ISA HK/China --- Review of Dr. Shigo's Tree Biology series

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Dear Station Members,

Arboriculture is an advancing profession & becoming a Certified Arborist (CA) is only the beginning of serious learning. Countless knowledge of arboriculture is confronting CA & modern Tree Biology is one very important subject for any CA to master. CA without good knowledge of Tree Biology is like a doctor not knowing well the human body. Can this CA go very far?

When it comes to modern Tree Biology, any CA would give respect to the name of Dr. Alex Shigo. It seems to be this giant who woke up the world on looking at trees with a totally new concept & Dr. Shigo practically has revolutionized Tree Pathology upon his research. His influence on arboriculture is profound & inviting. Without his research, maybe many Arborists would still carry on the old way of Flush Pruning, Wound Dressing & Topping the trees.

Dr. Alex Shigo, respected by many Arborists as the 'Founder of Modern Arboriculture', has published hundreds of research paper & several books on Tree Biology, Tree Pathology & Tree Anatomy. Most of them are not available in our part of the world for unknown reason. In order to discover his knowledge, this Station has spent some months to study through his published education as follows:

1. A New Tree Biology with Dictionary --- 636 pages for the book + 144 pages for the dictionary

2. Tree Pruning --- 192 pages

3. Modern Arboriculture --- 440 pages

4. Tree Anatomy --- 104 pages

5. Dr. Shigo's website (http://home.ccil.org/~treeman/shigo/index.html) & research papers

It is impossible to give a detailed account of the information contained above in a simple Station Mail. Our Station Members are encouraged to purchase Dr. Shigo's books & to browse through his website to understand the very useful information contained within.

The Station Manager has studied for years on Horticulture & Landscape Design to facilitate his work in nursery production & landscaping. But when he came to study Dr. Shigo's series, they turned out to be another world of knowledge that he had never seen or heard before. Dr. Shigo's Tree Biology is a unique vision of its own & appears to be rather different to conventional teaching. In fact, some of his research would be regarded as a challenge to conventional wisdom in the biology domains.

Dr. Shigo was the Chief Scientist of the US Forest Service from 1959 to 1985 to study the Discolorization & Decay in Forest Trees. In his work, he had found repeated patterns of tree responses deviated from conventional knowledge of wounding & pathogen development. He discovered that trees belong to a Generating System & are great Compartmentalizers to fight decay. He had carried out many research to prove his thinking.

Dr. Shigo challenged the wisdom of conventional Tree Biology in studying under microscope for dead cross sections of tree parts instead of longitudinal dissections of living trees which would give accounts on boundaries of defence & compartmentalization in fighting pathogen invasion. Dr. Shigo has taken the pain to dissect over 15,000 trees with chainsaws to study living & dead trees for his analysis. It may appear to be difficult to repeat Dr. Shigo's work today by dissecting so many trees anywhere in the world. We seem to be running out of trees nowadays.

Dr. Shigo looked at a tree as part of an ecological system & would incorporate tree with the organisms living on or around it together with the environment interacting with it. Whereas conventional Tree Biology would tend to focus on tree parts & the physiological functions of each part, Dr. Shigo would combine all the living parts into a system & call it Symplast. He studied the energy transfer of Symplast in performing its daily functions such as growth, maintenance, storage & defense, & viewed the tree as an energy pump where energy reserves are moved & converted in accordance with the requirement of the tree to respond to the outside environment. He had looked at tree from an angle where hardly anybody had done the same before.

Most CA in HK would probably know Dr. Shigo through the theory of Compartmentalization of Decay in Trees (CODIT) which is a tested subject in the exam. CODIT has become perhaps a distinction between the study of arboriculture with horticulture in major when it comes to Tree Biology. However, CODIT is really a simplified model & Dr. Shigo's literature would go into details of Reaction Zone & Barrier Zone in microscopic anatomy. Chemistry would come into play & anti-microbial compounds at cell level would be discussed. The knowledge would go far beyond the CA exam requirement.

Another point in Dr. Shigo's research suggested that CODIT are strongly affected by genetics. He tested Flush Cuts (forbidden by ISA education mostly) on trees of strong CODIT & found decay development well contained in some trees. On trees of same species & same size in the same lot, other trees would perform poorly, suggesting that trees are like animals with grading & fitness. The higher grade would be the winner of survival & the lower grade would perish by natural selection. His comment on our current forestry practice of harvesting only higher grade timer would leave behind community of poor grade to survive, which may lead to the downgrading of performance of our forest in future. By this theory, Dr. Shigo criticized our current nursery practice of ensuring high percentage success in seed germination & seedling production, to bring trees of poor genetic into our urban environment which would lead to maintenance aggravation.

In reviewing Dr. Shigo's literature, this Station has found Dr. Shigo's education is not easy to read or understand at all. For us here in HK who are used to British education, Dr. Shigo' writing in colloquial North American world be almost uphill battle in every page. For those whose English is not international enough may find it almost impossible to apprehend Dr. Shigo's literature. Also, Dr. Shigo's education is really meant for the understanding of researchers & practitioners. Anyone without sound background in Biology may find it hard to even proceed. Our AFCD Station Members are recommended to study Dr. Shigo's series because they may be relevant to their work especially in Tree Pathology, although the information can also be applied to Urban Trees which tend to be planted as individuals rather than in groups in a much more hostile environment.

If Dr. Shigo's work is so difficult to understand, some may ask then why bother ?

It is because Dr. Shigo's research is required for Arborist service such as Tree Selection, Tree Installation, Tree Inspection, Risk Assessment, Pruning, Diagnosis & Treatment, Tree Protection during Construction, Cabling & Bracing, & writing up Legal Consultation. In the important field of Tree Assessment, Arborists would need to understand how cracks are formed, how decay would advance, whether mushrooms would topple a tree immediately or later, how rapid is wound closure, how cavities may affect wind stability, how topping could be corrected, how to inspect Cabling & Bracing wound, etc.& etc. Many information in the series can be used for writing up Arborist Report & used as Court reference in Legal Consultation. Arborists need to be fact-finding & truth-telling, & we can not comment with our personal opinion without facts & research. Dr. Shigo's work would provide this support.

Dr. Shigo emphasized on ' Trees must be touched to be understood.' For those who do not touch trees & try to understand his work, it would be as tasty as chewing leather shoes. Dr. Shigo also said ' Education starts when you doubt something. Education occurs when you resolve your doubts.' When the CODIT model was brought up in 1985, there was skepticism all around the world. Conventional biologists felt challenged & would not accept Dr. Shigo's finding. Many biologists in Asia today still have not come to acknowledge Dr. Shigo's research & carry on the old thinking. Treating trees to a lot of scholars are still to be like treating humans or animals. Trees do not appear to be well understood by our public from viewing comments in the media. We have a long way to go indeed.

This Station would recommend the able & serious to try to study through the research of Dr. Shigo to improve themselves. Some of his books can be obtained on ISA website while some of his research can be downloaded from the internet.

The Station Manager would be pleased to offer any help, no matter how limited or ignorant, on any problem that anybody might encounter on understanding Dr. Shigo's education series. Please do enquire when needed.

best regards,

Sammy Au
Station Manager

The ISA Mission - Through research, technology, and education, promote the professional practice of arboriculture and foster a greater public awareness of the benefits of trees. (www.isa-arbor.com)