What really needs to go

daz

Hi,
This is my first post here. I ended up here while trying to find some actual emperical information (rather than just standards/rules/hearsay) regarding trees and soil movement/house cracking/damage. I've read most of the online sources posted in this threads and found it all very illuminating if somewhat inconclusive. Where I live we have highly reactive clay soil (fairly deep - at least in places) over river silt. I guess there is something solid down there somewhere. We also have a lot of old Queenslander houses (I live in one) and a lot of trees (of various ages). The average queenslander seems to have stumps that are almost certainly not deep enough to get down to something solid, however house movement is something accepted in these houses (timber house, just flexes). We also had an extension built a few years ago with footings complying with the current regs (it has a huge volume of concrete going down 2.5m or more under each steel "stump"). However in the 70s a few blocks of brick flats were built in the area on floating slabs (I wouldn't be terribly surprised if they were under engineered for the amount of soil movement to be expected without trees). Such things are now not considered "in character" for the area but one of these is behind our place and has some cracking/movement issues.

So, I'm the evil neighbour with trees (trying to screen out a 70s brock box block of flats). The trees have been there longer than I have (15 years) but of course have grown. There are a couple of trees that I've said repeatedly to the flat body corp over the years they are welcome to cut down, but I have never sent them a reply that says "please come and cut down every tree in my back yard" (which, is what they ask for).

After I said that I wasn't prepared to let them just cut down anything that was growing and I wanted a list of the specific trees that their consulting engineer wanted removed I was given as "expert advice" a quote from an arbourist for cutting down every tree adjacent to the boundary. No offense intended, but I don't really think the advice given in that context is entirely "impartial".

Along the boundary are 2 tall trees, both of which are things I would happily get rid of - a Silky Oak and a Cadagi. There are also 2 smaller Acacia mearasii (I think) and a rather stunted Leopard tree (Caesalpinia ferren).

While they are only about 3m from the flats, I find it hard to believe that the Acacias will significantly contribute to the soil movement given all the other factors. I see that these trees are often used/recommended by Councils for planting as roadside trees etc. Surely this suggests they are not invasive/damaging?

Anyway - what do any of you think - do the Acacias need to go? And what screening plants can I use instead to "break up" the view of a 2 story block that runs the full width of my block and 2 of my neighbours blocks as well?

Thanks for any suggestions!

mdvaden

This has been a good thread. I like seeing ideas put to the test.

When the guys were dabating elsewhere about whether removal of lower tree limbs makes a tree more top heavy or buffered, I thought about an experiment to put it to the test.

I'm planning to stack two box fans by a small pyramidal shape Douglas fir in our yard in a small grove of them. I can use a plumb bob over head, or a fixed marker near the tree top to record its vertical apex position with the fans runnning, WITH 100% CANOPY.

Then I can prune off the lower half, and if what the other tree guys say is true and those were buffering limbs, the tree top should move even farther away from that marker, and a second marker for the zero wind position. If the tree leans less with the lower limbs removed, it will show that the top heavy belief may be innacurate.

I alread took a torch to twigs on my madrone to prove it would not ignite after folks living around here talked about how flammable the foliage was. I couldn't ignite it until the torch dried the leaves into brown toast. Myth busted - for a landscape setting.

So with the tree soil thing, it was interesting to see how small or big an impact something like foliage reduction really has on soil - or doesn't have.

__________________
____________________________________


Grove of Redwood TITANS

Oregon BIGOOT trap

Ekka

OK, I brought relevant posts over from this thread

Soil subsidence and trees

to here. Lets keep the discussion here otherwise that thread will end up huge losing it's resource value. It's good to refer to it though.

Daz,

From experience with geotechs and engineers here I can say they'll condemn your trees no worries.

They'll apply regs that we dont have.

Some councils face the same problem you do when their street trees cause (allegedly) houses to crack. Now I bumped into something somewhere once but this is how it goes.

The councils criteria was ...

1. Roots must be beneath or adjacent to the building, proven by sample.

2. Soil core with moisture content required and same from side opposite without trees as a test hole (called control), comparison made.

If the moisture content is significantly lower where trees are and roots found >>> BINGO, council could be looking at a claim especially if homeowner requested tree works.

In some places the councils are now installing root barrier along fence lines to prevent these issues.

Also, from the soil core the geotech will give the clay rating. Depending on that rating it will give you the old height and distance rule for the trees. It could be as bad as the closest a tree can be is 1.5x it's ht.

So 10' tree must be 15' away.

Natives are very efficient water scourers, gums, wattles, bottlebrush etc are very efficient water miners.

This is a tough task, and it's going to be fought on engineering codes more than arborists knowledge unfortuneately.

These are the cases that go to court and cost lots of time and money. If the body corporate want to persue for costs of rectifying and underpinning a proportion of that cost can be appropriated to you. In my experience the cost and inconvenience of complying with there requests and moving forward with a new insight could be wise.

To install root barrier to existing trees at that proximity to the trunk might destabilize them or kill them. You did say the trees are within 3m of the flats.

With council trees they're not that close to houses, there's usually 3m wide footpath and then 6m to the house minimum unless there's a relaxation on the property.

Subsidence happens when soil moisture is depleted and the clay shrinks. The major cause of this is drought. Did this just happen in the last couple of years or is it a long term thing?

If you decide to replace and replant I would suggest trying to plant a little further away, install root barrier prior to planting, choose a columnar species with a height cap of 3m ... not something that needs hedging or trimming either. Also, the latest rage for the tighter urban yards is special bamboos which dont run. There's varieties that wont grow too tall now a days.

Hope this helps, I've had my share of these and can say from the legal aspect the tree owner will likely lose if up against geotechs and engineers. We have (pardon the pun) nothing concrete as evidence to the contrary for each specific case.

Remember the 2 point rule above if things go bad.

__________________

Free Tree and Green Industry Link Directory

Qualified Brisbane Tree Lopping | Stump Grinding and Stump Removal Brisbane

Brisbane Tree Care, Consultations, Developer, Tree and Arborist Reports

Forum Sponsors

daz

Yeah - was afraid that would be the answer. As it happens I can live with the loss of the trees concerned. My neighbour has good reason to be rather attached to the trees that they want removed from his yard. I was hoping that there was at least some precedent for being selective about it - I guess I should be thankful they haven't asked for the whole suburb to be clearfelled

The bambo idea makes a lot of sense for screening, but would like to get a couple of taller (but not massive) large shrubs/small trees in further from the boundary - but the whole 1.5 x height thing is just insane - if every house in the suburb was built the way the flats are and you applied that rule you really would have to clearfell - you couldn't fit a tree in anyones block.

Thanks
Daz

Ekka

You are dead right!

And if the builders/developers and engineers had their way they'd fell the darned lot too.

Also, ring your insurance company and ask them if it would be covered under your policy, some cover legal liability and some dont etc.

Maybe some pics would help us too.

__________________

Free Tree and Green Industry Link Directory

Qualified Brisbane Tree Lopping | Stump Grinding and Stump Removal Brisbane

Brisbane Tree Care, Consultations, Developer, Tree and Arborist Reports

Forum Sponsors