Quantification of realised genetic gain in radiata pine and its incorporation into growth and yield modelling systems

Realised genetic gain for radiata pine (Pinus radiata D. Don) was estimated using data from 46 installations of three series of block-plot trials spanning a wide range of site types throughout New Zealand. These trials contained 63 unique seedlots with different levels of genetic improvement. Realised genetic gain was quantified using two measures of productivity: site index and 300 Index (a measure of volume productivity). The level of genetic improvement of each seedlot was determined by its GF Plus rating, a genetic rating system based on breeding values used for New Zealand radiata pine. There was a positive relationship between GF Plus rating and both productivity measures. Differences of 25% in total standing volume at age 30 years and of 5.6% in site index were found between unimproved (GF Plus 9.9) and highly improved (GF Plus 25) seedlots. Each unit increase in GF Plus rating was associated with a 1.51% increase in volume growth rate. In absolute terms, the magnitude of the increase was greater on more productive sites compared with less productive sites, although in percentage terms, it varied little between sites or regions. Quantification of genetic gain in this manner enables it to be easily incorporated into existing growth and yield simulators.