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I was wondering if you help me how to use Transect-based sampling to select sample trees

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closed as unclear what you're asking by James, kmm, rg255, fileunderwater, March Ho Jul 22 '16 at 0:11

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More detail on what your studying, the question you want to answer, and how you want to go about doing it would be very helpful. But I can answer this basic question of how to select tree's with a transect.

You will need:

  • Forms to fill out for data.
  • A compass.
  • A transect tape (really a very long tape measure, about 100 yards or meters).
  • A sampling design that fits your study. (I'm assuming you already have this, but if you want to talk more about it see above.)
  • A wooden meter stick.

Once you are in your 1st area and ready to select a random subset of trees.

  1. Pick a random spot. (Usually done by throwing a stick or water bottle over the back of your head and going wherever it lands).
  2. Pick a random number between 0-360. This will be the random direction you go in from your random spot. Find north on your compass, then which way your random number points. In your mind mark a way point in that distance you can walk to (a mountain peak, a distinct tree, anything).
  3. Stick the beginning of your transect tape in the ground and start walking. The length that you walk should be predetermined from your study design.

Now you'll select trees to perform whatever measurement that you've decided on. But how? Most forests are not so dense that a straight transect tape will touch many of them. This is where the meter stick comes in. Walk back down the transect and choose any tree that comes within 1 meter of the tape on either side. Is the forest not dense enough to include enough trees that way? Then simply increase the length of your transect, or length that you measure out from the transect (ie. 2 meters, or 3 meters).

This is technically called a "belt transect". And it used in natural resources to measure things that are abundant, but not very dense. Such as trees in a forest or shrubs in the desert. It is essentially a giant quadrat.

Why all the randomness? Humans are naturally bias. Even if you think you are not being bias, you could subconsciously be choosing a starting point in a dense patch of trees, or a direction that will let you measure your favorite species. A rigorous study relies on a random sample of a population of interest, and small non-random decisions like this means it is not a random sample, but a bias sample.

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  • $\begingroup$ Thanks for the prompt reply. Some detail about my study I want to investigate the effect of browsing on above ground carbon-stock in boreal forest. I have two treatments browsed and unbrowsed. 20 x20 meters plots are randomly selected to exclosure or unexclosed plot on the site. Each plot has four subplots measure a radius of 2 meters. To measure the carbon stock I need to transfer sample trees to the laboratory. I want to select a total of 80 sample trees. I found out Transect-based sampling will easy method to select my tree sample. let me know if you need more detail. $\endgroup$ – Nunu Jul 20 '16 at 14:36
  • $\begingroup$ Hmm, based on what you said you should do it a bit differently. Within each 20x20 meter plot the 4 subplots should be placed either randomly or at equal intervals. If you will have enough tree's with this will depend on the tree density. You can increase the radius or number of subplots to account for this. $\endgroup$ – Shawn Jul 21 '16 at 12:09

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