Adapting Finnish Multi-Source Forest Inventory Techniques to the New Zealand Preharvest Inventory

Abstract

To measure many small areas in a forest, each to the required detail and precision, and sufficiently frequently, is too expensive using ground-based inventories alone. The Finnish satellite image-aided National Forest Inventory (NFI) method was modified and tested with a view to developing a new preharvesting forest inventory method for assessing the volumes of potential timber assortments (log products) in New Zealand radiata pine (Pinus radiata D. Don) plantations. Data from 188 ground plots were supplied by a forest company for a 1000 ha block of radiata pine. This material was combined with known stand boundaries from maps and data from a Landsat TM image in order to predict for each pixel and each stand the pruned and unpruned sawlog, pulp and total standing volumes. A k-nearest neighbour algorithm was applied for the estimation. Some stand characteristics, obtained from stand histories, were used as co-variates, in addition to spectral features. Cross-validation tests indicated that estimates of plot variables were unbiased, though with high RMSEs. Stand level estimates were also unbiased on average, but showed high RMSEs. Research into the effects of stratification and methods by which to segment stands into sub-areas uniform with respect to timber assortments is continuing.