engleski

Effect of rounding number of stems per diameter classes on stand volume

Forest stand structure is the basis for forest planning in Croatia. Most of the stand structure data are obtained by sample plot measurements. For every dominant tree species number of trees per diameter class is calculated as a number of trees per hectare both on the single plot or the stand level. Number of trees per diameter classes is displayed as whole (rounded) number in Management plans. When calculating total stand volume, two approaches are used. Most of the forest planners used raw (not rounded) data in calculation, while displaying rounded number of trees per hectare and only some of them used rounded number of trees for calculation as it is written in Management plans. This paper presents the effect of rounding the tree number (whole number, one decimal and two decimal places) on total volume calculation in two different Management units: ''Opeke'' and ''Sungerski lug''. Total volume in Management unit “Opeke” (even-aged stands) is higher if the tree number is rounded to whole number in comparison with volume calculated when the tree number per ha used for calculation is rounded to one or two decimal places. Volume calculated by whole number compared to the volume calculated from rounding to one or two decimal place is 0, 75 % and 0, 91 % higher, respectively. On a stand level volume differences vary from -3, 2 to +5, 1 % and -3, 6 to +6, 1 % respectively. Total volume in Management unit ''Sungerski lug'' (uneven-aged selection stands) is lower if the number of stems is rounded to whole number compared to the volume calculated when tree number per hectare used for calculation is rounded to one or two decimal places. In this case volume calculated by whole (rounded) number of trees compared to one or two decimal place rounding is -0, 70 and -0, 73 % lower, respectively. On stand level volume deviation varies from -6, 4 to +6, 4 % and from -6, 5 to +7, 2 %, respectively.

forest inventory; number of stems; rounding off; stand volume

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