Microsite conditions and spatial pattern in a boreal bryophyte community

Abstract

This study addresses the hypothesis that the spatial pattern of four bryophyte species on the forest floor of boreal woodland represents habitat partitioning, corresponding to microhabitat heterogeneity. Temperature, vapour pressure deficit, photosynthetically active radiation, incident precipitation, and litter fall were monitored at locations of pure colonies of Pleurozium schreberi, Ptilium crista-castrensis, Dicranum polysetum, and Ptilidium ciliare. From May through November 1990, the species received a mean total of 51.20 ± 1.09 cm of rain and 1.034 ± 0.639 g of litter, primarily spruce needles. They experienced temperatures as high as 40 °C, vapour pressure deficits to 7.3 kPa, and photosynthetically active radiation to 3200 μmol∙m⁻²∙s⁻¹. The results do not support habitat partitioning by the species on the basis of the variables examined: all four species tolerated the full range of conditions and their combinations that occurred in the study season, and experienced the same ranges during > 90% of the sampling period, with equally broad within-species variation. Although large pure colonies of P. ciliare were delimited by microsites receiving greater spruce needle litter fall and lower incident precipitation per rainfall event, smaller colonies and individual shoots were often found in mixture with other species. Overall, the spatial pattern did not correlate with microsite conditions, and we see no evidence of habitat partitioning in terms of currently occupied microsites. Key words: community structure, microclimate, Pleurozium schreberi, Ptilium crista-castrensis, Dicranum polysetum, Ptilidium ciliare.