Do you have any information on the effect of Ivy (English) growing up the bole of a mature Ponderosa Pine. Can the ivy cause decline or death to a confer. Do you have any reference to the literature on this subject. I'm a ISA certified arborist WC6122.

Reply to post by Philip A Bjorkman, on November 28, 2001 at 19:49:15:

I do not have specific information in respect of English Ivy on P. ponderosa. What I do have is personal observation of tree/Ivy conflicts which go back to the '60's. From my observations, most tree species are way more flexible than the Ivy is. If a tree is in good health and vigor the tree will outgrow any threat from the Ivy. Because the branches of most healthy trees are more flexible than the vines of the Ivy,it seems that the stems of the Ivy break before the branch does, thus in windstorms branches have greater flexibility than Ivy stems have.
This is totally anecdotal, I have nothing to back it up with, other than more anecdotes,

James.

Reply to post by James Causton, on November 28, 2001 at 19:49:15:

I think James is generally correct on branch breakage, although there is some chance that snow or ice accumulattion on ivy could cause a branch to exceed breaking weight. A bigger problem is competition for light.

I've seen no problems from Ivy on trunks (though some experts don't like it "hiding" things). But I have seen ivy outcompete tree foliage for light, killing off foliage - and thus branches - and leaving trees with too little active foliage for their woody mass.

There is also some anecdotal suggestion that a crown full of ivy offers greater wind drag and could lead to windthrow. I think that would only happen with compromised anchorage.

So you need to decide if you risk the foliage competition, or periodically remove ivy from branches to keep it on the trunk, or re,ove it all.

Some people like the look of ivy on a trunk and that's a personal decision. I have seen a combination of ivy and euonymous effectively more than double the visual diameter of a large trunk and thereby provide very desirable screening.

Reply to post by Scott Cullen, on November 28, 2001 at 23:53:14:

Here is a negative perspective on ivy, dealing more with environmental issues than with trees.

Reply to post by Scott Cullen, on November 28, 2001 at 23:53:14:

Hi Scott,
You wrote,"I've seen no problems from Ivy on trunks (though some experts don't like it "hiding" things)." I am one of those folks who are concerned about what Ivy hides. I was recently contracted by a client to undertake a tree inspection on 3 large Doug Firs. When I arrived on the site to undertake the inspections all I could see was Ivy. I explained that before I would be able to evaluate the trees, the Ivy would need to be removed. Never heard back yet.

You went on to state "But I have seen ivy outcompete tree foliage for light, killing off foliage - and thus branches - and leaving trees with too little active foliage for their woody mass.". I wonder if the situations in which you witnessed the Ivy "out-competing tree foliage occurred in trees which were already stressed or in decline.
Your points regarding windsail, "There is also some anecdotal suggestion that a crown full of ivy offers greater wind drag and could lead to windthrow. I think that would only happen with compromised anchorage.". Seem well valid except for the fact that in a healthy, vigorous tree, the whole structure of the tree would be making adaptive growth in order to deal with the increased windload created by the presence of the ivy.
I am not advocating that Ivy should be encouraged to grow into trees, in fact it possibly should be discouraged, my interest is in the real problems related to it's presence,

Interesting subject Scott, look forward to your responce, Thanks James.

Reply to post by James Causton, on November 29, 2001 at 07:46:05:

James wrote... "I am one of those folks who are concerned about what Ivy hides. I was recently contracted by a client to undertake a tree inspection on 3 large Doug Firs. When I arrived on the site to undertake the inspections all I could see was Ivy. I explained that before I would be able to evaluate the trees, the Ivy would need to be removed. Never heard back yet."

I guess you have to consider the potential for damage to a target and the likelihood of there being something hidden on a given species of a given size on a site with a given history. Certainly there are some cases when you really need to know what's under there. Maybe others where you don't. I think the real implications are for risk assessment in general. "Do you always peel away the ivy?" is no different a question that "do you always bore into each and every tree?" or "do you always do a root crown excavation on each and every tree?" or "do we really know from boring what the real inside picture is?" In other words do we always do everthing we know how to do just because we know how to do it... and it's such a neat tool... and.... It must be a case by case thing and we still have lots to learn.

And James wrote "I wonder if the situations in which you witnessed the Ivy "out-competing tree foliage occurred in trees which were already stressed or in decline." No doubt was in some instances. I guess climate is also an issue. Here in the NE for example exposed ivy gets defoliated - partially or completely - some winters by low temps with low humidity. That slows it down. Other climates that doesn't happen. Mark posted an interesting anti-ivy site from Portland, OR which from its tenor suggests overcompetition is too widespread to be limted to declining trees. And I suppose a tree on the edge of stress could easily be pushed over that edge as it loses foliage.

I wrote "There is also some anecdotal suggestion that a crown full of ivy offers greater wind drag and could lead to windthrow. I think that would only happen with compromised anchorage," and JAmes responded "seem well valid except for the fact that in a healthy, vigorous tree, the whole structure of the tree would be making adaptive growth in order to deal with the increased windload created by the presence of the ivy."

I suspect that in many trees there is already a sufficient safety factor that the tree will deal with the "increased sail." But if the anchorage is compromised that safety factor may be gone. I'd guess that it's possible fast growing ivy could add to "sail" before a tree could counter with adaptive growth. It also depends a lot on wind exposure. If a tree is really protected and gets little wind there will be little stimulus for adaptation regardless of sail area (and of course little risk of wind damage too!). The increase in area could mean a linear increase in load at a given wind speed if other things remain equal. If you double area, you double the load. If you had a Safety Factor of 4 (Mattheck's figure) before you still have a Safety Factor of 2 now. That also means you will get failure at 1/2 the ultimate wind load as before. If that means you will fail at 150mph rather than 200mph do you care? How likely is it that you will get 150mph?
(Note that once you get up into that speeed range load varies with the square of speed so you can't adjust artimthmetically). But it is also possible that the ivy will not reconfigure as wall as the tree crown normally does and so you will get a higher drag coefficient at lower speeds... so the increase in load will be greater than the increase in area. But it's also possible that the ivy will direct the wind around the crown rather than into it, resulting in a lower drag coefficient so load increase will be less than the area increase. (While it seems counter-intuitive the literature suggests that porous crowns actually may have higher loads than dense crowns... wind reacing into the crown hits "multiple sails" rather than simple the projected silhouette.)

So, I guess that means I think that a knee jerk reaction that ivy, by incresing "sail area" will uniformly increase rates of failure is much too simplistic. Especially in terms of windthrow, unless the anchorage is compromised. There is more chance of branch breakage under ice or snow load. I've also seen it under driven rain... just as we see it in trees heavily laden with nuts or fruit. But is it statistically a big deal? The fact that we're talking about trees full of ivy suggests to me that the branches are not falling off them all!

Thanks for your questions.

Reply to post by Scott, on November 30, 2001 at 00:08:05:

Scott, I know that every arborist who sells crown cleaning and crown thinning services, claiming they will reduce windthrow hazard, needs to get familiar with the "literature which suggests porous crowns may actually have higher loads than dense crowns".
Where can we find it?
The engineering formula "Halving the area halves the load" might sound simplistic but it does make good sense to me.
In North Carolina I maintain trees with ivy, pulling it off branches every few years to prevent tree foliage loss.
The trick is to bend and not break it, so it can cascade down to eye level and increase screen value. On one tree it hit a chainlink fence, engulfing it as it grew down to root.

Re inspection, if the customer likes the ivy I simply shear the foliage to expose the tree bark. the leaves will regrow.
If the ivy stalks are too thick to see the trunk, you have a good idea that bugs and spores have a hard time getting to it too.
Guy

Reply to post by Guy Meilleur, on November 30, 2001 at 06:01:47:

Guy wrote: "Scott, I know that every arborist who sells crown cleaning and crown thinning services, claiming they will reduce windthrow hazard, needs to get familiar with the "literature which suggests porous crowns may actually have higher loads than dense crowns".
Where can we find it?"

The material is pretty scattered... no one specific treatement nor a review of the applicable findings. Creating a list is on my list of things to do. My Tree-Wind Bibliography has been accepted for publication in Journal of Arboriculture... maybe Jan '02. It is not sorted by specific topic but does give some pointers to beginning reading.

"The engineering formula "Halving the area halves the load" might sound simplistic but it does make good sense to me."

The engineering formula most typically uses a "projected area," the silhouette facing the wind. (There are other ways to measure using the "wetted area" or surface area of the solid form for example but these are less used). If we were in fact dealing with a simple, plane, flat surface the principal issue would be area. Poke holes in it (like a banner) or make it smaller and there is less area and less load. But we have a solid form that is neither solid nor hollow. It has depth behind the silhouette and it has shape. So compare a cylinder and a flat plate with the same projected area. The cyliner has less drag becasue the air "wraps around it." You have a combination of pressure drag and surface drag (or friction). (You can get all tangled up in that relationship which is expressed by something called a Reynolds Number, but that's not really necessary in a basic analysis). The flat plate by contrast has almost all pressure drag. So a tree has a form like a cylinder or sphere or cone and a lot of the wind wraps around it. If, however, you start poking holes in that surface, by crown thinning, you mat be directing wind into the crown where it applies pressure drag against additional sails. Not only that some of those sailsmay be attached to leeward crotches which are now loaded in tension... where they used to be protected by windward foliage you've removed.

Also in terms of windthrow any applied load is multiplied by the length of the lever arm. So reducing "sail" down low doe snot have a proportional effect on reducing the base bening or overturning moment. John Moore at OSU found that on forest conifers crown raising had to reduce crown by 70% to significantly reduce base overturning moment.

Another phenomenon is that crown mass has the effect of damping wind movement. I think this happens in two ways. One is in disapting energy through crown movement before it can be transmitted to base overturing moment. The other is by damping sways and preventing resonance. If a top sways a lot it has energy in that sway. If it is just about to release energy in a sway and a wind gust is added to that a greater amount of energy is transmitted to the base.

There is anecdotal information that "pruned" properties in coastal areas sustain less damage. More work needs to be done to understand if that is in fact becasue of reduced sail area or if perhaps the pruning just removed weak limbs or perhaps encouraged stronger branching.

"In North Carolina I maintain trees with ivy, pulling it off branches every few years to prevent tree foliage loss. The trick is to bend and not break it, so it can cascade down to eye level and increase screen value. On one tree it hit a chainlink fence, engulfing it as it grew down to root."

That's pretty cool. like an inverted hedge or a living curtain.

"Re inspection, if the customer likes the ivy I simply shear the foliage to expose the tree bark. the leaves will regrow. If the ivy stalks are too thick to see the trunk, you have a good idea that bugs and spores have a hard time getting to it too."

Good solution. If you see something suspect you can always remove ivy stalks if you have to... but only as a last resort. How about that James?

Reply to post by Scott, on November 30, 2001 at 22:10:55:

Scott, you explain things very well. I appreciate the degree to which you treated this subject, and will look forward to further studies in this area. I was wondering if anyone was doing wind tunnel or computer simulation research on wind interaction with trees. (not that I know how they would ever set it up, but there must be some way to generate models, like they do with aircraft, etc.)

Reply to post by Mark Goodwin, on December 01, 2001 at 07:04:17:

I think UBC has done some recent wind tunnel work, but on stands rather than indivudals. Those results are recently published and are in the forthcoming bibliography. Some interesting wind tunnel work in the UK is reported in Coutts and Grace, 1995, Wind And Trees, Cambridge U. Press. Steven Vogel at Duke as done some wind tunnel work on foliage which is in his book Life in Moving Fluids. He also did a 1996 article in JoA. Rich Grant at Purdue did some wind tunnel work when he was at Syracuse... early '80's I think... and there are a number of journal articles. The most cited work was by Mayhead in the UK in the '70's (he was actually using '60's data from Fraser).

Tom Smiley put a tree on the back of a pickup truck (JoA last couple of years). Prof Nick Kouwen at U.Waterloo did the same thing. There's a similar Forest Service study from the early '50's.

If you do a search on "wind tunnels" and combine it with "building" or "NASA" you should find some pretty straighforward directions for building one... the site is intended for school science projects. You could pretty easily build one to hold seedlings or branch segments. Bigger depends on how ambitious you are, how much room you have and how neat a junk pile you have to pick from (or alternatively how much money!).

Reply to post by Scott, on November 30, 2001 at 22:10:55:

An excellent thesis on interactions between crown profiles and wind Scott!!.
I most certainly agree with your thoughts regarding "opening up" crowns of trees. I have witnessed a bunch of disasters, apparently caused by over thinning of crowns, where branches were left unprotected from wind which had previously been sheltered.
Now the Ivy issue; and as you stated, if Ivy is growing on or close to the trunk of a tree it will have a minimal absorption of energy from the wind, however further out from the trunk the effect of its presence increases. This effect, interestingly enough, should be greater when the foliage is dry rather than when wet, as water covered leaves will possess a smoother surface than dry leaves, thereby reducing the co-effients of drag on their surface.
I think we should also be considerate of the wind optimization of individual leaves rather than the simple "profile" of the whole tree, perhaps we could get into understanding the correlation between petiole thickness and shear strength on Ivy leaves in order to understand whether individuals will fail before host branches do. Of course this would involve a massive study in a few thousand species under unlimited conditions.
From my experience, Ivy stems and twigs are particularly inflexible, my observations have shown me that in a structurally sound, Q.robur, the branches and twigs of the canopy are infinately more flexible that the counterparts of Ivy are, thereby, the Oak "self prunes" the Ivy growing upon it. I guess we could take the whole thing a little further and discuss the development of re-active growth on Ivy petioles!!!
As far as visual attributes of Ivy are concerned, yes, we can do what the heck we please and, get away with it,
OK. How about that Scott.

James.

Reply to post by James, on December 01, 2001 at 07:04:17:

Sounds mostly good to me.

The water thing gets a little less simple than just drag. We've all seen, I think, soaking wet foliated branches... even more so fruit or nut loads... fail under light winds or even in still air. So even if the Cd is lower cause the water is slicker the moment may be enough higher becasue of the weight to cause failure.

If we're talikng about everday trees - no ivy - my intition is saying let nature take care of itself... how can we possibly improve on evolution... how can we possibly know how to thin the tree just enough but not too much? There are of couse exceptions where there is branch weakness or overextension or poor angle. Add ivy to the case and I guess you have to look at targets and personal (client) preferences. Maybe the tree has enough safety factors to deal with the ivy and maybe not.

The action of individual leaves often aggregates into better performance of the whole tree. Steven Vogel has done a lot of work on this. In the case of white oak he found that individual leaves actually don't perform very well but leaf clusters do.

Reply to post by Scott, on November 30, 2001 at 22:10:55:

Scott wrote: "The engineering formula most typically uses a "projected area", the silhouette facing the wind."
Is this the premise on which all this tree-wind discussion is based? It seems more basic physical properties should first be considered if we are talking about windthrow hazard.
First, doesn't wind on the top of the "projected area" cause more pull on the solid form than wind on the bottom, due to leverage? If not, raising the crown would lessen windthrow hazard as much as reducing the crown. The OSU study bolstered common sense on the inefficiency of the bottom-up approach, but is there data on shortening the lever arm? Inquiring crown reducers need to know.

Scott wrote "...crown mass has the effect of damping wind movement." True enough, but which crown mass where does how much damping? Don't inner branches do more of this, while top and side weight creates the most load? All this is another good argument against lion's-tailing, as is Scott's excellent point about "...leeward crotches which are now exposed to tension..."

[Re effects of pruning, is the effect of reducing sheer mass being given its due weight (nyuk nyuk) while we talk about sails? Does a 400-lb branch create twice the load than a proportionate 200-lb. branch?]
Scott wrote "So reducing sail does not have a proportionate effect on reducing the base bending or overturning moment".
What if the reduction is proportionate, i.e. evenly done throughout the crown? Wouldn't that make the effect more proportionate?

This wind-tree discussion has great merit, as the engineering data shows more of the effects of excessive crown raising and thinning.
But imo to keep the discussion relevant to tree care, these flights into the higher math of engineering have to be regularly checked with basic physics, and kept in the context of LIFE science. Trees are continuously adapting to stresses caused by the elements, and by humans fumbling to find ways to help them adapt.

Reply to post by Guy Meilleur, on December 01, 2001 at 07:04:17:

"Scott wrote: "The engineering formula most typically uses a "projected area", the silhouette facing the wind."
Is this the premise on which all this tree-wind discussion is based? It seems more basic physical properties should first be considered if we are talking about windthrow hazard.
First, doesn't wind on the top of the "projected area" cause more pull on the solid form than wind on the bottom, due to leverage?"

OK. The "sail" area is one element of the load, the others being the density of the air, the wind speed and the drag coefficient. The load is the force applied by the wind. The load is one part of the picture. What causes failure is the "moment," the load times the lever arm. This can be on a limb by limb basis or on an entire crown basis. So you can measure the area different ways. You can use the projected area or silhouette (a circle with radius = x has the same projected area as a sphere with a radius = x. Or you can use "wetted area" and the figure will be much higher. You use one or the other. Vogel calls this a reference area. You constantly refer to it in the analysis. Now if you set up an experiment to measure the load at different wind speeds you can calculate a drag coefficient (Cd). Since trees reconfigure, the Cd will vary with increasing speed... up to a point, then level off. So if you look to the literature for Cd values you just have to be sure they were calculated using the same form of reference area as you are using for your subject tree. And most of the published data are based on projected area. Now the more complex analyses take a slice of area at a series of heights starting ath the bottom of crown and progessing to top. Each higher slice has a longer lever arm and creates a higher moment for each unit of area. Simpler analyses, more applicable to tree care, estimate a "wind load point" which acts from a signle height. This is approximated by the center of mass of the crown. So I think to answer your question, both area and lever arm are important and there are different ways to deal with both.

"but is there data on shortening the lever arm? Inquiring crown reducers need to know."

Yes. You would calculate the moment for x crown, then reduce it and calculate moment for y crown... area and wind load point have both changed.

"Scott wrote "...crown mass has the effect of damping wind movement." True enough, but which crown mass where does how much damping?"

I don't know how we realistally know in a practical application. So I don't know how we know how much crown thinning is effective, though we have guidlenes on how much is damaging or at least sub-standard.

"Don't inner branches do more of this, while top and side weight creates the most load?"

Well I could see it happening both ways. In some trees the displacment of weight in the tall tops could exert it's own moment and contribute to failure. But I've seen big, squat trunks with big buttresses and long branches starting at about 1/3 of height. You watch those long branches swaying in long arcs and you visualize the wind energy being disapted by the sways... moving that mass around... before it gets transmited to base overturning moment. If you crown reduced that tree x amount maybe you reduce the area and the load but you reduce the sways and create a higher base moment... so maybe you have to reduce to y amount to actually reduce base moment. So my sense is crown reduction to reduce moments (the reason you reduce "sail") has to be based on calculation case by case rather than over simplified rules of thumb. And I'd want to see clear compromise in the system as a reason for underatking it. I just don't see it as a necessary or effective routine practice for general tree maintenance.

"[Re effects of pruning, is the effect of reducing sheer mass being given its due weight (nyuk nyuk) while we talk about sails? Does a 400-lb branch create twice the load than a proportionate 200-lb. branch?]" Dunno, I think it depends on angles and distribution of weight. But generally no, damping is not considered enough. General practice seems to consider only the single charateristic of "sail area."

"Scott wrote "So reducing sail does not have a proportionate effect on reducing the base bending or overturning moment".
What if the reduction is proportionate, i.e. evenly done throughout the crown? Wouldn't that make the effect more proportionate?"

No. Not uniformly anyway. If it's done evenly, I guess that means creating uniform porosity or thinness over crown, you're back to the point above... 1 unit of area x 1 unit of lever arm creates 1 unit of moment reduction. 1 unit of area x 3 units of lever arm only creates 1/3 unit of moment reduction. Might vary with crown form.

"This wind-tree discussion has great merit, as the engineering data shows more of the effects of excessive crown raising and thinning.
But imo to keep the discussion relevant to tree care, these flights into the higher math of engineering have to be regularly checked with basic physics, and kept in the context of LIFE science. Trees are continuously adapting to stresses caused by the elements, and by humans fumbling to find ways to help them adapt."

Yup. Most times we should just leave them alone. As I said above action should be based on clear need... a compromised system that adaptive growth can't catch up with and then calculated on a case by case basis.

SC

Reply to post by Scott, on December 03, 2001 at 07:48:04:

Scott, I agree that crown thinning and reduction should be done only in case of a clear need (often from aggravating factors other than form) and calculated on a case-by-case basis, with the whole tree in mind.
By routinely reshaping, the arborist assumes too divine a role.

I don't totally agree that this pruning needs to be a "system that adaptive growth can't catch up with" because it's never clear that the tree won't "overadapt" and the problem redevelop years later. Returning to reshape trees is never the goal but it's sometimes needed.

Will your Jan '02 tree-wind discussion have any consideration of fiber characteristics of different trees? Some sure seem more prone to snapping than others.
Thanks for responding to my points.
Guy

Reply to post by Guy Meilleur, on December 03, 2001 at 09:21:05:

Thanks for the discussion, it was helpful. Phil

Reply to post by Guy Meilleur, on December 03, 2001 at 09:21:05:

I think what I meant was that pruning should be undertaken when there is some compromise in strength that adaptive growth can't catch up with. We agree. Routine crown reduction is something we can't do any better than nature has already accounted for.

My Jan '02 article is just a bibliography, with some general comments on use. 240 entries about trees and wind (or fluid motion). Some of the citations probably consider wood strength.

Reply to post by Philip A Bjorkman, on December 03, 2001 at 13:05:27:

I'm glad to hear that. It was kind of a shock that with all the talk about "sail areas" and "wind loads" nobody really could talk in very concrete terms and there was not much awareness of published work. So I had to go looking and came up with a bibliography of 240 entries. And I think I'm starting to get a handle on it all... to develop a somewhat clearer picture.