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According to Measuring Trees:

The girth of a tree can be used to estimate its age, as roughly a tree will increase it's girth by 2.5cm in a year. So, simply measure around the trunk of the tree (the girth) at about 1m from the ground. Make sure you measure to the nearest centimeter. Then divide the girth by 2.5 to give an age in years.

According to Tree Age Equation:

Measure the circumference (in inches) of the tree’s trunk at breast height (or 4.5 feet above the ground). This is called the CBH.

  1. Take the CBH that you measured and divide it by pi (or 3.14159). This will give you the DBH (diameter at breast height) of the tree.

  2. Multiply the DBH by the “Growth Factor” that corresponds to the species of tree that you’re working on (found in the table below).

  3. You’re done! That number is the approximate age of the tree!

Now my question is which metric in lidR can provide me Circumference Breast Height (CBH) and Diameter Breast Height (DBH) values? And what are the default units of these metrics?

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    I agree with the accepted answer, there are too many assumptions, if you would have in-situ data you could constuct your own height-DBH curve to approximate it. This often works good enough if you have measures and only look at a SINGLE species, site, and layer. But you would need to collect this data first (or maybe you find some approximated allometric equation for your site and species). But with this error margin in place already, to use this extremely rough age-estimation on top of it will leave you with an error margin so big that you don’t need to bother imho.
    – Vincé
    Dec 7, 2023 at 14:13
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    As for your other question: diameter at breast height (DBH) ist measured at 1.3 m height and it's unit is CM. While the Circumfence at breast height (CBH) is also in usually, because one is sometimes calculated from the other as input for volume-calculations using the approximation of a circular shape for the stem.
    – Vincé
    Dec 7, 2023 at 14:13
  • @Vincé, thank you for the detailed guidance on this, cheers :). Dec 7, 2023 at 14:43
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    There does seem to be some research on this, a quick search revealed eg besjournals.onlinelibrary.wiley.com/doi/full/10.1111/… (but maybe that's terrestrial scanning... hmmm)
    – Spacedman
    Dec 7, 2023 at 16:23
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    @Spacedman extracting trees, yes, a lot of work. Extracting diameters no. At best some statistical inferences from crown diameter to trunk diameter. The paper you linked is with TLS
    – JRR
    Dec 7, 2023 at 16:31

1 Answer 1

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No one. Trunks are not visible with airborne lidar and lidR does not have tools for terrestrial lidar.

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    Would a tree trunk manifest itself in airborn lidar by lack of ground-level reflections? Whereas over the canopy you'd get early and late reflections from the ground?
    – Spacedman
    Dec 7, 2023 at 16:15
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    The density of ground point is too low for that. With drones and super high point density and clean forests, you can see some trunks because you have some sets of vertically aligned points. Nothing detailed enough to measure a diameter.
    – JRR
    Dec 7, 2023 at 16:24

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