FOREST HISTORY, MOUNT ST-HELENS

Ring counts on Douglas-fir (Pseudotsuga menziesii) stumps were used to reconstruct the early development of old-growth forests northeast of Mount St Helens, Washington, after catastrophic forest disturbance by tephra fall from an eruption in 1480. In addition to documenting volcanic and other disturbances in forests near the volcano, this investigation tests the hypotheses that distant seed sources, repeated disturbances, or competition from shrubs and hardwoods caused Douglas-fir to slowly (>90 years) recolonize sites in the western Cascade Range 400 to 500 years ago. Findings show that long distances from seed sources could have contributed to the slow development of regional old-growth Douglas-fir stands after catastrophic disturbances, but not repeated disturbances during stand development, and not competition from shrubs and hardwoods. The findings also suggest an AD 2020-2160 time-line for natural reforestation of the Mount St Helens National Volcanic Monument.