Plant macrofossils as indicators of vegetation and climate change in the Northern Black Forest of Germany during the last millennium - with focus on the Little Ice Age

In order to better understand the potential effects of climatic change on forest cover during and after the Little Ice Age (ad 1550 to 1880), a high-elevation cirque Lake (Wildsee am Ruhestein) was cored and analysed using continuous plant macrofossil analysis, supplemented by standard pollen analysis. The plant macrofossil record provides local information for climate changes not clearly seen in regional pollen records for the Northern Black Forest. Abundant deposition of white fir (Abies alba) needles is restricted to the Little Ice Age, suggesting reaction to climatic cooling. Human impacts, particularly forest clearing, are well documented historically during the past millennium, but discrete peaks in needle flux are only recorded at Wildsee once Little Ice Age cooling begins. The first needle flux event at 39–42 cm depth has a median modelled age of ad 1650, at the start of the Maunder Minimum, recognized as a particularly cold interval. Also of climatic significance is the flux of 19 immature Abies needles recovered from the 30–33 cm layer, dated around ad 1720. This finding is interpreted as clear evidence of severe spring frosts during the Little Ice Age, discrete events that are well-recorded in historical observations. Pollen analysis also supports cooling, beginning at a depth of 54 cm, modelled at ad 1560 during the beginning of the Little Ice Age. A decline in oak (Quercus) pollen begins around ad 1560 at the start of pollen zone IV, which also includes the lowest total pollen accumulation rates seen, suggesting a climatic influence. The significant forest dieback (Waldsterben) events that were observed during the late 1970 and 1980 s could not be identified in our pollen and macrofossil data. The combined approach of using pollen and detailed macrofossil analysis provides a better reconstruction of forest history than either technique in isolation, and the combination is potentially important for management of protected areas such as the Black Forest National Park.