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Stark Reality of Poor Pruning Hits Home at Harvest Time

The PF Olsen Otago/Southland team has recently had first-hand experience with late pruning and over-thinning.

As part of their appraisal process for the forest owner, Dave Thode (PF Olsen Regional Manager – Otago/Southland – see photo, left) and Mort Shepherd (PF Olsen Harvesting Manager based in Gore) felled trees and cross-cut the stems at the branch nodes. "Short of a more expensive, formal Pruned Log Index study, this is the best way of assessing pruned log quality", says Dave. "It becomes clear very quickly what you are dealing with".

The disks showed that pruning was late, especially the last lift. In addition, the final thin was too severe, leaving too few crop trees and encouraging large branch growth. In addition, the final prune was late. This has resulted in not only a large knotty core but also large occlusion scars (occlusion is the process of the cambium forming over the branch stubs and eventually laying down clear wood) – see photo below. This leaves little clear wood in the upper part of what would become the pruned log.

Contrast this with a well-managed pruning operation, minimisation of the knotty core and maximisation of the clear wood (see photo below).

"To put this in perspective", says Dave, " Over the 50ha area of the block, there is likely to be an average loss of about $12/tonne (average stumpage) if the logs don't meet the minimum acceptable pruned log recovery. This will equate to a loss of value of around $270,000 over the whole block. This really brings home how much value loss there can be from poorly scheduled and poorly managed pruning operations".