Impacts of portable sawmill logging on stand structure and regeneration in the lowland forests of West New Britain, Papua New Guinea

A project undertaken and supervised by H M Rogers, Booyong Forest Science, Canungra, Queensland

Small-scale portable sawmill logging, which is a component of reduced impact logging, is promoted across Papua New Guinea by NGOs as a sustainable development mechanism for village communities.  It can provide a technically feasible approach for landholders to manage their commercial forest resources rather than selling logging rights to international companies.  However, despite over 20 years of operational practice, little research has been conducted on portable sawmilling impacts or its silvicultural effectiveness. 

This study investigated the impacts of well planned and controlled portable sawmill logging on stand structure and regeneration in lowland hill forest at Kilu in West New Britain.  Logging impacts were compared to natural changes in unlogged forest.  Tree diameter increment, tree health, and stem mortality were assessed for a 1 ha logged stand and a 1 ha unlogged stand over 27 months.  Regeneration was assessed within the logged stand and in three logging gaps over 61 months.  Portable sawmill logging caused 1 – 6 % of the ground area to be heavily disturbed based on harvesting 1 – 2 trees ha-1.  The logging gaps promoted abundant regeneration of primary and secondary species.  Early regeneration was dominated by secondary species (61 %) but after 61 months the secondary species accounted for only 9 % of the juvenile population with primary species dominating.  Impacts in this study were low when compared to studies of conventional industrial logging in PNG, but the differences were less marked when compared to conventional logging at similar harvest intensities elsewhere.  A shift towards a slightly higher harvest intensity warrants consideration to reduce the impacts per stem harvested.

 

Figure 1. A newly created portable sawmill logging gap

Figure 2. Regeneration in a logging gap after 17 months

Figure 3. Regeneration in a logging gap after 61 months