Buried propagules in an old-growth forest and their response to experimental disturbances

Soil blocks collected from an old-growth Pseudotsuga menziesii forest were subjected to three types of disturbances (shaderemoval, surface burning, and soil churning) in a factorial experiment. Most emergents (88%) were vegetative sprouts. Totalemergence and emergence of vegetative sprouts were significantly higher in the undisturbed (control) treatment than in anyother treatment. As intensity of disturbance (measured by the number of disturbance factors applied) increased, the numberof emergents declined. Exposure to sun caused a significant decline in emergence of each of the six most abundant species;the effects of burning and churning varied by species. Burning decreased the emergence of species with shallow regeneratingstructures. None of the experimental treatments significantly affected seedling emergence. Density of emergents (both seed-lings and vegetative sprouts) was higher under greenhouse condition (411.7/m2) than in the experimental treatments (94.6/m2), indicating that greenhouse emergence is more suitable for quantifying the buried propagule bank.
Key words: seed bank, propagules, old-growth forest, disturbance, fire.