Structural Systems Atop Tree Root Systems

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    Caitlin Weller

    Can anyone offer me any insight into the following:

    I would like to allow foot traffic around/ over tree roots in a plaza. I would like to keep the trees alive for shade. Is there some sort of architectural system that could be applied over the roots such as grass pavers with some level of fill that you have heard about or had success with? Any thoughts? We would like to maintain a natural appearance, the space is not located in an urban setting. The other option in to cut the trees down.

    Plant type: Pinyon Pine
    Type of planting: Forest
    Soil Moisture: Deficient
    Terrain: Level
    Drainage: Good


    Andrew Spiering

    Take a look at DeepRoot. They have a product called Silva Cell that might do the trick. Although, I am not sure how it works with existing trees. Here’s a link –

    Trace One

    Don’t cover the flange! they will do FINE with architectural pavers over them! Pines are not great for that, but if they are mature trees (how big are the Pines?) they are worth a lot of money, so try to save them..There are many other biotic systems that are currently livng in those trees, and when you cut them down, you will loose them all, perhaps never to get them back..

    Other thing in your favor is Pines have small rooting system, compared to other trees…

    People in Ca. like to look at their backyards and say, that tree is ‘too big..’ ..How can a TREE be TOO BIG? It’s like saying you are too old, and must go!

    Matthew J. Sandy

    I would ask what is the expected amount of foot traffic? If the traffic is not in an urban setting (your words) and foot traffic can be controlled (im thinking circulation from entry of building to parking area) why not eliminate an overally engineered system entirely. Look into using locally available gravels bounded by naturalistic edging in the higher traffic areas, and why not a wood bark mulch beneath a majority of the drip line of the pines.

    david j bockman

    Not sure if this system is appropriate without more information on your program elements, however I’ve had good luck with Invisible Structures, Inc. , specifically GrassPave and GravelPave.

    Of course choosing appropriate shade trees which can tolerate compaction is important– American Elm for example.

    Caitlin Weller

    Thanks for the input….
    Although the setting is naturalistic, the foot traffic is very high…

    Andrew Spiering

    Do you have any pictures of the site?

    Mike G

    Is it possible to build decking or a suspended walkway above the soil?
    For mature trees soil compaction and construction damage cause a slow death and take years for symptoms to show up. Further more they stress trees allowing insects and diseases to quickly infest the tree(s). Usually the insect / disease gets the blame, when soil / root problems are the real cause of decline. Unfortunately and also often the case the most damage to trees gets caused by landscapers. Plans often look good on paper but the execution is just as important.
    If you need site specific help contact one of our allied professions in the consulting arboricultural or forestry industries. They should be better be able to help you with these decisions. Its often very worth our time and money to bring in specialist into the design team. They may suggest, root pruning, monitoring, fertilizing, constructing temporary barriers…
    Good Luck!

    Trace One

    sorry, Mike, I have found the arboriculture answer is “sadly, the tree must go..” We (LA’s) know more than them..I would rely on the judgement of an LA..Keep the trees..They are old, they are worth a LOT of money..

    Mike G

    Trace, Don’t loose faith… and sadly I am guilty of being an arborist, a trade I still consult in. I have conducted quite a few tree preservation plans. Some work, some don’t. And as unfortunately as it is individual plants ability to withstand construction damage varies as well as its overall health and vigor. And of course the economics of saving a tree and finding people willing to pay for them vary too and go into the decision making process.
    Mitigation really does suck but…cut one tree down, plant ten.
    There are a lot of decent consulting arborists out there. Always get referrals or talk to people that regularly deal with arborists, like a local arboretum or botanical garden. Just like the LA profession we abide to protecting human safety and protect property. When a tree conflicts with these priorities the decision makes itself.
    -‘The best time to plant a tree-twenty years ago; the next best time-now’ -unkn.

    Rob Halpern

    I might add that changes to the environment of older trees (soil moisture, humidity, reflected heat, etc.) can be devastating.
    The argument that “these trees are worth a lot of money” seems irrelevant to me.
    To “save them” temporarily only to have killed them a few years hence is pointless and will result in both great expense for the owners later and a failed design. So take a rational, dispassionate look at the situation and make your decision. If saving these trees is the goal, then design accordingly (limited foot traffic on restricted pathways or boardwalks for example), if getting alot of people through this area is the priority, then see if you can save some peripheral trees and allow that the rest cannot survive the construction and new use for long. Too often, L.A.s and contractors “save trees” for later horticulturists to remove.

    Trace One

    Mr. Halpern, I haven’t noticed that homeowners in the US were in the habit of ‘saving’ trees. Where is that a problem, in your experience? In thirty years of LA, I have not noticed that the LA’sget to ‘save’ the trees, later to be taken out by the sensible horitculturality..It is ALWAYS the opposite – the aborist is called on site, and oh so sadly the trees must go NOW (they obviously make more money that way…) You have it exactly backwards.

    I am trying to get at a more general sense of the value of a tree, I should not have been so specific that their value is in dollars, (although thank goodness out estimation of tree value has improved a lot with the introduction of replacement value based on DBH.)
    Save the old tree! What have you got to possibly loose? You will never get it back, in your lifetime..And if you think of it as something worth $60,000 each, then you may have more interest in trying to care for it, than replacing it with some lovely callery pears, 2″cal..
    If you entire design ‘fails’ because of one tree dying, you do not have a very good design..The first element, the site circulation, should be able to survive on it’s own merits, without the plantings at all..
    You have it exactly the opposite, from reality..Are you an arborist? (No offense intended..)

    Rob Halpern

    I can’t speak about homeowners, my experience is with institutions and bigger projects.
    I have seen projects re-designed to “save trees” and yet not sufficiently to actually spare the tree. So in the end (a few years) the tree is dead and the design is not what it ought to have been.
    My point is not (perhaps you misunderstood me?) that the trees ought to be cut down. Rather that if they are to be saved, then take it seriously and do the right thing by them. But if that is not what the L.A. or the Owner are willing to do and they are doing a half-Assed effort for the tree, then take it out. This project appears to be one where a vast amount of people are to circulate through an existing grove of pines. Can the L.A. plan that such that these trees are minimally impacted? That is the question
    I am not an arborist. I am a horticulturist and long-time grounds manager of large sites. I have employed arborists. I have brought in consulting arborists.

    Trace One

    I have had the identical experience with institutions, shopping centers, residential..No-one ever tries to save the trees..And small flocks of birds, here in CA. hummingbirds, are suddenly cast adrift in a barren landscape, for no reason – there is a huge predjudice against eucalyptus in this state, no matter how big, people in califiornia want to replace all eucs with with live oak.. Bye bye to decades old hummingbird habitat.

    I don’t know where you live and work that there is so much saving of canopy species..

    It should not impact the design,and it is worth doing, because you and the organisms you are killing will never get that system back, in your lifetime..

    Even if a tree is saved, in plan, the second most common experience is – — oops! – it is taken down one fine early morning by the can’t get it back then..

    Sorry, I have another take on reality from you, Mr. Halpern…

    I lived on a gorgeous Hamptons estate with a huge semi-circular entrance drive (I am talking over 1/2 mile in diameter) and it was lined with the most gorgeous European Lindens, mostly planted in the twenties..(1920,s). A bad storm caused a few of them to absolutely topple..Roots in the air..The intrepid german forester on the estate hooked a bulldozer up to them, hauled ’em back up, tamped them down and root fed them for a few months..They all lived.. I think both Central Park and Versailles could have benefited from this example, in their recent hideous tree-tragedies caused by really bad storms..

    Check out the prices for a 3 foot diameter american beech. (These can be bought at Marder’s nursery in the Hamptons). Is that really the value of that tree? Isn’t it’s true value much much more?

    Both landscape designers (who want their designs to balance) and arborists, are much more often in the business of taking all existing trees out, in this country.. I have seen it all to often, all over..Our lives can be much more interesting if we could absorb the complexity of dealing with existing conditions, giving them the respect they deserve..

    Rob Halpern

    It seems that I have had the benefit of more thoughtful clients than yours.
    I have worked all over the country…I wonder if there is something particularly anti-tree in Southern CA?

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