Spore capsules of four Sphagnum species were buried at different depths in peat on a bog. Spore viability was
determined after 0, 1, 2 and 3 yr. Viability generally declined with time, but viable spores were still found at all
depths after 3 yr. The light-coloured spores of S. balticum and S. tenellum retained their viability better than the
darker spores of S. fuscum and S. lindbergii. Survival was highest under wet but aerobic conditions, but was also
high under humid or periodically desiccated conditions. By contrast, most spores stored under wet, anaerobic
conditions died within 2–3 yr. These results, and predictions from them, are not consistent with earlier results for
spores of long-lived and dominant bryophytes, or for seeds of phanerogams of undisturbed wetlands and forests.
There was no correlation between spore size and longevity across species, but the small spores from small capsules
of S. balticum and S. tenellum generally showed higher viability than those from the medium-sized and large
capsules of the same species. This suggests a positive intraspecific relationship between longevity and dispersal
distance. There was an indication of conditional dormancy, controlled by weather, in Sphagnum spores. The
experiments indicate that Sphagnum spores can form a long-term persistent spore bank under suitable conditions,
with a half-life of between 1 and 20 yr (mean across species of 2.6 and 5.0 yr at two depths studied), and with
potential values in individual spore capsules of several decades, or even of centuries. Sphagnum spores kept
refrigerated showed 15–35% viable spores after 13 yr. The capacity to form a persistent spore bank that can be
activated whenever favourable conditions occur might help explain the wide geographical distribution of many
Sphagnum species in the boreal and temperate zones, where they have managed to colonize almost every suitable
patch of acidic, nutrient-poor wetland.