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I started thinking about this after seeing several articles about falling trees, in particular a few articles about very large trees falling in Los Angeles and New York City. Plus, just thinking about all the wildfires in the Western United States started by trees falling on electrical wires. Although I haven't done extensive research, I did some searching and found the following:

Trees and climate change: Faster growth, lighter wood. This article discusses how "wood density of European trees decreasing continuously since 1870."

So is this a current concern and a global phenomena? Are trees growing faster, but are less strong. Combining this thought with the fact that winds are getting stronger in North America seems very unsettling.

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  • $\begingroup$ Large trees would have been growing for anywhere from around 50 years (for a fast growing species like cottonwoods) to several centuries. Global warming has only shown noticeable effects in the last few decades. $\endgroup$
    – jamesqf
    Jan 17 at 3:49
  • $\begingroup$ Ah..this is what I am wondering about. So your sense is that it is mostly younger trees that would be less dense? On the other hand, larger trees grow big branches that could be growing much faster due to the past few decades. Roots could grow faster, but be less dense, etc. I appreciate your point, but will have to think about it more to be convinced. $\endgroup$
    – user21648
    Jan 17 at 4:00
  • $\begingroup$ It's really not weak wood that is the main cause of falling trees, at least in my casual observation. You may get large limbs breaking off, but generally when the whole tree falls, it does so from the roots. That is, the roots break and/or pull out of the ground, rather than having the trunk snap above ground. WRT the wood of younger vs older trees, I would think this could be settled by looking at annual growth rings. $\endgroup$
    – jamesqf
    Jan 17 at 18:08
  • $\begingroup$ Where i live the rains have reduced by 30% of the average 100 years ago. Trees in drought limited zones simply lose branches, until a big tree just has 30 or 60% of boughs without leaves. I.e. drought is a big menace to big old trees. Many huge thousand year old deciduous trees grow above underground streams. Naturally their branches become so big they break. Traditionally, cutting above the trunk for firewood encouraged 500 year old trees with massive trunks and small upper branches, upper prunung makes trees very resustant to wind damage, a tree pruning tradition that is lost to the past. $\endgroup$
    – DwayneDeSouza
    Jan 20 at 0:33
  • $\begingroup$ Coppicing at 2-3 meters above high above the ground on a 2-3 meter wide trunk encourages millenial trees. $\endgroup$
    – DwayneDeSouza
    Jan 20 at 0:39
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Nothing to do with climate change . Faster growth produces somewhat lower density and strength. There are strength tables for wood written more than 50 years ago that have separate listings for "new " growth and "old" growth. "New " growth being trees growing faster in clear cut areas with less competition for water, light and nutrients. Old is trees in areas that not previously been harvested and grew slower in crowded conditions. Power line failure is related to the increase in numbers of power lines in expanding populated areas, and to how much money utilities spend trimming trees near the power lines. When I drove in western Europe in the 80's , I was impressed by how many of the forests had been "managed". Large old trees had been planted in regularly spaced straight lines ,maximizing growth speed = lower density . As silviculture is a minor hobby of mine I expect I noticed things others would not.

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  • $\begingroup$ Interesting, thanks. Perhaps stronger winds are also responsible for blowing down more branches and trees onto power lines. Wasn't thinking in terms of "new" and "old" growth, so I'll have to think this through a little more. $\endgroup$
    – user21648
    Jan 20 at 4:55
  • $\begingroup$ Locally ( E TX , piney woods) many areas were clear cut before the depression of the 30's. So many pines are now about 100 years old and are now dying . As they are taller than power lines they take down power lines when they fall . So outages are common here now ; more than a third of my neighbors have stationary back-up power. I only have a portable generator. Most seem to be brought down by rain , not wind . Two fell in my yard during the Harvey rain event ( 40 "). $\endgroup$
    – blacksmith37
    Jan 20 at 16:11
  • $\begingroup$ @blacksmith37: Same here (northwestern Nevada & northeastern California). What seems to bring trees down is the combination of heavy rain and strong wind. Saturated soils exert a weaker hold on the roots, which means a strong wind can uproot the tree. $\endgroup$
    – jamesqf
    Jan 20 at 18:29
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Many tree species do grow faster in climates that are warmer than their native range, especially where the added heat is combined with moist conditions, and faster growth is generally associated with lower density wood. This is why a lot of New Zealand's plantation pine is only good for paper pulp, the warmer wetter climate means that the trees grow fast and have wet low density wood that doesn't have good structural performance. But this doesn't really account for most of the changes seen in European forests over the last 150 years; trees also grow faster, and therefore have "lighter" wood when grown in lower density stands. In managed forests trees are separated at intervals convenient to human maintenance staff and their equipment and are thus considerably farther apart than they would be if they had grown from seed in a wild setting and as tree farm mechanisation has increased so has tree spacing in plantation stands. Climate change could alter wood densities in the long run but at this stage we aren't seeing those effects in timber yet, it may be effecting young stands right now but we won't see the results for a number of years.

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  • $\begingroup$ I'm very glad that you say the impacts aren't being felt yet. Very interesting about the New Zealand plantation pine. $\endgroup$
    – user21648
    Jan 20 at 4:58
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A one degree rise in temperature is barely a noticeable change. The biggest change is additional atmospheric carbon dioxide leads to sustained growth and longer growing seasons. CO2 availability is prime indicator for sustained plant growth. Alot of the tree's in LA and New York........ Are old. Some 2-3 centuries, which is why some are falling or dying. But faster growth rates do yield less wood density because tree rings. When faced with stressful or unfavorable conditions, a tree might hardly grow at all. Even in ideal climates Trees have to Compete for sunlight, water and nutrients. Overall a warmer climate certainly benefits tree growth; certainly not kill it. enter image description here

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  • $\begingroup$ Downvoted - it doesn't answer the question and suggests global warming is insignificant, contrary to the best available science based advice. $\endgroup$
    – Ken Fabian
    Jan 19 at 22:43
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    $\begingroup$ Hi Ken, OP here. Looking over the answer, some good points are made. The photo shows high CO2 causes faster growth. I don't think the poster is saying global warming is insignificant but that, in terms of faster growth and less density of trees/plants, CO2 plays the bigger role. $\endgroup$
    – user21648
    Jan 20 at 4:52
  • $\begingroup$ Some years ago there was similar testing done on pine trees in N or S Carolina . The results were similar , faster growth with more CO2 , they did not have a low CO2 test. Clear plastic walls were put around a few smaller trees and CO2 was continuously added . No top so that sunlight would be the same. $\endgroup$
    – blacksmith37
    Jan 20 at 15:59

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