Consequences of a fixed-top DOB assumption on the estimation of pine chip-n-saw and sawtimber tonsThis article is part of a larger document. View the larger document here.
Many pine plantation growth and yield simulators allow the user to define products based on the size classes and top diameters corresponding to local market specs. Top d.o.b. is typically set at a constant corresponding to the local product specification. Examination of individual tree data collected in cruises of loblolly pine stands across the South show that the top d.o.b. for pine products is not a constant, but varies directly with d.b.h. Median overstatement of individual tree PST volume due to use of a fixed 6 inch d.o.b. top instead of the top d.o.b. implied from merchantable height is about 10 to 15 percent, but can range from zero to almost 400 percent. Volume overstatements at the stand level are more muted. PST is in the range of 0-149 percent and with a median value of about 16 percent. CNS and PPW have smaller ranges (0-60 percent) and median overstatements of about 8-2010 percent. These overstatements are inversely related to the ratio of merchantable height divided by total height. PST overstatement was less than ten percent only when height ratio averaged 0.75 or more. Overstatements of 100 percent or more occurred when the product height ratios drops below about 0.35. Overstatements are not associated with stand attributes or geographical location in any meaningful way.