failure, he says that “in general, more trees uproot than break in most soils.”

For the last three questions, I provide more complete answers from the experts because I think the details they give are worth your time to read.

Do some species of trees grow much more extensive roots — both wider and deeper — than other trees, which protect them from toppling? What role does the type of soil play?

Red maple. Photo: Kevin T. Smith

Red maple. Photo: Kenneth R. Dudzik, Northern Research Station, US Forest Service

Foster: “Rooting depth and extent varies among species. But it also varies with soil conditions. The same species [will] produce very different root characteristics in very wet soils than in very dry soils or rocky versus rock-free soils. In wet areas roots tend to be shallow and trees susceptible to uprooting.”

de Vos: “ Deciduous trees tend to have a greater lateral root spread compared to conifers which tend to have a more fibrous and compact root system. Soil type and its appropriateness for the species of tree in question is paramount to success. … Sandy soil has good aeration but poor nutrient holding capacity while clay soil has poor aeration and excellent nutrient holding capacity. The best of both worlds is a clay loam with a bit of both. The better the relationship between soil and species the better the root development as long as there are no limiting urban factors like walls and roads, buildings and pipelines. A good soil will promote deeper roots as it will have oxygen to a lower level as the water leaches out.

How do I know if a tree in my yard is at high risk for falling?

Smith: “First, look at the tree and its environment. Is the tree leaning? If so, has the lean increased in recent years? Are there obvious cracks in the stem? Is the crown healthy with respect to full foliage in the growing season and good bud set for the winter? Root problems are often reflected in crown condition. Are there noticeable cracks, particularly between buttress roots at the base of the stem? These often indicate root or butt decay. Do you notice mushrooms of wood decay fungi on the stem or on the soil, associated with woody roots? Most mushrooms growing on the soil near trees are harmless to the tree, but some species can indicate decay. Remember that the simple presence of decay does not mean that the tree has a high likelihood to fail! Look for included bark in codominant stems and at the base of major branches.” Such an area is weak and vulnerable to snapping.

Is there any way to test my tree to see what risk there is that it may topple or drop limbs?

de Vos: “There are a few more sophisticated methods for testing tree structure such as Resistograph Drill Test and Sonic Tomography. This could help predict the possibility of toppling due to structural insecurity of the trunk. Check the health of the root collar ( look for constrictions)… Check the crown for dieback and general health. See how high the limbs are elevated from the ground and for heavy lean or abnormally imbalanced limb structure. It takes 3-5 years after construction around trees to see the signs of what trees will survive.”

Damage from megastorm Sandy in Franklin Lakes, NJ.. Photo: William de Vos

Damage from megastorm Sandy in Franklin Lakes, NJ. This tree failed during Sandy due to the loss of internal structure. It appeared for all intents and purposes to be in good health as it had a full crown with little if any decline apparent. The diameter of the light colored tissue is the extent of necessary live wood needed to keep a tree in full leaf. The entire center of a tree except for this small strip just under the bark can be decayed and destroyed, as is the case here and have no visible signs. “Physiological health in trees is not an indicator of structural . Photo: William de Vos

This is a lot to examine and, given that mushrooms may or may not be an indicator of tree failure, and noticeable disease may or may not affect the tree’s stability, it is probably prudent to get a tree specialist out to your house to examine a tree that gives you concern. You may want to get more than one opinion before authorizing one of the sophisticated tests mentioned above which can both provide information about a tree’s stability and potentially harm the tree. Smith suggests finding a licensed arborist who participates in organizations such as the International Society of Arboriculture and the Tree Care Industry Association which provide continuing arborist education. Forestry or agricultural extension educators at state universities may be another choice.

Although they can become unwilling weapons in severe weather, I think most of us would not want to live without our trees. They give character to our properties, shade in the summer, beautiful leaf colors in the fall, and homes to our wildlife. Most trees were living long before we were and, hopefully, will be living long after we are gone. But inevitably nature will periodically rise up and destroy some. “When we have a truly intense storm (Category 2-3) we will see unfathomable damage to forests in the Eastern U.S.,” warns Foster. “ A 1637 or 1938 hurricane will return.”

Images: Both graphs are from “Species and Stand Response to Catastrophic Wind in Central New England, U.S.A.” by David R. Foster in Journal of Ecology, March, 1988.

Mary Knudson About the Author: Mary Knudson writes more often about the health of people than of trees and teaches health and science writing at the Johns Hopkins School of Medicine. Though concerned from one storm to the next about the safety of trees in her yard, she still pines to live on Maple Avenue. Follow on Twitter @maryknudson.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. sparcboy 10:51 am 11/12/2012

    I remember reading years ago about a category 1 hurricane going across an area of Florida that hadn’t been hit in years. It uprooted trees and caused substantial damage to structures. The next year a category 3 hurricane went across the same area and cause minimal damage. The category 1 hurricane had removed all the weak trees and structures.

    Link to this
  2. 2. julianpenrod 1:25 pm 11/12/2012

    This may not be printed because it will take issue with the claims of the article, but there are a number of points to be made.
    In fact, this article comes across as an attempt to manufacture perceptions and interpretations about the abnormal, unnatural condition of the environment in general, indicated by Sandy, as a result of chemtrail poisoning of the atmosphere.
    Among other things, the article says tree root structures “can extend 1-2.5 times the radius of the branches. It can be questionable, if not disquieting, if someone offers only what “can” be the case and not what the average case “is”. It can be difficult to make a case for the majority of events based only on extremes. In fact, most trees seem more than happy with roots that extend no more than five times times the trunk width or so. And roots don’t just go outward, they can penetrate deep in the soil, too. And it can be the deep roots that anchor a tree more than the surface platter. Among other things because lack of surface soil can threaten stability and, if a tree has no deep tap roots, it’s just wobbling on a stand.
    The roots can be a major area of concern. Chemtrail chemicals in the air, washed down by rain or snow, can kill root structures. The trees in the pictures in the article show no deep root structures. And, if you look, there is a general pattern of extreme effects on foliage from chemtrail substances.
    For years, now, there has been consistent spot die off of foliage. One branch in an entire tree may suddenly have all brown leaves, even in the middle of summer. A patch in a hedge may turn brown, but no other foliage around it. One tree in a row of similar trees will be brown and dead, but the others unaffected. This isn’t disease or an insect. And the affected portions of larger plants aren’t brokwn, they are still connected to the rest of the plant. The chemicasl from chemtrails seem to be dangerous only in concentration, and the particular branches or plants that get that random isolated concentration in the soil are the ones killed.
    Much of this mirrors, too, the patently non credible claim that “wet snow” last year cause tree limbs to snap because “the limbs had snow and leaves on them, and that made them too heavy”. But leaves are light, especially dry ones! One person could lift a bag full of the entire collection of leaves on an average tree! What’s more, tree branches can hold the weight of children! It is not acceptable that leaves made tree branches so heavy that ordinary snow made them break. What fell from the skay last Halloween was abnormally heavy because it had other chemicals in it. There are patches of snow in New Jersey from the storm last week thart still haven’t melted.
    But, then, at least in New Jersey, there are numerous aberrant situations of saplings blown down, saplings blown down while trees on either side of them, only a foot or so away, are still standing, trees falling down that weathered more serious events many times in the past. Much of Sandy looks deliberately engineered. right down to individuals pulling down healthy trees.

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  3. 3. John McKay 1:56 pm 11/12/2012

    In the far north, even below the permafrost zone, trees root very shallowly, but broadly. Last winter, Anchorage, AK was hit by a couple of storms with hurricane force winds. Some of the pictures my friends sent me showed toppled trees in the city with root disks that took half of the owner’s yard with them when they fell.

    Of course, the shallow roots and 100 mph winds didn’t really cause them to fall; the Illuminati made them fall.

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  4. 4. julianpenrod 3:24 pm 11/12/2012

    John McKay appears interested in mocking what I said about chemtrailing and engineered “disasters”. That use of mockery demonstrates an inability to actually provide anything substantive to disprove what I said or verify that damage from “storms” is never man made to displace populations, seize land, gouge the government for disaster funds and, in general, dispirit the public so they accept being slaves. Does John McKay have any verifiable film that proves the trees in Alaska weren’t pulled down deliberately? If John McKay has no such proof, they are being disingenuous in mocking the idea of trees being deliberately pulled. The article “Reality Laughs Again At North Carolina”, and a number of comments following it, also in Scientific American, it is insisted that “science” devotees use ridicule only because “the other side” won’t listen to reason. But John McKay’s response is demonstrative of the very real fact that “science” devotees tend to favor mockery over discussion. It certainly has to be asked, too, if there was such a constant threat to growth, how could there ever be any even moderate groth, if not old growth, trees there? If they have as wide a spread of roots as John McKay describes, then they are at least medium old growth trees.

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  5. 5. Mary Knudson 4:02 pm 11/12/2012

    How interesting, Sparcboy. Makes sense that the first hurricane took the weakest trees.

    Julianpenrod, you use words in direct quotes that are not from my story about limbs with snow on them. I sure do not think that during or immediately after a major storm, lots of people go out and intentionally pull down trees as you suggest happened in Alaska. And, since you don’t believe the force of powerful storms and hurricanes takes down trees, how could mere mortals pull them down.

    I appreciated the wisdom of your comment, John McKay. Wow, root upheaval took half the owner’s yard, I can imagine! Hope their homes were spared!

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  6. 6. John McKay 6:23 pm 11/12/2012

    Julian Penrod misses one of the basic rules of debate. Julian Penrod is the one making outrageous claims, therefore the burden of proof lies with Julian Penrod and not with John McKay and his “science.” John McKay is not required to prove a negative by putting a camera on every tree in Alaska to show that the Illuminati are not pulling trees down for whatever purpose during once a year storms.

    PS – “John McKay” is a singular noun, not a plural.

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  7. 7. filebunch 7:56 pm 11/12/2012

    I have a very non-scientific theory for my own trees that have fallen; first Irene last year then Sandy this year. I live in Huntington, NY on Long Island.

    During Irene I lost one Sassafras tree (of three that were close together) and nothing else, in totality.

    During Sandy I lost the other two Sassafras and an American Elm. The American Elm still had full, green leaves. The trees surrounding it had dropped their leaves.

    I have over twenty large mature trees in my yard; a mix of different oaks, walnut, maple, birch and hickory. Not one suffered any more than some branches falling.

    My assumption? The sassafras were suspect to the high winds and the elm fell due to its leaf density. The elm killed my car.

    An aside, if someone can help. Do elm and sassafras burn well in a fireplace? The sassafras were good size; the elm was huge. Thanks!

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  8. 8. ClareM 8:06 am 11/13/2012

    Elmwood burns like churchyard mould
    Even the very flames are cold.

    Not very appealing! though fine if mixed with other wood. A search will bring up the rest of the poem.

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  9. 9. Wit'sEnd 11:14 am 11/13/2012

    New Jersey looks like the ecopocalypse has arrived – still!

    It seems obvious that the sea-level rise and the size of the storm are related to the energy humans are adding to the system by burning fuel and releasing millions of tons of greenhouse (heat-trapping) gases into the atmosphere. That’s high school science and as obvious as plate tectonics. Remember when that was a controversy? Or that seat belts in cars, or helmets for bikes save lives? Asking if climate change has something to do with Sandy is like asking if smoking has something to do with lung cancer. Remember when people could say with a straight face that it didn’t?

    Having said that, there is a very large story that isn’t being reported which has little to do with climate change although it derives from the same processes.

What is being ignored in this storm (and Irene as well) is the real source of the massive power outages that are so disruptive – which is all the trees that are falling on the lines. Trees didn’t used to fall with regularity on power lines – or people, cars and houses. The winds in both those storms were not extraordinary, nothing that a healthy tree shouldn’t be able to withstand.

    Why are they falling now? 

The answer is pretty obvious if you trouble to actually LOOK at them. They are all dying. Every species, every age, every location. They have obvious symptoms – broken branches, cankers, splitting bark, holes, thin crowns, early leaf drop, lack of autumn color, yellowing needles, bark covered with lichens and fungus. You can’t find a healthy tree anymore.

    So the question becomes, why are they dying? Most foresters and scientists will say, climate change and/or invasive pests. But those explanations don’t fit the empirical evidence which is that even native pests and diseases have run amuck, and even young trees grown and watered and fertilized in nurseries exhibit the identical symptoms of decline. Even annual, tropical ornamentals in enriched soil in pots that like heat, and aquatic plants in ponds have injured foliage and stunted growth.

    What do all of these plants have in common? 

The answer is, the composition of the atmosphere. Most people don’t realize it, because it’s invisible, but the background level of tropospheric ozone is inexorably increasing. Precursors from Asia travel across oceans and continents, and the persistent concentration has reached a threshold that is intolerable to the plants that absorb it when they photosynthesize. Agricultural yield and quality are reduced, and especially trees that are exposed to cumulative damage season after season are universally – around the world – in decline.

This process has been well known to foresters and agronomists for decades, and demonstrated in field observations and controlled fumigation experiments. They just don’t want to publicize it, or even admit it, because the source is the emissions from industrial civilization itself. They would rather point to drought, insects, fungus and disease EVEN THOUGH it is well known that ozone debilitates plants causing their root systems to shrink as they allocate more energy to repairing damaged foliage, rendering them more vulnerable to drought and wind…AND impinges on their natural immunity to attacks from insects, disease and fungus, which exist precisely to break down dying trees, not destroy healthy trees.

    Most of the trees that fell during Sandy were rotted inside. Photos here: http://witsendnj.blogspot.com

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  10. 10. filebunch 12:53 am 11/14/2012

    Thank you Clare!

    As a footnote to Wit’s End, in my case none of the trees were diseased/dying. The Elm especially healthy. It it is its good health that dealt its end. It snapped 25 feet above the ground!

    I don’t like the “seems obvious” tone to the human cause of warming by the way. Too much science out there as to why the Ice Age ended due to warming and no sign of burning fuel back then.

    I lived on the NJ coast 30 years ago and it was not as built up as it is now. When you put things in harms way, they are going to get damaged.

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  11. 11. esmith4102 8:52 am 11/16/2012

    Do the same wind-thrown principles apply to tall tropical palm trees? It seems, to me, few are toppled by storms, unlike their cousins. And, if the rule of root depth is approximately double the circumference of the branches, then palms should have shallow roots, making them easier, at least to me, to topple. Any answers?

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  12. 12. Mary Knudson 9:20 am 11/18/2012

    Good question, esmith4102. I asked my sources for this story if they have an answer and got back this surprising explanation from registered arborist Willliam E. de Vos, president of Treeworks in Montpelier, VT:

    “I have transplanted a few extremely large palms and the root system is not much larger than the trunk ( in this case the palm was 30″ diameter plus and weighed around 40,000 pounds. The roots are extremely dense and fairly deep. In this case about 48″ deep by a 5′ square block wide. The trunks of many palm can flex substantially more than dicots (deciduous and coniferous trees). Palms are monocots like grasses. The bud is all that needs to stay alive to keep the tree alive. The outside of the palm is non-conductive tissue ( basically dead) whereas the outside of dicots is where the conductive tissue lies. I suspect this fact helps in the flexibility as the center is all that must remain intact. Also, some palms will lose their fronds in order to survive high winds and they will grow back in short order ( couple of months). Not all palms can withstand high winds as well as others that have adapted to their particular environmental needs.

    “The big factor is greater flexibility due to their monocots status. This is my opinion based on my particular experience.”

    Palms are often in harm’s way in hurricane areas and they certainly seem to have a survival means that most other trees don’t.

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  13. 13. Eric Frei 5:17 pm 02/5/2013

    Although there are some optimum root area sizes often uprooted trees only heave soil in close proximity to the trunk. Kim Coder calls it CRZ (critical root zone) and in Australia we have a formula for determining a close “no go” zone to trunks in AS4970. Generally you will see soil upheaval is within 10′ to 12′ of the trunk.

    We have a lot of palms here and some do fail. I have seen the heads torn off (rare as fronds tend to shed first) and I have seen them uprooted (often for valid reasons). Palm roots are fibrous and have no secondary thickening. It is accepted that tree roots can exert around 140psi of pressure and palm roots perhaps 30psi. Where palms have it over trees for anchorage is numbers, they have thousands of roots unlike trees which often have less than a handful of structural anchoring roots. Palms will also always have roots in a 360 degree configuration where as tree are biased to the slope or predominant wind. Recently here we had thousands of trees blow over as the wind was 95kmh NE which is unusual as our predominant wind is SE and storms come from SW so many trees had no tension roots on the windward side and flipped over in sodden soils. There is evidence out that the old ways of transplanting palms isn’t always the best and that secondary branching of cut roots does take place on some species. The old tight small root ball and lots of pruned fronds is not best practice in every case. http://www.treeworld.info/f29/palm-transplanting-phoenix-canariensis-canary-island-1113.html

    What is concerning in many tree failures is the lack of VTA symptoms. Would an arborist have been able to see a defect or something that would alert him to decay? In many instances no. One of the failures of the Picus and to a lessor degree the Resistograph is the ability to test roots and test beneath the trunk. Many uprooted trees had advanced decay in roots with no visible signs above ground. One could have air spaded the basal flare of the trunk and still not found anything. All of this makes it very difficult to know the structural integrity of the tree therefore one could be advised to apply treatment regardless (pruning to reduce canopy and lever arm). I even witnessed a jacaranda tree that received a 50% canopy prune fail by falling over at the base about a year later in relatively light winds, it is erroneous to think that if the tree withstood a high wind force in the past it will again.

    The solution to all of these issues is appropriate species selection and location. Trees not only need room to live they also need room to die.

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