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The largest root of this street tree in Marrickville has been severed.

The largest root of this street tree in Marrickville has been severed.

By accident I came across this Letter to the Editor in the Adelaide Advertiser written on Tuesday 23rd April 1901.

It makes for very interesting reading if you are interested in history as well as soil, footpaths & trees as I have become.  What makes this letter especially worthy is that 112-years has passed; yet we still encounter the same problems & the same attitudes towards trees & tree roots.


To the Editor.

Sir.  For many years it has been an article of municipal creed that the cracks in tar-paved and tar-dressed footpaths are due solely to the roots of trees, and untold numbers of the trees on or along such footpaths have fallen victims to this belief.

For several years, distinguished by great drought, I have collected observations on this subject, especially during the present season, and I have arrived at the conclusion that, excepting a single species in common use, the trees and their roots have nothing or very little to do with the cracking of the tar-paving or tar-dressing, that is, directly and indirectly, no more than gas or water pipes or any extended resisting object near the surface.

The real cause is, on the contrary, to be found in the physical properties of the soil and the material employed, and this is so obvious now that anyone who cares to see may do so on his way to and from town.

Let me explain first the physical properties of materials.  The soil is largely or chiefly made up or clay.  Now, clay expands and swells when wet, more when warm and moist, than when cold and moist and contracts when drying in the opposite way.  Cracks are then found wherever there is least cohesion.  Straws, dry rootlets, pieces of wire, in fact anything notchy, operates in the same way.  The materials used for tar paving form, on the other hand, a kind of sandstone more or less impervious to moisture. Consequently they form a rigid implastic sheet, entirely subject to contraction by cold, expansion by heat, and in direct proportion to the variation of temperature, viz., from near freezing point to near 200°F.

The difference in length with the great extension is, therefore, many inches, perhaps some feet, between kerbing and kerbing. What are the results? Nay, what must they be? Such footpaths are formed usually when the surface of the ground is moist.  In this state it is leveled and compressed, and the soft, plastic material spread over and leveled by  heavy rollers.  As soon as the tar-sandstone sets it becomes a rigid mass, pressing against the kerbing along one side and both ends, and on the other side against the walls, fences, or merely the soil of the opposite side, and in all cases has to overcome, in its diurnal and seasonal motion, the friction between the surface covering and the soil, but it must move somewhere, and does with irresistible force.  It occurs in this way between the two forces acting on it.

As the clay yields in drying beneath the impervious surface, the latter is depressed and forced down upon it, and slight depressions are formed where the soil is softest-the surface becomes puckered as it were.   By the longitudinal strain slight transverse bulges are formed, by the transverse strains between kerbing and walls each in the longitudinal direction.  Wherever any pipe, board, wire within a few inches of the surface, occurs there is an extended obstruction to compression.

At that place an elevation will remain, and consequently, upward bulging is promoted so long as the surface remains plastic to some extent and the ground beneath firm.  As the heat and drought increase the bulges become larger, but the clay soil beneath gradually becomes dry, and the traffic above, be it vehicle or human feet, forces the surface covering down upon contracting clay, pulverising it, while the now rigidly-set tar-paving expands and contracts daily more and more.  In its motions the bulges are raised by the strains and compressed by the tread of the passengers until they crack at the weakest spots to relieve the former.

Later on the rains set in, the clay soil swells with the moisture imbibed from the ground alongside, or ground and water tables, for moisture must diffuse equally below, and a difference of distance only means a difference in time.  The ground not only slips below the rigidly-sat paving or dressing (this the cause of it always being found as loose rubble beneath separated pieces), but also swells most at the bulges, thus exaggerating constantly the elevated spots, these being places of least resistance.  The foundation being gone after some time, and the material weak and unyielding in itself, the latter become broken up, and kicked aside by the passers-by.

That this is the true explanation, and that the roots of trees are only very indirect causes, one may see most plainly where the tar-paving, crosses bridges and culverts, as in Pirie street, Kent Town, where it is cracked and destroyed, just in the selfsame way as elsewhere, without the possibility of “roots” thicker than a cord being present.

If such are supposed to cause the cracks it supposes a magical and superstitious power in them indeed!

The above illustrates again the saying of one of our writers, that the generally accepted theories are usually those requiring revision most urgently and it is hoped that in future the trees and shrubs will be spared destruction and ill-treatment for damage of which they are wholly innocent.

The fig trees, which furnished the excuse at first, possess the quality of many trees habitually growing in wet or flood-exposed localities, of raising themselves on their trunk-roots above the wet surface.  As such are of course, wholly unfit for street or garden planting, but eminently suited for the park lands, where, however, they are rarely found, thanks to the wisdom of the ruling powers.

However, of whatever kind, the green foliage of trees and shrubs is probably of far more important than all the footpaths put together for town and country in general, on account of the cooling, air-purifying, and soil-disinfecting properties which it possesses and exercises, not withstanding the superstitious beliefs to the contrary.

J.G.O.T. Norwood,  April 20, 1901.


This was the Council Meeting.  All Councillors present. The following is how I understood the meeting & all mistakes are mine.

Smoke Free Outdoor environments in Marrickville – This was for the Marrickville LGA & included no smoking in all outdoor areas, dining, public footpaths, sports grounds & fields, at a Council owned buildings, within 10 metres of a Council owned building or a children’s playground, including parks or a bus stop or at any Council outdoor event/function. Recommended to be released for community consultation until 28th February 2011.

A resident & representative of the NSW Cancer Council spoke about the health statistics of second-hand smoke.  Clr Phillips supported the motion saying the more Council discourages smoking, the more people will stop smoking.  Clr Thanos was against the motion saying he supported the right of people to choose. He thought “a blanket ban was dumb & stopping people smoking in a park was ludicrous.” He said smokers have rights reminding that it is legal to smoke. He said there was no one to police this.  Clr Wright supported the motion saying smokers are impacting on the health of others & the policy will make people change.

Clr Hanna said that despite the report saying so, no one had contacted the Marrickville Chamber of Commerce or the restaurants listed. He said there should be freedom for everyone.  Clr Olive said he had concerns about ability to police  & no smoking in outdoor areas is a problem.

Clr Tsardoulias supported the motion saying he has seen it work in Singapore. Clr Macri thought 50% introduction was better & that it would alienate café owners.  Clr Iskandar spoke about the cost of smoking on the health system. He also said every smoker throws their butts that land in the Cooks River. Mayor Byrne thought education was better than an impost. Carried.  Against Clr Thanos, Hanna, Macri & Olive.

Notice of motion to remove a street tree outside 104 Windsor Road Dulwich Hill – Council staff assessed the damage & the tree & said it was unlikely

Showing the crack opposite the street tree

that the tree caused the damage to the fence at the front of the property. Council refused the application to remove the tree. Behind the 500 mm high brick fence the yard is a 350mm high raised garden bed with a 2 metre Callistemon & low plants.

The owner spoke saying that the street tree had caused a crack to his brick fence. He wanted the tree removed & replaced with a “less invasive version.”  Clr Thanos said Council should remove the tree because of the distress it is causing the resident. He said the tree will cause more damage & that the staff report was not helpful. Clr Olive did not support the motion saying that while the distress of the resident is important, the report said there was minor cracking. He said the crack can be re-pointed & doesn’t justify removing a tree valued at $1,500.

The closest street tree is the one that was requested to be removed. The dark patch in the pavement shows where Council dug up the footpath to examine the roots

Clr Tsardoulias said that the photos of the footpath tell him that the tree is affecting the fence & that street trees are affecting the whole estate & endangering people’s property. He supported the motion.

Clr Peters said she sympathized with the resident, but noted that the there is extensive cracking all down the street. She spoke about movement with clay soils. She did not support the motion. Mayor Byrne said it was wrong to let street trees ruin people’s homes. She said staff would have seen the roots & that the dirt behind the wall makes it lean out & the crack is pressure from below cracking up. She said the Councillors should support the removal of this tree & replace with an appropriate tree.  Clr Hanna said 47 trees were removed for the Enmore pool, but we can’t remove a street tree & “Trees are a written asset, not a real asset.”

First vote was on Clr Thanos’ motion to remove the tree. In favour: Clrs Thanos, Hanna, Macri, Byrne & Tsardoulias. Against: Clrs O’Sullivan, Wright, Olive, Peters, Phillips, Iskandar & Kontellis. Motion failed. Then the vote was on the staff recommendation to retain the tree. All Councillors voted for this except for Clrs Macri, Hanna, Thanos & Tsardoulias.


Community tree preservation groups Save Our Figs Wauchope & Save Our Figs Group have a big fight on their hands with Port Macquarie-Hastings Council who intend to remove 13 Fig trees in the town centre “to prevent future damage to private property & public infrastructure.” The roots of the Fig trees are presenting a trip hazard & 3 residents have complained of damage to their property they say was caused by the trees.

These 2 massive Figs next to Marrickville Youth Resources Centre enhance the building & the area.

Thing is, the Council have just completed major works on the streets with the trees described as the centerpiece.  Importantly, 3 years ago the community fought to retain these trees & won.

Now the threat of litigation has reared its head & if history is anything to go by, a very small number of people are going to get their way & have the trees removed.  Council can’t take the risk that people will start litigation in the future.

A couple of days ago I posted that Goondiwindi Regional Council chopped down healthy Fig trees despite community opposition.  It’s the same story.  Now that the trees are gone, the Council has made the decision to spend $96,000 on floating footpaths.  They are doing this now because they, “understand how important these trees are to residents.”

Using floating footpaths means the trees can grow normally. There is no need to cut off or shave down roots, nor cover them in bitumen.  Nor will they need to chop the trees down because of a trip hazard or damage to footpaths. Seems like sensible spending to me.  Given that any large healthy tree can be worth around $100,000, spending money to keep them is a good economic decision.

This Fig is literally holding the building up. There is no visible damage to the exterior of the building

The large street trees in the centre of both these towns are what bring beauty & a sense of place. The towns use their street trees as a tourist draw card.  The Fig trees also provide a tangible history & are held dear by most of the community.

Take the trees away & you have substantially changed a place. Not only have you removed things that are worth a great deal of money & with 13 Figs we are talking in excess of a million dollars, but their loss will have an impact on spending in the shops. Researchers have concluded 11% more money is spent in shopping areas where there are big healthy shady trees.  To their credit Port Macquarie-Hastings Council plans to replace the Figs with 11 advanced Brush Box trees.

My question is why don’t Councils or organizations take pre-emptive action on their big trees when the trees are in areas that could damage property or cause trip hazards?  Ultimately it is worth the financial outlay when one considers how much these trees are worth in a monetary sense. Then there are all the other factors to take into consideration, history, place, future, community cohesion (fights like these in small towns could escalate into severe divisions), trust in the Council/organisation & stating the obvious, climate change.

These roots have infiltrated a parking area. I found it interesting is to see that the roots didn't travel far from the tree despite its size. It has been like this for years & the tree is still healthy even though cars park on the roots, proving it is unnecessary to remove a tree when this happens. It might look unsightly, but the tree itself is gorgeous.

Root barriers can be put in place.  Sewerage & water pipes can be replaced with pipes that can’t be invaded by tree roots or re-routed & be done with the problem forever. In Canada, they use a system that allows pipes to be replaced without digging, disturbing or damaging tree roots. They use a water flushing vacuum system to remove the soil from around the roots, pipes or wires, then install the new pipes & put the soil back in.

You don’t even need to put in concrete foundations near a tree when you are building anymore.  Again in Canada, they insert giant steel screw piles into the ground that are just as stable as concrete foundations & require no digging.

There is also a high-density plastic grid system that I have seen used in Sydney.  Once laid over the ground the grid disperses the weight of vehicles over a larger area. The grid also prevents soil compaction, which can damage roots.  Best of all, the grid allows rainwater to permeate the soil, reducing the need for irrigation & improves storm-water management. Ground cover or other plants can be grown in the spaces within the grid.

The grid also prevents soil erosion. I can see these grids used to support riverbanks & to create cement-free car parks. They could also be used to channel water into the ground near a street tree rather than be wasted by pouring down drains.  There is no reason why a section of the gutter cannot be a grid.

There is also porous concrete used across City of Sydney & North Sydney Councils.  Porous concrete provides a seamless surface allowing people to walk across it, but still captures any rainwater that falls on it, watering the tree.

There are quite a number of beautiful Figs in Marrickville LGA & many of them are planted near buildings. Unfortunately many of these trees live in less than perfect conditions with cement & bitumen almost to the base of their trunk. Many have cars & trucks parked right next to them. As we have seen, it is only a matter of time before branches get gouged or broken off by trucks.

Canary Island Palms line Graham Avenue Marrickville. I hope these trees are heritage protected.

The only reason why money isn’t spent on protecting trees before problems start is that trees are not held in high importance or the Council is so strapped for money that understandably, urban forest issues get moved down the list of priorities.

Many Councils do hold their trees in high esteem & look after them. They use floating footpaths & permeable rubber surfaces or permeable ‘solid’ surfaces. They put garden beds around trees to prevent or limit the amount of vehicles that can park under them. They put ‘no parking’ signs for vehicles over a certain size & weight & they do other things like prune dead branches & normal die back. They probably feed them occasionally as well.

I would do all of the above & if property damage occurred with people saying get rid of the tree/s, I would think it is the community’s & Council’s best interest to fix the damage (within reason, once proof & access has been given to Council) & put things in place to ensure the problem won’t repeat itself.  Too many people & future generations miss out for cracks to walls & pipes, both which are easily fixed without costing as high as the value of losing a tree.

Trees are the only things Councils own that increase in value each year.

I have written about clay soils & how they affect buildings at –

You can read both stories at the following links –

I was invited by Marrickville Greens to go to watch the magnificent Lemon Scented Gum street tree in Cambridge Street Stanmore being chopped down by Marrickville Council.  For various reasons I declined, but I know I did not want this image imprinted on my memory.  I have come to love this tree & I am distressed about its loss.  To me, it was no ordinary street tree.

Marrickville LGA has some gorgeous trees, mostly in parks, though there are also good ones that are street trees.  However, we have thousands of butchered, stumpy & not good-looking street trees all over the LGA & it is noticeable if you look.

I think many of us have become desensitised to the ugliness of our street trees because their disintegration happens over time & we just get used to seeing them in this poor condition.  Leave the LGA & you immediately notice the differences.

This magnificent street tree is gone

The Lemon Scented Gum in Cambridge Street Stanmore was one of the better-looking street trees in the whole LGA & this is not an exaggeration.  Do I think this because I like Gums?  Yes & no.  I do like Gum trees, but I also like most other trees.  I am an all-round tree lover though I admit to preferring tall stature trees & especially trees which flower & provide food for insects, birds & animals.

I think it is necessary in an urban environment to think about wildlife when choosing trees to plant.  I also think we have a duty to provide food for these creatures who are losing more & more food resources every year.  If you don’t believe me, put out a birdbath in a safe place in your garden & watch how long it takes for birds to arrive.  They are short of water as well.  When we built a fishpond, the rare frogs of the area arrived within 2 days & there wasn’t other ponds around.  Where did they come from, we wondered.  If you plant flowering trees & shrubs that feed birds, they will come in droves & the air will be filled with birdcalls.

So for a tree of this magnitude to be cut down seems ridiculous to me.  The tree provided refuge for both wildlife & humans because it was a flowering native tree & its canopy significantly cooled the air in the street.  This is not a feeling I am used to when I walk the streets of my local area.  Mostly I cannot walk during the day because the streets are so hot with the heat reflected by the road & concrete.  I believe that as temperatures rise due to global warming, the heat island effect is going to get worse & we are going to bake.  City of Sydney Council recognises this & intends to plant 10,000 more trees in the CBD this year to counteract the heat.

I am aware the residents who wanted the tree removed said it was causing cracking to their house & Council felt hamstrung because of the potential of litigation.  However, because we do not have a Significant Tree Register, our public trees are vulnerable.  Cracking to houses can always be repaired & it is something we should expect when we live in 100 year old houses, which are built on clay soils & with poor quality mortar.  In fact, even renovated houses in the Inner West need regular work as they are always deteriorating.  It comes with the territory. That’s why many people prefer to live in modern units or project homes that are built on cement slabs.  As a norm, tree roots are not strong enough to lift a concrete slab.

Ordinary street in Chatswood with multiple large street trees- a very different outlook to our LGA

When we respect trees & fully appreciate their positive impact on our lives &  vital role in our civilization’s existence, if atmospheric levels of CO2 continue to rise as expected, then we will do everything we can to keep our mature trees that sequester large amounts of CO2.

The removal of this tree affects the whole community, not just the residents of Cambridge Street.  First is it one tree, then another tree & so on.  Before we know it, the whole streetscape is changed & not for the better.  It took 40 years for that tree to grow a 2.5 metre girth & it had at least another 60 years of life left in it.  Eucalypts often live 100 years or more.  All it took was 4 ½ hours for it to be gone.

The Marrickville Greens tried to get a stay of execution to try other methods to repair the cracking & fix the problem at ground level. The Labor & Independent Councillors had to power to grant this so that amelioration could be tried to give the tree a chance to be saved.  I would have conceded defeat if all avenues had been tried & agreed the tree needed be removed, but these avenues weren’t given a chance.   I am sure the Greens feel the same as I do.  This tree was also worth a lot of money to the community & especially to Cambridge Street.  Better to sell a house before a tree is cut down than after.

Our tree assets get voted out because of concrete, their particular species, because they are old, because, because, because.  I have not yet seen tree saving strategies voted in during council meetings, only the opposite.  Trees are seen as a nuisance & a liability.  The reality is: not having trees is a liability.

I will work with Labor & the Independents as well as the Greens if they are pro-trees & the greening of Marrickville LGA.  However, since I have started, I have noticed that support for my vision comes from the Greens & not from Labor or the Independents.  To be fair, Labor did reverse their decision over the Mackey Park Figs, but not until after a community protest of 300 people & an even larger petition.

Once again, regarding the Cambridge Street tree, the Greens voted to keep the tree.  Once again, the vote to remove the tree comes from the other counsellors.  Is it a pattern? Saving Our Trees hasn’t been alive long enough to be able to answer this question.

Frankly I was shocked when I read on the Greens website that:  Independent Councillor Dimitrios Thanos recently emailed Councillors & staff saying: “I’ll grab my chainsaw & meet the staff down there on the appointed day.” I just know he & I are not on the same page when it comes to trees.

Getting back to my intro, I didn’t want to go & watch the ‘Elle McPherson of trees’ be chopped down, but the Marrickville Greens did witness this.  You can read their posts about this tree –’s-biggest-eucalypt-to-the-chainsaw/ & you can also view 2 photos taken today by the Greens at – & &

The Cambridge Street Stanmore Lemon Scented Gum tree is going to be chopped down soon.  I feel very sad about this.  During the Council meeting to decide the fate of this tree, the people who wanted this tree removed spoke about a large branch that fell on the street needing 2 people to carry it away.  The danger the tree posed from falling branches would have been one of the major factors why their request was granted.

Gum street tree in Petersham - 2 Currawongs have a nest in this tree

Gums trees do drop dead branches as a normal feature of their species.  Unfortunately, I think this is the reason why Marrickville Council appears not to not regard Eucalypts favourably.  Then include the fact that they grow tall & have a significant canopy.  In comparison to the usual street trees Council plants, Eucalypts are an anomaly.  I would guess the Gums are left over from the 1970s & before.

Suburbs like Petersham which have a lot of Eucalypts as street trees look fabulous as a result.  Everyone I have spoken to in this area always mentions the trees, most saying they were a major reason why they chose to buy in Petersham.  However, the Cambridge Street issue is likely to repeat itself for two reasons unless these are managed.

Firstly, building movement that causes cracking.  The Inner West is mostly clay soils & when there is drought (we have had a long one which is still continuing) the clay soils shrink. This results in movement of buildings & cracks to the walls, porches & paths, especially as most of the housing is 100 years old & the mortar used then was of very poor quality.

Roots of mature trees would have stopped growing years, perhaps decades ago. Often the tree has nothing to do with movement.  Arborists constantly have differing opinions about the impact of tree roots on house foundations.  Personally, I think it is too easy to blame the tree.

This Gum street tree in Brighton St Petersham deserves a medal for surviving pruning by Energy Australia for power lines

Even buildings that do not have a street tree out front can suffer from movement & cracking, especially during drought.  If your property is built on clay soil, removing most or all the trees on or around your property is unlikely to prevent further house movement.  It is a fact of life in the Inner West.

To minimize cracking to your house during drought, you need to water thoroughly along the exterior walls on a regular basis.  If you keep the soil moist, the clay will not shrink & your foundations are less likely to move.  Many people have concreted their yards, so they will definitely have house movement & cracking, drought or no drought.  If you already have cracking, you can assist by watering around the building to get the moisture back into the soil.  Our front door, which had started sticking, returned to normal 2 months after I recommenced watering our front garden.  I have written more fully about clay soils in the following post –

Managing dry clay soils does take time & patience.

Secondly, Eucalypts develop dead branches, which they shed as a normal feature of their development.  This does not make the species dangerous.  The process of the branch dying off until it eventually drops is not a quick one.  I have been watching trees with dead branches for 12 months now.  (It’s been one of my ‘must do posts’ which hasn’t happened until now.)  However, Gums are called ‘widow makers’ for a reason. A falling branch can kill a person if they drop on their head, but then again, so can most things that drop from a height.  I was young when I first heard the term ‘widow maker’ & I remember being told the following with much laughter:

The tree branch is dying over many months, sometimes years.  The wife asks the husband to do something about it.  Time moves on.  She nags & nags, but he watches footy & says he will prune the branch later.  Then, one day when he is mowing or something, the dirty big branch falls on his head & the wife is left a widow. The moral of the story is that men should do what their wife asks when she asks it to be done, husbands are lazy & her nagging is warranted.

Maybe you had to be there & times have changed.  The story made a big impact on me because ever since I have a keen eye to notice these branches.

This tree cnr Illawarra & Addison Rds has multiple dead branches. 3 other Gums further down towards Marrickville Rd also have dead branches

Whether or not Council should be responsible for checking trees for dying branches is not something I have an opinion about.  However, I do think we see the street trees in our neighbourhood almost daily & if we notice a tree branch is dying, a quick call or e-mail to Council should have the branch pruned before it becomes a problem & drops.

If we leave it until the branch drops, Council is likely to say the tree is dangerous & needs to be removed.  Then the community suffers another loss of a tree & eventually we lose all remaining Eucalypts & other tall trees.  Our suburbs suffer as a result because we lose the beauty that tall trees offer.  We also lose out on property values because great street trees have a surprising positive impact on local property values.

The street trees near our homes, especially the large ones, remove pollution & particulate matter which causes breathing problems.  They collect CO2 & emit oxygen making the air cleaner & cooler.  They lower temperature which helps lower our power bills, they slow down traffic, make the footpaths safer for pedestrians & generally make people feel happier.  I have written more about the value of trees in the page 100 Tree Facts, which can be located on the left hand column of this site near the top.

Lastly, if Sydney’s North Shore can have hundreds of thousands of Eucalypts as street trees, why can’t Marrickville LGA?  Let’s look after & keep the ones we have left.  They are necessary for our wildlife.

What concerns me about the removal of  street trees when they have been accused of causing damage to property is the following:

  1. We have just experienced a long & protracted drought & more than 3/4s of NSW is still regarded as drought-affected.  The long-range weather forecasters say we have entered into another phase of drought. The Inner West has been affected, as has the whole of the Sydney metropolitan region.  This drought has resulted in severe water restrictions & this has affected our soils to a great degree.  Trees are stressed & quite a few have died within our local LGA.  Many of the saplings Council plants do not survive the summer because they are not watered.  This must result in significant financial loss to Council.
  2. Even though we had quite a bit of rain over winter, we are still on water restrictions.  The park trees were able to capture much of the water when it rained, but our street trees have only a slight chance at getting a proper drink.  Most of the street trees in our LGA have been given very little ability to capture rain water or storm water run-off.  Most have a small opening left open amidst the cement or

    Newtown street tree

    bitumen. I have only seen 4-5 street trees planted in cement where I feel they have been given adequate soil space around them to give them a fighting chance to capture rainwater.  Two were in a back street of Newtown & I doubt Council did this, as the kerb had been removed.  Both these trees had a lot of soil around their trunk.  The other example is new plantings bordered by raised brickwork on Unwins Bridge Road Tempe.  I think it would be wonderful if all our street trees that are in cemented areas could be planted in this way.  I would also very much like to see Council give funding for the watering of young street trees as they do in other Councils.

  3. Much of the Inner West is built on clay soils.  Clay soils are quite volatile as they shrink when they do not get sufficient water & expand when there is too much water.  Both these extremes affect the foundations of buildings & footpaths.  The term Seasonal Fluctuations describes the normal variations of the moisture content of clay soils through the seasons.  When clay soil gets a lot of water it is called Field Capacity.  When the soil is dry due to evaporation, heat  & lack of rain during drought it is called Desiccated & suffering from Soil Moisture Deficit.  If a drought is lengthy & the soil does not return to Field Capacity after some rain & then enters into another dry period, it is called Persistent or Permanent Moisture Deficit.  This is likely to have already occurred in the Inner West or will do during the next period of drought in which we are now entering.
  4. Soil movements cause what is termed Subsistence & Heave.  With Subsistence, the soil moves downwards.  With Heave, there is an upwards or lateral move of building foundations or footpaths.  While the clay soils go through Seasonal Fluctuations foundations of buildings don’t move much, though that depends on how much clay soil is directly under the foundations.  When the clay soil suffers from Persistent Moisture Deficit, foundations of buildings move & walls start to show cracks, paint peels & doors & windows are suddenly off balance.  Just last week our front door over night became hard to open & stiff on its swing.  It is recommended that you don’t fill in the cracks or shave wood off door or window surrounds when the ground is dry, but wait until the soils have returned to normal moisture content before doing repairs.  Most times the doors & windows will realign & the cracks will come closer together though paint work will need repairing.  If you do fill cracks while the soil is dry, the space will not be available for the building to move back into place & new cracks will appear, generally on the other side of the building.
  5. The experts suggest occasional watering of the exterior of the house as this will help keep the clay soil moist so that your foundations don’t move during a drought.  In my case, I have been keeping the water up to the back garden, but to save water, I have left the front garden manage as best it can.  Here is the reason why our front door has moved. Also, it is our hallway & the front room that are suffering the cracks & peeling paint.
  6. My research has shown that trees can increase the seasonal movements of clay soil, however, engineers also stress there are too many factors to consider before one blames the presence of a tree for causing the damage.  One of the problems is, if a mature tree is removed, this has a major impact on clay soil moisture & the property can actually sustain more damage as the soil fills with water & starts a process of Heave.  It is hard to stop Heave because there is no longer a tree to be taking up the excess water.  Because it is so difficult to categorically say that tree roots cause damage even if the roots do go towards & under the house, many engineers recommend using water to restore the water levels to clay soils rather than removing the tree.  I have read that a tree is not able to lift a house because of the weight of the house. A footpath is a different story.

Trees ... we need them

There are things we can do to minimize or prevent further cracking or movement of buildings which do not involve removing trees.  According to eminent scientists, we have entered a dangerous period of existence with CO2 levels actually threatening life on this planet.  All agree on the supreme value of trees.

Just today in Copenhagen, the Food & Agriculture Organisation of the United Nations & Brazil’s National Institute for Space Research signed an agreement to work together in the field of emissions measuring and reporting by monitoring forests & calculating CO2 sequestration.  Essentially they are going to map & monitor the green canopy of forests of the world.  This clearly demonstrates the value of trees in dealing with climate change.  We should only be removing them after all options have been exhausted.



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