LiDAR and Liriodendrons - Deep Creek Watershed

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ianb
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LiDAR and Liriodendrons - Deep Creek Watershed

Post by ianb » Wed May 26, 2010 5:31 pm

Everyone,

I spent a few days with my Dad in the Deep Creek watershed in the Smokies this past weekend and we found some notable trees that might be of interest to ENTS.

As a first-time poster, I should introduce myself first. I'm a graduate student at UNC in their Curriculum for the Environment and Ecology. My research regards forest growth rates on abandoned agricultural lands in Eastern North Carolina, and I'm using the State LiDAR dataset for my research. I've had plans to go backpacking with my Dad in the Smokies for a while, and I decided to extract some tall-tree LiDAR points near our route and bring a tape and clinometer along. I told my dad we'd be doing some "recreational research".

After setting camp on Saturday afternoon, we wandered up Fork Ridge Trail to the first point that I had picked out, which indicated canopy heights of 189' only a few hundred meters from the trail on a steep hillside. After sliding off the ridge we quickly transitioned from the short Quercus montana - Kalmia latifolia ridgetop through a thicket of Rhododendron to a small rich cove dominated by Liriodendron and Aesculus. At the center of the bowl-shaped cove was a small seep lined by giants - even for oldgrowth standards. Five large Liriodendrons >12' cbh towered above the surrounding forest.
P1000036.jpg
We took three height measurements on the largest of the giants, an 18.4' cbh tree with a flawlessly straight bole unbranched to at least 80 feet. Not bringing a laser rangefinder with us, we were limited to using the Tangent-baseline method with a slope correction on the baseline for our heights. All of our measurements came in above 195' (averaging a marginally-unbelievable 201.9')
fork_ridge_poplar3.jpg
The next day we dropped down into the Left Fork watershed to hunt a few more points. After battling Rhododendron for two hours we finally got to another giant Liriodendron about 150m from Left Fork Deep Creek. This one had a LiDAR estimated height of 196', but our measurements showed it was a bit more modest 167' - 171' in height and 17.1' cbh. Its slope position probably accounted for the LiDAR overshoot.

LiDAR also indicated a small grove of trees > 170' near the confluence of Left Fork Deep Creek and Hermit Branch, but after bushwhacking down there we were disappointed to find That they were all hemlocks, dead as a doornail and dropping limbs in the stiff breeze. We didn't dally to measure these dead behemoths -- a bit too risky.
P1000051.jpg
On our way back to camp we stumbled on a wonderful 16.4' cbh Northern Red Oak on the eastern bank on Left Fork Deep Creek. It was late in the day so we didn't have a chance to get a height for it. Impressive nonetheless. At the end of the day, we felt like we had just scratched the surface as far as tall trees in Left Fork of Deep Creek. There were at least a dozen LiDAR points > 170' in the lower part of the watershed that we didn't get a chance to visit. These areas would be challenging to access, but more giants may be in store.
P1000041.jpg
Even considering our lack of laser equipment, I think the 'Fork Ridge Poplar' that we found on Saturday deserves a revisit. Our measurements put it (at least) in the same neighborhood as the current champion Liriodendron measured by Will in 2008. I'd love to come back with some more experienced ENTS and/or some better equipment for a second look.

Cheers,
Ian Breckheimer

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dbhguru
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by dbhguru » Wed May 26, 2010 7:12 pm

Ian,

You certainly have identified a hot spot. Thanks for letting us know. I hope Will Blozan will catch your post. If I don't see a post by Will, I'll give him a call.

There isn't much chance of being close on heights of such tall trees without applying the sine method with laser and clinometer, but I expect you know that. Anyway, we appreciate what you've discovered and will get to the site sooner or later.

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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edfrank
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by edfrank » Wed May 26, 2010 7:28 pm

Ian,

Welcome to ENTS. I am sure you will find people here who share your interests and who are interested in your explorations. A number four people have been experimenting with LIDAR and have found some very nice trees.

You wrote:
All of our measurements came in above 195' (averaging a marginally-unbelievable 201.9')
Well, I must say that the heights you are finding are indeed unbelievable. If you want to get accurate measurements of tree heights, you really need to get a laser range finder. The basic discussion of the problems with tape and clinometer based measurements are well documented. Some of the mathematical treatments are available on out website http://www.nativetreesociety.org under the measurement section. You also really should download out tree measuring guidelines: http://www.nativetreesociety.org/measur ... vised1.pdf

Essentially there are two primary sources of errors in the methodology of using a tape and clinometer.

1) first the top of the tree is rarely directly over the base of the tree. Therefore this assumption inherent in the methodology will give a false height reading, almost universally exaggerating the measured height. The amount of error will be sin(angle of measurement) x offset of the top from the base x the cos(relative angle between your position and the angle of offset). In general most of the error will be in your direction. That means that if you are shooting at an angle of 45 degrees and the offset is on the order of 15 feet, your height will be off nominally by 15 feet in height. The steeper the angle of measurement the more the height will be mis-measured. This is a built in function of the methodology and can't be fixed by making your tape or angle measurement more accurately. In a data set of over 1500 trees we found an average offset for all trees to be close to 13 feet. Many of these were pines. For the subset of broad canopy trees, like the tuliptrees, the average offset of the base from the true top is more likely in the range of 20+ feet. With the laser methodology you are measuring the height above the plane of your eye and the height below the plane of your eye and adding the two together. it doesn't matter if the top is offset from the base, the two are measured independently relative to a horizontal plane at eye level.

2) the second problem is misidentifying the true top of the tree. Even with experience it is next to impossible to tell which sprig represents the actual top of the tree and which one represents a slightly forward leaning branch or a shorter top closer to your position. A misidentified top, and that is much of the time the actual case, can lead to height errors in the 20 to 30 feet or even more. With a laser range finder, you can read your display and tell which top is the tallest and search out the actual top of the tree. At approximately the same inclination, whichever top is the farthest away, will always be the taller of all of the possible tops. This error is all but eliminated. There still may be a hidden top that is taller back in the mass of the tree that can't be seen from the ground, but you can certainly pick out which of the visible tops are the tallest. Again the offset of these tops from the base doesn't matter and does not create an error in the height calculation when using this methodology.

Here is a listing of mis-measured trees that became part of the published literature:
http://www.nativetreesociety.org/measur ... _trees.htm

Here is a listing of trees measured with the laser methodology compared to actual tape drops made from the top:
http://www.nativetreesociety.org/measur ... _trees.htm

This demonstrates an exceptional degree of accuracy with the laser/clinometer methodology. Practice and better technique in recent years mean that generally the heights measured with a laser are usually within a foot of those measured by tape drops.

If you are looking at tree heights as part of your research, and you are attempting to ground truth the LIDAR data, you really need to be using the laser range finder methodology we have outlined. It is likely that differences you are measuring between sites will be less than the errors in height generated by the basic tape and compass methodology. To get meaningful ground truthing of the LIDAR you really should be using the laser range finder methodology.

All laser rang finders are not created equal. Currently the best inexpensive model is the Nikon 550 which has both a range finder and clinometer in one instrument. A better option if you can find one is the older discontinued Nikon Prostaff 440 because it has a narrower beam that works better when looking through small canopy holes and twigs. It is just a range finder and you would need a separate clinometer to measure the angles. I recently purchased one on eBay - used slightly - for under $100.

Ed Frank

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"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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Will Blozan
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by Will Blozan » Wed May 26, 2010 8:41 pm

Ian,

Welcome to ENTS indeed! Wow! Sounds like a revisit is in order. What was the typical baseline distance you were using? I agree with Ed and Bob's comments above and hope you will use a laser in your research. You have to, basically.

I'm sure you have seen the recent posts on LiDAR and the ENTS measuring methodology. As a seasoned ENTS measurer and climber there is no possible way to be scientifically accurate with tape and clinometer on large, broad crowned hardwoods. Regardless, I do hope your numbers are close!

I would love to accompany you on a return visit or verify the tree for you. Let me know and we'll plan a trip.

Will Blozan

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James Parton
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by James Parton » Wed May 26, 2010 11:22 pm

Ian,

What a way to enter ENTS with your first post. Awesome dude! Hopefully I will get to meet you and share some " woods " time with you in the future.

You did well on heights. Forest trees are often hard to measure this time of year with the leaves on. Most of ENTS forest measurements take place in late fall to mid spring when the leaf canopy is absent or thin. Naturally this does not apply as much to open grown trees. Still, some of us get good measurements in summer. Like Bob Leverett!

James
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Josh Kelly
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by Josh Kelly » Thu May 27, 2010 9:33 pm

Ian,

Nice report!

What cell size and parameters are you using in your canopy height models?

Josh

ianb
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by ianb » Fri May 28, 2010 11:16 am

Thanks for all the great feedback, guys. I'm definitely not making any claims about the 'Fork Ridge Poplar' just yet. Laser rangefinders are definitely in my future...

Will -- Lets schedule a revisit trip sometime this fall after leaf-off. The baselines that I was using for the height measurements were typically 80 - 120 ft, and I was sighting on the highest point I could see that was positioned directly above the trunk, which doesn't have any lean to it-as far as I can tell. I still anticipate errors of up to 15%

Josh -- The canopy height model I was using for the Smokies I got from a guy at the US Fish and Wildlife Service named Doug Newcomb. The model has 60 ft cells, and he subtracted the elevation range within each cell (from the state 20ft DEM) from the initial LiDAR canopy heights to correct for topographic errors.

The Smokies data is dense enough to make a higher-resolution surface. An ideal strategy would be to fit a smoothed surface to the first returns (canopy top) and last returns (ground surface) and then rasterize the output. I think FUSION has the capability to do this. You will still get errors when tree canopies lean downslope, however.

The Smokies data should also be dense enough to pick out individual trees and estimate their crown sizes using another piece of free software, TreeVaW (http://ssl.tamu.edu/personnel/s_popescu/TreeVaW/), which takes a raster canopy surface model as an input. I'm not dealing with any of these datasets for my own research, but I'd be glad to give someone some tips if they want to tackle this.

Cheers,
Ian Breckheimer

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Jess Riddle
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by Jess Riddle » Sat May 29, 2010 9:14 pm

Ian,

I’m very intrigued by the trees you found on Deep Creek. That largest tree looks very promising. Ents had previously identified a few exceptionally tall trees in the watershed, but they were few and far between. The tallest I know of were a large tuliptree along the lowest section of the Fork Ridge trail, and a young tuliptree on Dancing Branch, both around 175’.

Jess

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dbhguru
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by dbhguru » Sun May 30, 2010 7:00 am

Ian,

Just a few additional comments. I second Jess's comments. What an entry post! I'll also amplify on what Jess said about summer measurements. It is possible to do better in the summer measuring a site for some species than initial results reveal. There are lots of caveats though. I continue going after conifers in the summer because by moving around enough, you do find holes in the hardwood canopy to spot the tops of super-canopy pines. But the magnitude of the effort requires a measuring masochist and basically no limits on one's time. I return to the same grove and same trees time after time. I haven't kept detailed records on the effort that I put into particular trees, but it is enough to cause eyebrows to lift - as if to say, don't you have a life? But the effort over the years has sharpened my skills to where I can "smell" a spot where I can view a new higher twig. By measuring and remeasuring the same tree at different times of the year, I get a feel for the probability of success on a new tree after 1,2, 3, .... measurements. Crown shape, leaf size and density and canopy dominance all figure in, but these factors become simplified for the conifers mixed in with hardwoods. Then there the dense stands of conifers(white pine and hemlock for me) with lots of trunks separated by 5 to 15 feet and crowns of comparable height. That is a challenge even with the understory clear of foliage. Still, when there is a will, as the saying goes.

I do hope you, Will, Josh, and Jess can get out together. In addition, please join us in November as we begin studies of the tuliptrees at Montpelier and Poplar Forest estates in Virginia. If you want details, I'll be posting more as time goes by.

Again, welcome to ENTS.

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

ianb
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Re: LiDAR and Liriodendrons - Deep Creek Watershed

Post by ianb » Sun May 30, 2010 8:44 am

Thanks for all the great feedback, guys. I'm definitely not making any claims about the fork ridge poplar until we can get some better measurements. A laser rangefinder is definitely in my future...

Will -- Lets try and do a revisit in the fall after the leaves drop. The baselines that I was using were between 80 and 120'. The trunk doesn't have any lean to it, and I was sighting on the tallest part of the canopy that I could see directly above the trunk.

Josh -- I was using a LiDAR canopy model from a man named Doug Newcomb who works for the US fish and wildlife service. The model has a 60ft cell size, and he uses a very simple slope correction (subtracting the elevational range in a pixel from the initial height. The LiDAR data for WNC would probably support a higher-resolution analysis. I won't be tackling this as part of my research, but I'd be glad to give people some tips if they want to tackle it.

Jess -- Was the poplar on the lowest section of Fork Ridge trail the one that's on the creek bank right next to a campsite along Deep Creek at the intersection with Deep Creek trail? We passed a giant right there, but we didn't measure it.

Cheers,
Ian

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