Recovery after volcanic ash deposition: vegetation effects on soil organic carbon, soil structure and infiltration rates

Background and purpose: Volcanic eruptions of pyroclastic tephra, including the ash-sized fraction (< 2 mm; referred to as volcanic ash), have negative direct impacts on soil quality. The intensity (deposit thickness, particle-size distribution) and frequency (return period) of tephra deposition influence soil formation. Vulnerability and subsequent recovery (resilience) of the plant-soil system depend on land-uses (vegetation and management). Few previous studies covered the whole deposition-recovery cycle. We investigated the volcanic ash deposition effects on soil properties and their recovery across land-uses on a densely populated volcanic slope. Methods: We measured the canopy cover and volcanic ash thickness six years after the 2014 Mt. Kelud eruption in four land-use systems: remnant (degraded) forests, complex agroforestry, simple agroforestry, and annual crops. Each system was monitored in three landscape replicates (total 12 plots). For the soil recovery study, we measured litter thickness, soil texture, C_org, soil C stocks, aggregate stability, porosity, and soil infiltration in three different observation periods (pre-eruption, three, and six years after eruption). Results: Post-eruption volcanic ash thickness varied between land-use systems and was influenced by the plots slope position rather than canopy cover. The average soil texture and porosity did not vary significantly between the periods. Surface volcanic ash and soil layers initially had low aggregate stability and limited soil infiltration, demonstrating hydrophobicity. While C_org slowly increased from low levels in the fresh volcanic ash, surface litter layer, aggregate stability, and soil infiltration quickly recovered. Conclusions: Different land-use management resulted in different recovery trajectories of soil physical properties and function over the medium to long term after volcanic ash deposition.