Bryophyte responses to experimental climate change in a mid-latitude forest-line ecotone

Climate change, such as warming, is a threat to mountain ecosystems in the forest-line ecotone. This influence could seriously affect bryophytes, because they easily lose their internal water at high temperatures. We conducted experimental warming using open-top chambers (OTCs) in a forest-line ecotone in central Japan and examined its influence on bryophyte cover. Six years after the experiment was initiated, the total bryophyte cover was not significantly different between the control and OTC treatments. However, the two dominant bryophyte species (Pogonatum japonicum and Dicranum majus) responded differently to the OTC treatment. The cover of P. japonicum significantly increased under the OTC treatment, while that of D. majus decreased to approximately 14% of the initial cover under the OTC treatment. These results could be explained by D. majus being better adapted to high-elevation climates than P. japonicum. The decline of D. majus cover was potentially further enhanced by the decrease in rainfall and fog within the OTCs. These are important water sources for D. majus because the species lacks water-conducting systems that enable mosses to absorb water from their substrates. As the OTCs in this study were tall (210 cm high), they may have blocked slanting rain and fog from reaching the plants, increasing water stress in D. majus. In contrast, P. japonicum develops water-conducting systems and may be less susceptible to the decrease in rainfall and fog. These results can aid future experimental studies in the mountains to elucidate the mechanisms underlying bryophyte responses to warming.