## ECO - Pith union below ground and multiple trunked trees

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greenspaceintern
Posts: 9
Joined: Wed Jun 03, 2015 7:29 am

### ECO - Pith union below ground and multiple trunked trees

Hello, I have another question I was hoping someone could help me with. According to the manual, if the pith union is below the ground then different trunks are counted as separate trees. The height and crown base can be the same but how would you document crown width for a tree like a crepe myrtle with branches overlapping each other? Would you do canopy missing for the whole or for each trunk?

If the GPS coordinates are the same then does it even matter?

Thank you so much.
Jason.Henning
i-Tree Team
Posts: 170
Joined: Fri Dec 21, 2012 7:45 am

### Re: ECO - Pith union below ground and multiple trunked trees

I think this is a case where you have found that some of the Eco methods can be impractical in the field. If you are treating each stem as an individual tree you just have to do your best to measure the crown associated with each stem separately. That being said you could always choose to treat it as a single tree even though the pith union is below ground.

In the case of something like crepe myrtle I think it is much more practical to treat it as a single tree with multiple stems even though the pith union is just below the ground line. Within the model all of the stems you have measured will be combined into a single stem using the formula: Estimated DBH = square root (sum of (individual dbhs squared)). This is equivalent to the diameter of a tree that would have the same cross sectional area of all the individual stems.
The tree diameter mostly contributes to the estimates of carbon storage and sequestration so this should be a reasonable approximation. The bulk of the additional benefits estimated in Eco are a function of leaf surface area which is much more related to the tree crown measurements. I would expect the total crown volume estimated from your crown measurements should be nearly identical regardless of whether you treat it as a single tree with one crown or multiple trees with multiple crowns. Also, typically those crepe myrtles will be managed as a single stem not lots of individual stems but if they are entered as individual trees they may be over represented in your project results.

So there are actually benefits to treating a crepe myrtle as a single individual with multiple stems beyond the fact that it is easier to measure. The approach you take won't have a very big impact on the benefits estimates but it will impact the estimate of the number of trees for your project. So you can decide which of those is more important and if it even makes sense for those crepe myrtle stems to show up as a bunch of individual trees in your results and base your field methods off of that. It will definitely be more efficient to treat them as a single tree but the choice is up to you.
A member of the i-Tree Team
greenspaceintern
Posts: 9
Joined: Wed Jun 03, 2015 7:29 am

### Re: ECO - Pith union below ground and multiple trunked trees

I see, that was very helpful. I think I'll go with treating them as a single tree because I don't want to over represent them.

Thank you so much!