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In situ survival of forest bryophytes in small-scale refugia after an intense forest fire



Question: Species can persist in landscapes with recurring disturbances either by migrating to places suitable for the moment or by enduring the threatening conditions. We investigated to what extent boreal forest bryophytes survived an intense forest fire in situ and whether bryophytes had started to recolonize the area 7-8 years later.

Location: Tyresta National Park, eastern Sweden.

Methods: We recorded bryophytes in 14 burnt and 12 forest reference plots (50 × 50 m). In each plot we investigated 15 random 1-m2 micro-plots. In plots in the burnt area we also examined micro-plots at locations of all fire refugia, and in case of the forest references, of 10 potential refugia.

Results: We found on average three small refugia per 50 × 50-m plot; each containing on average 4.8 forest bryophytes, a level similar to that of micro-plots in the references, but significantly higher than in random micro-plots in the burnt plots (1.5 species). Many refugia were located in rocky areas, but few were in wet sites. The burnt area remained dominated by a few fire-favoured species, even if recolonization of forest bryophytes had begun. There was, however, no significant correlation between number of refugia and number of forest species in random micro-plots, leaving open the question of the importance of refugia as regulators of early succession.

Conclusion: We conclude that small-scale refugia can also occur for sensitive species such as forest bryophytes, and that the refugia in our case were frequently found on rocky or mesic rather than wet sites. The role of such refugia in recolonization, however, warrants further investigation.