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Welcome to The Green Man Arboricultural Consultancy

This website supports the consultancy business based in North Wales and which operates throughout the United Kingdom providing a wide range of arboricultural services including: home buyers tree reports, tree condition reports, development site surveys and reports, woodland assessment and management plans and general advice relating to trees.

For further information or to discuss your requirements please contact us on: 01978 821 851/ 07981 912 162 or via green.woman@hotmail.co.uk

Sunday, 23 November 2008

An Introduction to Tree Biology: How Trees Grow # 1

Understanding how trees grow enables us to better care for them throughout their lives.

Trees do not grow from the bottom up, continuing to push from the bottom of their stems, rather they elongate from their shoot tips and expand around their circumference by generating new cells annually.

The end of every shoot contains an area termed a meristem which develops new growth each year. This new growth is called extension growth. New layers of cells are developed at the end of an existing shoot.

The length of the extension growth in any one year is a result of the trees available energy and therefore can give an indication of the trees health. Extension growth may vary from year to year dependant on available energy however, in a healthy tree would appear uniform from year to year.

This picture (Picture 1 - Extension Growth) shows the extension growth on a Rowan tree (Sorbus commixta 'Embley'). The rings around the shoot at the bottom of the picture are the terminal or apical bud scale scar.

In other words this is where the tree grew to last year and marks the start of this years extension growth. (The terminal bud scale scar is not so obvious on all tree species however on rowan and cherry trees it is particularly easy to observe.)

As this is occurring another meristematic area beneath the bark of existing shoots, branches, and the main stem, develops new growth to provide an annual increase in the width of a tree, and its branches.

Therefore at the same time that the tree is growing taller by production of annual extension growth it is growing wider by production of annual tree rings. These are the rings that can be counted in the cross section of a felled tree from which people calculate tree ages.

When observing a young tree predictions can be made regarding its form in maturity from it’s existing branch structure.

This picture (Picture 2 - Beech Union) of a beech tree shows a co-dominant branch union, where two branches have developed almost at the same time and are therefore of a similar size.

The branches would have started growing with an acute angle between them indicating that in maturity, through the development of annual ring growth around the circumference of each branch, the branches would eventually come into contact with each other.

Tight unions can be structural defects occurring in stems, branches and shoots, and can be susceptible to failure. In the instance of the beech tree, in Picture 2, as the branches continue to develop growth around their circumference they push against each other and the result may be failure of one of the branches or splitting of the union.

The union in this Goat Willow (Picture 3 - Willow Union) has split and although the tree has managed to remain intact the split has progressed down the main stem and the tree is predisposed to failure. (There is another defect associated with tight unions termed included bark which will be discussed at a later date. Not all tight unions develop included bark.)

In a young tree identification of such defects means they can easily be remedied. In the instance of the beech tree (Picture 2) one of the branches could have been removed when the tree was young by means of secatuers resulting in a small wound that would have quickly callused over promoting the remaining branch as the lead stem of the tree.

As you can see it would be extremely difficult to remove one of these branches now and the resultant wound would be much larger and significant in terms of wounding.

Identifying growth and structural defects in young trees and affecting the necessary pruning to remedy them is termed formative pruning.

Formative pruning should be undertaken at the nursery stage. It is something to be aware of when purchasing trees. If formative pruning is undertaken it can negate the requirement for significant and costly tree pruning at a later date or prevent tree or branch failure.

It is important that if you have any concerns regarding the form or condition of your tree/s you seek professional advice from a qualified arboricultural consultant. They usually offer advice for free and will be able to advise you whether further investigation is required and what if any remedial actions you should or can undertake in order to address your concerns.

They will also be able to recommend a good arboricultural contractor to undertake any proposed tree works. Contractors are not all consultants and tree works and tree consultancy should be treated as separate areas of expertise. N.B. Many arboricultural contractors have a good consultancy knowledge however this should not be assumed.

6 comments:

  1. I would like to contact you regarding a speaking engagement for ISA Ontario in February 2011. I am President Elect and Education Chair. Please contact me when you have time.

    Linda Hawkins
    lahawkins77@gmail.com

    ReplyDelete
  2. Dear Green Man,

    After reading about tree growth in a few articles, I still feel left wanting to know more, which to my surprise I couldn't find in any articles on tree growth so far.
    How does a tree decide when and where it will grow new buds or when it will grow leaves instead of branches and at which location on the tree?
    Is it somehow aware of the location of all its existing leaves, so it would grow new branches and leaves in areas not covering existing leaves? I mean when, and why does it decide to build a new branch instead of a leaf, or flower and vice versa? And where?

    As I have come to understand buds can contain leaves, flowers, or branches. Does that mean they could also develop into two things at the same time? If not, would the order be to always first grow a new branch and then leaves along it, or somehow simultaneously? As the brance develops this year it brings leaves with it?

    I am just trying to understand how, when and why a tree develops new parts, it fascinates me, and I love trees.

    For example I just had a thought recently; I was trying to follow the development of a tree in my mind from its seed, to a little tree. And the only point I got to before wondering what will be next, is a little green plant with two little leaves coming out of the soil (forgive me for not knowing the specific name for this :).

    From there I just wondered, what next? How much further would it grow upwards before growing a new branch, and when it does, how many branches would it start growing simultanously, and at which location? And would it perhaps continue developing new leaves on its main "stem" first, before growing brances, so it could collect more energy?

    I have so many unanswered questions and don't know where to find the answers. Please help me out.

    Thank You in advance, I would greatly appreciate it.
    Kind Regards,
    Sean

    ReplyDelete
  3. Hi Sean, Thanks for your brilliant message, its always great to come across someone who has your kind of thirst for knowledge about trees. It is a little too much to answer in a comment but is exactly the kind of thing I cover.

    You may have noticed that my blog is moving to the following website http://nesshop.co.uk where I will be covering tree biology and many other topics in great detail in the weeks and months to come. Can I suggest that you visit there and register as a member? You will then be able to keep up with any new posts and I will make sure that I start with an introduction to tree biology covering the questions you have posed.

    I am afraid I am going on holiday for 2 weeks this evening however please come back and I will start posting about tree biology on my return.

    I know there is not a great deal available on the internet about arboriculture and although I could direct you to books that would help I will be going over everything you have asked about on my website.

    I hope you will stay tuned as they say and as time goes on you have further questions please don't hesitate to get in touch or leave another comment.

    Thanks again and bye for now.

    ReplyDelete
  4. Thank You so much, I feel so happy I found Your website! :)

    I can't wait, I will definetely follow You over there and already registered on - and bookmarked the new website.

    ReplyDelete
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