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The harmonisation of growing stock volume estimation standards, used in national and stand wise forest inventories
Date Issued | Start Page | End Page |
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2013 | 18 | 18 |
Differences decrease with increasing heights of trees or mean heights of stands. The largest differences are estimated for spruce and the least – for ash trees or stands. Form factor of the mean stem, received by the model, mean diameter and mean height of trees in stand is underestimated comparing with mean form factor, derived from the mean volume, height and diameter of tree stem. Due to this reason growing stock volume of stands with mean diameter up to 12 cm is underestimated by 5-15 percent, while in stands with major mean diameter than 12 cm is underestimated up to 5 percent. Form factor models, used for growing stock volume estimations which are not accounting tree distribution by diameter in stand, is the reason for growing stock volume underestimation in average up to 2 % per all species. As the result of the study there were elaborated eight form height models for stands of the main Lithuanian forest tree species. These models ensure growing stock volume estimation in stand wise inventory without bias, as well as comparability of data received by stand wise and national forest inventories.
Different inventories use different methodological background for growing stock volume estimation that is not always adopted for this purpose as standards, and usually is the reason of unjustified differences between results of inventories. Object for growing stock volume estimation in stand wise inventory is stand, while in national forest inventory it is detailed to the individual tree. Form factor models, depending on height or height and diameter, sometimes are used not considering different nature of objects in the inventory. This paper deals with peculiarities of standards used for estimation of growing stock volume in stand wise and national forest inventories of Lithuania and their influence on the results of these inventories. Data of 5992 permanent plots (data source - NFI 2006-2010) and 3290 temporary plots (data source - mature stands inventory of 2009) with 137.9 thousands DBH measurements and 26751 tree height measurements were used for study. Form height models employed in stand wise inventory and form factors models employed in national forest inventory were used for study too. Form factors of trees as well as form factors of stands decrease, when height is stable, but diameter of tree or mean diameter of stand increases. Differences in form factors of trees or stands of the same height, but different diameter varies up to 5-12 percent.