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A comparison of two growing stock assessments by stratified sampling– how does accuracy of inventory affect our interpretation of the results

机译：通过分层抽样比较两种成长中的种群评估–种群准确性如何影响我们对结果的解释

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Since 1967, when the Polish State Forests were first inventoried, a continuous increase in the volume of growing stock has been recorded. This increase in timber resources is mainly the result of sustainable forest management. However, during this time period inventory methods have been changed a few times and this may have affected the estimates of of wood resources. Since 2011 new instructions have been in place for forest management plans in the Polish State Forests. Despite this, the method of taking forest inventories remained consistent with the previous guidelines. This should allow us to consider changes in the volume of growing stock in relation to inventory methods and their accuracy. In this paper, the results of growing stock estimations based on two assessments made using stratified random sampling are compared. After five years of inventories made for forest management plans, 422 sample plots in two forest districts were measured within 15 strata. Predicted age classes structure at the beginning of successive management plans was used to determine new strata. Data from two inventories were compared on the basis of age class. In addition, data from the State Forests Information System i.e. updated stand level inventory data (on felling and tree growth) were analyzed. Comparing data from the two inventories, in three of seven age classes there was a decrease in the volume of growing stock after a five year period. We found no rational explanation for this. The extent of felling in the analyzed stand was very low, as confirmed by data from State Forests database. However, the largest decrease in volume was 1.5%, whereas the accuracy of growing stock assessment of discussed age class was estimated at some 9% in 2006 and 8% in 2011. Hence, from statistical viewpoint there was no differences between the results of both inventories. However, the differences between volume of growing stock of examined age classes, updated in the Information System of the State Forests and results of assessments by stratified sampling are less than 95% confidence intervals for means of samples. Because of that, updated information could be used in the long term management planning. The results clearly suggest that changes of growing stock, estimated as a difference between two assessments, should be interpreted in conjunction with the accuracy of these inventories. The accuracy of sampling should be also taken into account when creating management plans.
机译：自1967年首次对波兰国家森林进行盘点以来，已记录到不断增长的蓄积量。木材资源的增加主要是可持续森林管理的结果。但是，在此期间，盘点方法已经更改了几次，这可能影响了木材资源的估算。自2011年以来，波兰国家森林的森林管理计划已经有了新的指示。尽管如此，盘点森林的方法仍然与先前的指南保持一致。这应该使我们能够考虑与库存方法及其准确性有关的生长库存量的变化。在本文中，比较了基于使用分层随机抽样进行的两次评估的种群估计值的结果。在为森林管理计划编制了五年清单之后，在15个地层内对两个森林区的422个样地进行了测量。连续管理计划开始时的预测年龄等级结构用于确定新的阶层。根据年龄段比较了两个清单的数据。此外，还分析了来自州森林信息系统的数据，即更新的林分级清单数据（有关砍伐和树木生长的数据）。比较来自两个清单的数据，在七个年龄段中的三个年龄段中，五年后增长的种群数量减少了。我们对此没有找到合理的解释。国家森林数据库的数据证实，被分析林分的砍伐程度非常低。但是，数量下降最大的是1.5％，而讨论的年龄组的生长种群评估的准确性估计在2006年约为9％，在2011年约为8％。因此，从统计角度来看，两者的结果之间没有差异库存。但是，在国家森林信息系统中更新的，经过检查的年龄类别的生长种群数量与分层抽样评估结果之间的差异小于95％的置信区间。因此，可以在长期管理计划中使用更新的信息。结果清楚地表明，应将这两种评估之间的差异估计为增长存量的变化，并结合这些库存的准确性进行解释。创建管理计划时，也应考虑抽样的准确性。

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