RPA for a pollard

[benedmonds]

2 hours ago, daltontrees said:

I'm going to give an alternative perspective (otherwise known as disagreeing).

The only constant measure of the balance that would be achieved naturally is the stem diameter. And by simplistic methods, this is used to determine the root protection area. The stem is the main plumbing for the tree, up and down. BS5837 assumes its cross sectonal area is proportional to the root protection area. 

 

As I understand it there is no scientific basis for stem diameter x 12 formula, no field tests and no real research.   If there is I am happy to be corrected.

 

A trees stem diameter has to get thicker every year, however it's rooting area doesn't. While I agree there is likely to be a correlation of stem diameter to root area, there is likely to be a correlation  between height : root area  or leaf area: root area, these are ignored in the formula. Sticking to what BS5837 says is too simplistic.  It is a guide a starting point and hugely unrealistic.

 

   

[Anno]

As others have said very little research into the extent of root systems has taken place, however it is clear that they extend well beyond the 'drip' line and within the top 30cms due to oxygen limitation.

Another point is the consideration of mycorrhizal fungi in the surrounding soil.

I think that the 12x formula is in place of nothing - a line in the sand, it probably should be increased, it isn't really simplistic, but it acts as a yardstick, I am pretty sure that anyone who wanted to do a really interesting PHD could use modern technology to plot and monitor actual root dimensions, but at the minute I cant afford to give up work - unfortunately.

[Island Lescure]

 Sorry for the slight derail. I got to see if the BS5837 RPA recommendations made sense in a tree in south east India ;-) We dug near the calculated RPA to be sure to give accurate recommendations. Though this is only one tree, it was nice to see that the figures made sense (in my opinion). Attached is the report after the original survey and tree constraints plan. I would be curious to hear what you guys think of the recommendations and the findings (obviously it is not a tree in the UK and therefore cannot be compared to anything there). Cheers!

Tree Ref. Number

Common Name & Species

Life Stage

Height (M)

Height of Crown Clearance (M)

Branch Spread (M)

Stem Diameter (MM)

Number of Stems

RPA (Radius in M)

RPA (Area in M2)

Physiological Condition

Structural Condition

Comments

Preliminary Management Recommendations

ERC (Years)

Category

N

E

S

W

T1

Enterolobium cyclocarpum

M.A.

19

2.5 meters south

17

16

16

19

1600

1

15

707

Good

Fair

Good overall condition. Branch on north east side, 9 meters up, 7 meters out shows signs of previous damage. Large dead wood present, typical of species (habitat for bumblebees).  Previous pruning wounds by electric lines. Minor wounds throughout. Abundant surface roots, typical of species. Coping well with dry summer through exhibition of new shoots. Minor crossing branches in the center of the crown.

Branch on north east side, 9 meters up, 7 meters to be reduced by approximately 4 meters to reduction points.

40+

A1

Pony Farm Digging Tree Report.pdf

[daltontrees]

On 04/04/2018 at 17:48, Paul Barton said:

 

Julian - your observations about incremental thickening of pollards is very interesting.  I don't have any stumps or cross-sections to dispute your point, but I do recall hearing a talk a few years ago from Mr Barrell where he showed some slides of some small pollards in a church yard - the assumption was they were quite young as their stems were slender but when they were felled they were found to be really quite old. Maybe a long-term regime of pollarding does reduce incremental thickening?  Or maybe those trees were just growing in poor soils and had somehow struggled on for more than a century!

I really meant an isolated topping will encourage new wood with increments as big as previous years. But yes I expect regular cyclical pollarding would stunt stem development. And even with small increments, they might not get smaller after re-pollarding. And the question remains, would the stunted stem DBH give an adequate RPA per 5837. I expect so.

[daltontrees]

On 04/04/2018 at 20:02, benedmonds said:

As I understand it there is no scientific basis for stem diameter x 12 formula, no field tests and no real research.   If there is I am happy to be corrected.

 

A trees stem diameter has to get thicker every year, however it's rooting area doesn't. While I agree there is likely to be a correlation of stem diameter to root area, there is likely to be a correlation  between height : root area  or leaf area: root area, these are ignored in the formula. Sticking to what BS5837 says is too simplistic.  It is a guide a starting point and hugely unrealistic.

 

   

Do you have an alternative more relaistic formula based in science?

 

I have never seen justification for 12x, but it usually works, which is justification of a kind, as the trees tend to carry on. It may be too big, but I don't thnk it's too small. Based on the empirical evidence I would disagree that it's 'hugely unrealistic'. I would say 'simplistic' and I'd drop the 'hugely'. I too am happy to be corrected.

 

And what we are dicussing here I think should be thought of as potential crown volume correlating with rooting volume, and whether these are reliably linked by stem diameter. Physiologically ongoing vitality for pollards should reflect potential crown volume, not artificially reduced crown volume, relating that to rooting volume. I still see no rationale for reducing RPA below 12x for pollards. Whether 12x is the right number for all trees is another matter.

[daltontrees]

Great opportunity Island Lescure. You were the guy on the ground so it's hard to comment on the judgements you had to make. 

 

You were still finding roots as thick as a wrist out at 15 and 17m, that must be some tree. And the spread is c.17m. I see you capped the RPAr at 15m for a DBH of 1600mm. Maybe in areas of different climate where rain is less consistent a bigger RPA might be particularly important. My gut feeling is that the area around the tree on the very edge of the crown is partularly important for water. It's called the drip line for  a reason. For biger trees, like yours here, the 15m RPAr cap seems to deny the tree this collection area. Maybe the full 1600 x 12 = 19.2m would have been beneficial if building pressure hadn't been there, giving a 2m ring around the crown fro water collection? And speculatively it might be beneficial to reduce the spread artificially by pruning (I see you have anticipated pruning anyway for future buildings near the tree) so that the drip line water contribution is brought closer to the stem.

 

Anway, a good read it was, thanks for sharing it.

[Island Lescure]

16 hours ago, daltontrees said:

Great opportunity Island Lescure. You were the guy on the ground so it's hard to comment on the judgements you had to make. 

 

You were still finding roots as thick as a wrist out at 15 and 17m, that must be some tree. And the spread is c.17m. I see you capped the RPAr at 15m for a DBH of 1600mm. Maybe in areas of different climate where rain is less consistent a bigger RPA might be particularly important. My gut feeling is that the area around the tree on the very edge of the crown is partularly important for water. It's called the drip line for  a reason. For biger trees, like yours here, the 15m RPAr cap seems to deny the tree this collection area. Maybe the full 1600 x 12 = 19.2m would have been beneficial if building pressure hadn't been there, giving a 2m ring around the crown fro water collection? And speculatively it might be beneficial to reduce the spread artificially by pruning (I see you have anticipated pruning anyway for future buildings near the tree) so that the drip line water contribution is brought closer to the stem.

 

Anway, a good read it was, thanks for sharing it.

Thank you Julian for the feedback! I am glad it was of interest.

 

Yes I capped the RPA, though what you say makes sense. I had a look at the Australian standard just now and it is the same as the UK regarding this though they have huge variations in conditions. If I suggest something, I would like to have a reference to something else to back up my suggestion. I will have to check the US recommendations or maybe HK or Singapore. I have no idea what they recommend.

 

Regarding the dripline, I am not so sure. I agree that trees will get more water to the roots just outside their dripline but

1: some trees can get water from their leaves and another link here.

2: short rains (after long periods of drought, easily 6 months here) here are not always beneficial for trees as they can provoke the trees into a growing mode which then potentially leaves them with less energy once the drought resumes and with more to maintain (such as half developed leaves). Here the dripline farther out would prevent water getting to the roots closer to the trunk and so maybe avoid the growth spurt? No idea, just thoughts at this point.

 

Never thought about the dripline before.

 

Cheers!

[benedmonds]

1 hour ago, Island Lescure said:

. I had a look at the Australian standard just now and it is the same as the UK regarding this though they have huge variations in conditions. If I suggest something, I would like to have a reference to something else to back up my suggestion. I will have to check the US recommendations or maybe HK or Singapore. I have no idea what they recommend.

 

Island, as has been said before, the standards don't appear to have any real scientific  basis (except "it seems to work") even in the UK, I imagine the Australian leans heavily on the BS5837 findings, (I think saw a draft copy years ago).  When you start applying them to totally different conditions and trees not even contemplated by the UK  based writers they are going to be even more vague...  Would anyone consider using 5837 for the RPA of a baobab?

 

I would be interested in seeing how other countries do things? Surely the Germans and Americans have something similar?

 

[Island Lescure]

I would be really curious to see what baobab roots look like!

 

Here I also have the issue that a lot of mature trees have tap roots and we don't know how deep or important they are. This affects the idea that trees have most of their roots in the top 2 feet under the soil. More digging required... I really need to get an airspade.

[benedmonds]

This is on a similar theme.. 

I was surveying these neglected willows (with an apprentice..) for a hydro scheme..

Individually nothing special so C1.. but as a landscape feature they pretty valuble.. so B2. 

Or do the veteran features make it an A3..?  

 

If you pollard them does it still need an  11m, 385 m2 RPA?

 

Edited April 13, 2018 by benedmonds