Mt. Hekla is among Iceland‘s most active volcanoes, erupting at least 23 times since the island was settled in c.871 AD. It is located on the highland margin bordering the Southern lowlands, the largest and most productive farmlands in Iceland. Hekla is a ridge shaped stratovolcano, producing both tephra and lava during eruptions. Due to the mountain‘s proximity to inhabited lands, its historical eruptions have been contemporarily documented. Tephra deposited during eruptions is often preserved in soils. Tephrochronologists have accurately dated the lava fields of Hekla by linking together the historical descriptions of Hekla eruptions and tephra layers found in soil profiles. The objective of this study was to study primary vegetation succession spanning over 800 yrs by the means of Hekla’s lava–chronosequence. Field data was collected in summer 2015-2016, within lava fields formed in 1158, 1206, 1300, 1389–90, 1554, 1693, 1725, 1766–68, 1845, 1878, 1913, 1947, 1970, 1980–81, 1991 and 2000. Vegetation and soil parameters were measured around the mountain with elevation range 100–800 m a.s.l. DCA ordination was applied to investigate primary succession stages. Regression models were used to analyze the relation between lava age and vegetation and soil parameters.
Preliminary results show three succession stages: Stage 1(a) is the initial succession found on lavas <70 yrs of age. Mosses and lichens dominate especially Racomitrium lanugionosum and Stereocaulon vesuvianum. Vascular plants are almost absent. Stage 2 or the intermediate stage generally features a thick Raco.lanu. moss mat with dwarf shrubs. This stage was found on lavas 300–700 yrs of age. Stage 3 represents the most developed vegetation where Betula pubescens shrubland is forming. This stage was only found on the oldest lavas <600 yrs. An additional stage was identified, Stage 1(b) representing areas heavily affected by tephra deposition where succession is reset and tephra now favors establishment of vascular plants. The Hekla lavas are mostly covered by the moss Racomitrium lanuginosum. Regression analysis shows that Raco.lanu. cover does not significantly change with lava age, yet its thickness seemingly reaches maximum in lavas between 400–600 yrs of age, coinciding with the intermediate 2nd succession stage. This supports the inhibition model, where the thick moss mat prohibits the establishment of vascular plants in the lavas. The development of birch woodland, the climax ecosystem of Iceland, takes several centuries under the conditions southwest of Hekla.