Size dependency of gametophytes decay in Athyrium brevifrons Nakai during spring desiccation

Gametophyte populations in Athyrium brevifrons were analysed with respect to population size and surviving area (%) of individual thalli in a transplant garden at Sapporo during 5–26 April 1983, to study the safe‐microsite for gametophyte establishment in nature. Spores dispersed in August 1982 germinated and grew into thalli of various widths (<10 mm); 10.3% of the thalli matured by early October 1982. Maturation was attained by gametophytes of width 4–7 mm. The number of gametophytes gradually decreased with increasing width. By April 1983, 20.5% of total gametophytes were mature with a mode of 5–6 mm in width. The relative number of gametophytes with surviving area of 2–20% increased and that of 85–100% decreased in accordance with collection days delayed until after snow‐melt. Surviving area (%) on gametophyte of all widths decreased with decreasing soil moisture contents. In particular, immature gametophytes of 2–4 mm width showed a significant correlation ( P <0.01) between soil moisture content and relative number of gametophytes with 0–20% surviving area and mean surviving area (%) of every width of thalli. The spring desiccation might be a factor that reduces or limits gametophyte populations in nature.