Analysis and modelling of cohort life tables of jack pine seed cones

Abstract

Life tables for jack pine (Pinusbanksiana Lamb.) seed cones were constructed for cohorts at three sites in northern Ontario from 1985–1987 to determine the causes and temporal sequence of mortality. Seed cone abortion and feeding by the red squirrel, Tamiasciurushudsonicus (Erxleben), accounted for 65–75% of mortality. Insects killed about 4% of the total cone crop. Losses from the jack pine budworm, Choristoneurapinuspinus Freeman, the webbing coneworm, Dioryctriadisclusa Heinrich, and the red pine cone borer, Eucosmamonitorana Heinrich, combined, accounted for about 1%, while the cone resin midge, Asynaptahopkinsi Felt, and the red pine cone beetle, Conophthorusresinosae Hopkins, each killed about 1%. Three models, linear-exponential, Gompertz, and Weibull, were examined to describe seed cone survivorship curves, of which the Weibull generally gave concise descriptions and fitted very well. Significantly different patterns of cone survival occurred at different sites during the same period, and at the same site over different periods. The age-specific mortality rate increased with age most slowly in the bottom third of the tree's crown. There were significant differences in the age-specific mortality rate among the north, south, east, and west aspects in the same cohort, but there was no consistent pattern among cohorts, or between trees within a cohort.