No Country for Old (and Young) Trees

Perhaps in view of the incidences of large trees, especially Khaya sp. (African mahogany) falling down and causing loss of lives and damage in property, they have been felled in large numbers. Well except in the case below, that tree has been "halved".

 

Photo on the left mentioned in this post: http://openplants.blogspot.sg/2016/10/pruning-of-trees-for-wind-resistance.html

The Rain tree (Samanea saman... or as the rest of the world know it by Albizia saman) that used to be in that spot used to be as large as the one in the background. I suppose defects on the tree called for it to be removed, and it was replaced by this young Rain tree. But it did not last long, possibly broke in half by strong wind travelling through that "wind tunnel". Its root ball was dug up, and the hole was left uncovered.

Photo on the left mentioned in this post: http://openplants.blogspot.sg/2017/04/arboriculture-happenings-at-bugis-area.html

 A replacement tree of the replacement tree seen on 23 Oct 2017.

Papers Excerpt - Strength Loss Due To Decay

Journal of Arboriculture 18 (4): July 1992
Determining Strength Loss from Decay by E. Thomas Smiley and Bruce R. Fraedrich

SL% = d^4/D^4 x 100 ;Originally developed by engineers to compare the strength of pipes.
SL% = d^3/D^3 x 100 ;Wagener modified it to take into account the irregularity of  trees.

SL% =     d^3 + R(D^3-d^3) x 100
               -------------------------------
                              D^3
SL = Strength loss
d = Diameter of hollow and/or nonstructurally sound wood
D = Diameter of sound wood
R = Ratio of cavity opening to stem circumference

The R(D^3-d^3) modification was developed by the Bartlett Tree Research Laboratories to account for wood which is "missing" at a cavity opening.

Among trees that broke from internal decay, average strength loss was 33% with a SD of 22% [could be between 11% and 44%].

Severity of decay in the trunk predisposes trees to failure [felling, breaking into half, etc.]. Other factors include crown density, branching structure, leaning, location of decay (e.g., in crotches), site exposure, storm severity, [and might I include inherant wood strength]. A lower threshold (20-25%) may be used for trees that are more predisposed.


Journal of Arboriculture 27(2): March 2001
Comparing Formulae that Assess Strength Loss Due to Decay in Trees by Brian Kane, Dennis Ryan, and David V. Bloniarz