How to etimate tree root spread.

[Gina Rackley]

Hi all, there is a new Sainsbury's superstore proposed adjacent to my local nature reserve in what is now a car park. Along the side of the boundary fence, among other smaller trees, are pollarded Hybrid Black Poplars, Ash and Sycamore. How do I estimate root spread under the car park tarmac so see if it will be inside the new foundation plans? Gina

[treequip]

Trial pits, hand dig

[Paul Barton]

Trial pits is not a method of estimation - it's a way of finding what is really under the tarmac (which is better ultimately).

 

Gina, root spreads are commonly estimated using a formula based on trunk diameter. The spread of roots are typically estimated to extend to a circle around the stem equivalent to 12x the stem diamater (measured at 1.5m above ground level).

 

So, for a tree with a diameter of 500mm, the root protection area (RPA) would be a circle with a radius of 6 metres (6000mm).

 

There is a more complicated way of estimating for multi-stemmed trees.

 

In this situation, a trial pit may be the best option (as treequip suggests) as the above calculations are very crude and cannot accommodate species characteristics, soil types or factors such as tarmac surfaces, foundations etc.

 

Where is the site? Perhaps you can get an expert on-site opinion from someone here?

[Callum]

Hi Gina

 

Firstly you could work out the root protection areas (R= 12x the DBH on single stems, or 12x the total cross section at 1.5m on multistems).

 

This would give you a rough idea whether the roots are likely to be affected by the develpment works.

 

If the tarmac surface is within the RPA then as treequip says, you would have to do some digging to find out how far the roots might extend under the tarmac (or not).

[Callum]

Hi Paul

 

You got your message in while I was typing- sorry to duplicate

[Gina Rackley]

Hi everyone, and thank you for getting back on this so soon. The site is Abney Park Cemetery, Stoke Newington, and the proposed Sainsbury's is in Wilmer Place, behind the High Street line of shops south of Abney's main entrance. I will make an estimate of RPA from your information (thank you!), but I can't see myself digging test holes in tarmac on property I have no rights on. (It is still used as a car park). Gina.

[Lee Winger]

You need to work with the architect and your tree consultant, digging up the car park and excavating with an Air-spade is the only way to properly determine if there are roots present. I carry out thousands of trial pits for this purpose in the course of a year Arbor Aeration - Tree Healthcare Specialist I'd have thought planing would of insisted on this, haven't you had an arboricultural impact survey carried out?

[Gina Rackley]

I am merely a volunteer with an interest in fungi, especially inkcaps and Ganoderma, which is why I came to this site. I understand that objectioins to the original Sainsbury's plan was broad based and involved a wide community rejection of the plan. The original plan involved removing some trees from the boundary of Abney. A second plan is now proposed which keeps all the trees, and talks have happened between the Trust running Abney and Sainsbury's, but I don't know what was happened with those. A change to the treatment of the boundary is now in place, but I don't know exactly what. I don't think any ecological evaluation of Abney and how it would be affected has happened. The car park has certainly not been dug. I am going to be looking at the new plans when they are published online, which will be soon, to see if there is anything that I can determine is going to affect Abney. I have no expertise in this, but there is only 3 weeks at that point to try to sort out what the plans mean and put in any objections.

 

I have agreed to look at the situation with regard to a breeding site for Tawny Owls close to the site of the build. If the trees are damaged and subsequently die the barrier between the build and the breeding birds will be reduced and disturbance to the owls may become intolerable. Not damaging the tree roots is high on my list of things to assess. I didn't know how to go about this. Now I will be out there tomorrow getting measurements. It is a start.

 

I am hoping that I will be surprised by seeing an arboricultural evaluation in the plans and some determination of how the nature reserve will be affected, otherwise this will also be in my objections to the plans.

 

I don't know what planning has asked for.

[Gina Rackley]

Hi eveyone,

I did some measuring and found a RPA of 10.25 meters. However some discrepancy may have arisen between developers and those resisting the developement, as to what a veteran tree is. There are many old trees in Abney providing an excellent habitat eg pollarded hybrid black poplars along the fence at the boundary of the proposed developement. The developers see these as low catagory trees, as they might well be in a park, so ripe for ignoring / removal. Whereas veteran trees, as they are considered in a nature reserve, have a higher status then that. Does the position in a nature reserve make any difference? Anyone know? Gina.