Mosippans (Pulsatilla vernalis L.) reaktion på brandstörning : en populationsstudie på en av Sveriges rikaste mosippslokaler

Sammanfattning: Spring Pasque Flower, Pulsatilla vernalis (L.) Mill, is a perennial plant which grows in open and sandy pine forests. It is considered sensitive to competition and in need of repeated disturbances. In Sweden P. vernalis has declined severely and was assessed as endangered (EN) in the latest Red List. The boreal forest has historically been disturbed by wildfires but in Scandinavia wildfires are rare today and this is thought to have affected many species negatively, including P. vernalis. The aim of this study was to examine survival and growth of P. vernalis after fire disturbance. A prescribed burning was made in August 2020, covering parts of a large P. vernalis population at Hokaberg, Härjedalen, northern Sweden. Before burning 108 plants were marked and the first re-growing plants were observed within only 18 days. In the summer of 2021 all marked plants were inventoried, showing that 78 percent had survived the fire. Plant size increased between the summer and autumn of 2021 in spite of considerable grazing. None of the plants in the burned area flowered in 2021 but in autumn many had set flower buds. In the unburned area at Hokaberg few plants flowered in 2021 and no seedlings were observed. Here many of the plants were hardly grazed and 20 percent lost all their aboveground parts. A seedling experiment with burned and unburned soil from Hokaberg was set up in the lab. Growth was marginally better in burnt soil but the main result was that growth differed markedly between individual soil samples. Half of the plants were given an external nitrogen source, but this did not affect the growth. To conclude, the fire resulted in low mortality and strong post-fire growth. Many plants in the burned area are set to flower in 2022, in spite of the grazing pressure. Observations of abundant seedling establishment at a nearby older burnt area suggest that the population at Hokaberg will expand considerably in the coming years in response to the prescribed fire.