Wind damage research

There has been a wind damage research programme at Scion for over 30 years. There was a lot of activity in this area following Cyclones Bola and Bernie in the 1980s. Much of this research is documented in FRI Bulletin 146. In the 1990s I worked with researchers from the British Forestry Commission to develop a model that would enable forest managers to quantify the impacts of site, stand structure and species on the risk of damage (see NZ Journal of Forestry, May 1998).

This model has been used to evaluate the risk associated with different timing and intensities of thinning as this silvicultural operation has been associated with much of the damage that has been observed in NZ's forests. Recent research by colleagues in the Forest Protection Group at Scion has also looked at the issues associated with salvaging wind damaged trees, particularly the window of time available before discolouration from sapstain fungi occurs.

Scion has also maintained an unofficial database of wind damage losses. This database contains records documenting 63,000 hectares of damage spanning the period 1945 to 2012. Most recently this was analysed in collaboration with Bruce Manley, Dawoon Park and Carl Scarrott from the University of Canterbury. Our analyses showed that for NZ as a whole approximately 0.21% of net stocked area is lost to wind each year. A similar analysis for fire that has been undertaken by Scion's fire research programme showed that on average 0.11% of net stocked area is lost to fire [annually]. However, without intervention through fire management it is likely that losses would be higher, so care needs to be taken when simply comparing these two figures.

The recent Canterbury wind damage event is probably the largest event since Cyclone Bola in 1988 and the largest event in Canterbury since the gales of 1975. We would welcome the opportunity to assist the owners of affected forests in any way we can. If there are opportunities to improve management of wind damage risk in the future, then we should see what we can learn from this event.

This article was reproduced courtesy of the NZ Institute of Forestry, Newsletter Number 2013/42, 8 November 2013 and the author John Moore, MNZIF, Rotorua

Windthrow can cause catastrophic losses but its incidence can be minimised by silviculture and its impacts minimised by careful harvesting and marketing of affected stands. Insurance is also a risk management option. This photo shows a windthrown stand of a PF Olsen client's forest in the Marlborough Sounds. Salvage harvesting is now in full swing to maximise recovery of as many merchantable logs as possible.