Alison AplinWhy are trees falling during storms?

As an avid tree lover, and even hugger, it disappoints me to see news broadcasts showing trees that have toppled during yet another major storm. And I have real concerns about what I am seeing with the root mass of these trees.

ANC News 16 October 2016

This tree has a thick trunk with a diameter of at least 1 metre, from what can be seen. So the visible root system is pathetic for the dimension of the above ground trunk and canopy. All of the lateral, anchoring roots appear to have disintegrated, leaving the tree vulnerable to wind damage with the likelihood of toppling in high wind.

I am becoming, in my travels, increasingly aware of road widening or even sealing of roads where verge trees have had their lateral roots trimmed to accommodate the new carriageway. Too often, it can be seen that not only have these lateral roots been cut, but that at least 50 to 60cm of soil has been heaped up at the base of the trees; soil from the road base that has been removed and then dumped on the sides of the road at the base of trees while not being removed from the site.

These practices are fraught with problems later on. The build up of soil will eventually kill the tree – it is a fact. It also weakens the tree as it goes through the death throes, making it susceptible to falling over. And with the associated problem of having one side of the tree’s roots severed, this tree, among often many, will fall.

There is an Australian Standard for determining the Tree Protection Zone (TPZ) around trees to remain in situ, with development occurring around them. This standard was developed in 2009 with the intention of preserving the integrity of trees within construction zones. I firmly believe that these standards are possibly now being ignored or are inadequate. Or the bad practice was effected prior to 2009, and we are only now seeing the results of this bad practice.

Dumping of soil at the base of trees during road widening is not being controlled properly. There are supposed to be overseers of these practices to eliminate this sort of future problem. Is this a potential litigation issue, with the wild winds being blamed as a distraction to prevent litigation? When I consider that the top soil is deemed as useless and so is just dumped against the base of trees, when this quality soil could be recycled elsewhere is ridiculous. Quality soil is hard to come by. This top soil has all of the necessary microbes and mycorrhiza essential to a good soil, and is especially suitable for growing natives. So it is worth money if a buyer can be found.

The current formula for measuring the Tree Protection Zone (TPZ) is based on the diameter of the girth at 1.4 metres from the ground. This then gives the protection zone for any development. But I am currently working with a site where a young, fast growing tree has its protection zone less than the external width of the drip line, so I feel that this tree would be in danger of future damage if the TPZ were the ruling theory. The TPZ here, in my opinion, is inadequate.

If this has happened in my experience, it is quite likely that it has occurred with many other arborists, who maybe have not questioned the formula for determining construction at the base of existing trees. And I believe that this may be the cause of many large, magnificent trees falling, with the power of the wind being blamed for the tree falling.

Eucalypts are supposed to have the capacity to sway in high wind. My home is surrounded by massive eucalypts. We get regular intense wind storms and very rarely get any damage to the trees from these winds. As part of my regular maintenance, I check the base of my trees, to ensure that there is not a build-up of debris at the base and to keep their trunks clean to the ground. Sandy topsoil can erode and build up at the base of trees – this needs to be scraped away if this occurs.

I do not believe that it is necessarily the high wind that has caused the problem. I believe that there is a latent problem behind many of the trees falling.

At the time of planting eucalypts, we double stake using hessian ties. I also believe in formative pruning, although there are those who are against this. I have found it to be excellent practice when done properly. Of course mallees do not have their lower growth removed, and trees like Eucalyptus leucoxylon ssp megalocarpa that naturally put out low laterals as stabilisers are also left alone. But trees that naturally produce a central leader can be formative pruned while young.

The ties are removed as soon as possible, to enable the trees to start their natural rocking motion. This is imperative to the long term viability of the tree that they are able to rock. Trees that have been tightly strangled to a single stake for years should just be removed altogether – they will never be any good and will likely fall later on.

So why does a tree topple in high winds? Often the reasons are that:

1) roots have been severed on one side of the tree that are stabilising roots
2) soil has built up at the base of the tree or,
3) there has been incorrect advice about the protection zone of the tree in a construction zone.

Like this post? Why not share it with a friend?


Alison Aplin

About Alison Aplin

Alison is a passionate, multi award winning sustainable landscape designer, Horticulturist and arborist. She has been the owner and designer of 2 Ecotourism gardens that have both won significant awards. Her writing is based on knowledge, empirical learning which is essential to sustainable ethic, and a questioning mind leading to much research. Her articles are often controversial - with a disclaimer that she is responsible for the written matter, and not Garden Drum. A deeply caring person about the natural environment, Alison's writing endeavours to explain why sustainable landscapes are so important. Without people like her, they will be lost and gardens will become merely concrete

16 thoughts on “Why are trees falling during storms?

  1. Prickles on said:

    I’m not a tree expert, but perhaps have a bit more common sense than some ‘supposed’ experts who were employed by my local council to ‘tame’ the plane trees in my regional city street. I have to admit that the trees, planted in 1936, showed some damage – dead branches, etc. – from prolonged drought and did need a little attention.

    Firstly, a deep trench, cutting the roots, was dug about 1.5 metres from the trunk on the gutter side of the trees and a deep root guard inserted to prevent the roots from growing under the footpath and into front yards. Fair enough, I suppose, but surely this compromises the stability of the trees which, on my side of the road, had less support/hold against the strong winds which we receive throughout the year, but particularly in winter.

    Where previously there was no hard surface on the road between the trees, the contractors laid compacted blue metal which was then tarred – right up to the tree trunks. This meant that the trees only had access to moisture through underlying ground water and, in an area which doesn’t have a high rainfall, and the long years of drought, must surely be very depleted.

    It took a small group of residents almost a year of harassing council staff to have the tar removed from an area around the trees to allow water, from either rain or hoses, to reach the roots. Since the depth of material was not great and the compacted material was not loosened, not an ideal solution but better than nothing. I suppose.

    There are a number of streets in town which are planted with plane trees. None of them were subjected to the same brutal and idiotic ‘improvements’ and, boy, does it show!

    • Thank you Pickles for your input.
      There are many more reasons for tree failure than those listed I.e. Inappropriate tree species for the site, consistent with sustainable solutions, overwatering causing root rot or a canopy that is much bigger than the root system caused by overwatering etc.
      It appears, in my opinion, that often the wrong people are being used as advisors – they may have the requisite academic qualifications, but without essential experience, learning about plants and absorbing this information though years of attaining this knowledge, then this is the outcome.
      And when the average person sees trees falling as they are too often doing, it is sending a bad message to these people to avoid growing trees. This is a real disappointment to me as a tree lover and environmentalist.

  2. Kate Wall on said:

    great article! I do hope more people think about the needs of a tree rather than simply assume it will always be there

  3. Judith Baghurst on said:

    Very helpful and informative article. We share the concern. I have a question:
    Where can I buy the hessian ties that you mention for staking trees? We live on a very windy hill and need to stake some eucalypts – eg Eucalyptus caesia
    Thank you.
    Judith Baghurst

    • Hello Judith
      As regional workers we are limited with where to purchase things. Bunnings sell the hessian in rolls. You then cut to size.
      Cut one piece and attach to the extra sturdy stake. Loop this around the trunk and fix the end to the same stake.
      Repeat on the other side, ensuring that the support is firm, not tight. If rubbing of the bark occurs, you may need to tighten them.
      Leave for 12 to 18 months and remove, leaving the ties attached to the stakes in situ. If the tree remains wobbly, then consider retrying one if not both for a while longer.
      If this doesn’t work, cut the tree back all over by 50% and allow lateral growth to happen. This will then naturally help to support the tree.
      Alison

    • I got mine from a serious local nursery. Haven’t checked the Big Box sources. Just get on the phone and ring around.

  4. Thank you Kate. I totally agree with you.
    Alison

  5. I have wondered whether trees that are “planted” rather than those which grow naturally have different root structures. Those massed roots look to me as if they have come as the result of being pot-bound – the absence of a tap root seems a dead give-away. Buying small tube stock is often recommended as being almost as good (in terms of height gained over time) as buying more advanced stock. I wonder if tube stock allows the development of tap roots and that these are the safer planting in that they allow the tap root to develop and grow downwards, rather than round and round the base of even a 200mm pot which, when planted out, form a surface mass, rather than having a deeper anchor.
    Just thinking out loud!

    • You raise an interesting point about tap roots and being pot bound when planted.
      We are being told that many of these really big trees don’t have a tap root. That they have a pretty shallow root system that spreads widely.
      I am not convinced. I still believe that a large gum with a strong central shaft through its growing stages, is going to have a tap root. Deciduous trees maybe not so much. These really big eucalypts need more than a lateral root system to support them – deep anchorage into deep soils. Albeit some big trees, like the Angophora costata, Eucalyptus cladocalyx, Eucalyptus cinerea and Eucalyptus maculata as examples, actually like rocks in the soil to help stabilise them.
      This is where sustainable landscape design needs to be paramount into the future. Using the principles of sustainability means that the trees are chosen to suit the type of soil and climatic conditions.
      Exotics can also be handled with the same principle although to a lesser degree of sustainability.
      In regard to tube stock, I have 2 Eucalyptus leucoxylon ssp megalocarpa in my garden – both planted at the same time close to each other in the same conditions. 1 was in a tube and the other in a 20cm pot. The tube stock, selected for it freshness has outgrown in height and width the pot grown plant. It is healthier all round.
      I know for a fact that some not so reputable nurseries plant up tube stock into bigger pots – plants that should have been thrown away because they were pot bound when planted up. These nurseries don’t deserve trade, but the bulk of consumers don’t know that this is done. But I stress, it is only the dodgy growers who do this!
      I only deal with the very best suppliers. I cannot provide a guarantee on the plants that we plant if they are dodgy from the outset.
      Tube stock need to be planted in autumn when they are fresh.
      Unfortunately the consumer needs to become more aware.

  6. Clare Bell on said:

    Thank you Alison for highlighting a very serious issue that deserves serious re-thinking by our State and local Governments, Arborists, Townplanners and Landscapers.
    I had not heard of the TPZ before and was most interested!
    I would like to offer these points as to why trees fall in storms;
    1.Seed grown trees grow a tap root and lateral roots which can anchor well in good deep soils- not common in Sydney shale and sandstone outcrops.
    2. I find a lot of tubestock is cutting grown and does not produce a taproot.
    Seed grown trees produce have shallow root systems.
    As the number of seed businesses has declined in the last 10 years, I would be interested to research what method is used by the State Forest and Council nurseries to produce tubestock ie. seed or cutting grown.
    3.I hold Councils and their Tree service agents(butchers) responsible for the lop-sided pruning methods used for the sake of costs (they are paid by the branch pruned) which must de-stabilise trees in time.
    4, Established trees may be doing well until Council or development projects decide many years later to concrete or use bitumin to cover the existing root systems.
    5. Cars are allowed to park under trees and compress the soil around the trunk preventing rain and oxygen to the roots.
    6. Thinning out of other tall canopy trees providing protection (through development construction work)which allows intense wind and storm events to de-stabilise lone trees.
    I hope this subject receives even more broader press. I have written to Hornsby Council and expressed my views and I urge everyone to become involved!

    • Thank you Clare for your comments.
      All naturally occurring specie trees are grown from seed. Those that require specific flower colour are either grafted or cutting grown.
      Any tree I feel should be OK if managed from its germination correctly. Most gums for example are pricked out while very young and usually put into tubes to grow bigger. They are sold in this form or potted on into bigger pots. This is usually incremental potting on through stages until the plant is in the required size pot by the wholesaler. But the reputable suppliers stage manage each event properly. Not merely potting on stock that should have been discarded many months before.
      A lot of the problem is that road widening or construction etc is put to tender. I am assuming that there is a landscape component attached to the documents, and many construction companies, and architectural firms, have in-house landscape designers who I believe, from looking at tendering documents, have no idea AT ALL about the veracity of their recommendations.
      I have tried to make my local council aware of this. It’s like talking to a brick wall.
      Unfortunately there are many tree loppers masquerading as arborists who are offering councils and the power companies unbelievably bad advice about tree pruning. They fell trees. They have no right to offering advice as professionals. But once again, it is the dodgy ones who ruin it for ethical providers!

  7. Matthew Hunt on said:

    Hello Alison,

    I am looking for some advice if you don’t mind.

    I have a young Stenocarpus sinuatus which is about 3m tall now. Following the recent wet and windy weather here in South East Qld it has become loose at the base. It is now leaning slightly. I had it secured from one side but the wind came from another and has pushed it the other way.

    It’s not so heavy that I can’t reposition it to a fully upright position as it was, it’s still quite a young tree. But my concern is whether the damage is done now. When I move the trunk the ground moves at the base noticeably. Not in all directions but in about a 270° range.

    Would you recommend removal and starting again?

    Thank you for your advice.

    • A few things:
      We had a Barklya with the same problem – probably about 3 metres high, a bit spindly (searching for the light) and a wiseacre tree person who pushed on it and noted that it wobbled a little in the ground.
      One source of advice suggested pruning the tree to force new root growth – except that this would interfere with the natural shape, and in the case of the Stenocarpus with its natural columnar shape, that would be a travesty.
      My analysis was that I had bought a plant that was too long in the pot and I had failed to tease out and re-direct the roots – for fear of sensitivity to root disturbance of natives. So I didn’t haul it out, check the roots and re-plant it – I think that for sure would set it back severely, if not permanently. But I wish I had helped to spread the roots when planting originally.
      So I left it alone. Now it is over seven metres tall and has quite a firm grip on the earth. It is also sheltered for much of that length by other shrub/trees – so I am hoping it will not be too severely challenged by wind.
      So – either take a risk and lift the plant and spread the roots.
      Or – leave it alone, allow it to do its own thing. Maybe brace it carefully for a season. If it is not too exposed it might survive wind pressure. Check a full grown specimen in a botanical gardens – I think they have a pretty robost root system.
      Or – start over. Buy a new specimen and plant it so that the roots are gently directed into the surrounding soil.
      After all, the loss of a couple of years growth with your present specimen is nothing compared to losing it in four or five years or more when it is tall enough to be subject to wind damage.
      The latter is what I would do.

      • Matthew Hunt on said:

        Thank you very much for the info. I’m going to give the tree a bit more time and see.

    • Thank you for your question Matthew. I will answer as best I can not knowing your conditions.
      I need to ask what type of soil the tree is growing I.e. clay (heavy or well drained) or sandy. I am assuming clay which makes it harder to resurrect.
      Is there any wilting of the foliage? This would indicate root damage. If so, I would start again. It sounds to me as tho it will be OK, especially if it isn’t wilting. If there is damage of the main root it is pointless persevering with it, as it may topple in later years.
      It is a real shame when this happens to young trees. You would be better supporting the tree with two thick and strong stakes well out from the trunk with a figure of eight tie with proper tree tie.

      Alison

      • Matthew Hunt on said:

        Thank you very much Alison.

        No there’s no wilting and I left it untethered for a day in light breeze to see what it would do. It didn’t change posture so I’m going to tether it well and give it more time.

        I’ve bought some stakes today!

Leave a Reply (no need to register)