Over the years many of our clients from forest owners, harvesting crews and forest supervisors have asked about harvest cutover assessment methodology. Many have struggled with the concept of the line intersect sampling procedure, so I thought it might pay to document a little practical history about this method, and why it is used.

To some, cutover waste assessment is called ‘Wagner Logging Waste Assessment” and actually many of the Forest Industry training documents still refer to this assessment in this manner. This term was commonly adopted by the NZ Forest Service in their manual of procedures written by Swale in 1974. The name “Wagner” refers to a person, Van Wagner whom in 1968 used and applied the technique during his involvement in Fire Research for the Canadian Forest Service. He used it for estimating the quantity of slash or larger sized fuel on the ground.

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Figure 1 Typical Harvest Cutover in P.radiata

However it is little known that he adapted this from a technique developed in 1957 by a young forester Peter Olsen (whom later created his own company PF Olsen here in New Zealand), whom was faced with the problem of determining an economic means of estimating volume of logging residue.

To quote Olsen at the time;

“There was a need to focus on recovery of all merchantable material (being min 1.2m length and 10cm SED). The logging company at the time believed it was not worth the hassle to extract to this limit so normal practice was to leave somewhat larger pieces. Hence need to measure as a penalty payment was introduced”

He experimented with circular plots but quickly found them time-consuming and difficult to quantify as many pieces trans versed the boundary, and inter-plot variation was so great that a huge number of plots were required to obtain precision levels required to justify any royalty payment. Transect plots were long and narrow and reduced the inter-plot variation, but were still very time consuming and many more pieces trans-versed the boundary (unlike standing trees) making it more difficult to quantify. He decided these traditional techniques were simply uneconomic to implement in relation to the value of the merchantable material remaining. And moved to develop the idea of the Line Intercept Technique (LIS) with Dr William Warren, which is used for cutover waste assessment today. This builds on a “relationship between the number of pieces intersected by a line run at random through an area and the volume contained in that area”. At the time and still true today, the Line Intercept technique took 20% of the time and yet was able to give a more precise answer, in which confidence in royalties could be allocated.

It was implemented in 1958 in Kaingaroa Forest and designed specifically for the purposes of penalty royalty payments by the forestry company for remaining merchantable material. Dr William Warren a researcher with the Forest Service at the time worked with Peter Olsen on the sampling design and methodology and later published this work in 1964. It was this paper that Van Wagner picked up and used.

This is no different to today’s reasons for carrying out a cutover waste assessment.

  • Stumpage Sales Administration: where standing volume is sold, it is often the buyer’s responsibility to harvest and remove all merchantable logs. Waste assessment is used to determine volume of wood left behind, and is charged to the buyer even though it has not been removed.
  • Yield Reconciliation: most forest areas have a pre-harvest inventory carried out prior to being harvested. Waste assessment is required to correctly reconcile any differences between the pre-harvest inventory and log volumes produced.
  • Logging Compliance: quality assurance standards for harvest contractor in terms of a key performance indicator for value recovery.
  • Planning for Re-establishment: volume of waste in the cutover indicates hindrance, or additional site preparation tasks for establishment operations.

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Figure 2 Typical line intercept sample across a clear-fell harvest cutover in P.radiata.

The line intercept sampling can be tailored to identify any type of mechantable material volume remaining onsite.   If you would like more information about cutover assessment or would like to get some done for any of the reasons above feel free to contact us.

Original Published Science Papers of Interest

Van Wagner, C.E., 1968. The line intersect method in forest fuel sampling. For. Sci., 14: 20-26. De Vries, P.G., 1986. Sampling Theory

Warren.W.G. and Olsen,P.F.,1964: A line intersect technique for assessing logging waste. Forest Science, vol.10 pp.267-276

Warren, W.G., 1989. Line intersect sampling: a historical perspective. In: State-of-the-art Methodology of Forest Inventory: A Symposium Proceedings. USDA Forest Service, Pacific Northwest Research Station, Portland, OR, pp. 33–38.

Further detail on this can be found in a review of the line intercept approach.