Pedogenic development of volcanic ash soils along a climosequence in Northern Taiwan

Andisols have been shown to evolve over time to other, more weathered soil types. However, more information is needed on the time-scales over which these changes occur under different climatic conditions. In this study, we analyze mineral weathering and soil formation along a soil climosequence formed on volcanic deposits of >400 ka of age in the subtropical climate of Northern Taiwan. We sampled 6 pedons at elevations between 140 and 1090 m above sea level (asl), representing a climatic gradient from about 22 degrees C mean annual temperature (MAT) and 2000 mm mean annual precipitation (MAP) to about 16.5 degrees C MAT and 5000 mm MAP. Our results show that phosphate retention, Al-o + 1/2Fe(o), Si-o and the Fe-o/Fe-d ratio significantly increased with elevation. The high-elevation soils (>900 m asl) contained metastable poorly crystalline materials (e.g. allophane, ferrihydrite) and classified as Andisols, whereas the low-elevation soils (<300 m asl) contained thermodynamically more stable minerals (e.g. kaolinite, hematite) and classified as Inceptisols. The soils at intermediate elevation (400 to 500 m asl) were at the threshold of andic soil properties and classified as Andic Inceptisols. Our study demonstrates the strong influence of climate on pedogenesis in subtropical volcanic landscapes. (C) 2010 Elsevier B.V. All rights reserved.