Height–Diameter Relationships for Jack Pine Seedlots of Different Genetic Improvement Levels

Differences in height-diameter (H-DBH) relationship were investigated using the Chapman-Richards function among jack pine seedlots planted in a realized genetic gain test in New Brunswick. Three seedlots representing the bulk mixed cone collection from the 1979 J.D. Irving’s first-generation seedling seed orchard (JDISSO) before rogueing (UNR), after the first time genetic rogueing (1STR) and after the second time genetic rogueing (2NDR), respectively, were planted in the test. Unimproved commercial seedlots (UC) were also included for comparison. Results indicate that an overall H-DBH relationship for all the seedlots was not appropriate. Seedlot pairwise comparisons in H-DBH relationships showed that, whereas most seedlot pairs were significantly different from each other, there was no significant difference between the UNR and UC and between the 1STR and 2NDR. Two models were developed with one targeting the UNR and UC (UNIMPROVED) and the other targeting the 1STR and 2NDR (IMPROVED). The difference between the UNIMPROVED and IMPROVED models was caused only by asymptote of the Chapman-Richards function. Applying the UNIMPROVED or IMPROVED model to predict height of the 1STR and 2NDR or the UNR and UC would result in an under-estimated or an over-estimated bias by 2 to 3% in height. In light of this study, seedlot differences in H-DBH relationships should be integrated into growth and yield models by a multiplier for height depending on genetic improvement levels.