Microsite Tolerance of Four Bryophytes in a Mature Black Spruce Stand: Reciprocal Transplants

Abstract

In the feather moss community under mature upland Picea mariana in northern Ontario, four bryophyte species coexist over periods of decades. The bryophytes comprise a thick, dense carpet with more or less discrete patches of Ptilium crista-castrensis, Dicranum polysetum, and Ptilidium ciliare in a matrix of Pleurozium schreberi. A previous study showed that the four species occupy microsites which overlap in temperature, light, moisture, and litter input. We used three experiments to determine whether spatial pattern was attributable to microhabitat in existing microsites. 1) Individual shoots and 10 cm diameter colonies of the four species within one stand were transplanted reciprocally and grown for one and three years, respectively. Shoot growth was evaluated as elongation; colony growth was assessed as a ratio of final:starting biomass. 2) Colonies of Ptilidium from one stand were transplanted to three microsites in a stand from which the species was absent, and growth assessed as above. 3) A thick layer of spruce needle litter was applied to one of each pair of preweighed colonies, and growth assessed as above. All four species were cabable of surviving in all microsites currently occupied by others in their community, at least over three growing seasons. A single episode ofheavy needle deposition enhanced growth ofallfour species. This suggests that spatial pattern is not due to habitat partitioning, but does not rule out slow competitive exclusion by vigorous/invasive growers.