Empirical errors of small area estimates from the multisource national forest inventory in Eastern Finland

The precision of multisource national forest inventory (MS-NFI) estimators and simple synthetic estimators based on NFI field data only was assessed employing an independent inventory data set of several small areas in Eastern Finland. There were seven test units of size 100 km(2) and three test units of size I km(2) for which a systematic field sampling was carried out. The 'improved' MS-NFI method yielded the most precise estimates for mean volume and mean volume of pine and spruce: relative root mean square errors (RMSE*) were 5%, 12% and 15% for 100 km(2) test units and 13%, 27% and 40% for I km(2) test units respectively. The stratified MS-NFI method was best for broad-leaved volume estimation. Synthetic estimation based on the NFI9 field plots post-stratified with coarse scale forest variable maps from NFI8 resulted in RMSE*s comparable to those of the ordinary MS-NFI in areas of 100 km(2) for mean volume and mean volume of pine and spruce. The amount of variation between the field inventory estimates for the test units explained by the MS-NFI estimators remained the same or increased when the size of the area increased from of I km(2) to 100 km(2) and up to 2000 km(2). The validation of the largest areas was made against the NF19 field inventory estimates for groups of municipalities in the study area.