Vegetation on lava fields in the Hekla area, Iceland (original) (raw)

The vegetation development on 13 dated historical lava fields around the volcano Mt. Hekla is described. The lava fields have been divided into three main topographical categories, the main surface, holes and crags. The investigation was concentrated on the main surface at 22 sites in the 11 oldest lava fields, the oldest from 1 158, the youngest from 1947. At each site the topography, substrate (profile, pH and loss on ignition), flora and the physiognomy and the floristical composition of the vegetation were studied. Local climatic conditions (temperatures) are described for one lava field. The vegetation description included a floristic inventory, quantitative analyses (releves) of the vegetation both of permanent and non-permanent plots, drawings and photographic documentation. The total number of analyses made were: 1566 for the main surface, 81 for the holes and 13 for the crags. At each site the fo llowing abiotic factors were recorded: (a) the irregularity of the topography, (b) the age of the lava field, (c) the elevation, (d) the number of deposited tephra falls, (e) the quantity of deposited aeolian material between the tephra layers, (f) the cover of tephra and (g) the surface roughness was judged for every plot. In studies of the colonization of plants in the youngest fields records were also made of: (a) the position within the layer of clinkers, (b) the microsurface (texture) of the lava blocks and the age ofthe lava field when the analyses were carried out. The analyses made ofthe main surface were treated with the clustering and relocation program TABORD and with the ordination program Canonical Correspondence Analysis (CCA, CANOCO program). First, local clusters were obtained for each of the lava fields. These primary clusters were then clustered again to obtain a set of second-order clusters. The CANOCO results were used to check whether the second-order clusters were ecologically and floristically homogeneous or needed to be subdivided. The classification results were compared with vegetation types described earlier. Due to the phytosociologically incomplete floristic composition of many clusters an ad hoc typology was used with three hierarchical levels: communities, variants and facies. Eleven communities, some variants and facies are described and their distribution interpreted in terms of the prevailing environmental conditions. The dynamics of the vegetation in the historical lava fields is in the Hekla area, Iceland.-Acta phytogeogr. suec. 77, Uppsala. 110 pp.