Volcanic Ash Weathering and Pedogenesis in Mount Penanjakan: Soil Evolution Supporting Pioneer Vegetation

Volcanic ash deposits play a fundamental role in soil formation processes and the establishment of pioneer vegetation in highland ecosystems. This study investigates soil evolution and pedogenesis derived from volcanic ash in Mount Penanjakan, Bromo Tengger Semeru National Park, East Java, Indonesia, focusing on its role in supporting Edelweiss (Anaphalis spp.) as a pioneer species. Field surveys were conducted at three sites—Lemah Pasar, Bukit Prau, and Tikungan S using transect-based soil profile observations up to 2 m depth. Soil samples were analyzed for organic carbon (Walkley and Black), texture (pipette method), soil pH (pH meter), and porosity, bulk density, and aggregate stability. Results indicated that soils were predominantly silty clay loam, with moderately acidic to neutral pH (5.5–7.5) and organic carbon content ranging from 1.2% to 2.1%. Taxonomic classification using USDA Soil Taxonomy (2014) identified variations from Mollic Hapludands (Andisols) at Lemah Pasar, Typic Dystrudepts (Inceptisols) at Bukit Prau, to Typic Hapludands (Andisols) at Tikungan S. These findings reflect a pedogenic gradient from weakly developed Inceptisols to more advanced Andisols influenced by volcanic ash weathering. The edaphic conditions, particularly high porosity, moderate organic matter, and andic properties, provide favorable habitats for Edelweiss species, each occupying different soil development stages. This study highlights the importance of volcanic ash pedogenesis in shaping soil-vegetation interactions and provides a scientific basis for designing ex-situ conservation strategies that mimic natural soil conditions.