Optimized cellular automaton for stand delineation

Timo Pukkala

doi:10.1007/s11676-018-0803-6

Abstract

Forest inventories based on remote sensing often interpret stand characteristics for small raster cells instead of traditional stand compartments. This is the case for instance in the Lidar-based and multi-source forest inventories of Finland where the interpretation units are 16 m × 16 m grid cells. Using these cells as simulation units in forest planning would lead to very large planning problems. This difficulty could be alleviated by aggregating the grid cells into larger homogeneous segments before planning calculations. This study developed a cellular automaton (CA) for aggregating grid cells into larger calculation units, which in this study were called stands. The criteria used in stand delineation were the shape and size of the stands, and homogeneity of stand attributes within the stand. The stand attributes were: main site type (upland or peatland forest), site fertility, mean tree diameter, mean tree height and stand basal area. In the CA, each cell was joined to one of its adjacent stands for several iterations, until the cells formed a compact layout of homogeneous stands. The CA had several parameters. Due to high number possible parameter combinations, particle swarm optimization was used to find the optimal set of parameter values. Parameter optimization aimed at minimizing within-stand variation and maximizing between-stand variation in stand attributes. When the CA was optimized without any restrictions for its parameters, the resulting stand delineation consisted of small and irregular stands. A clean layout of larger and compact stands was obtained when the CA parameters were optimized with constrained parameter values and so that the layout was penalized as a function of the number of small stands (< 0.1 ha). However, there was within-stand variation in fertility class due to small-scale variation in the data. The stands delineated by the CA explained 66–87% of variation in stand basal area, mean tree height and mean diameter, and 41–92% of variation in the fertility class of the site. It was concluded that the CA developed in this study is a flexible new tool, which could be immediately used in forest planning.

Highlights

Forest inventory methods based on remote sensing often produce inventory results for small square-shaped pixels
The results show that the obtained stand borders very well followed the border between mineral soil sites and peatland (Fig. 6a), which is important for forest planning, because only winter cuttings may be prescribed for peatland sites whereas upland forests can be harvested in summer
This study described a cellular automaton for delineating homogeneous stands from inventory data where stand variables are interpreted for grid cells

Summary

Introduction

Forest inventory methods based on remote sensing often produce inventory results for small square-shaped pixels. This is the case for instance when the inventory is based on the interpretation of satellite images. When the inventory uses laser scanning and the area-based interpretation approach (Næsset 2002; Maltamo and Packalen 2014; Vauhkonen et al 2014), the optimal size of the interpretation unit is of the same magnitude as the size of the field plots that are used as ground truth (Pippuri et al 2013). Lidar inventories cover most of the privately owned forests of Finland (www.met sakeskus.fi). The results of these inventories are freely available at www.metsaan.fi/paikkatietoaineistot

Methods

Results

Conclusion