Defining crown spread

General discussions of measurement techniques and the results of testing of techniques and equipment.

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Yeti
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Re: Defining crown spread

Post by Yeti » Wed Oct 30, 2013 1:29 am

If your able to get a google eath shot of the canopy, you could measure the area of the canopy.

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Will Blozan
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Re: Defining crown spread

Post by Will Blozan » Wed Oct 30, 2013 7:04 am

NTS,

If crown spread was a measurement of area the points would be in square feet, not linear feet. I think we need to stop referring to this measurement as area.

How about a minimum of four spokes at Cardinal directions, then averaged?

Still not sure of how to deal with the weighting of DBH and dissing of spread other than TDI.

Will

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Don
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Re: Defining crown spread

Post by Don » Wed Oct 30, 2013 2:42 pm

Joe-
Aerial photogrammetry has been around about as long as planes and hot air balloons have been around, so infatuated with the view were early pilots, passengers.
Certainly today's aerial photography is capable of the resolution necessary to effectively measure crown spread, area, cover and a host of other descriptors...closed canopy forests can make measurements more tenuous, but perhaps the number of national register candidates found in closed canopy forests are in the minority.
Closely aligned task-wise are the array of satellites capable of high spectral and spatial resolution imagery capture. And particularly intriguing are the Quadcopter and other remotely operated flying 'devices' that some of our NTS members are experimenting with. We just have to catch up with these technologies:-)
-Don
Joe wrote:Just a curious aside from someone not in this debate- but how effective might aerial photography be for a measurement of crown area? If it's high quality photography, you could draw the exact shape of the crown, then measure that. I presume, though, that most aerial photography just isn't good enough for this purpose, but if it was.... would this method solve the problem?
Joe
Don Bertolette - President/Moderator, WNTS BBS
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Don
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Re: Defining crown spread

Post by Don » Wed Oct 30, 2013 3:07 pm

Will
Your post merits attention. As I thought about whether we measure maximum diameter, it occurs to me that we are actually measuring the average diameter (the argument of diameter versus girth and how few trees are really perfectly round, and everything else is less than what the calculated diameter portends). A more accurate measure of the tree's cross-section is its cross-sectional area. Cross-sectional area of a tree's dimension doesn't necessarily depend on it's circular nature and is free of involutions and such.

Maximum height? We both agree I'm sure that a multiply stemmed tree (or is that "trees") needs to be separated from direct comparison (apples and oranges...), but when it comes to measuring volume of same multiply stemmed tree(s), would we not be providing an average height for the final calculation?

Maximum crown spread? Would that be a fair measure of a tree's crown that was 60' wide and 10' deep to say it had a crown spread of 60'? Yes, I know, how likely is it to find such an example?

Maybe it's just me, but a crown to me is a three dimensional thing, and has volume...that takes three measurements to define (at a minimum). I'd like to see national registry candidates have their crown volumes be part of the AF formula.
Defining the crown spread by it's maximum width is akin to defining the tree's diameter as the maximum of two right angle measurements (if a tree is not a circular, by definition it will have a maximum and minimum diameter, eh?)

As to formulaic weighting, I'm completely open to the science on this (a pandora's box for sure), but would want to have crown volume as part of the equation, before weighting considerations.

These are just my own thoughts, which I hope will continue our discussion on how to do this right. Change my mind! You've a lot to offer to this discussion.
-Don
Will Blozan wrote:Bob, Don, AF

Stop this nonsense. We measure maximum diameter (at given height), we measure maximum height, so why the hell not measure maximum spread? What, exactly, is the point to an average???

Will
Don Bertolette - President/Moderator, WNTS BBS
Restoration Forester (Retired)
Science Center
Grand Canyon National Park

BJCP Apprentice Beer Judge

View my Alaska Big Tree List Webpage at:
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Matt Markworth
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Re: Defining crown spread

Post by Matt Markworth » Wed Oct 30, 2013 9:10 pm

Don wrote: A more accurate measure of the tree's cross-section is its cross-sectional area. Cross-sectional area of a tree's dimension doesn't necessarily depend on it's circular nature and is free of involutions and such.
Don,

Cross-sectional area is a fun concept to entertain. In practice it’s obviously not as easy to measure as circumference, but it is a measurement that I find appealing. The chart shows a series of perfectly round trees starting with 2’ CBH through 32’ CBH. The crossover point when area (ft²) produces a bigger number than CBH (ft) is at 12.57’ CBH.

If the technology was in place to easily measure area and if it ever replaced CBH, then the formula would need to be changed to avoid an even bigger bias for really fat trees.
CBH,Area.PNG
Matt

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Bart Bouricius
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Re: Defining crown spread

Post by Bart Bouricius » Thu Oct 31, 2013 6:56 am

Realistically it is possible for many people to measure a height and a girth, however trying to calculate an area or an average spread is prone to great inaccuracy due to the difficulty of seeing what you are supposed to measure in many cases. In any closed canopy forest, you may be able to get what appears to be the widest spread, but no way can you be accurate even in temperate forests when trying to do more than get the longest spread, so I definitely go with Will on this and argue that doing anything else is simply pretending that precision trumps accuracy, and putting into effect a measurement that 99 out of a hundred measurers will fudge or ignore because of it's being to cumbersome or simply impossible on certain trees without spending rediculous amounts of time on it. It would be interesting to get 10 measurers to get an area or average spread on the same tree independently and see how much their results varied.

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Will Blozan
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Re: Defining crown spread

Post by Will Blozan » Thu Oct 31, 2013 4:26 pm

All,

My original post on this thread should have read maximum circumference, not diameter... sorry.

To me, the point system is so inherently flawed that any more time or complication of crown spread is not worth it.

Will

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dbhguru
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Re: Defining crown spread

Post by dbhguru » Thu Oct 31, 2013 7:24 pm

Will,

The current AF crown spread weighting isn't set in concrete. We began debating the weighting in our last telephone conference. If Don and I can make convincing arguments to get AF to change the 1/4th weighting of crown spread plus insure an apples to apples comparison of tree forms, what then would be your take on the formula?

We've moved a long way from where we started and I'm optimistic that if we keep exploring the alternatives and seeing where they lead us, we'll eventually get a much improved system. We'll likely have to do it in stages, but I'm more and more confident that we'll get there.

Bob
Robert T. Leverett
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Co-founder and President
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edfrank
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Re: Defining crown spread

Post by edfrank » Thu Oct 31, 2013 8:08 pm

Bob,

All of the values are weighted. The height is in feet, the girth is in inches (12 x weighted), and the crown spread is weighted at (1/4 x) The balance is arbitrary and seems to be as good as any other. Other tree programs around the world use essentially the same structure. I don't really see the need to reinvent it, but simply fix the flaws in how these parameters are measured. If you want a to do it in an unweighted manner, then the best option is to go with the TDI stuff and throw out the old stuff completely.

Ed
"I love science and it pains me to think that so many are terrified of the subject or feel that choosing science means you cannot also choose compassion, or the arts, or be awe by nature. Science is not meant to cure us of mystery, but to reinvent and revigorate it." by Robert M. Sapolsky

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dbhguru
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Re: Defining crown spread

Post by dbhguru » Thu Oct 31, 2013 9:22 pm

Ed,

Yes, I do realize the system is weighted. What I actually meant to ask NTS members is whether or not we see a reason to change any of the weights. In particular, is 1/4th for crown spread a roll of the dice? I do believe that one can make an argument for greater crown weight for forms like those of live oaks. But a system of weights based on crown shape would move us toward more complexity. There are good arguments against doing this.

BTW, we were asked the question about changing the crown spread weighting factor in the last AFMGWG telephone conference. So, often when I pose a question on the BBS, it is to solicit comments from NTS members to insure that we have thought through all the possibilities and ramifications of a change in direction. We're also looking to the future.

Don sees a justification for moving toward crown area and eventually volume. We could measure crown area using a modified spoke method approach, but the computation algorithm would need a spreadsheet. Alternatively, the process might be invoked primarily to break ties for really large trees.

In terms of TDI, AF has so much invested in the current system that moving to an entirely new method of selecting a champion at the national level with no reason to believe that the states would follow suit could be a prescription for disaster. We need to keep the whole playing field in mind.

Bob
Robert T. Leverett
Co-founder, Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
Co-founder, National Cadre

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