New National Growth Model for Radiata Pine Validated

FFR has just completed a round of member meetings in Nelson where the outcomes of the research programmes across all four themes were presented to members. Over the course of the four days over 100 people from across the country attended to get an update on the FFR research programmes. Included in the visit was an inspection of a new and very impressive three storey wooden building being constructed for the Nelson Polytech to demonstrate the use of engineered wood products in a large commercial building. The building is a world first for both its timber earthquake resistance design and its unique laminated veneer lumber (LVL) primary structure multi-storied building; this building will be an inspiring learning environment that feels good to be in. Click on this link to see more of this innovative NMIT Arts Media Building.

A highlight of the Radiata Theme programme was a presentation on the validation of a new national growth model for Radiata Pine. Called the 300 Index, the growth model is based on approximately 15,000 growth measurements over 750 permanent sample plots throughout New Zealand. It is a measure of productivity expressed as the Mean Annual Increment (MAI) in cubic metres for a final crop stocking of 300 stems per hectare grown to a rotation age of 30 years. In comparison, the old Site Index measure we are all familiar with was a measure of tree height at age 20 and took no account of volume production.

Growth models are extremely important in forestry because they enable foresters to make predictions of wood yield by log grade at clear fell for a whole range of sites allowing planning of harvesting and marketing strategies and economic evaluations of alternative growing regimes to be undertaken. Prior to the development of the national 300 Index, eight different regional growth models developed in the 70's and 80's were needed to cover all sites in NZ.

The very thorough testing and validation that has been carried out shows that the model can be used with confidence across all sites in New Zealand and that there is minimal bias in terms of predicted volume at rotation age. The validation has shown that within the range of normal final crop stockings there is minimal bias and importantly that it can also be used across different genetic material without separate adjustment.

The benefits of a single national growth model that predicts volume production for all sites and ranges of forest management is a significant step forward for forest growers.