Voronoi tessellation methods to delineate harvest units for spatial forest planning

Spatial forest planning requires delineation of potential harvest units, and the size, shape, and spatial arrangement of harvest units can affect forest values such as aesthetics, harvest volumes, and wildlife habitat. When the desired harvest unit size is smaller than the size of polygons created with a GIS (geographic information system) overlay then some method of subdividing polygons into smaller units is required. This paper presents three methods that might be used to divide stands (polygons) into potential harvest units for forest planning. The methods compared are (1) simple overlay with a rectangular lattice, and Voronoi tessellations with travel cost as a distance metric and either (2) regularly spaced generator points or (3) generator points created with a max.-min. procedure. Each of the three methods provides a different distribution of harvest unit size and a different spatial arrangement of potential harvest units over the landscape. Interviews with industrial forest planners indicate that the usefulness of an automated delineation method for an individual company would depend on the method of stand mapping, the silvicultural methods used, money and personnel committed to planning and GIS implementation, and site-specific conditions such as topography, roads, and forest types.