Growth and genetic predisposition of induced acorn production in pedunculate oak (Quercus robur L) within 15 years of planting

Abstract

The primary objective of this study was to evaluate the growth, genetic predisposition and potential for early fructification of pedunculate oak trees (Quercus robur L.) using two different planting stocks: Root Production Method (RPM®) and Cell Grown (CG). The second objective was to investigate the effect of crown clearance on acorn production. This study was undertaken between 2001 and 2016 at an experimental site at Castlearchdale in Northern Ireland initially comprising of 150 CG and 150 RPM® derived one-year old Q. robur seedlings. Both tree seedling groups were each subdivided into two groups of 75 trees based on height: CG1 (20–50 cm); CG2 (>50 cm); RPM® 1 (<76 cm) and RPM® 2 (>76 cm). Viable acorns were produced by each category of tree in the seventh year after planting: CG1 - 1 tree (1.3%); CG2 - 2 trees (2.7%); RPM®1 - 6 trees (8%) and RPM®2 - 12 trees (16%). The RPM® trees were significantly (p < 0.001) taller, thicker and more likely to show early fructification than CG trees. A weak but very highly significant correlation (r = 0.23, p < 0.001) was established between height at planting and early fructification for RPM® Q. robur trees eight years later. Crown clearance in year 14 after planting had no significant effect on acorn production in the following year within the oak tree population. The genetic analysis shows no obvious genetic groupings within the treatment groups nor genetic predisposition. A similar pattern was found for samples producing acorns versus those not producing acorns.The potential of RPM® planting stock to enhance home grown seed production in Britain and Ireland is discussed in relation to fructification dynamics of oak trees, and physiological and climatic conditions.