Dealing with privet in a non-shrub model

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RaleighUFAT
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Dealing with privet in a non-shrub model

Post by RaleighUFAT » Wed Feb 20, 2008 8:17 pm

When surveying sample plots we came upon a thicket of privet, approximately 15ft in diameter and with 40+ stems of 1" DBH or bigger, all converging below ground. Due to time constraints we have opted to measure only trees. How should we survey this? Some options we have discussed are:

Measure all stems as individual trees
Treat as 1 tree with multiple stems
Estimate the number of stems and area covered and divide into individual trees
Note as shrub cover in the non-shrub model

Is there anything you can recommend? Thanks!
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Heythatsmybike
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Post by Heythatsmybike » Tue Feb 26, 2008 9:40 am

The field data procedures are to count them as each a separate tree. This has happened many times in the field data collection. I have had first hand experience with this issue. In Syracuse, there was a black locust that blew over and sprouted close to 40 new individuals in a hedgerow. With many groans I measured all of the stems hoping to eliminate some of them as multi-stemmed trees (with no luck).
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fescobed
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Post by fescobed » Fri Feb 29, 2008 6:15 pm

We have the same issues in Florida with mangroves, brazilian pepper stands, etc.

What to do- It depends on the amount of times you will run across this situation.

If it's rare then measure all stems. If physically or logistically impossible:

*Only measure stems with a DBH > 3"?
*Do sub plots

Hope this helps.
Francisco Escobedo
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Jerry
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Post by Jerry » Sun Mar 02, 2008 11:26 am

This is an interesting question, and I have certainly faced it often in the field--though usually with sumac or another of the native colony-forming shrubs.

What the protocol says is clear: collect them all. I see, however, some problems with this:
  • Field people do not have the time that researchers do, and need to produce in an environment where time is money
  • Shrubs constitute a very small percentage of the environmental benefits compared to trees; I have been told by a prominent researcher that it is typically on the order of 5% at the highest
  • The species-specific and even genus-specific data available to the model is reportedly poor for shrubs
Possible field solutions?
  • Don't collect shrub data unless shrubs constitute a significant portion of the woody plants in the domain of interest
  • Aggregate the stem areas and enter a single generic tree.
Using the second method in the particular case here, 40 1" stems is the equivalent of a single 8.6" stem, if I do the math correctly (see below), and the error associated with such a short cut is probably well below the uncertainty inherent in the UFORE model itself.

What do you think?
----------
Math:
--Area of all 1" stems = 40 * 0.5 * 3.1416 = 62.832
--Equivalent single stem area: 3.1416 * R2 = 62.832, so R = sqrt 62.832/3.1416 = 4.3, and thus D = 8.6
RaleighUFAT
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Post by RaleighUFAT » Mon Mar 10, 2008 11:55 am

After reading the posts and speaking with i-tree personel, we decided that the best option is to measure all stems and aggregate as 1 tree. We then measured the total canopy as if it was 1 tree.
Jerry wrote: Aggregate the stem areas and enter a single generic tree.
Thanks for your help!

We found 10 stems at 3", 20 stems at 2", and 40 stems at 1"! Using the math below we found the privet to have a basal area of 14.4"... which seems to be a reasonable measurement.

Area of all 1" stems = 40 * 0.5 * 3.1416 = 62.832
2" = 20 * 1 * 3.1416 = 62.832
3" = 10 * 1.5 * 3.1416 = 47.124

Equivalent single stem area: 3.1416 * R2 = 172.788,
R = sqrt 172.788/3.1416 = 7.2,
D = 14.4
Jerry
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Glad that was useful

Post by Jerry » Mon Mar 10, 2008 12:38 pm

Great, though I have two cautions to add:

1) It looks like I forgot to square the radius in the first step of my calculation...

:mrgreen:

So let's do that again! In general, if

N1=first number of stems, N2 = second number of stems, etc.
R1=first radius, R2 = second radius, etc.

The calculation would go like this (^2 = squared):

TotalArea = (N1 * pi * R1^2) + (N2 * pi * R2^2) + ...

For Aggregate Stem (Rt = radius of aggregate stem)

pi * Rt^2 = TotalArea

Rt = sqrt (TotalArea/pi)


Then I think your diameter should be 10.4 -- sorry!

2) You still have to treat the thing as a shrub, assigning it a correct shrub species and taking the shrub measurements called for (height, width, etc.). Otherwise, if UFORE thinks you have a tree, it will carry out a regression on the aggregate stem diameter and I would think that would result in a severe overestimation of parameters such as the biomass and leaf surface area that are critical to function calculations. The UFORE researchers can tell us more precisely about that.
smaco
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Post by smaco » Mon Mar 10, 2008 6:22 pm

The Forest Service's Forest Health Monitoring program uses the diameter at root collar (DRC) calcultion for multistemmed trees:
DRC = SQRT [SUM (stem diameter2)]
Round the result to the nearest 0.1 in. For example, a multi-stemmed woodland tree with stems of 12.2, 13.2, 3.8, and 22.1 would be calculated as:
DRC = SQRT (12.22 + 13.22 + 3.82 + 22.12)
= SQRT (825.93)
= 28.74
= 28.7

There is an easy-to-understand interpretation of this method in the following document:
http://www.itreetools.org/streets/resou ... tocols.pdf
(See page 3 of PDF)


Hope I didn't muddy the water. --Scott
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Jerry
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Post by Jerry » Mon Mar 10, 2008 6:40 pm

That's a nice document--I didn't know it existed. That will go on my short list of "handy dandy" docs.

The only problem here is that it is talking about trees, and we have a shrub, which by essential definition has no root collar. Still, we might be able to adapt it if we think about it.

Thanks.
RaleighUFAT
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Re: Glad that was useful

Post by RaleighUFAT » Mon Mar 10, 2008 9:08 pm

Jerry wrote: You still have to treat the thing as a shrub, assigning it a correct shrub species and taking the shrub measurements called for (height, width, etc.). Otherwise, if UFORE thinks you have a tree, it will carry out a regression on the aggregate stem diameter and I would think that would result in a severe overestimation of parameters such as the biomass and leaf surface area that are critical to function calculations. The UFORE researchers can tell us more precisely about that.
Since we are not including shrubs in our model (due to our limited time--being a semester project) our only options are to include it as a tree (with all data taken) or note it as % shrub cover only. Since it has stems of > 1" at DBH, we are planning on counting it as a tree with DBH 10.4. Would this skew the data too much, or do you agree with the method?
Jerry
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Post by Jerry » Tue Mar 11, 2008 5:36 am

In the practical world, I think what you are proposing makes the most sense. One further advantage might be that, since the model extrapolates for the whole domain from the sample, you will probably have a more reasonable estimate of privet in your final species distribution this way!

I put in that second caution because I am not quite sure of how that will be treated by the model. But since you are providing a "tree" height and "crown" height/width, now that I think of it, things may work out just fine.
Amy
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Re: Dealing with privet in a non-shrub model

Post by Amy » Sun Nov 17, 2019 9:09 am

I’m also conducting a sample inventory without shrubs or herbaceous species models included and had the same question (albeit 11 years on).

Is aggregating the dbh of all stems >1”, and then measuring a single canopy width and tree height still the preferred/recommended solution to measuring privet thickets? Wouldn't it be best to cut them out and paint the stumps with glyphosate...a win-win?

What about other shrub species gone wild like eleagnus?

-Amy
azelaya
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Re: Dealing with privet in a non-shrub model

Post by azelaya » Sat Nov 23, 2019 2:12 pm

The i-Tree Eco protocol for considering when woody vegetation is a tree is still the same as it has always been and stated by others above. Woody vegetation that is 1 inch or greater at breast height is entered individually. The practical recommendations to aggregate stems or consider specific vegetation as shrubs are up to users to decide. These are options to consider depending on individual project objectives, time,and resources.

Below is text copied from the current Eco Field Guide pg22
What Is a Tree?
At different stages of its life, a tree can be classified as ground cover, shrub, or tree in the Eco model. The following information is adapted from the journal article “A Ground-Based Method of Assessing Urban Forest Structure and Ecosystem Services” (available at www.itreetools.org under Resources > Archives) and may help Eco users distinguish between available options.

Typically, shrubs are defined as woody material with a diameter at breast height (DBH) less than 2.54 cm (1 in), whereas trees have a DBH greater than or equal to 2.54 cm (1 in). Woody plants that are not 30.5 cm (12 in) in height (e.g., seedlings) are considered herbaceous cover.

Trees and shrubs can also be differentiated by species (i.e., certain species are always trees or always shrubs) or with a different DBH minimum threshold. For example, in densely forested areas, increasing the minimum DBH to 12.7 cm (5 in) can reduce the field work required by decreasing the number of trees measured, but less information on trees will be attained.
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