A strong and on-going research question is understanding the drivers that can cause the shuffling of species into combinations not seen at present. Quaternary paleoecological records convincingly show that plant communities are ephemeral, and that plant taxa individualistically track shifts in climate. Much of our work has used the late-glacial of eastern North America, when 'no-analog' plant communities were widespread, as a model system for understanding the processes leading to the formation of no-analog communities. In previous work, we have linked the formation of these no-analog communities to no-analog climates, in which a major characteristic was a higher-than-present temperature seasonal range (Williams et al., 2001, Williams and Jackson, 2007). We have also shown that novel climates are also likely to develop by the end of the 21st-century, with the risk proportional to end-century greenhouse gas concentrations (Williams et al., 2007). This suggests that it is quite possible that novel plant associations will develop in response to current climate trends.
Now, we are using the late-glacial no-analog communities as a testing ground for ecological models, as a way of testing their predictive ability for climates outside the modern domain. With Steve Jackson at the University of Wyoming, we are also conducting a major field campaign to re-core and redate key ENA pollen records, in order to more precisely constrain the development and disaggregation of the late-glacial no-analog communities. An exciting development from this work is evidence that the formation of the no-analog plant communities may also be linked to the population declines of the North American megafauna (Gill et al., 2009), which we are continuing to investigate.
Past formation of no-analog plant associations is indicated by the shifting colors on the maps at left -- compare the right-most map, representing the present, to the series of late-glacial maps to the left. Maps from Williams et al. 2001. Each color repreasents a unique mixture of taxa, based on the pollen percentages of Picea, Cyperaceae, and Betula (top map series) and Fraxinus, Ostrya/Carpinus, and Ulmus (bottom map series).
Climate-similarity maps for late-21st-century climates. Areas in red indicate future climates with no close analog in late 20th-century climates. In these analyses, which were based on mean temperature and precipitation for the four seasons, tropical and subtropical regions are at the highest risk of developing novel climates, because they are at the leading edge of a warming world. How will species respond to these novel future climates? What are the implications for biodiversity conservation and preservation of ecosystem services? From Williams et al. 2007.
Gill J.L., Williams J.W., Jackson S.T., Lininger K. and Robinson G.S. (2009) Pleistocene megafaunal collapse preceded novel plant communities and enhanced fire regimes. Science 326: 1100-1103.
Gonzales L.M. and Grimm E.C. (2009) Synchronization of late-glacial vegetation changes at Crystal Lake, Illinois, USA with the North Atlantic Event Stratigraphy. Quaternary Research 72: 234-245, doi: 210.1016/j.yqres.2009.1005.1001.
Gonzales L.M., Williams J.W. and Grimm E.C. (2009) Expanded response-surfaces: A new method to reconstruct paleoclimates from fossil pollen assemblages that lack modern analogues. Quaternary Science Reviews 28: 3315-3332.
Williams, J. W. and Jackson, S. T. (2007) Novel Climates, No-Analog Plant Communities, and Ecological Surprises: Past and Future. Frontiers in Ecology and Evolution 5: 475-482. doi:10.1890/070037.
Williams, J. W., Jackson, S. T., Kutzbach, J. E. (2007) Projected distributions of novel and disappearing climates by 2100AD. Proceedings of the National Academy of Sciences 104: 5738-5742.
Jackson, S. T. and Williams, J. W. (2004) Modern analogs in Quaternary paleoecology: Here today, gone yesterday, gone tomorrow? Annual Review of Earth and Planetary Sciences 32: 495-537.
Williams, J. W., Shuman, B. N., Webb III, T. (2001) No-analog conditions and rates of change in the climate and vegetation of eastern North America. Ecology 82: 3346-3362.
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