Fork failure Duncan Slater

[Amelanchier]

do you realise how stupid that sounds? does Duncan understand Shigo's model?

 

Would you like to explain why it's stupid or are you just happy with heckling?

 

Perhaps once you have systematically refuted that point you might try the other five...?

[scotspine1]

Would you like to explain why it's stupid or are you just happy with heckling?

 

Perhaps once you have systematically refuted that point you might try the other five...?

 

Tony,

 

Page 86 of Modern Arboriculture is right in my opinion, I have split wood many times and have seen exactly what he is referring to.

 

Your belief in Duncan's paper is based on faith. My belief in Shigo's model is based on experience.

 

Remember Tony (both of you).........human progress is an illusion.

[Tully]

Tony,

 

Your belief in Duncan's paper is based on faith. My belief in Shigo's model is based on experience.

 

Remember Tony (both of you).........human progress is an illusion.

 

I am sure Darwin faced similar opinions.

[Amelanchier]

Tony,

 

Page 86 of Modern Arboriculture is right in my opinion, I have split wood many times and have seen exactly what he is referring to.

 

Your belief in Duncan's paper is based on faith. My belief in Shigo's model is based on experience.

 

Remember Tony (both of you).........human progress is an illusion.

 

Do you split your wood in a CT scanner?

 

A very transparent deflection Tim and if I may say, unworthy of your considerable talents. You haven't refuted any of the above problems with Shigo's model and I'll keep bringing you back to that despite your tempting and well aimed sideline into epistemology.

 

I suspect you're bored and this is sport .

[scotspine1]

Ok Tony,

 

maybe this would help Duncan in his research -

 

Mechanical stability of trees under dynamic loads -- James et al. 93 (10): 1522 -- American Journal of Botany

[Amelanchier]

Ok Tony,

 

maybe this would help Duncan in his research -

 

Mechanical stability of trees under dynamic loads -- James et al. 93 (10): 1522 -- American Journal of Botany

 

Maybe it would. How about those 6 points?

[D Mc]

Below is a letter to the editor from Kevin T. Smith, Ph.D., in response to D. Slater's presentation on branch attachments. Strange format but hopefully you can read it. I tend to agree with Kevin.

 

Dave

 

 

Arboricultural Journal, Letter to the Editor, Page 1 of 3

Kevin T. Smith, 7 February 2011

The recent article “Towards a new model of branch attachment) 1 by D. Slater and C. Harbinson

2 (Vol. 33: 95-105. 2010) strongly criticizes the model of branch attachment described by Dr. Alex

3 Shigo in 1985. As I recall, my first glimpse of Shigo’s model was literally drawn on the back of

4 an airline cocktail napkin. He rushed into the lab that morning, in full flush of his “eureka”

5 moment. At the time, I was a postdoctoral researcher with Dr. Walter C. Shortle who was part of

6 Shigo’s team at the US Forest Service. The ball-point sketch showed the key elements of

7 overlapping branch and stem tissues, with the vasculature of branch and stem continuous only on

8 the underside of the branch.

9

10 For me, one crucial difference between the 1985 and 2010 publications rests on the distinction

11 between codominant stems (referred to as “forks” in the recent article) and branches.

12 Codominant stems arise from multiple buds at the shoot apex or the fusion of appressed shoots.

13 Branches arise from lateral or epicormic buds. Slater and Harbinson maintain that for

14 arboriculture, the distinction is arbitrary and solely determined by the relative size of the two

15 joined members. For them, the shape of the surfaces or “topological equivalence” is critical. I

16 agree that most of the mechanical load of a uniform column is borne by the outer circumference.

17 But the relative strength of the branch attachment is due to the overlapping stem and branch

18 tissues which are absent in codominant stems (E. Gilman. 2003. Journal of Arboriculture 29(5):

19 291-293).

20

21 Shigo emphasized that unlike the codominant stem crotch, the branch base contains constitutive

22 and inducible boundaries that facilitate branch shedding and resist the spread of infection. This

23 distinction is a reason to avoid tree topping and the removal of large codominant stems (which

 

Arboricultural Journal, Letter to the Editor, Page 2 of 3

Kevin T. Smith, 7 February 2011

 

have no collars) versus acceptable pruning cuts to the outside of the 24 branch collar. Such “natural

25 target pruning cuts” as promoted by Shigo minimize injury to stem tissue and the loss of the

26 protection zone at the branch base. Distinguishing intact codominant stems from branches can be

27 difficult (A. Shigo. 1986. A New Tree Biology. Fig. 12-12).

28

29 The substantial difference in structure of the attachments of branches and codominant stems is

30 readily seen in dissection. Of course, the practicing arborist or student can’t dissect every

31 encountered union, but transverse and axial dissections of a few of each with proper

32 interpretation would make clear that the differences are not merely of relative size of the joined

33 members.

34

35 A complete point-by-point response to Slater and Harbinson (2010) is not possible in this space,

36 but that may not be necessary. Some of the difficulties come from simple language usage. The

37 recent article points to the obvious attachment at the upper side of a branch and stem as

38 refutation of Shigo’s description of the connection being exclusively beneath the branch. For

39 Shigo, connection always meant communication or flow. Back in the old days of wired

40 telephones, lack of a phone connection didn’t mean the absence of wires, just that no message

41 was flowing through them! The lack of connection described for the upper part of the

42 branch/stem union referred to the lack of flow in the plumbing of the wood, not the absence of

43 contact.

44

45 Other difficulties come from the artistic limitations of representing the 4-dimensional process of

46 growth at the branch/stem union in 2 dimensions. The “tail” to which Slater and Harbinson refers

 

Arboricultural Journal, Letter to the Editor, Page 3 of 3

Kevin T. Smith, 7 February 2011

 

to in Shigo’s illustration is simply the growth increment 47 which is continuous and confluent

48 through the lower portion of the branch and the stem. Conceivably, that connection could be

49 drawn to the root collar, but would make the illustration unwieldy. Shigo had the illustration

50 drawn to show the length of connection along the stem axis to be in the same proportion as for

51 branch knots in decaying logs.

52

53 The biomechanics of trees has a lot to teach us and we have a lot to learn! We don’t have to

54 blindly accept old teaching just because of tradition. Nor do we need to jump on the latest

55 bandwagon that passes by. The challenge for the practitioner and the student is to understand the

56 biological context for the elegant mechanical engineering that enables trees to survive and thrive.

[Amelanchier]

Thanks for posting that! I'm using my phone at the moment so I'll edit the format in a repost when I get a chance.

[KTSmith]

The post by D Mc seemed to be a bit garbled, above, so I have attached my letter to the editor of the Arboricultural Journal below. Please excuse the redundancy!

 

****

The recent article “Towards a new model of branch attachment) by D. Slater and C. Harbinson (Vol. 33: 95-105. 2010) strongly criticizes the model of branch attachment described by Dr. Alex Shigo in 1985. As I recall, my first glimpse of Shigo’s model was literally drawn on the back of an airline cocktail napkin. He rushed into the lab that morning, in full flush of his “eureka” moment. At the time, I was a postdoctoral researcher with Dr. Walter C. Shortle who was part of Shigo’s team at the US Forest Service. The ball-point sketch showed the key elements of overlapping branch and stem tissues, with the vasculature of branch and stem continuous only on the underside of the branch.

 

For me, one crucial difference between the 1985 and 2010 publications rests on the distinction between codominant stems (referred to as “forks” in the recent article) and branches. Codominant stems arise from multiple buds at the shoot apex or the fusion of appressed shoots. Branches arise from lateral or epicormic buds. Slater and Harbinson maintain that for arboriculture, the distinction is arbitrary and solely determined by the relative size of the two joined members. For them, the shape of the surfaces or “topological equivalence” is critical. I agree that most of the mechanical load of a uniform column is borne by the outer circumference. But the relative strength of the branch attachment is due to the overlapping stem and branch tissues which are absent in codominant stems (E. Gilman. 2003. Journal of Arboriculture 29(5): 291-293).

 

Shigo emphasized that unlike the codominant stem crotch, the branch base contains constitutive and inducible boundaries that facilitate branch shedding and resist the spread of infection. This distinction is a reason to avoid tree topping and the removal of large codominant stems (which have no collars) versus acceptable pruning cuts to the outside of the branch collar. Such “natural target pruning cuts” as promoted by Shigo minimize injury to stem tissue and the loss of the protection zone at the branch base. Distinguishing intact codominant stems from branches can be difficult (A. Shigo. 1986. A New Tree Biology. Fig. 12-12).

 

The substantial difference in structure of the attachments of branches and codominant stems is readily seen in dissection. Of course, the practicing arborist or student can’t dissect every encountered union, but transverse and axial dissections of a few of each with proper interpretation would make clear that the differences are not merely of relative size of the joined members.

 

A complete point-by-point response to Slater and Harbinson (2010) is not possible in this space, but that may not be necessary. Some of the difficulties come from simple language usage. The recent article points to the obvious attachment at the upper side of a branch and stem as refutation of Shigo’s description of the connection being exclusively beneath the branch. For Shigo, connection always meant communication or flow. Back in the old days of wired telephones, lack of a phone connection didn’t mean the absence of wires, just that no message was flowing through them! The lack of connection described for the upper part of the branch/stem union referred to the lack of flow in the plumbing of the wood, not the absence of contact.

 

Other difficulties come from the artistic limitations of representing the 4-dimensional process of growth at the branch/stem union in 2 dimensions. The “tail” to which Slater and Harbinson refers to in Shigo’s illustration is simply the growth increment which is continuous and confluent through the lower portion of the branch and the stem. Conceivably, that connection could be drawn to the root collar, but would make the illustration unwieldy. Shigo had the illustration drawn to show the length of connection along the stem axis to be in the same proportion as for branch knots in decaying logs.

 

The biomechanics of trees has a lot to teach us and we have a lot to learn! We don’t have to blindly accept old teaching just because of tradition. Nor do we need to jump on the latest bandwagon that passes by. The challenge for the practitioner and the student is to understand the biological context for the elegant mechanical engineering that enables trees to survive and thrive.

****

[Tony Croft aka hamadryad]

I am sure Darwin faced similar opinions.

 

and his work is also being improved upon, his work was just the beginning, the story of evolution is still to be told.