The environmental conditions during the Pleistocene offered a climate that was more productive for plant species than climate conditions that exist today. This is evident through extensive records of high abundances of broadleaved trees Ulmus, Ostrya, Fraxinus and Quercus mixed with boreal conifers such as Picea and Larix during the late Holocene. New evidence states that deglacial temperatures are now hypothesized to be a major contributor to the formation of no-analog plant communities in the Midwestern US. Christensen bog fauna during this time period also represent a significant example of no-analog assemblages from the Pleistocene. It is also possible that these plant assemblages formed due to influence from megafaunal extinctions during the late quaternary, and there is also evidence that shows connection between novel plant assemblages and new fire regimes.
