Using auxiliary data to rationalize smartphone-based pre-harvest forest mensuration

Timo P Pitkänen,Jari Vauhkonen,Pekka Hyvönen,Minna Räty,Kari T Korhonen

doi:10.1093/forestry/cpab039

Timo P Pitkänen, Jari Vauhkonen + Show 3 more

Open Access

https://doi.org/10.1093/forestry/cpab039

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Abstract

Abstract Accurate mensuration of forest stands for pre-harvest planning will pose high costs if carried out by a professional forester as an on-site evaluation. The costs could be reduced if a person with limited mensuration expertise could collect the required data using a smartphone-based system such as TRESTIMA® Forest Inventory System. Without prior information, the field sample with sufficient number of measurement points over the whole stand should be selected, so that the entire variation will be covered. We present and test a rational framework based on selecting the sampling locations according to auxiliary data. As auxiliary variables, we use various spatial data sources indicating forests’ structural or spectral variation, as well as previously predicted inventory variables. We construct two variants of sampling schemes based on the local pivotal method, weighted by the auxiliary data, and compare the results to simple random sampling (SRS) with corresponding sample sizes. According to our findings, the benefits of auxiliary data depend on the considered stand, species and timber assortment. The use of auxiliary data leads generally to improved results and up to three times higher efficiency (i.e. lower variance) as compared with SRS. We conclude that the framework of applying auxiliary data has high capabilities in rationalizing the sampling efforts with little drawbacks, consequently providing potential to improve the results with similar sample size and possibility to use of non-specialists for the pre-harvest inventory.

Highlights

Roundwood procurement for the Nordic forest industry is based on cut-to-length harvesting, in which the trees are cut to timber assortments in the forest
Errors were always highest for birch, which was the least common species with 7.2–9.5 per cent proportion depending on the stand, and lowest for either Norway spruce or Scots pine depending on their dominance
Variation in the absolute levels of error index (EI) values between the stands derived largely from the number of photos used in the Trestima calculation, as indicated by the total stem distribution (Figure 4)

Summary

Introduction

Roundwood procurement for the Nordic forest industry is based on cut-to-length harvesting, in which the trees are cut to timber assortments in the forest. Manoeuvered measurement devices rely on an experienced field operator, which to an on-site evaluation by a wood sourcing professional, will lead to high mensuration costs. To decrease these costs, one solution would be to emphasize strategies that enable the collection of applicable and standardized pre-harvest information by means of simple tools and relatively low level of expertise. One solution would be to emphasize strategies that enable the collection of applicable and standardized pre-harvest information by means of simple tools and relatively low level of expertise This would allow, e.g. the non-professional forest owner to perform the actions needed for on-site data collection

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Conclusion