The response of a jack pine forest to late-Holocene climate variability in northwestern Wisconsin

Abstract

Terrestrial plant communities have the potential to respond to climate change rapidly, if dominant species are killed by a series of extreme events, or slowly, if the cumulative effects of shorter-term climate fluctuations result in long-term compositional change. We used pollen and charcoal records from a lake and a testate amoebae-derived history of water-table depth in a nearby peatland to assess the response of the jack pine-dominated forests of northwestern Wisconsin to the climate variability of the last ~2000 years. The hydrology record and the charcoal record indicate that the climate near Warner Lake over the last ~2000 years was characterized by multidecadal variation in moisture availability with no apparent multicentennial-long trends in moisture balance or fire frequency. However, the pollen record suggests that there were multicentennial-scale changes in the vegetation composition around Warner Lake. Direct comparison of the three proxy records is challenging, because of their differing temporal resolutions and the complexity of potential ecological responses to climate variability. Therefore, we developed an interpretive model to compare multiple simulated proxies under two scenarios of environmental variability in order to determine under what conditions apparently contradictory records are likely to be found. The interpretive model reveals that a record of multicentennial-long change in vegetation is possible if multidecadal climate variability interacts with ecological processes influencing the direction and magnitude of succession. Compositional changes in the Warner Lake pollen record could reflect long-term variation in temperature, seasonality or other climate factors independent of moisture balance; however it is also possible that multidecadal moisture variability interacted with ecological processes affecting recruitment and mortality of species following fires of varying size and severity. Decadal-scale climatic variability can lead to altered successional pathways and to changes in forest composition that last for centuries.