The maintenance of species diversity is becoming a key component of sustainable forest management. In the boreal mixedwood of northern Alberta, conifer dominated stands over one hundred years old are among those most threatened under present harvesting regimes. These stands are also important habitat for many bryophyte species. Wise management requires an understanding of the mechanisms controlling bryophyte species richness and evenness in order to either facilitate the identification of species rich areas or to improve the bryophyte habitat in managed stands. This study examines the relationship between microclimate and substrate availability, and bryophyte species richness and evenness at different scales. I sampled bryophyte species occurrence and abundance at three scales: the stand (10 ha), the mesosite (25 X 25 m plots to capture within stand variation), and the microsite (structural elements of the boreal forest providing unique substrates for moss colonization). Percent full sun, PPFD (Photosynthetic Photon Flux Density), soil moisture and pH, vascular plant species richness, microtopography and area of available substrate were measured to estimate inter-mesosite variability. Microsite variability was estimated using a relative measure of mean exponential temperature in combination with descriptive classes of substrate quality. Sampled microsites consisted of 74 stumps, 88 logs, 90 trees, 90 patches of undisturbed soil and 33 patches of disturbed soil. Light and temperature were more variable within stands than between stands (57% and 19 % of the variation respectively), while soil moisture and pH were more variable at the stand level (72% and 30% of the variation respectively). The stand with the greatest species richness had the greatest vascular plant species richness, as well as the highest soil moisture and pH. Bryophyte species richness and evenness is related to variability in forest structure and environment both within and between stands.

Key words: boreal, bryophytes, Canada, diversity, management, moss