Large explosive volcanic eruptions can cover wide areas of land with tephra, sometimes with profound hydrological, ecological, and societal impacts. However, while consequences of tephra fallout and flow deposits have been well studied on annual to decadal timescale, little is known about centennial and longer-term changes in vegetation composition. Here, we consider the enduring impacts of the 946 CE Millennium Eruption of the Changbaishan volcano. We reconstruct the pre-eruption vegetation composition based on species, age, and size of carbonized trees recovered from the pyroclastic deposits and analysis of phytolith records in peat cores. Compared with the early 10th century forest composition and structure, the present montane forest hosts a higher abundance of broad-leaved species. Higher elevations, which today are dominated by alpine tundra, were covered in a spruce forest before the eruption. These differences reflect the long process of ecological recovery following the eruption rather than the effects of recent warming, as has been suggested. However, present warming trends are likely to drive the ecological succession towards a reduction of the alpine vegetation zone. Our study emphasizes the importance of interpreting contemporary ecological change in the context of past massive disturbances, together with subfossil evidence of vegetation composition.
Volcanic eruptions are among the most impactful natural disturbances on Earth. They perturb ecosystems, landscapes, and climate. Their deposits range from subtle but very widespread dust fallout to proximal tephra fall and flow sequences that can mantle topography and infill valleys to depths of tens of meters or more. Globally, more than 1300 volcanoes are known or thought to have erupted in the Holocene, and in the modern period, around 80 eruptions a year are recorded. While there have been many studies of the impacts of volcanism on vegetation dynamics, their focus has been on the aftermath of a small number of eruptions, spanning relatively short timescales of up to decades, including Krakatau 1883, Mount Usu 1910, Surtsey 1963, and Mount St Helens 1980. Factors that influence ecological recovery include depth of burial of the seed bank in pre-eruption soils, nature of the deposit, local climate conditions, herbivore activity, and proximity to refugia. For example, the type, amount, and distribution of biological legacies sparse on the landscape after a volcanic disturbance are key drivers of vegetation succession.
Despite this progress in understanding the ecological impacts of volcanic eruptions, little remains known about longer-term post-eruption ecological succession and the influences of local and regional factors (e.g., hydroclimate, pedogenesis) as well as eruption characteristics (e.g., depth of burial, deposit characteristics). Under harsh environmental conditions (e.g., cold and/or dry habitats), the ecological repercussions of volcanic eruptions may play out over centuries and millennia. The factors that influence a post-eruption landscape, vegetation succession, and forest recovery over such extended time periods can be challenging to disentangle, as they can reflect the history of land-use and changing climate as well as volcanological and geomorphic factors that influence recruitment and recovery.
One site where the long-term consequences of a major volcanic eruption appear remarkably evident is Changbaishan (Mt. Paektu), situated on the border between PR China and DPR Korea (Fig. 1). Precisely dated to late 946 CE and involving rhyolitic and trachytic phases, its so-called Millennium Eruption (ME) ranks among the largest explosive eruptions of the Common Era. It disgorged an estimated 7-36 km (dense-rock equivalent) of magma as 96 ± 19 km (40-98 km ) of tephra fallout and pyroclastic current deposits, the latter infilling valleys dissecting the mountain to depths in excess of 100 m. The volcanic plume dispersed eastwards more than 1000 km, resulting in widespread deposition of up to several cm thickness of ash in parts of Japan. Today, the thickness of deposits, their hydraulic properties, the short growing season on the mountain, and low annual temperatures of the region sustain an alpine tundra environment around the summit of the volcano. These same deposits, however, contain the stems of trees, some that lived for centuries until they were killed by the eruption, suggesting profound and enduring changes in vegetation composition resulting from the ME.
The immediate impacts of the emplacement of tephra fall deposits were surely extreme on terrestrial ecosystems, within a radius of around 50 km from the summit of the volcano. While, despite its high magnitude, the ME appears to have muted impacts on northern hemisphere climate, syn-eruptive volatile emissions (sulfur, halogens, and trace metals) likely affected aquatic and terrestrial environments. Previous modeling studies suggested the importance of remnant trees and seed sources as well as environmental factors (e.g., climate, terrain, and soils) in influencing vegetation dynamics on the northeastern sector of Changbaishan over the past three centuries, but hitherto there has been no focused study of the pre-ME and present vegetation species composition in order to evaluate the millennium-scale picture of recovery.
Here we analyzed of preserved carbonized and partially carbonized tree stems embedded in ME deposits and phytolith records in peatland cores to compare pre- and post-ME vegetation species composition. Based on 102 pre-eruption carbonized samples we collected at two elevations on Changbaishan (Fig. 1), we reconstructed the pre-ME forest composition on Changbaishan. The elevation of the tundra vegetation where carbonized stems were found lies well above the current alpine treeline. We hypothesize that the vegetation species composition and distribution are observably different between the two periods due to the effects of ME. We also reconstructed paleovegetation for different periods during the past millennium using phytolith records. Additionally, complementing our earlier carbonized tree-based study, this work provides additional insights into millennial-scale climate dynamics through comprehensive reanalysis. This study builds upon our long-term scientific investigation at the study site, synthesizing previous researches and expanding the knowledge of the ecology of this area after ME. By incorporating both newly discovered materials and historical data through complementary analytical approaches, we aim to characterize and disentangle post-eruption vegetation change and global warming-induced vegetation dynamics on the volcano, and to present novel perspectives, to our knowledge, on post-ME ecological succession.