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Fork Ridge red spruce LiDAR hunt

Posted: Sun Jun 26, 2011 10:27 am
by Will Blozan
ENTS,

I took the opportunity as a trip leader at the Smoky Mountain Wildflower Pilgrimage in early May to ground-truth some tall LiDAR hits in the spruce zone of Fork Ridge. Fork Ridge (yes, the same system as the tallest tuliptree) is a gently sloping southeast running ridge covered in some of the finest red spruce (Picea rubens) forest in Great Smoky Mountains National Park.
Old giant on Fork Ridge Trail
Old giant on Fork Ridge Trail
Josh Kelly sent me some waypoints and I uploaded them to my GPS. All seven of the hits were above 140' (42.7 m) which is significant for the elevations being sampled; ~5,000' (1,500 m). There were only three options for what the hits could be; tall spruce, moderately tall hemlock (Tsuga canadensis), or erroneous readings from leaning trees. We found all three.

Hit #1 was a 143' (43.6 m) return in old-growth red spruce forest. The stand was steep, dense and tall so finding the tree took some time. The search paid off with a 151.2 footer (46.1 m)- the third spruce ever documented over 150'. Diameter was a respectable 35.2" (89.3 cm).
Dense grove with 151.2 foot spruce
Dense grove with 151.2 foot spruce
151.2 foot spruce
151.2 foot spruce
Hit #2 was a 141 foot return which turned out to be a 148.1' (45.1 m) spruce with a large trunk 37" (94.0 cm) diameter. This was the same tree I measured to 147' (44.8 m) back in 1996-7.
148.1 foot spruce
148.1 foot spruce
Hit #3 was a 148' return which was actually a respectable hemlock. Dead from HWA.

Hit #4 was a 154' return which we were really excited about. Damn, downslope-leaning ancient hemlock. Dead from HWA.

Hit #5 was a 144' return at the base of a narrow ravine. A towering spruce resided there and stood 152.6' (46.5 m) tall on a large base 38" (96.4 cm) diameter. The tree had just died and would have been the third tallest specimen ever documented.
Tallest dead spruce 152.6 feet
Tallest dead spruce 152.6 feet
Hit #6 was nearby and turned out to be a leaning spruce with an interesting multi-topped crown. LiDAR suggested 143' (43.6 m) but it was actually 136.6' (41.6 m).
136.6 footer with split top
136.6 footer with split top
Hit #7 was hoped to be the crowning tree of the day. A 157' LiDAR hit in dense spruce forest instead yielded a large leaning hemlock over a steep slope. Yep, you guessed it- dead from HWA.

On the way out I stopped to count the rings on a freshly cut fallen spruce log. It was solidly over 400 years and not very close to the base. Back in the late 1990's I also ring counted a 380 year log about 50' from the base. This is a really old spruce forest and I have no doubt a 500 year tree could be found here.
400+ year log
400+ year log
We have ground-truthed LiDAR hits in hardwood forest and this was the first spruce zone foray. The LiDAR data do tend to underestimate height so this, coupled with the rather coarse 20' (6 m)sampled grid left a high possibility of the heights being significantly low for narrow-topped spruce. This also suggested that the LiDAR would commonly miss tall trees with a narrow top not near a sampled point. This is definitely the case- as we found adjacent trees not recorded by LiDAR that were taller than 140' (42.7 m). Basically, the current LiDAR data are insufficinet to accurately assess individual spruce heights but they do give a good indication of where the tall trees are. This fact alone is immeasurably helpful as red spruce forests are one of the nastiest to traverse. Of all the eastern forests types red spruce is one of the least sampled and remains the last frontier for superlative specimens. Nearly every trip into the red spruce zone yields new records for the species. We are at the tip of the iceberg so to speak for this species.

Thanks to Hugh Erwin for his help with measuring in the difficult terrain!

Will

Re: Fork Ridge red spruce LiDAR hunt

Posted: Sun Jun 26, 2011 11:34 am
by Lee Frelich
Will:

If lidar underestimates the true height, just think how much it would underestimate the tangent-based 'height'. I hope someone doesn't try to ground truth lidar using tangent based height and then recalibrate the lidar and instantly make all the forests in the world 10 or 15 feet taller than they really are.

The champion white spruce in northern MN is supposed to be 130 feet tall, but I doubt that its more than 115 feet--I would visit it and get an accurate measurement, but I have seen how mad people get when you shorten their champion trees, so I have not done it.

Anyway, this is a great data set you are building up, on the trees and the tree-lidar comparison.

Lee

Re: Fork Ridge red spruce LiDAR hunt

Posted: Sun Jun 26, 2011 9:04 pm
by James Parton
Will,

Awesome! I have never seen Red Spruce so tall or so old. I bet it was a beautiful forest.

Re: Fork Ridge red spruce LiDAR hunt

Posted: Sun Jun 26, 2011 10:06 pm
by Steve Galehouse
Will-

This would have to be the tallest spruce in the east, of any species, native or introduced---great find!

Steve

Re: Fork Ridge red spruce LiDAR hunt

Posted: Sun Jun 26, 2011 10:40 pm
by Will Blozan
Steve,

Yes, with two reds at 155' the closest is a Norway at ~151' in western MA. I have no doubt we will find a red spruce over 160' soon.

Will

Re: Fork Ridge red spruce LiDAR hunt

Posted: Mon Jun 27, 2011 2:36 am
by KoutaR
Lee Frelich wrote:I hope someone doesn't try to ground truth lidar using tangent based height and then recalibrate the lidar
German researchers try this (although for terrestrial lidar) in this paper in 2007:

http://www.isprs.org/proceedings/XXXVI/ ... k_2007.pdf

They conclude: "The validation of lidar-derived tree height measurements in a forest is not possible based on Vertex measurements, since these depend too much on visibility limitations." They also write: "same horizontal distance is a presupposition for correct measurement with the Vertex instrument".

Kouta

Re: Fork Ridge red spruce LiDAR hunt

Posted: Mon Jun 27, 2011 10:20 am
by James Parton
Will Blozan wrote:Steve,

Yes, with two reds at 155' the closest is a Norway at ~151' in western MA. I have no doubt we will find a red spruce over 160' soon.

Will


I find it amazing that they can grow so tall at the altitudes they are found. Most trees are short and stubby in the boreal zone of the Southern Appalachians.

Does anyone know how tall their companion, Frasier Fir, can get?