The influence of volcanic eruptions on growth of central European lowland trees in NE-Germany during the last millennium

Palaeoclimate proxies have shown links between climate changes and volcanic activity. However, not much is known about the impact of volcanic outbursts on growth of lowland trees. We investigate the effect of large volcanic eruptions on the growth rate of trees. The study is based on an unexplored comprehensive database with 1128 samples of long tree-ring width (TRW) chronologies of Quercus robur L. and Pinus sylvestris L., correlating with forest net primary production (NPP), originating from three different sites in eastern Germany (Greifswald, Eberswalde and Saxony). This study focuses on trees in rarely examined temperate zones where tree growth is less temperature limited. Growth relationships were compared against 52 large volcanic eruptions known for the last 1000 years. Dendrochronological methods revealed a predominantly negative (60.2%) effect of large volcanic eruptions on the tree-ring chronologies. Nevertheless, also positive (31.7%) and neutral (8.7%) tree growth reactions were detected. In the tree-ring width chronologies of Q. robur and P. sylvestris, we detected a negative influence on tree growth for up to four years after large eruptions. The chronologies of Q. robur revealed a stronger negative response (68.1%) than those of P. sylvestris (53%). However, at the Greifswald site both tree species (79% Q. robur and 73% P. sylvestris) show a negative response in tree growth after every volcanic eruption. Furthermore, the results suggest that volcanic aerosols originating from the Northern Hemisphere cause a greater reduction in tree growth than aerosols being emitted from Southern Hemisphere volcanoes, which might be related to the long distances between trees and volcanoes, as well as the global atmospheric circulation patterns. This study demonstrates that the effects of major volcanic eruptions are less clear in trees from central European lowlands than in trees growing at the altitudinal or latitudinal timberlines.