Species properties and recovery from disturbance: Forest herbs buried by volcanic tephra

Question How do forest herb species differ from each other in their spatial and temporal dynamics during recovery from volcanic disturbance, and how are dynamics related to species traits? Location Northeast of Mount St. Helens, Washington, USA. Methods Following deposition of volcanic tephra in 1980, we measured herb density and cover in permanent 1-m(2) plots during 1980-2005 in three old-growth forests with differing tephra depths. For 26 species, we calculated the frequency of plots with residuals (individuals that survived the eruption) versus re-establishment on the tephra, timing of establishment, turnover, influence of nearby conspecific plants, importance of three components of cover increase, and relationship of flowering frequency to succession. Results Tephra depth affected species behavior. Deep tephra produced fewer residuals, a greater increase in shoot size, and more shoot turnover; favored species that established late; and allowed establishment of early seral herbs. Nearby presence of conspecifics increased permanence of first establishment and rate of plot occupancy. Most species spread significantly in deep tephra but not in shallow tephra. Among species, frequency of flowering increased with fewer residuals, later establishment, and higher turnover. Species behavior seldom differed among growth forms based on leaf longevity and vegetative spread. Conclusion Population dynamics at the small-plot scale differed from those of the entire population. The timing and permanency of establishment and mechanism of expansion differed among species and with tephra depth. There was some consistency among species with similar habitat breadth and degree of flowering, but little consistency associated with the usual growth form classification.