A proposed terrain classification for harvesting in New Zealand

A terrain classification is required to give an adequate description of the terrain conditions encountered in harvesting operations in New Zealand. Terrain classifications developed overseas have not fully met our requirements and have been modified and extended to the needs of New Zealand harvesting researchers and forest planners. The major terrain features considered are ground condition, ground roughness, and ground slope. This follows international convention. The measurement of ground condition relies on a cone penetrometer which relates to soil strength the number of blows to penetrate the soil to 50 cm. Ground roughness is expressed by size and frequency of the obstacles on the ground and whether they are permanent or impermanent features. Ground slope is expressed in a variety of ways (slope type, slope angle, slope length, slope aspect, and slope height) to ensure a clear expression of this terrain characteristic. Other factors considered are slash ground cover, and standing vegetation. Proposed data collection sheets designed for subsequent computer summary and analysis are included. A worked example shows the results of a field test. The terrain classification requires further extensive testing by field practitioners. This will certainly result in further modification as experience is gained. The development of a relatively simple and accurate technique to measure soil moisture would add to the precision of the terrain classification. The terrain characteristics measured are linked to a table developed by the British Forestry Commission setting out the approximate terrain limits of the more common forest extraction machinery. A task yet to be addressed is the linking of terrain difficulty to production rates. This information should be more readily available when the terrain classification is in place and an integral part of harvesting research, forest management procedures, and stand record systems. (auth)