The Project Arborist| Australia|AS4970-2009

Eric Frei

AS 4970-2009 Protection of trees on development sites on page 6 section 1.4.4 States what a project arborsit is:-

The purpose of this post and thread is to expand a little on what the Project Arborist really does and the chronology of stages in the development process.

In order:-

Site acquisition:- Developer/renovator/builder etc acquires the property

Detail surveys:- Existing trees accurately plotted on survey plan

Preliminary tree assessment:- Evaluate trees for retention, provide TPZ's for design layout to consider retained trees.

Preliminary development design:- Ensure retained trees adequately accommodated in design with no adverse impact. Check cuts and fills, pipes, drains etc.

Development submission:- Provide tree retention and protection specification for development to be lodged with DA

Development approval:- Hopefully little change and adhere to approval plan.

Pre-Construction
Initial site preparation:- Tree removal, pruning, transplanting. Install TPZ protection measures.

Construction
Site establishment:- Locate temporary site infrastructure to minimise impact on trees. Be aware of traffic and even exhaust emissions (trucks idling under tree canopies is not wise). Maintain protective measures, monitor and report.

Construction work:- Maintain and monitor protective measures, monitor and measure tree performance on frequent basis with valid data that can be historically checked in generic form (soil moisture, mulch depth, canopy density, pH etc)

Implement hard and soft landscape works:- Remove protection measures as necessary to complete (as per plan) landscape works, ensure no damage or compaction to trees. Monitor trees.

Practical completion:- Remove TPZ fences etc, report on final condition of trees with generic information.

Post Construction:- Maintenance and monitoring with final certification (tree condition reported upon). Once again generic style consistent information would be suitable.

That's pretty much the written aspects but still you ask, what is generic information and what is reported on?

The key to frequent inspections and monitoring is to have information that is collected consistently and can be referred to later. Just imagine a tree starts dying for some reason, your checks for the last 6 months on a monthly basis could be the saviour to show all was well as far as your indicators went but it wasn't anyone's fault the fuel tanker crashed and spilt 10K litres of diesel down the road flooding your site.

Whatever method you use, try to use it throughout the project, same measuring tools etc.

I report on as many items as I can. I take core samples and measure plus estimate root density. I also measure soil moisture. Have rain gauges so methods of monitoring rain and watering can be done. If some council guy pops up and says the tree looks worse off today than 6 months ago you need some facts right. I have a compaction tester in PSI, I take pictures of the tree every visit .... up here most are not deciduous so a foliage density comparison is good (pics validate it).

Expect to see from core samples:-

Soil pH at varying depths
Soil moisture at varying depths
Root density at varying depths

Compaction tester to validate any changes, but often it's the most mulch a tree will ever see or get in it's life so can improve.

Pest/disease inspection

Root flare/soil inspection

From a recent report I offer this extract
Now it would also be wise to have the same generic information way earlier in the project before anything starts, that way you'd have a reference point. Often developers are accused of mistreating trees, often the allegations are unproven or opinion, often remedial works are far more beneficial than nature would have done on it's own.

Do not over look root baiting if you get to a site early enough. By bagging out the perimeter of a TPZ and applying soil conditioners and mulching within you will increase the root density closer to the tree so when development comes along there will be a lot less impact. You can root bait to design contours too, no-one says all TPZ's have to be circles.

Look to favour natural soil advantages, if one side is lower and has more water likely there will be more roots in that area, be wise and consider natural root preferences and work with them.

Consider the sequence of events, remember what you write and be sensible. I know some-one who wrote that no equipment over a certain weight was to enter the TPZ's and then he wanted to use an EWP to deadwood the trees .... too bad, the old 28m EWP weighs like 10T. So be wise, work on PSI ground pressure, placing of boards or steel mats over mulch can dissipate the weight.

I like to write a "Project Arborist" report at the stage between Pre-Construction and Construction. After clearing and pruning, dead wooding etc you get a real open fresh look at the remaining trees, especially if you were up in the canopies. You can see defects clearly, I see this as your last chance to bring up issues, if a tree needs extra TLC or the axe now is the time to do something about it, not 6 months time when the finger may be pointed down the non-compliance fine path.

To many this is a new thing, councils Australia wide will be embracing it, it's important that we as arborists have a good grasp on what this is all about. It is a hands on in the field activity. One of the best benefits the people who work with me have is I also get my hands dirty and do a lot of the work, oversee a lot of the process near trees and do more than watch.

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Eric Frei

AS4970 has a one size fits all 12 x DBH as a TPZ with some minor allowance of 10% deviation with relatively little documentation, however if you want to change things around more then you'll need to explain why and how to most councils.

All sites are different, soils too are different.

On the current project I am engaged this particular tree has a 0.92m DBH, according to AS4970 we should have a TPZ of 11m as a radius from centre of trunk.

Now as you can see there is an existing road behind the tree with gravel and that has become the access to this site (beneath the canopy of the ficus tree). That road is approximately 6m away from the tree, has been used before as it's where the groundsman equipment is stored and tractors etc housed.

So we have an existing thoroughfare.

Soil, well it's sand.

And an important fact is that between 1.4m and 2m below grade there is ground water which is only 800ppm saline (within tree scope).

Now the builder needs access to the site but if AS4970 is adopted then that road will become a TPZ unless certain things are done.

We decided to leave that access as the preferred access because ficus trees are very resilient to root damage and an existing road is nearby.

Some more facts, I would say a ficus tree in sand sitting only a few meters away from acceptable ground water would have few lateral roots and a horde of sinker roots guzzling away. That is also reflected in the well coloured dense canopy of the tree. Sand is a large particle, plenty of air pores and easily penetrated by tree roots.

So next piece of evidence to support a road beneath the tree canopy and over the TPZ is soil cores. We took 2 cores from 5.5m away adjacent to the roadway and beneath the drip line.

Guess what, no roots, none, ZERO. As expected.

Soil moisture at 5cm to 15cm depth was 10%
Soil moisture at 25cm to 35cm depth was 15% .... moisture increasing at depth as expected. Ever dig a hole in the sand at the beach? Then you'd know that as you dig deeper it gets more moist and soon there's water in the bottom of the hole you dug.

So the TPZ fence will be at the edge of the road and only 5.5m away from the tree.

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esky79

Ekka

You make some very valid points. The arboricultural industry really needs to improve in regards to report writing and retention and protection of trees on development sites. I often see and have been involved in several situations where the plans for a building have been drawn up and everything submitted to council only for the client to be told to submit an arborist report on the trees that are proposed to be removed and to give measures to protect trees to be retained. There was one building i was invloved in that had problems with the local council for about 2 years. The part i was involved in took about 6 months to be resolved. Arborists need to be involved from the earliest stage possible to prevent a lot of issues. Also our methods need improving. Like you say a more hands on approach in the field would be better and what you do in regards to soil samples really doesnt take that much longer but can cover your butt when it hits the fan.