We have pollarded plane trees on the UC Berkeley campus nearly ninety years old, most in areas with heavy pedestrian traffic. The pollards have gotten so heavy that every year several branches break, even though the branches may have no other structural defect. I have two questions. First, does anybody have any suggestions regarding reducing the weight of the pollards -- amount of reduction, experience with decay after pollard heads have been cut, optimal time of year, whatever. Second, is there another location in northern California that has old pollarded plane trees or other sycamore species?

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:

I don't have any specific experience with pollarding, but I have read about it. One article in particular that addressed it was in "Arborist News" a year or two back, called "What Was Old is New Again."

Once a tree has been pollarded, it should be maintained on an annual basis. If the original pollarding was done correctly, there should not be a significant amount of decay (I think). Each year, the two-year growth should be removed back to the branch collar, leaving the one-uear growth. Thus there should always be some branches, but no branches should ever remain on the tree more than two years. Because the branches are cut back to collars, the branches form the distinctive pollard heads that give this pruning style its character. Please note that this is entirely different from topping (sometimes called "hatracking"), a thoroughly discredited process in which the branches are cut back to bare stubs. Topping removes much of the tree's stored energy reserves and all of its food factories. It leads to poorly attached branches and excessive decay. Whatever you do, please do not go in and lop off the pollard heads back to stubs.

Good luck,

Keith

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:

It has been many years since I saw them, but I think I remember some pollarded plane trees over near the Steinhart Museum/Aquarium area in San Francisco.
The only trees in the Chico area that are pollarded are some of the fruitless mulberries. Often, they are not done correctly, but some seem pretty well maintained.
I believe one requirement for a pollard candidate species is that it forms wound wood quickly and "compartmentalizes" well, thus reducing the potential weakness from decay.

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:

I've seen pictures of those trees, they looked gret when taken. They are true pollards.

Is there space to get cables in? Cobra is great and I'm starting to use Libra. I like it better, less parts, easier install. The lines are black, may be somewhat conspicuose, but dynamic cable should help.

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:

All,
Thanks for your various comments. I don't think I made myself clear in my first posting. I know how to maintain pollards,and that cutting into the heads will induce decay. My problem is that I am faced with a Hobson's choice. The heads have gotten huge,some are certainly over fifty pounds, while for some reason, a number of the horizontal branches have developed very little taper, and are having an increasingly difficult time supporting the weight of the pollard heads. Regarding the possibility of cabling, these are flat-headed trees, so there is no reasonable point to attach a cable to, plus these are a focal point of campus and externsive cabling would generate a lot of negative reaction.
So, I've got a bunch of trees with branches liable to breakage (increasing risk over time, as well), with only two options to mitigate the rick of limb failure. The first is to remove entire limbs, which I am loath to do, as doing this on any scale would severely disrupt the formal patterning of the trees. The second is to cut into the pollard heads, knowing full well that it will lead to decay. My experience with plane trees is that the wood is very strong and that a branch can withstand substantial decay without breaking. My personal inclination is that I would rather have some decay out on the pollard ends, where the most likely failure is a tear-out of a year-old sprout, than risk branch failure, which may in turn induce decay into the main scaffold of the tree. Compounding the problem is that a fair number of the branches, otherwise perfectly healthy, have some dead wood on top, apparently as a result of sunscald (there may have been some year when for some reason the trees were pruned during the growing season. A more likely alternative explanation is that the trees were exposed to heavy does tear gas several times in the late sixties and early seventies,usually in late spring. We lost a magnificent hickory to teargas that way). Any suggestions regarding the least damaging way to reduce the size of pollard heads?
Thanks,
Richard

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:

This is off the top of my head (not pollarded)...
When you prune the sprouts, how many do you allow to remain on each head, and how is that determined? I was thinking that if you reduced the number per head then you might reduce the weight the sprouts add. Of course the remaining ones might grow larger than they might have.
Are you are talking about cutting into the head itself, to take a portion of the head off for weight reduction? Are you talking about doing this to each and every one? (Or just the worst?) Is this to slow down the addition of weight, or only to reduce existing weight?
Have you considered whether some bridge grafting might work on the branch tops? (On a limited, experimental basis)?

Mark, with more questions than answers

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:


My Gawd,

I read with irritation about the California police spraying pepper spray right into the eyes of protesting tree-huggers. Do you mean they've been gassing trees out there too?

Maybe shutting off all the lights is a merciful thing to do.


Bob Wulkowicz

Reply to post by Richard Trout, on May 09, 2001 at 16:50:20:

I'm assuming that you are removing all of the sprouts in the dormant season.

How big are these small limbs? Would they start to sprout and eventualy get new heads?

My guesse would be to remove a few of the worst ones and see what happens. It is an attempt to extend the servic life of the plants. Also replacing the worst trees and strating new pollards would also be a good long term solution.