Volcanic eruptions can have a significant influence on adjacent ecosystems; however, little is known about the long-term vegetation change related to eruptions. In this study, we examined phytolith records in paleosols at multiple sites in the southern Kyushu District, Japan, to assess the influence of the Kikai caldera eruption 7300 years ago on vegetation. Our results show the vegetational difference before and after the eruption in the study region. Specifically, in the area where the pyroclastic flows distributed more thickly, the original evergreen forest was replaced by Andropogoneae grasslands after the eruption, which has been dominating the landscape in this area for at least 900 years. By contrast, in areas only mildly affected by pyroclastic flows, despite the temporary replacement of forest by grassland, the forest developed and flourished within several hundreds of years of the eruption. This is because a large amount of pyroclastic flow would have devastated all of the vegetation, whereas smaller amounts would have left some untouched forest sites within refugia. Our findings suggest that the vegetation varied significantly depending on the amount of pyroclastic flow reaching the area, even within the pyroclastic flow distributed region.

火山喷发会对邻近的生态系统产生重大影响；然而，对于与喷发有关的长期植被变化知之甚少。在这项研究中，我们检查了日本九州南部南部多个地点古土壤中的硅藻土记录，以评估7300年前奇凯火山口喷发对植被的影响。我们的结果显示了该研究区喷发前后的植被差异。具体来说，在火山碎屑流分布较厚的区域，喷发后原先的常绿森林被Andropogoneae草原所取代，喷发一直在该地区的景观中占主导地位至少900年。相比之下，尽管草场暂时取代了森林，但在仅受火山碎屑流轻微影响的地区，火山喷发后的数百年里，森林发展并茂盛。这是因为大量的火山碎屑流会破坏所有的植被，而较少的火山碎屑流会在避难所内留下一些未触及的森林地带。我们的发现表明，即使在火山碎屑流分布区域内，植被也取决于到达该地区的火山碎屑流的数量而发生显着变化。