Articles

Trees that surfed on a landslide by the river

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A large area of soil, approximately 50 meters by 60 meters has slid down a bank towards a river during the heavy rainfall in late 2015 that caused flooding in the northern part of the UK.  The slide was of at least a meter in some areas and in others perhaps 5. The depth of soil that has moved was suspected to be several meters deep. There is a shale layer above a clay layer and the former seems to have slid over the latter.

We had been called in to clear an access for land surveyors to assess the ground. Other staff were also digging bore holes to inspect the soil bellow ground in numerous areas. This latter operation was sending vibrations throughout the area.

With the trees that have followed the landslide in their entirety (as the majority of their roots are only in the top meter or so) still standing and alive, it was impossible to assure that they were not a risk to the persons working around them.

We therefore deemed the area unsafe and removed the most obviously potentially dangerous trees near the area where people would be working. Some of the trees had been observed tilting whilst the workmen were on site and these (and others) had the area up to 1.5 meters away from the base of the trunk lifting/tearing away from the ground.

It was very interesting to see this as it is not something I have come across before and wonder how one could properly inspect the damage done to the tree roots. Many of the roots will have been severed and as it has not been very long since the event, circa 8 months, decay will not have set in fully. I expect a few more of these trees will fall down in the next few years.

Many of these trees are white poplars though there are some sycamores, beech and ash in the area as well.

The sycamores that have landed in the river are obviously dead, most probably from oxygen starvation with the roots being entirely submerged rather than, or in addition to, direct physical damage as again, these are still standing. They have tilted further since our first visit.

Uprooting trees
Detail of root-plates.
Uprooting trees
Both of these trees moved whilst people were there.

 

Uprooting trees

 

A bit of work in a garden reveals a few interesting things

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An ancient ash tree, Fraxinus excelsior, topped 18 years ago due to the presence of excessive decay which was compromising its safety. It has since been pollarded every six years or so (including when I just did it). An example of how habitats can be preserved and encouraged to grow without posing any risk. Can you spot the 3 cavities visible from this direction?

Ash tree full of hollows and features

A horse chestnut tree pollard which was removed to make space for the neighbouring trees was ringed up (cut up into manageable pieces) revealing interesting patterns inside due to fungal decay. It was interesting to try to ascertain where the decay had originated from by looking only at the decay in the trunk. I would have thought that the more decayed area would be closest to its origin but it was not so evident.

Closest to the base of the tree
Closest to the base of the tree
another 30cm up
30cm higher up
Another 60 cm up
Another 60 cm up
Another 30cm up
Another 30cm up

Trees need surveying for multiple reasons. Here are a few.

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When tree surveys will/might be beneficial:
1: When buying a property that includes trees which might affect the initial or long-term price due to maintenance or removal of said tree(s).
2: Tree safety surveys (anywhere where many pedestrians or motorists visit often): in public areas such as schools, on private land or on commercial areas such as car parks. This serves to prove that the landowner is fulfilling their duty of care (not being negligent) and as such reducing the risk of damage to persons and property.
3: Development surveys compliant with BS:5837, 2012 Trees in relation to design, Demolition and Construction. To be included in planning applications where trees are present. This will also include trees that may be damaged by vehicular traffic on the site and will also include trees in neighbouring properties whose roots and/or branches may be affected.
4: A Condition report, to give a idea of the state of the trees on a site. This would possibly also include a management plan: what tree work is required or if other inspections (possibly aerial) are required down the line. This would include timescales for the work required or re-inspections.
5: Management plan: More often for older trees, veterans and ancient. If retrenchment is required to keep an old tree with a lapsed pollard from failing structurally, it may be beneficial to reduce the tree in stages and perhaps help it in other ways such as removing some competition (other trees), ameliorating the soil (perhaps with an airspade) etc… to enable reducing the tree without killing it a few years down the line.

Laetiporus sulphureus on willow
Fungus fruiting bodies on willow
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A few pics showing how much defect can be present in a tree before it fails. The first picture is of a larch on a woodland edge that was mostly dead, leaning heavily in the direction of the chainsaw. It was approximately 10 meters high with foliage on the leaning side. You can see that some parts of it have been dead for a while. Only the really light stuff on the bottom was alive.

mostly dead larch The next two pictures are of a sycamore which managed to remain standing even after we disconnected it from the neighboring tree. There was very little sound wood left and yet it managed to support probably about 2 tons of tree.closeup of tree full tree

Chalara conference and visit to Staveton

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On Thursday, I went down to the Woodland Trust’s Pound Farm in Suffolk to attend an informative day on Chalara fraxinea, or ash dieback, courtesy of MTOA. We were shown the various different stages of the disease on trees at different stages of their life cycle and of different levels of severity of infection. We even came across the fruiting bodies of Hymenoscyphus fraxineus, the fungus responsible for the disease. I did not take pictures as they are widely available. However, I did take pictures at Staveton as the trees there, none ash, were interesting veteran and ancient trees. First pic is a phoenix birch, or a birch which has failed and yet continued growing. In this case, apparently, it started off growing out of an oak (though probably already dead) and when the oak decomposed, after having sent down aerial roots, fell to the ground and continued growing by sending out some of its branches vertically(now the trees to the right).Phoenix Birch Next we have an oak that has cracked due to torsional loads in a rather interesting way.Torsional damage of an oakThen we have an oak that has grown in a peculiar way after possibly having lost its leader early on:peculiarly growing oakAnd finally a pollared oak (most oak here were pollarded):pollarded oakA very nice and informative day out with other arboriculturists.

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Today I attended a council meeting in Sheffield which included a debate regarding a petition that received over 10000 signatures. It was concerning the policies and framework in place to remove and replace trees along the roads in Sheffield. I am an arboriculturist. I was curious to witness the meeting even if I don’t believe that this sort of debate can happen verbally as too many factors are involved. In the end, all it came down to was the councillors voting on the two choices: one was to carry on as usual and the other was to scrutinise the methods in place to ascertain that the work was carried out in the best possible way. I was astonished at how 10 or so people could overrule over 10000, as the majority of councillors voted to keep things as they are. In some ways it is understandable; stopping the work would cause financial losses to the parties involved (perhaps breaching the contract), a study into the most appropriate strategies to manage the trees would require funding (which is unavailable), not all the facts are known and finally, emotion is believed to be responsible for certain people’s response and therefore secondary (fine in my opinion). There was talk of creating a forum for decisions regarding Sheffield’s trees. What is really needed is a plan that is not only approved by residents but also by experts. A plan that takes into consideration the many beneficial factors that trees bring to people whilst still retaining a view of their limitations. Trees do a lot of things but like us humans, have limitations.

Here are some aspects of trees:

Environmental

Values:


• Trees can help with water management in the sense that they can reduce the speed at which water reaches drainage pipes by catching and retaining water on their leaves.
• Trees can reduce noise pollution by screening the area where noise is coming from.
• They can reduce the amount of wind flowing in an area by dampening it with their leaves.
• They create shade with their leaves and branches reducing heat and evaporation from the ground.
• Trees improve air quality by releasing oxygen into the atmosphere through photosynthesis.
• Trees can intercept pollution and particulates on their leaves and their bark.

Drawbacks:


• Trees may block light by being very dense.
• May break sidewalks or structures over time with the growth of their roots.
• May drop fruits or leaves creating a messy area.
• May create noise when the wind blows amongst their leaves such as on some poplars.

Ecological

Values:


• Trees can build up humus through the shedding of their leaves which improves the soil through the addition of organic matter.
• They can associate with nitrogen fixing bacteria which also improves soil but in a different way.
• They can provide food for birds and insects with their fruit, leaves or pollen.
• Trees can provide homes for squirrels and other small animals.
• They can provide nesting materials for various animals, not least birds.
• They can provide green corridors which can extend the amount of space animals, such as squirrels, can utilize in urban settings.

Drawbacks:


• Trees can provide food for fungi which may help them colonize new areas and decay other things such as shrubs.
• Some trees make the ground around them toxic by allelopathy, the exuding of chemicals, preventing other plants from growing.
• Some trees may require so much water that they deprive nearby plants of it.
• Some trees can attract large quantities of certain insects, such as stink bugs, which may then start feeding on other plants.

Social/Economic

Values:


• Trees provide work for people that maintain them.
• Trees can help in the recovery rates of medical patients through their calming effect.
• Trees provide timber and many other products required today such as toys, picture frames, paper etc...
• Trees can increase property values as they are seen as beneficial or they might be rare specimens offering a type of status symbol.
• They provide educational material in the form of habitats for other species or just in themselves.
• They provide a meeting/recreational area or a place where one can hang a hammock or a swing.


Drawbacks:


• Trees may fail causing injury or damage or both.
• They can shed multitudes of leaves making a mess which requires sweeping and therefore expenses or maintenance.
• They can host insects such as aphids which coat everything under them with a sticky residue.
• They can encourage anti-social behavior by creating areas where people can hide or are not easily seen.
• They can reduce the value of a property if they require expensive work to make them safe or if they are simply too imposing or just create a lot of shade.

Amenity/Landscape:

Values:


• Trees can be beautiful by their leaves, bark or flowers in form or color.
• Trees can attract pretty birds/wildlife with their fruits.
• They soften the landscape with their leaves and swaying branches in areas containing multitudes of angular structures.
• They can conceal entirely or partially things that may not be pleasing to the eye.
• They can frame views or create avenues when rows of trees are present.
• They can be the centerpiece in a garden defining its theme.
• They can provide welcome shade on a hot, sunny, day.

Drawbacks:


• Trees can obstruct views whether panoramic or otherwise, simply due to their location.
• Trees can block street lights and CCTVs with their leaves and branches making areas unsafe.
• They can grow roots which protrude from the ground creating a trip hazard or that may impede people in wheelchairs from accessing certain areas.
• Trees with low branches may tempt children into climbing them which may deter their parents from living nearby or visiting to avoid the risk of their children hurting themselves.
• Trees may impede the construction of access for motorists through the campaign of people that know better, or the opposite, preventing their removal.