Determining mid-slope on a steep slope

[Matt Markworth]

All,

In the following diagram, the gold lines are 4.5' long. Would you measure girth at Point A or Point B? This has implications for girth and also for height.

I would use Point A based on it being 4.5' above the point on the ground where I approximate the seed to have sprouted. Point B is the halfway point between 4.5' above the up-slope side and 4.5' above the down-slope side. For this example, assume that the down-slope side has only trunk exposed and no roots are showing.

tree on slope.JPG (21.05 KiB) Viewed 2793 times

Matt

[Steve Galehouse]

I would agree with A; how could it be anything else?

[Will Blozan]

Matt,

I suspect this is another case where a pith trace would be appropriate. Using the high and low in the diagram would "move" the center of the tree below where the seed could have been.

Will

[dbhguru]

Will,

I agree with what you are saying. It is an example of the direction we need to go with pith tracings. In the interim, I'd choose A. We'll have to think about upgrading the AF Measuring Guidelines Handbook before long.

Don,

What say you, Oh Godfather of the Tracings?

Bob

[Matt Markworth]

Steve, Will, Bob,

Cool, thanks for the ideas. The motivation behind the scenario is that I often find myself "eyeballing" mid-slope and could easily be off by a little bit. Or, if I would have walked up to the other side of the tree I may have arrived at a different mid-slope. It, of course, will have an impact on the measured CBH, but I'm more concerned of the impact it has on the reference point used for height measurement.

The conversation has given me an idea on a possible way to take some of the judgement out of it and works towards a more repeatable process.

Maybe something like this:

- Stand on the up-slope side of the tree
- Use calipers for a diameter measurement (this actual diameter measurement isn't important and the height of the diameter measurement isn't important)
- Hang a plumb bob from one side of the caliper and let the plumb bob touch the ground - measure the vertical distance from that point on the ground to the caliper
- Repeat on the other side of tree
- Add those two measurements and divide by 2, the caliper is positioned at this calculated height above mid-slope and can be used as a reference point for height measurement and to find 4.5' above mid-slope.

tree on slope-plumb bob.jpg (25.34 KiB) Viewed 2760 times

Matt

[Matt Markworth]

If the tree leaned at all, then that last process wouldn't work. So, would be back to the pith trace.

Matt

[dbhguru]

Matt,

Excellent start to a discussion that we need to keep going. Here is a graphic to illustrate what you've just said.

Over the coming months, we need lots of input from our arborist members on where pith lines are likely to located for a wide variety of shapes and species and what to do in cases of disagreement among experts.

Bob

[sradivoy]

Interesting paradox! I was wondering why 4.5 ft is measured from both down-slope and up-slope in determining the mid-slope position in the first place. Why not take half the distance between down-slope(at ground level) and up-slope (at ground level) in determining the mid-slope position and then measure 4.5 ft from that reference point? Thanks.

[Will Blozan]

You can do either but the 4.5 is used for the subsequent diameter or girth. Doesn't really matter, just saves a step.

Will