Characteristics of vegetation according to the micro-climatic conditions of a lava pit on Jeju Island

Jeju Island is a volcanic island created by the eruption of a lot of basaltic lava through plume activity. Lava pits come in many shapes and sizes and have unique environmental conditions. This study aimed to examine the vegetation characteristics of various lava pit microclimates of Geomunoreum lava tube system formed 100-300 thousand years ago, and is one of the largest on Jeju Island. Seven plots on Geomunoreum surveyed using the belt transect method, and air temperature and relative humidity were also collected for each plot. The similarity index of the lower area (plot 3) and outside flattening-out areas (plots 6 and 7) were 14.6% and 17.5%. The lower area has the highest mortality and lowest growth rates, and therefore having a simple structure compared to other areas, with no observed changes in dominant species. At the midpoint areas (plots 2 and 4) the dominant species transitioned from Quercus glauca to Acer palmatum and Camellia japonica. The species composition of the shrub and subtree layers remained almostly unchanged. At the higher areas (plots 1 and 5), changes in species composition were frequently observed in all layers. At the outer flattening-out areas (plots 6 and 7), the lowest mortality and highest growth rates were observed, the variety of competing species were high diverse in the tree layer. The daily average temperature of plot 3 (low) and plots 6 and 7 (flattening-out areas) ranged from 4.1℃ to 13.2℃, and the daily average humidity ranged from 1.2% to 39.3%. The simple vegetation structure of the lower area can be attributed to this low temperature and high humidity. The concluding observation is that on the Geomunoreum lava pit, areas where microclimate conditions remain fairly constant, there is no dramatic change in vegetation compared to the perimeter. These characteristics are not always observed on other lava pits on the island.