The millennial dynamics of a boreal forest stand from buried trees

Abstract

Summary We reconstructed the dynamics of a black spruce (Picea mariana) and jack pine (Pinus banksiana) forest stand in northern Québec using a continuous, 5200‐year‐long sequence of stem remains buried in adjacent peatland. Simulations of recruitment of such remains provided guidelines for inferring past ecosystem structure and composition at the stand scale. Compared with the late Holocene (4650–0 cal. year BP (CYBP)), the mid Holocene (5200–4650 CYBP) period was characterized by faster tree growth, larger stems and higher stem density, indicating higher forest productivity in association with a milder climate. The presence of stem remains of both species from 17 out of 20 contiguous 250‐year time intervals suggests that the spruce‐pine stand exhibited high compositional stability, with both species regenerating after fire from canopy‐stored seed banks. Relative species abundance closely followed the duration of past fire intervals deduced from the number of tree rings in buried conifers. Time periods of long (4650–3950, 3400–1850 and 250–0 CYBP) and short fire intervals (4950–4650, 3950–3400 and 1850–250 CYBP) were associated, respectively, with decreasing and increasing pine abundance, probably reflecting faster juvenile growth, lower shade tolerance, earlier sexual maturity and shorter longevity in jack pine compared with black spruce. We conclude that both climate change and climate‐induced fire disturbance have been driving long‐term ecosystem dynamics. Our field evidence supports the idea that interactions between disturbances and the life‐history traits of species modulate the impact of climate change at the scale of forest stands. At the same time, disturbances may result in long‐term stability of disturbance‐adapted ecosystems.