Hello everyone,
My question is simple. I have some data of some little seedlings (3 months old) and I was checking the volume (it's not part of the experiment), but the measures I have are the stem length and the diameter in the base. I estimated the volume of the stem as if they were cylinders because I considered that the variation can't be so big in so small seedlings. But I wonder if it would be better to estimate it as a cone, for example. What would you recommend me?
Thank you very much,
Aitor
you can calculate the volume using the following formula:
V= d2h
where d is the diameter of the stem of seedling and h is the height of seedling
Foresters have developed equations for this purpose, but mostly applicable to older saplings and trees. Some years ago I have done such calculations for relatively small seedlings. The answer would be that for most species the real shape will be somewhere in-between a cone and a cylinder. We assumed a conical shape for young silver birch seedlings (Aphalo and Rikala 2003).
Article Field performance of silver-birch planting-stock grown at di...
I will suggest you to go through the following paper : Burdett A. N. 1979. A nondestructive method for measuring the volume of intact plant parts. Canadian Journal of Forest Research, 1979, 9(1): 120-122 Simple displacement method would be useful. You can try.
Check the morphology of the stem in some specimens and compare it with a cone. In case you have to assume such geometry, there are two options, often used in this studies:
i/ measuring two diameters (at both ends) and promediate. ii/ measure a central diameter (you will find that it is an "average" if you check it.
In any case, for comaprative studies (if it is the aim of the study) those are minor questions as long as you introduce a similar bias in all the samples.
In morphometry the growth is described by replication rates of basic elements. In woody seedlings the element can be a node with N axillary buds and a plastochron value http://www.amjbot.org/content/101/11/1821.full. Node geometry can be approximated by checking sections shape with a vernier scale. https://helda.helsinki.fi/bitstream/handle/1975/8533/silva_1997_31_3_%2810%29_godin.c.pdf?sequence=3
To calculate stem volume knowing basal diameter and length, you have to make an assumption about taper. In trees, the clear trunk excluding the root flare often tapers as a parabaloid (to calculate which you'd need either top diameter as well as basal diameter, or diameter at the mid-point), while the top part of the tree, within the crown, often tapers as a cone..
If you have only one diameter measurement you also have to assume that the cross-section of your seedling stems is circular, which may not be strictly correct, and you may also be most interested in stem volume in relation to some other variable (leaf area, growth rate etc).
It might be best to accept that you can calculate an index of stem volume, rather than actual stem volume. In that case the index would probably be equally informative whatever you assume about taper and cross-sectional shape.
Thank you very much. I'm getting a lot of interesting information out of this question.
I am curious! What's the species? Why do you need to calculate stem volume of 3 months old seedlings? I would recommend dry biomass.
Hello Raimo,
Nice to see you here :).
They are just some seedlings we had in some experiment here. I was thinking a bit about different things to measure, and I realized that it could be possible to measure volume... but I didn't know how.
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