> Date sent: Mon, 24 Oct 1994 19:52:00 +0200 > From: KEN POLSSON 387-6948 <KPOLSSON@galaxy.gov.bc.ca> > Subject: re: stem analysis > To: forest@nic.funet.fi > Priority: normal Hello, Ken: Your question should have been answered by some one(s) from forest measurition easily. I don't know why you have not get proper answeres yet. However, here I am trying to answered your question. > MR> Most of the first samples are taken at chest height / 4.5 feet. > MR> What is the significance of chest height / 4.5 feet? > > I think it is just a convenient height that: > - is above butt swell, > - everyone can measure diameter at this height, and > - it is above the height of most competitive brush, so that the > tree is well established. > > In metric, we use 1.3m, rather than a direct conversion to 1.37m. The first question is above "chest height". Actually, in forest literature it is normally called "breast height", thus the diameter at this point is named "breast height diameter" or "diameter at breast height", or simply using DBH (d.b.h.). Why foresters use breast height? There are major reasons. The first one is the convenience. When one measures how thick a tree is at this point, one does not need to bend your waist or to use ladder. Also for convenience, when feet is used, we use 4.5 feet. while metric system is used, we use 1.3 m. In any case, 7 centimeter difference in height around this point do not make any meaningful difference in diameter. Indeed 1.2 or 1.5 m point did used or may still be used in some countries or places. The second reason is that this point (DBH) is a good reference to estimate timer volume of a tree. Thus volume tables are based on dbh, more precise tables are based on dbh and height. Still more precise tables may use diameters at several height positions along the stem, which makes measurement difficult and slow. > MR> Is there a "standard" distance to be maintained between samples? > MR> If not, what determines how often the samples are collected? The purpose of stem analysis is to find out annual growth of trees, including diameters (at differet point), height, and volumes. Then this information can be used to correlate climatic soil or other enviornmental factors for modeling or predicting growth. With stem analysis, one can draw a vertical section figure of a tree, seeing growth situation at "any points" of the tree. Since samples collected only at certain height points, the growth at other points are infered from. Thus the growth at other points other than the sampled points is not the real situation. If you want your analysis more precise, you should collect samples at short distance. Still more precise method is to split the tree. This is really done by foresters in some cases. The normal samples for stem analysis should include 1 sample at buttum, 1 at 0.5 meter high, 1 at dbh. then every 2 meters. The reason for collecting at 0.5 meter is that the buttress part changes quick and generally showing hyperbola curve. If the tree is very big and stem is very regular, you may take samples at longer distance, otherwise you may take samples at short distances. This is also very much depending on how precise you wand in your results and money and labor you will afford. Yingmou Yao, Ph.D. plant breeding (Ms. Forestry) Dept of Plant Biology University of Helsinki > MR> Once the samples are collected, does what is analyzed vary according to > MR> what the individual researcher is studying? > > Several people where I work have done stem analysis many times. I > think they take ten detailed measurements of diameter outside bark. > But aside from that, the level of detail of dissecting the trees will > definately depend on what they are analysing. They will usually > split each log, and identify exactly where the "pith nodes" are, > at least for the species where this is possible. They want to know > how the tree grew to where it is now. > > For the most part, the stem analysis we do is to calibrate a tree > growth model. We typically choose open-grown trees, so that we can > model the extreme condition of unrestricted growth, both up and out. > >From the stem analysis, they will create various equations to model > height growth, ring width, basal area increment, crown shape, etc. > In one case, a researcher spent many months measuring branch angles > and foliar volume. > > Now that I've said all that, I'll step back again, and let the *real* > foresters correct any points that I may have gotten wrong... > > --- Ken Polsson - Stand Modelling Analyst - BC Ministry of Forests --- > --- kpolsson@galaxy.gov.bc.ca --- "The opinions expressed --- > --- CompuSpec BBS (604)479-0418 --- here are not necessarily --- > --- RelayNet: ->1797 --- the views of my employer." --- > > > >
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