Dendrochronological reconstruction of jack pine snag and downed log dynamics in Saskatchewan and Manitoba, Canada

Abstract Dendrochronological techniques were used to investigate tree mortality and the persistence, fall rate, time since falling, of snags and downed logs in jack pine ( Pinus banksiana Lamb.) forests in Saskatchewan and Manitoba, Canada. The earliest dateable snag died 70 years prior to sampling (in 1935). The earliest dateable downed log died 62 years prior to sampling (in 1943). The fall rate of individual snags ranged from 0.014 to 0.050 trees year −1 . Most downed logs were estimated to have fallen 10–30 years prior to sampling, and the oldest dateable downed log fell 43 years prior to sampling. Overall, time of mortality could be dated for 95.5% of the 308 snags, and 64.8% of the 291 downed logs. The year of death for excessively decomposed trees was estimated from the mean year of death of the six dead trees nearest to it in size. The method was unbiased, with a mean absolute difference of 3.3 years (S.D. 2.4) between the measured and estimated year of death for 84 randomly selected trees where both were known. Maximum mortality rate ranged from 0.87% to 3.25% at the 10 stands, peaking from age 38 to 66. Mortality accelerated maximally at an average age of 34, at a rate between 0.030% year −2 and 0.315% year −2 . The observed timing of mortality relative to that expected from past observations of self-thinning and past observations of the half-life of downed logs suggest that the growth and dynamics of jack pine forests in this region about can be reliably reconstructed 50 years into the past with these techniques.