How can these trees survive?

My wife and I spent a week in Sydney, Australia over the Christmas holidays after a cruise from Singapore (visited some fabulous botanical gardens along the way, by the way). We stayed in the Rocks area of Sydney, which is the oldest part of downtown Sydney, where a large number of street trees were doing quite well despite the fact that they were surrounded by concrete. Indeed, the 4ft x 4ft area around the base of the tree that appeared to be open to the elements was, upon closer inspection, covered by small pebbles in a masonry mix.

Everyone is aware that covering trees with an impermeable cover will greatly reduce water and gas exchange through the air/soil interface. Most folks would then argue that doing something like this will assuredly kill said tree in the not too distant future. So, how are trees able to exist when the soil they are planted in is covered in concrete? Before someone mentions that this must be an Australian phenomenon, this same (or similar) situation exists with street trees throughout large cities in the U.S.

Curious minds want to know.

The concrete is simply mulch.

Al

And some trees, normally swamp dwellers, can survive with very little oxygen at the root level. There is a pecan at a dairy whip near where I live that has asphalt right up to the trunk--no open soil for at least forty feet and not even much of it there. But the tree is located in a river valley near many gravel mines and a very high water table. Perhaps the combination of gravelly soil (beneath the asphalt) and ample water have achieved a functional balance. I have been watching this tree for fifteen plus years, expecting to see some signs of stress, but haven't yet.

Scott

I understand that asphalt breathes to some small degree. The Saint Louis Botanical Garden's parking lot is cleverly paved with bricks with liberal holes to accomodate the excellent trees growing under it.

My theory is that those trees' roots are spead far, much like they would be in an open setting, but with high congregation of fine roots around (and probably increasing the size of) small cracks and joints in the concrete. Every crack in the sidewalk is a potential oxygen source... as well as sewer, raised flower beds, basements, etc.

I am digging a bed along the sidewalk in my front yard, and have encountered the two types of tree roots that I expect from my property: Sycamore and Locust. Yesterday, however, I found cherry roots from the neighbor's tree across the street, which is a good distance away. I think we just don't give these amazing creatures the credit they deserve.
K. James

Excellent question.

I'd ask if Copperbaron took any pictures! That would make for a great essay here, and some vigorous discussion/interpretation. I'll lend some experiential speculation.

If the trees mentioned (by any of the above posts) have some age to them (oh, say, 10 years or more, and caliper above 10-12" which is 25-30 cm give or take), would you speculate that the tree came first, and then the current paving, or did the tree reach its current size with exactly the same circumstances that you see today?

Many street (or urban) trees had some better conditions getting started, and have tolerated the later manifestations of improvements to human comfort. So, the pecan that Decumbent mentions may have had a much more generous soil/lawn area that gradually was eaten up by increased paving desires. There are innumerable instances of these at Louisville Metro Parks, though they decrease annually as trees succumb to the less than favorable air/moisture infiltration and are further negatively impacted by rapid runoff of unnatural substances (like oil, gas, road salts) and unnatural impacts of automobiles. Some species last longer than others (Ulmus, Fraxinus) and some die really fast (Acer, Liriodendron).

More modern instances of installation in pavement sometimes include the manufactured or structural soil solution, where larger aggregates are included to provide support to paving above while providing an aerated soil matrix for root growth. I've not come across any planting scheme with NO allowance for air/moisture penetration from the surface. Usually, if the condition appears impermeable, there still is some kind of porosity to the application. Alternatively, there are contrived situations "piping" in air/moisture to root zones beneath pavement. Expensive, but true, like hot water piped to thaw walks and drives in cold places. There are many versions of porous concrete and porous asphalt nowadays; this may be the situation Copperbaron relates in Sydney. I will be able to report many more positives about this technology if the coming years. I will be managing a rather large EPA-funded project in Louisville applying emergent technologies in porous paving and natural stormwater management in one of the old Olmsted parks. This promises to be an interesting endeavor.

Got a little OT there, sorry. Faulknerian stream of consciousness and all.

K. James relates one porous parking lot; some other notables are at Morris Arboretum in Philadelphia area; a pretty new one at the Morton Arboretum outside Chicago; and this kind of work is getting to be common in the nearly frost-free south on sandy soils where infiltration has fewer barriers (coastal plain areas, Florida, etc.).

Finally, tree roots are adventitious and adventuresome little beasts! They will follow in the paths of their dead forebears. I mean, a former street tree (now dead) left behind a former root system which decays over time. This leaves organic aerified and sometimes preferentially moist little highways for new tree roots to exploit. The new tree loves this, and moves right on through. This is why you should NEVER plant trees on dams. Root systems will become the downfall of the structure, by creating little erosion pipes by which water will weaken and cause eventual failure. Don't live downstream of one of these.

Got pics, Copperbaron? If not, then get right back Down Under and take some. Please, please....

Yet when my house was graded for a small foundation most of the nearby Ponderosa Pines have slowly perished from root compaction. (No beatle in the bark) The rest are thriving. Trees like people are sensitive ones and tough ones. I have always wondered about trees living in a concrete jungle. Thanks for the input.

Good stuff, Faulkner. (I like it) Excellent point about what came first: 'the concrete or the roots.' Keep us "posted" on the study. Are Betulas not one of the more sensitive to O2 loss in suface roots?

That reminds me, Soferdig.
I'm sure I'm not the only person in here who recalls reading about the ironic and fitting action of soil compaction in the great redwood forests. Roads and impromtu parking lots accomodate heavy vehicles, which dibilitates a section of root system and cooresponding massive aboveground growth. The tree hanging over the very culprit falls down. (Paraphrased Headline):

"Centuries-old redwood crushes parked SUV. Environmental revenge?"

Does anyone happen to know if the capillary path of a Sequoia is in a spiral up the trunk like other evergreens, or is it like most angiosperms, (North roots to north branches)?

K. James

There is also an old pecan tree in a parking lot in my town that has asphalt all the way up to the trunk. I will try to get a picture and post it. The tree and the parking lot has been there all of my life and i'm 26 yrs old. I did notice last summer that the canopy was looking a little thinner than normal, but that could have been wind damage.

Kenton : Way cool I never thought that capillaries would travel in anything but a straight line. The spirals must require less sugars to transport to greater heights. Therefore no dormancy but at end of growth season for evergreens? I see the older needles fall in the fall. BUT WHAT DETERMINES THE LACK OF DORMANCY IN EVERGREEN SPECIES? I know in decidious trees stop making sugars and go dormant. I suspect decidious trees are Democrats. IE sleep for 3 to 6 mos and Evergreens are Republicans working all the time. HA HA.

The hard-working Labour party evergreens can adapt to a short warm season by continuing to photosynthesize in the winter sun, although at a greatly reduced rate. But Tory party deciduous trees find that working in the winter is too demanding, and elect to retire to their roots to sip tea during the cold winter months.

If one was to chop a 90 degree quadrant of the roots off of the average living gymnosperm, (a 25% slice of the root-pie) there would be a "spiral of death" up the tree, in the branches that fed to and fed from those roots. Some species go clockwise, others counter. I think it is Betula. No, Fraxinus? Someone help me. One of these trees has a capillary system at a complete 180 twist. -Damage the North Roots, goodbye South branches.

Then there are those novel Taxodium, Metasequoia, and Larix. My kind of tree: Pretending to be round-season workers in all their delicate lazy elegance.

Weren't you going to the last American frontier, Soferdig, or have you already?
K. James.

That is facinating. I have made it to Kodiak and they even have access to the internet. I have to sit here on the 2nd floor and look out at a rocky beach across the water to the waves pounding on the beach. The eagles are everywhere here, like seagulls in Seattle. Lots of Snow on the mountains around here but none down here in town. Quite a beautiful place. I'm on dial up so can't send pictures.

Hi Sofersogood:

OK, DG community. Let's help out our poor fellow who's stranded on the Alaska island and can't send pictures to rub it in. Hours from civilization, surrounded only by grizzlies and baldies for companionship...maybe a stray salmon or halibut, or seal lion. I bet there's a few lounging down by the docks?

Does it look anything like this, perchance?

Can you make the pictures smaller to send via dail-up?

Yes, open them and resize them to about 200K and you'll be able to do it. No one has a more miserable, pathetic, Neanderthal connection than I do, but I can upload pics on this forum.

Guy S.

Ok I'm going to try and show you how difficult it is here on Kodiak. Today I walked on a beach with the whitest sand surrounded by beautiful rock strewn beach. There were sealions and eagles everywhere. Not a bad way to spend the early afternoon on a walk.
Good picture of ferry dock, loading dock for container shipping. Oh yeah a few sealions basking in the foreground.

My view out the house to the rocks beyond.

sofer, is this some penance, purgatory, or punishment for showing the VP how to conduct himself in an "old boy" quail shoot? ken

I miss your drift other than I don't feel guilty.

He he he...

OK I bite, how do you send from 2 sites? Is one of your computers from Presque Isle and the other one from Colo. By the way Presque Isle is in Michigan. I used to be a michigander. We claim the most beautiful spot in Superior.

I'm afraid I don't catch your drift! Oh, you have pictures on a computer at which you do not currently sit? Heavens, I have no idea.
K. James

I'm getting a ken on both JamesCo Colorado and kandlmidd Presque Isle when you respond to my comments.

a common name among handsome men. The "progressive" state of WI also has a presque isle ( frog for "almost an island" ) named by some very confused early fur traders.

I was confused thank you for clarifying. Now I know a Libertarian in Wisconsin! You must be quite alone in that state. I thought the other Ken was a republican. Hello other ken. Your responses in the blog are similar. Where is Presque Isle WI? Is it in the Apostle Islands? Steve

This message was edited Feb 13, 2006 4:40 PM

I think you're still condused.
(Kenton) James

I am afraid that one of those "republican" seals made off with our MT trees & shrubs man. That's what happens when you venture out from the home 40. Anyone seen the Ohio duo lately?

I'm still here trying to catch fish in the snow. I actually had to work today. We publicans feel guilty when we goof off for 2 months. I needed a fix to get some capital moving. The GNP is dropping every day I don't work. Then what would Wisconsin do if I didn't have large taxable income. We know they need their cheese supports. The nice thing about working in Alaska is there isn't much to do when the fleet isn't in town. Well thought I'd send a photo of todays catch.

Hijack of the year!

Here's the picture I promised of the old pecan tree growing in the parking lot. It has a few dings on it.

Why would a pecan suffer parked in a parking lot when it has Jesus looking over it!

Scott

If you don't get that, look at the license plate of the car. I will take a picture of my local parking lot pecan. It's situation is even worse than that one.

I am looking at that bed next door to the Pecan, and all those pavement cracks. I'll bet the soil is completely laced with fine hairs in that planter.

We're all impervious to things as charming as asphalt with Jesus watching over us.
K. James

I'm sure Kenton you saw the Jesus plate on the car. We know that the pecan is pulling nitrogen out of the hydrocarbons in the asphalt. Along with the urine all the dogs in the neighborhood deposit on the only tree in the neighborhood. "He who marks higher is the ruler" If only we humans would learn this lesson we would not need big expensive houses.

James, that planter that you were talking about has crape myrtles growing in it. That seems to be all that they know how to plant in my town. They keep bragging about how they are planting more trees because of the ones lost to hurricane Ivan. Crape myrtles are pretty shrubs but they cannot take the place of a large oaks lining a street. If that city arbor board only knew what I thought about them. LOL

Let them know- they won't listen, but it gives your credibility a higher mark up the tree, eh? Our town planted hordes of Fraxinus sp. 'Autumn Purple.' Pretty and all, they are attracting the boreres like mad. The city is beginning to encourage Bur oak, which is great. There are saplings on a noticable scale.

Down with Monoculture!

Up with Private decision making! (For tree diversity)

(For you, soferdig:) Up with small houses! -more room for trees.

K. James.

We need to start to change society by teaching young males how to "Mark territority" so they can spend their lives gardening not climbing the ladder to success. The only problem would be the trees and fire hydrants outside of bars.
When I lived in Bellevue WA and the city was growing they were planting all kinds of Maples that were all the same so I decided to transplant the trees. I replaced them with Styrax Japonica, Japanese Maple, and a European Hornbeam. They kept them like they didn't know what was planted there in the first place. I was bad! I know that certain trees don't like emissions but all of these seem to be thriving even today. 20+ years later.