My customer is asking how to estimate the diameter of a standing tree some 20 or 30' up the tree.
I don't know how to do this. Is there a way without climbing the tree and measuring it with a diameter tape measure?
Jim Rogers
closest I can come is form class tables by species tables. Not exact but close enough for sales.
I would measure DBH, then step back and estimate. what is the reason for the question by your students? is there a purpose that might lend to a different answer?
As Texas Ranger said 'form class tables'. But if this is a yard, park, or open area tree they may not be as much help depending on the species of tree.
My maths is a bit rusty, but does anyone make a gauge for doing this? If you had a stick that you held at 45°, with an V aperture at the end. Now walk back 20ft from the tree, and look up at the 45 angle. The point in the V that matches the trunk will then be 28.3 feet away. If the stick is 2ft long, and the gap is 1", then the trunk at that point is about 14".
Lara is out at the moment, but she has just passed her year 11 maths exam, so should be able to double check my calculations. It's basically a variation on the "measure the height of the tree with a stick" trick.
Form tables will give you an average for a stand of a species / area etc, which is good enough as it averages out over 100+ trees. But I assume the guy wants to know if he can for example cut a 20 ft long 10x10 beam from that tree? If the small end comes out at 14", then not quite. If it's 16" up there, then he probably can.
The USFS tables claims that most taper occurs in the first 16' log and then more less becomes uniform for most species of hardwoods at 1" per 8' of height above the first 16' log. Average Form Class for most woods grown common hardwoods is Form class 78(78% of your DBH will be the scaling diameter of the first 16' log and then subtract an 1" for every 8' or height above that. You asked for an estimate. Won't apply to open grown shade trees. Plantation Pine and Yellow Poplar will have a higher Form Class ratio.
Example:
24" DBH Red Oak tree with 32' of merchantable stem height would measure:
24" DBH 4.5' above ground.
Form class 78 24"DBH x.78=18.75 inches at 16', 17.75" at 24', and 16.75" at 32'.
Its probably just me but they look straighter in the woods too :)
Oh no doubt they get bent when felling from hitting the ground. Ever seen video of a crane that crashes? That's steel and it ends up all bent, so must be the same thing happened to the logs. :D
Southside, is that lump on the side of your face your tongue?
Thanks for everyone's advice and comments.
I copied the webpage address of this post and sent it to my customer so he could read up on it and figure out his diameters.
Jim Rogers
The tool you could use for this is a relascope. There are old school versions and modern laser versions if your client is so inclined.
Wud
Quote from: Wudman on February 02, 2023, 05:52:21 PM
The tool you could use for this is a relascope. There are old school versions and modern laser versions if your client is so inclined.
Wud
Where would we find one? do you have a webpage link?
Jim Rogers
Yes, it is done with the Spiegel Relaskop which is a precision tool for the professional forester. However, it is a very expensive tool, and it is usually difficult to justify its cost unless such precision measurements are really necessary. Some skill is required in using them.
The last one I had was $1,000.00 years ago. They are probably $1600.00 plus now and are available at Forestry Suppliers, Inc. or The Ben Meadows Company.
Thanks for that info.
Jim Rogers
Forestry Suppliers has them listed at $2065.00 up to @2400.00 bucks.
With a transit and appropriate application of trig you could also get there. It can also measure sweep with 2 setups if the trees are critical.
I've told it ad nauseum but if we have a new victim/ client reading... it feels like yesterday. We needed 16" dia at 60' up. We were scouting all over a clients property for trees for big barn beams. 2 were whoppers. I had found plenty in places we would never get them out at that length. We had felled one of the trees, rigged and rolled it uphill to a bench in the hill for a work area. And on our second day of making the beam in the bush, we slid off the slab, to a rotten pocket at 40'. You could lay your arm in the hole. Looking at the slab there was indeed a slight divot in the bark from a poorly healed broken branch that had let water in. Back to the "store" we went. Having started with the largest beams on the list first, we used the reject as a shorter beam. Still a bummer but not a total loss. Probably a lawn chair, binoculars and leisure to inspect the entire bole carefully if you are trying to get as many as possible with the fewest rejects. I also change sawing plan fast if a log is not panning out as a beam. It is shorter, sheathing or something else. The immediate "need" won't improve a reject beam. You're going to end up back in the woods either way. Immediately switch gears and make something else. Lead yourself not into temptation. Know when to fold em and make boards.
I'm Jim's crazy customer Jake! Thank y'all for all the great advice!!!
I was hoping to just point at the block of woods and tell the building inspection dept "Those thar are the trees", then start layin' 'em down until I have all I need. Unfortunately they are requiring me to have all the trees marked I plan to use. I'm building a Timber Frame from trees on my property, because doing so allows me to do it without grade inspected/stamped timbers. FYI: I have a well designed engineer-stamped plan from The Great Jim Rogers!
So I took the info you guys provided and built a spreadsheet to try and help ID the needed trees. I'm sure the old timers just eyeballed it, but I'm green.
The math is DBH minus an inch for bark, with taper figured at 2" every 4ft until 16'... then 1" every 4ft above 16'. I then figured 70% of the log diameter to give the largest possible cant size at varies heights.
Hope the spreadsheet posts properly.
(https://forestryforum.com/gallery/albums/userpics/66124/Clean_Hearts_Farm_Timber_Frame.jpg?easyrotate_cache=1675404600)
Given the constraints put on you by the building inspection dept, suggest you put extra trees into your plan. I'd assume you are not required to cut all of them if you fill your needs for timbers and can stop cutting.
Look forward to seeing your plans unfold.
Quote from: jacobcbass on February 03, 2023, 01:11:58 AMUnfortunately they are requiring me to have all the trees marked I plan to use.
Welcome Jacob :)
In NC, ummm, that ain't the law... and on an outbuilding? (why do I want to let my maker sort the sob's out).If you have an attorney friend, draw up some form of affidavit. Choose your battles though.
@jacobcbass (https://forestryforum.com/board/index.php?action=profile;u=56124) I know you are being conservative but just as an FYI, the Form Class tables were derived from measuring the diameter outside the bark at breast height and the corresponding value of the diameter at 16' is inside the bark.
On a 25"x 1/4" thick Biltmore Stick, at 66' away from the tree, if aiming the stick like a rifle, the 8" top of the tree will disappear behind the 1/4" thick end of the stick. On longer, 5/16" thick Biltmore sticks (that measure five logs instead of four), a 10" top will disappear when done the same way.
This is not exact but on a tree that does not have a lot of taper, no obvious "cut me here points", this is a decent method to estimate 8" and 10" tops.
Are we looking at hardwoods or softwoods? I'm also on the side of marking extra trees for the ones that you miss with the estimates or get bent when they hit the ground. When you start cutting and sawing them go for the biggest and longest ones first. If they fail to make a big or long one then the can make some of the smaller or shorter ones on the list.
What he is wanting to see is basically enough trees marked to do the frame, then enough stumps to feel confident you weren't buying ungraded timber in. You won't be arguing over one stump this way or that.
NC is more of a homestead exemption than a grading exemption when you compare the language to other states. He's being somewhat picky, but for a reason.