In nearly all national forest inventories (NFI), some sample plots are unable to be measured such that nonresponse may be an issue of concern. Thus, it is of particular interest to understand the phenomenon in terms of current status and temporal change in nonresponse rates and the associated spatial distribution on the landscape. In the NFI of the USA, denial of access permission on privately owned forest land and hazardous conditions has led to an overall nonresponse rate of 9.8% with some areas exceeding 20% of plots being inaccessible. Further, it was found that nearly 50% of the areas studied were exhibiting increasing rates of nonresponse over time. Comparisons between response and nonresponse plots via remote sensing characteristics suggested there may be systematic differences in some parts of the country, which may cause bias in the sample and resulting estimates. The findings indicate that improved communication strategies with private landowners are needed to reduce nonresponse rates. Due to the unlikelihood of eliminating nonresponse entirely, methods to mitigate potential nonresponse bias should be considered for incorporation into the estimation of population parameters.
Keywords: Denied access; Ownership; Population estimates; Sample bias; Tasseled cap.
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