INTERANNUAL VARIATIONS IN THE SEED PRODUCTION OF PINUS-BANKSIANA AT THE LIMIT OF THE SPECIES DISTRIBUTION IN NORTHERN QUEBEC, CANADA

Interannual variations in cone and seed production of Pinus banksiana Lamb. were studied at the species northern limit of distribution in Quebec (Canada). Cone number per cone-bearing branch, potential number of seeds per cone, number of formed, filled, and viable seeds per cone, and seed viability, germination rate, and mass were determined for two populations of the species, over a 9-year series. There were significant differences among years, but not between populations, in all the variables considered. The populations were well synchronized with each other, suggesting that climatic influence on the variables considered might be significant. Apparent periodicity in reproductive output also suggests the existence of some internal cycle, possibly in relation to tree reserves. Annual viable seed production is the result of a combination of events in the reproductive cycle of an individual (i.e., cone initiation, pollination, fertilization, and embryo maturation), each one specifically affected by climate. There are no apparent trade-offs between seed mass and number of filled seeds per cone over time; moreover, there seems to be a positive relationship between seed mass and number of viable seeds per cone. Climate conditions during fertilization and embryo maturation (both of which occur during the same season) appear to significantly influence the species reproductive output. We present regression models based on meteorological variables to estimate cone and viable seed production, and seed mass.