Abstract
The productivity of fast-growing forest plantation stands varies across short distances depending on site and forest characteristics. This indicates that forest managers would benefit from a site-specific approach to forest management. One tool used to characterise such productivity variations is a yield map, and a cost-effective source of data for these maps is automatically collected by harvesters. In order to generate such maps, it is necessary to understand the effect of geospatial accuracy of tree location recorded by the harvester. This study investigated data sets from four stands, and very accurate tree location was available for two of these. The tree-location data for the remaining two sites were collected by a harvester and contained some inaccuracies associated with Global Navigation Satellite System (GNSS) recording under forest canopy and the physical dislocation of the GNSS. The GNSS unit is on the cabin of the machine, but the tree is felled using a boom and could be up to 12 m from the cabin. A suitable spatial resolution for studying variations in stand productivity, mean tree volume, and stocking rate across stands were established that enabled useful forest-yield maps from harvester data to be developed. By assessing variability in volume per hectare, stocking rate, and mean tree volume across a range of cell sizes from 10 × 10 to 100 × 100 m, we conclude that a cell length between 30 and 40 m is suitable for use as a reference when calculating volume per hectare and mean stem volume, while a 60-m-long cell is more suitable for evaluating stocking density. The variability pattern is consistent for the various accuracy levels. When the known positions of trees are relatively inaccurate, using mean tree volume and stocking rate per cell might be a method for mapping productivity from harvester data.
Highlights
The productivity of fast-growing forest plantation stands varies across short distances depending on site and forest characteristics
It is expected that the CV will stabilise, which indicates that the variability due to cell size is small and the remaining variability is from the stand itself
Based on the changes in CV across the studied range of cell sizes, we conclude that a cell length between 30 and 40 m is suitable for use as a reference when estimating volume per hectare and mean stem volume to further compare and develop the concepts of forest-productivity maps
Summary
The productivity of fast-growing forest plantation stands varies across short distances depending on site and forest characteristics This indicates that forest managers would benefit from a site-specific approach to forest management. Rotation ages of 6–8 years and 9–12 years have been achieved in Brazil and Uruguay, respectively, for pulpwood plantations (Andreoni and Bussoni 2014; Gonçalves et al 2013) A 3.6-ha stand of Pinus taeda L. located in Auburn, Alabama, USA was divided into four separate management zones based on a survey of the variation in stocking and productivity across the stand (Brodbeck et al 2007) These results indicate that forest management in general would benefit from a site-specific management approach to make the process more efficient while with reducing costs and environmental impact. Forest managers would expect to see clear benefits in production before considering implementation of the additional complexity this approach requires
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