Tuliptree Modeling - bold new NTS project

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#1)  Tuliptree Modeling - bold new NTS project

Postby dbhguru » Wed Feb 14, 2018 10:19 am

Ents,

  Recent email communications between Erik, Elijah, Jared, and myself are pointing us toward a project to volume model tuliptrees over a wide range of ages and shapes. It is our growing belief that the ratio of limb to trunk volume changes dramatically over the life of the tuliptree. You might say, Duh! Doesn't just looking at tuliptrees from youth to full maturity and beyond tell us that? It certainly appears to, but we have almost no hard data on the change of the ratio of limb volume to trunk volume, and now thanks to the reticle and our volume models, we are finally equipped with those tools to calculate limb volumes without spending an eternity of time on each tree. Trunks have never been a problem, but limbs?

  A practical result of the project could be getting a better handle on how the species accumulates mass over time. Larger, older trees may be a lot more important for carbon sequestration than would be apparent from modeling just the trunk. Getting an answer to the question is of interest to Erik. He expressed as much just the other day.

  How do we go about the project? We have a number of regular geometrical forms to use in volume modeling: frustums of circular and elliptical cones, paraboloids, and neiloids to name the main ones. We can consider other trunk/limb taper models, but the amount of work quickly gets out of hand. We could apply them only where they would lead to significantly greater accuracy for important trees. For the present, we'll stick with the principal forms and look for ways to apply them ever more efficiently. For example,a more complete modeling of a conspicuous limb or limb segment could be used as a shortcut to modeling similarly shaped limbs. Lots of possibilities. Ideas are welcomed.

   One of the first steps for me is to assemble the formulas for the frustums named above and present them in a single document for easy access by all. The formulas are presently scattered all over cyberspace. Heretofore, there wasn't the impetus to create a single document because it wasn't clear that it would be used, and I've long be a champion of creating stuff that nobody uses, including myself. I realize that limb and trunk volume modeling is never going to make it to the top of the popularity charts. But at least we now we have some committed volume modelers. Presently, they include Erik, Elijah, Jared, Dale, Michael, and myself. We're hoping others will join us. Our Mississippi buddy Larry comes to mind. In the past, Will Blozan and Jess Riddle did groundbreaking work that immortalized them in the annals of NTS. Maybe we can persuade them to rejoin us. Jess has more recently measured some humdinger tulips in northern Georgia.

   The invitation is open to all who would throw in with us. We'll get you through the initial period of pain. Ooh, did I say that?

Bob
Robert T. Leverett
Co-founder and Executive Director
Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest

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#2)  Re: Tuliptree Modeling - bold new NTS project

Postby Erik Danielsen » Wed Feb 14, 2018 1:27 pm

Bob, a quick thought- I reread some of the early reports on volume modeling this morning and as I think about it, I think we're unlikely to find a consistent relationship between trunk volume and crown volume across trees of similar age. I say this because, if we compared two hypothetical trees, both with identical dbh and identical diameter at the highest point below the crown dividing, with identical limb architecture and with both crowns occupying the same amount of vertical space, but due to site factors one tree has a main trunk 15 or 20 feet taller than the other (a realistic scenario comparing zoar's upland tulips to those in the canyon) both trees might have identical crown volumes but very different trunk volumes, and therefore different ratios of trunk to crown volume.

An alternative avenue for predicting tulip crown volumes might be finding an average percentage of cylinder occupation for crowns of tulips in different age categories, using the trunk diameter where the crown diverges and the vertical height of the crown as the inputs. We'll need to model plenty of trees, of course!
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#3)  Re: Tuliptree Modeling - bold new NTS project

Postby dbhguru » Wed Feb 14, 2018 8:13 pm

Erik,

 Good points. I have no doubt that you're right about the lack of a reliable ratio that would relate limb to trunk volume across a range of ages and tree shapes. There's just too much variability, and we can see it without ever calculating it. However, might we be able to establish a range of ratios, and particular establish some maximums? I'm not aware of any statistics that do that. We could model a sample of young versus mature trees over a range of ages and shapes and perhaps determine statistically reliable trends. As we discussed in a prior email communication, the implications of this kind of analysis for carbon sequestration are considerable.

  I expect that methods are being developed (or have been) that predict the biomass contained in crowns versus lower trunks for whole stands of trees, but I seriously doubt that any method intended for large numbers of trees in fairly uniform stands would ever be applicable to individual trees.  

Bob
Robert T. Leverett
Co-founder and Executive Director
Native Native Tree Society
Co-founder and President
Friends of Mohawk Trail State Forest
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