Sampling

[SkidrowJoe]

For most large crusies what sampling methods do you guys use:

100 % census, Fixed area, Point, 2 P, or 3 P, or other?

[beenthere]

2 P  (unless I drink a lot of water, then it's 3 P)

[Furby]

 

[Ron Wenrich]

Depends on what you're doing.  If you're looking at a selection harvest, then its 100%.  You're marking the tree, so you might as well take the measurements.

If you're looking at either an appraisal or management data, I normally take plots on a grid.  I use an angle guage, but a prism works just as well.  I do these on 200' centers, which comes out to about a 10% cruise.  On a really large area, you may get away with a 5% cruise, if you can catch all the different types of areas within the property.

I will also break down the property into areas where the timber is similar in size and species combination.  That is put on the map as I do the cruise.  When I'm done with the map, I'll take put a dot grid on the map to figure up acreage.  The number crunching would combine all plots of the same timber types and come up with a total volume. 

I've found the method to be pretty accurate.  I have marked a few 100% after a preliminary cruise and have been off by just a couple of % on the total. 

Cruising is part art, part science. 

[Ron Scott]

We do it similar to what Ron W. has stated. Selection harvests are 100 %  tree measurement during tree marking. Large areas of aspen pulpwood and red pine plantation thinnings may be sample tree measured, i.e 1 in 20 measured in aspen pulpwood; 1 in 100 measured in red pine plantations etc.

Point sampling is done for timber appraisals with a "rule of thumb" method"

1) Never take less than 10 sample points
2) If the area is less than 40 acres, take one sample point per acre
3) If the stand acreage is between 40 and 80 acres, take 40 points plus one additional point for every two acres over 40 acres, e.g. 60 acres will requiire 50 total points.
4) If the stand acreage is between 80 and 200 acres, take 60 points plus one additional point for every four acres over 80, e.g. 100 acres will require 65 points.
5) If the stand is over 200 acres, use "the formula" rule which is more complex.

[SwampDonkey]

I sample on 100 x 100 m grid making sure there are at least 4 points in each stand. As far as % area sampled using variable/prism cruising, plot size varies with tree size in each plot. So, you never know until your done cruising what % you sampled and even then it's based on statistics, and the % area sampled is only an estimate and not as accurate as fixed area plots. If your talking % of the population sampled, then either way it's a statistical estimate because one plot can be less dense than another. Also, never put a plot near a stand edge it can throw volumes way off in certain stand types.

[SkidrowJoe]

Ron Scott for five do you use n=(t^2 x CV^2)/E.

[Ron Scott]

Yes, I first  stratify the stands across the larger acreage either by species, acreage,value, etc. then determine the coefficient of variation, then the limit of error, then the number of sample items whether tree measurement or fixed radius plots and etc.

Much more complicated. I follow the formula's from the "book". Don't use them to often. The "rule of thumb" is used most of the time.