An analysis of age-age correlations in white spruce and lodgepole pine and how it applies to the growth and yield projection system (GYPSY) in Alberta

Abstract

Tree improvement is considered an effective method to address the shrinking forest land-base in Alberta, Canada. It is also of great necessity to quantify the potential harvest from deployment of improved trees. However, the growth and yield models currently used in Alberta were originally developed based on growth measurements and projections from fire origin stands, and therefore, there is no widely accepted method to recognize the impact of managed stands, and even less information available to properly incorporate genetic gain in volume from tree improvement into managed stand models. Furthermore, there are considerable challenges associated with acceptance of an appropriate age-age correlation when selecting trees at a young age and projecting their anticipated increase in volume at rotations as long as 80–110 years.White spruce (Picea glauca (Moench) Voss) and lodgepole pine (Pinus contorta Dougl.) are the most important commercial tree species in Alberta, and the focus of this study. Based on the most recent and comprehensive datasets from progeny trials from both species, two available age-age correlation equations, one developed by Lambeth (1980) and another by Rweyongeza (2016), were compared and adjusted. This study also explored a new method for age-age correlation prediction based on a sigmoid parabolic branch (SPB) equation.The results show that the adjusted Lambeth equations, with re-estimated parameters for white spruce and lodgepole pine in Alberta, are the most robust for both species and should be further incorporated into the growth and yield models, based on cross-validation results at a relatively young age (7–31 years for white spruce and 6–30 years for lodgepole pine). The phenotypic age-age correlation shows no significant deviation from the genetic age-age correlation for white spruce and lodgepole pine in Alberta. The stand volume generated from the growth and yield projection system (GYPSY) using an age-age correlation from the adjusted Lambeth equations shows that white spruce has a higher age-age correlation and therefore, a higher percentage improvement in volume per hectare compared to lodgepole pine regardless of rotation age.