SODF(Single degree of freedom) 當只有一個枝條時，我們可以觀察樹木震幅程度。
2DOF(Two degrees of freedom)2個枝條可以看出樹木震幅少了一半以上。
MODF(multi degrees of freedom)多個枝條可以把風的力量巧妙消去大部份，震幅程度變為更小更破碎。
為什麼不可以修剪樹木內生枝條，因為這些樹枝是樹木的避震系統，具有阻尼效果，關係樹木穩定性。
在1985年Shigo說了，沒有樹枝的樹不是樹因此不要輕易修剪樹木內生枝條。
A tree without branches is not a tree. -Alex Shigo 1985.
資料來源:
KENNETH RONALD JAMES
Submitted in total fulfilment of the requirements of the degree of Doctor of Philosophy October 2010 Melbourne School of Land and Environments The University of Melbourne
The council prunes trees for health and safety reasons. Trees are also pruned in response to proven instances of tree-related subsidence and to resolve nuisances covered under UK law, for example a tree blocking a highway.
The council does not prune or remove trees for the following reasons:
Interference with satellite, TV or media reception
Touching telephone wires
Falling leaves, fruit, pollen, honey dew or bird fouling
Where a tree is considered to be too large
Obstruction of view
Overhanging branches
Lack of/too much light
Because someone is willing to pay
The perceived risk that a tree may damage a building
Pruning requests made to the council involving any of the above issues will be logged. If pruning is due as part of the routine maintenance programme of the tree in question, consideration may also be given to any logged issues.
Additional information
For more information on how Ealing Council manages trees throughout the borough, please refer to the Ealing tree strategy.
Picked up this London Plane pollard fall into the road dashcam footage through a Facebook post (hat tip to Linda Saretok). The dashcam footage is here.
The photos show the changes in hard standing going back to 2008 from Google Street View.
The main resurfacing was between 2008 - 2012.
Half the surfacing at the structural roots changes to black stuff between 2012 - 2014
An additional rectangle of black stuff is added shop-side between 2016 - 2017
Then some crops of the uprooted tree.
From the dashcam footage it looks like it's rotated by about 90 degrees when it fell. The decayed roots at about 9 O'Clock are what were facing South Ealing Road - the direction the fell.
The most intact roots, with the root hairs, looks like it's come from under the most recent black topdressing between 2016-17
I was asked about how this would’ve been risk assessed by VALID. Here's my take on it with VALID's Tree Risk-Benefit Management Strategy. It's based on the dashcam footage and Google street view images and is made with those limitations.
This a 'Very High' level of occupancy (on average more than one person. Or more than one vehicle. Or more than person and more than one vehicle). It would've been managed by Active and Passive Assessment. There are three levels of Active Assessment. Basic, Detailed, and Advanced.
Passive Assessment - Risk is Acceptable If you walked or drove past this tree, there's no obvious tree risk feature to trigger taking a closer look.
Active Assessment
Basic Assessment - Risk is Acceptable On foot. There are no obvious tree risk features. It looks there has been no recent major infrastructure work within the structural root zone to warrant any concern. I can't see a trigger to go beyond a Basic Assessment to a Detailed level. New surface dressing in structural root zone would’ve encouraged a tap at the root collar.
Detailed Assessment - Risk is Acceptable I'm not sure a Detailed Assessment, triggered because some decay was picked up by a sounding hammer, would've revealed the extent of decay in the roots. There's some uncertainty about this, but the buttressing looks like it's nicely developed for a tree of this size, age, and management history.
Advanced Assessment - Risk is Not Acceptable I think only an Advanced Assessment, involving a Static Load Test, would've established that the tree had a Safety Factor of less than 1.0. But I can't see a trigger to reasonably justify this.
It wasn't THAT windy on Sunday in South Ealing. I wonder whether primary failure happened with the storms we had earlier (or last year), and it's only as the tree's come into full foliage, 3-4 years (?) into its pollard cycle, that the moderate wind load intercepted by the canopy hit the critical point.
Of course, it could be a 'black swan'. Generally, the chances of regularly pollarded London Plane, with no obvious tree risk features, and no obvious recent root damage, falling are incredibly low.
It now presents an interesting problem for the council. That paving specification at pedestrian crossings might be of concern given how long ago it was done and the root system resembles that of spring onion.
