11:15 AM - 11:30 AM
[MIS03-05] Influence of feral goat and seabird activities on chemical properties of surface soils on an oceanic island in Japan
Keywords:Nakoudojima Island, natural world heritage, plant-available phosphate in soils, soil exchangeable acidity, exotic species, soil erosion
To conserve the indigenous natural ecosystem and help the recovery of the natural vegetation, we conducted field survey and investigated the chemical properties of surface soil (0‐5 cm) and aboveground plant biomass in relation to the topography of this island. Under grassland vegetation where influence of feral goat would have been severe, the chemical properties of surface soils, such as soil pH value, total C and N contents, exchangeable acidity, and plant-available phosphate (Bray II P), were highly variable even in a small area. By comparing soil profile characteristics under natural and disturbed vegetation and distribution patterns of these soils on the island, the changes in the soil chemical properties were reasonably assigned to the effect of soil erosion caused by feral goats for increased soil acidity (mainly found in inland valley area) and to the effect of seabird activities for increased Bray II P and soil acidity (mainly found in outer rim area with high altitude). It was also clarified that the high soil acidity was significantly related to the low productivity of plant biomass. Soil erosion would have removed surface soils having weak acidity and exposed subsoils having strong acidity to the ground surface, resulting in inhibition of plant growth and delay of vegetation recovery. Based on the findings obtained in the present study, several options were proposed to stop soil erosion and to recover the vegetation, although careful preliminary examination would be necessary for applying them.