Monday, July 9, 2007

IS AHK/China --- Review of BS 5837 Trees in Construction

*** Attention pirates: We can not stop you from reading our correspondences, but do not broadcast your own messages to our members without their permission. Our members are the elite of the HK/China society & do not want to hear from you without prior consent. If you break this rule, you have intruded into our privacy & each member of our Station may take their own individual actions towards you which will be outside the control of this Station. May you be warned on this!! ***

*** Please do not be alarmed if you do not see your name appearing on the distribution list. We are hiding your valuable privacy from the internet pirates. ***

Dear All,

The BS 5837 'Trees in relation to construction --- Recommendations' is the usual tree protection reference guide for a lot of tree work in HK. Even the recent Wong Tai Sin Tree Transplant specifications are making reference to it, although they are referring to the older version of 1991 edition. This older version is now replaced by the 2005 updated version.

Like any other British Standards, the BS 5837 is well written with consideration on all aspects on tree work, although the main emphasis is on temperate trees growing in the British Isles. BS 5837 is a joint effort with contribution from the UK Arboricultural Association, Institution of Civil Engineers, Institution of Structural Engineers, Landscape Institute, Royal Institute of British Architects (RIBA) & a few othres. Therefore it can be seen as an agreement between arborists & professionals of the other trades.

What is significant in this Standard is that the name of 'Arborculturist', or 'Arborist' which we normally call for short, has ever appeared in any of the British Standards. As the British Standards are frequently used in law cases in the UK, Commonwealth & HK, in a way, the position of Arborist is now given a recognition in Courts if this British Standard is ever referred to. This is a significant advance in aboriculture for us in HK indeed.

The term 'Arboriculturist' is defined in section 2.1 of BS 5837 as follows:

"person who has, through relevant education, training & experience, gained recognized qualifications & expertise in the field of trees in relation to construction."

There is no further detailing on the qualification & it will be up to the Court Judges to decide whom an Arborist is. In general, certified arborists, urban foresters, persons holding certificates in arboricultural training, members of the UKAA, etc. would be considered to qualify into the 'Arboriculturist' definition, unless special legal circumstances prevented it so.

BS 5837:2005 has given guidance for a balanced approach on deciding tree preservation on a construction site in a Flow Chart form for easy refernece as in Fig.1. In many of the decision making processes, the requirement of the Arboriculturist is specifically referred to. Trees are carefrully categorized for Removal & Retention. Subcategories are listed to further exemplify on how trees are retained for their arboricultural values, landscape values & cultural values, & not just for their sizes & maturity. Also, a Young Tree is regarded to be a tree with a stem diameter of below 150mm at DBH, & is considered to be relocabable. Transplantation of Mature Tree is not recommended by this Standard, in line with ISA practices.

Tree survey in BS 5837:2005 is not limited to just sizes, amenity value & health condition only, but a concept of Arboricultural Implication Assessment (AIA) is brought up to consider the full impact of the retention effect of the trees in concern in a development. The life expectency of the tree & its future integration with the development are considered. This is an excellent approach indeed.

With regard to the Tree Protection methods on site, BS 5837 has given several details on the approach & also a guidance on the minimum distance between Young Trees & structure in Table 3, although this Standard is meant to refer to temperate trees in the British Isles. If we refer to this Standard for our subtropical trees in HK, we have to make allowance for that.

Design recommendation is also given to new plantings in a development with considerations for the future impact of the new plantings. A good design in the beginning will save a lot of maintenance work in future, & this Standard recognizes this effect in its section 13.

Lastly, various British laws concerning trees in the design & protection are listed out. It can be seen that trees in Britain are well protected by legislation & are required to be managed by trained professionals.

In summary, BS 5837:2005 is an excellent guide. This Station recommends any professionals working in this field to get a copy & study through it. In ISA, there is a similar book called "Trees & Development --- Matheny & Clark 1998" which can be purchased on ISA web of . This book gives great details on tree design & protection in a development & is 184 pages in total, comparing to the 33 pages of BS 5837. With this book & the BS 5837 on hand, a lot of the confusions in dealing with trees in a development process can be clarified, although the help of a professional arborist is always recommended to give advices all round.

best regards,

Sammy Au
Station Manager

No comments: