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Re: Poplar Forest
Posted: Tue Apr 19, 2011 2:23 pm
Bob, Wish I could join you guys. Wow what an equipment list! Sounds like a great outting enjoy. Can't wait to read the postings about your trip. Larry
Re: Poplar Forest
Posted: Wed Jun 08, 2011 9:43 am
Attached is the spreadsheet model of the tuliptree in Poplar Forest that Will and I modeled on April 22nd. Below is the email sent to Jack Gary, Chief Archeologist at Poplar Forest
I apologize for this having taken so long. But back from California where he was helping Drs. Steve Sillett, Bob Van Pelt, and team model a giant sequoia, Will had a chance to add up the numbers for the tuliptree we modeled on the lawn of Poplar Forest on April 22nd. The attached Excel spreadsheet shows the numbers and the percentages of volume contained in the trunk, limbs, and branches. As you will see, the total volume is 1,102 cubic feet or 31.21 cubic meters (sounds better in feet). Based on this volume, I expect that the big tulip down the hill at the edge of the woods will go about 1,300 cubes. In pre-settlement times, mature tuliptrees in the vicinity of forest Thomas Jefferson's properties would likely have held between 500 and 1,500 cubic feet. However, some would have gone over 2,000 cubic feet and an occasional tree might have reached between 2,500 and 3,000.
For comparison purposes, the largest tuliptree ENTS has modeled is the Sag Branch Tuliptree in the Great Smoky Mountains NP. That huge tree has a combined trunk and limb volume of approximately 4,000 cubic feet. Hard to image isn't it until you've seen it. The tallest we have measured (climbed by Will and tape-drop measured) is also a tulip in the GSMNP with an astounding height of 191.9 feet. The tallest tuliptree in Virginia we have measured grows at Montpelier and is an impressive 168.7 feet in height. A nearby specimen is 168.6 feet.
The 5 large tuliptrees in front of the Poplar Forest estate including the one down the hill at the edge of the forest have the following dimensions:
TT # Height Girth
1 133.0 15.9
2 113.0 14.1
3 110.0 11.2
4 103.0 14.0
5 90.0 16.2
Far down the hill near the stream and in the grove, Will measured a tuliptree to 146.0 feet in height on a visit 5 or 6 years ago. When we return, I'd like to relocate the tree and remeasure it. It may be close to 150 feet by now.
I'd like to now say a few words about our measurement methodology. First, the modeling method we used. Each section of trunk or limb was modeled employing the frustum of a cone as the controlling geometrical form. The formula applied to calculate the volume of each section was
In the formula, h = length of segment and r1 and r2 are the radii at each end of the segment. This model assumes that the cross-sectional area of the segment is circular. In many cases, the form is either elliptical or irregular in ways that would defy using a simple formula. However, for a specified girth (circumference) and a regular geometrical shape, the circular area is a maximum. So we are not shortchanging the tree, but probably overstating its volume slightly. A straight-trunked tuliptree with a girth of 16 feet at 4.5 feet above ground level and a height of 150 feet would have a conical trunk volume of 1018 cubic feet. But the forms of actual trees are more complex often going from neiloid at the base to paraboloid and then to conical. Unless a tree is broken up into relatively short sections, large modeling errors can result. That is why Will climbed the tree and we broke its trunk and limbs into sections.
In terms of the heights measured for the lawn and edge of the forest trees, I used a Laser Technologies TruPulse 360 hypsometer. I have tested this instrument exhaustively. It measures distance accurate to +/- 0.1 feet on close, distinct targets. On distant targets, such as the highest sprig of foliage, it is usually within +/- 1.0 feet. Angle accuracy when placed on a tripod is +/- 0.1 degree. These accuracies exceed the advertised specifications. However, I was one of those who field tested the instrument for laser Technologies. It is an exceedingly good instrument. Also, the method employed for determining height used the ENTS sine top-sine bottom method which gets around situations where the high point is horizontally offset from the base of the tree - the fatal flaw of many tape and clinometer measurements.
Thank you so much for the opportunity to participate and provide data on a tree that no doubt Thomas Jefferson would have treasured. We look forward to returning next year and resuming the documentation. We have a productive partnership with you and we value it. Hopefully our dendrochronological partners Drs. Dave Stahe and Neil Pederson will be able to join us.