Questions from the Field ...
“What BAF Should I Use?”
Use a BAF where you can detect all the trees. If you have severe brush, and can only use a BAF that would give you an average of 3 trees - then do it. If it is less efficient, use some extra plots to make up the difference. One of the first rules of all field work is to get the data right, even if it is not "efficient". Pick a bad field situation when viewing a large tree and back off until you are worried about seeing the tree, then check what BAF would make the tree about borderline at that distance. That should be the minimum BAF to use. If that is a 60 BAF, use that or a larger number.
Try to get about 4-8 trees as an average for the cruise. This makes for the best balance of effort between counting trees on a point and putting in more points. Some counts will be higher or lower, that that is not a problem. What BAF do you need for that ? It's really quite simple. Use any BAF to get the approximate basal area per acre for the stand. Your thumb, if you have calibrated it, will work fine here. It is just a rough estimate.
Divide the stand basal area per acre by 6, and that will tell you the BAF which will give you an average count of 6. It is just that simple. The size of the trees makes no difference at all - only the basal area controls the tree count. If this BAF is smaller than the one determined from rule #1, use the BAF that will give you reliable counts.
Don't worry about zero counts when you get a sparse area. You are out there to find out what is there, and the answer is "nothing". Just what you wanted to know. Live with it. Don't change to a prism that will provide trees at that point (or move the plot, which is a similar mistake). That is a bias, and what is the point of getting the wrong answer and working harder at the same time?
Way too many trees on some plots? You can live with it, or "split" the plot and randomly choose one half. It is best to roughly split the plot so about half the trees are on each side before making the actual count, but the scheme has to be acceptable to the check cruiser, so maybe some arbitrary rule will have to be used. Measure half the plot and write the answers down twice.
It is possible to use different BAF's during a cruise, but the chance of messing up the paperwork usually makes this unwise. If you use different BAF's for different purposes, such as a smaller one for smaller trees, make sure that they look or feel differently when using them so you do not mix them up.
Originally published October 2002
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