While watching the TV coverage of the four hurricanes that have devastated Florida over the past few weeks, I started paying attention to the ‘live’ photos of palm trees standing up to the horrific wind. Of course you see shots of downed palm trees, but, what’s the story with the ones that stand tall and defie the gods to take them out? Are they an unusually strong tree? Are they rooted very deep into the ground? What makes them so tough?
Well, the general category “palm trees” would include quite a range of trees and shrubs of varying strength and typical root depths. At least some tropical species are not particularly deep rooted.
The most obvious factor I can think of is that the typical palm tree is considerably “cleaner” aerodynamically than a broadleaf or conifer tree of the same height and diameter, i.e., palm trees do not make very good sails.
I’ve dug up quite a few specimens of Washingtonia robusta in my time, and I can testify that the roots go straight down at least three or four feet. This doesn’t sound like much, but somebody once told me that the Stratosphere Tower in Las Vegas is only sunk ten feet into the ground—so I guess it doesn’t take much. The trunks are also very flexible, fibrous, and filled with water. If anybody is ever shooting at you, by all means duck behind a palm tree. Add to that the fact that they present such a narrow profile, and you can start to see what holds them up. But it still amazes me, too.
Palms have a lot going for them in high wind areas. They generally have a single stem topped by a crown of very flexible fronds. The trunk profile is very narrow compared to the heighth of the plant. Palm trunks are incredibly flexible and the cross section resembles a spongy bundle of straws.
The average palm, while not particularly deep rooted, throws out a dense mat of root, the largest individual root being no larger than your thumb. I’d say the average palm tree root weighs more than three times what the above ground part does, once you factor in the enormous amount of soil in there. The thin roots can also “worm” into underlying subrock effectivly “tying” them to the ground.
Palms while not necessarily having evolved in high wind areas (in the sense of all of them) do fare quite well in high winds. Primarily because the fronds tend to “fold up” when wind blown, compared to an oak, whose branches hold out a MUCH greater surface area. It’s like holding a flag out in a gust compared to a parachute.
As palms initiate new roots from the trunk (rarely do they branch) it’s like sending out a bunch of stabilizing lines. As the trunk grows they continually send new roots out. If you dig up a mature tree you’ll see hundreds of roots (which are pretty strong to begin with anyway).
Most of the palms that blew over from what I saw were Queen Palms (Syagrus romanzoffianum). This palm is not adapted to high wind areas (as it is from Brazil all the way to southern Argentina, IIRC). Their fronds will usually break or the tree gets blown over. However quite a few do make it well in high winds. Coconuts are so strong that in Cyclone Heta earlier this year, which was a cat 5 (185 MPH winds) most of the coconuts just snapped off mid trunk (or near the crown). There was a photo of a coconut tree grove in I think Niue where most of the trees had simply snapped. Other palms are not so stable. When Caryota gigas dies it then becomes a hazard and tends to suddenly fall one day (Which of course any palm could if just left in the ground to rot).
Palm “wood” is generally quite hard as well. I’ve heard of people ending up with dulled axes and chain saws fron trying to cut down certain palms. There really isn’t a fibrousness to Palm wood. Palms also don’t form annual rings, which is where splits can occur. I’ve heard queen palms are incredibly tough to use tree climbing spikes on because they don’t easily enter the trunk.
There is one palm that is very strong in high winds, the Hurricane Palm - Dictyosperma album. It is from the Mascarene islands.