Treffer: Late Holocene Human Impact on Tropical Soil Erosion in the Maritime Continent.

Human activities have profoundly modified the fluxes in the global sediment cycle. However, the anthropogenic forcing on soil erosion beyond instrumental records or historical documentation is largely unknown. Here we analyze markers for low‐intensity fires and soil erosion in East Java over the past 5,000 years. We find evidence of a substantial human impact on fire occurrence due to the onset/intensification of swidden cultivation around 3,500 years ago, in the absence of changes in regional hydroclimate or vegetation. Highest soil erosion occurred during the past 500 years, coinciding with a transition toward permanent agriculture. Human‐impacted soil erosion was further amplified by intense monsoonal rainfall and strong rainfall seasonality around 2,000 and 300 years ago. With such rainfall anomalies projected to occur with higher frequency and severity in the tropics under the ongoing greenhouse warming, our results suggest an accelerating erosion rate in the future, posing risks for natural resources. Plain Language Summary: Present‐day human activities, such as agriculture and deforestation, are causing soil erosion and the associated removal of fertile soils. Land use throughout tropical Southeast Asia is especially intense with increased establishment of oil palm plantations. However, the manner and degree to which humans influenced soil erosion in this region in prehistoric times when instrumental records or historical documentations were not available is largely unknown. In an attempt to gain a picture of human land use and its effect on the soils and landscapes of East Java, Indonesia, we analyze chemical fossils preserved in the sediments of the seafloor. We find evidence of an increase in human activities around 3,500 years ago related to early farming practices. This timing corresponds to archeological evidence indicating the arrival of the Austronesian‐speaking people in Java. Human‐impacted soil erosion was further amplified by high summer rainfall and strong rainfall seasonality around 2,000 and 300 years ago. Such rainfall patterns are projected to occur more often and more severely not only in Southeast Asia but also in the global tropics under the ongoing global warming. Our results indicate that under these conditions, greater soil erosion will occur in the tropics in the future. This may pose risks for agriculture and human use of natural resources. Key Points: Elevated fire occurrence and soil erosion around 3,500 years ago was most likely due to early swidden agriculture and Austronesian dispersalThe impact of human land use on soil erosion was further amplified by increased rainfall intensity and seasonalityThe transition from swidden to permanent agriculture likely further accelerated soil erosion [ABSTRACT FROM AUTHOR]

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