Paleoecological studies indicate that nearly all terrestrial ecosystems on Earth arose within the past 11,000 years, as dominant plant species responded numerically, functionally, and biogeographically to changes in climate. Development of these ecosystems was accompanied by decline of previous ecosystems. In some cases, ecosystem turnover was incremental or gradual, while in others it was rapid, even catastrophic in nature. Ecosystem turnover was driven largely by climate change, which was in some cases gradual, but often episodic and even abrupt. Human activities played important roles in certain regions at certain times. These turnover episodes provide a broad array of case studies for examining ecological consequences of climate change and human land-use.

Results/Conclusions

These paleoecological perspectives indicate that ecosystem turnover is natural. But is it desirable? Should we be complacent in the face of global climate change predicted for the coming century and beyond? Consideration of the rate, magnitude, and geographic coverage of projected climate change under realistic greenhouse-gas scenarios gives cause for alarm. Terrestrial ecosystems across the globe are at serious risk of collapse in the coming decades, and such collapse may already be in train in some regions. The paleoecological record suggests a number of important management challenges. First, climate change is more likely to be episodic than gradual, with substantial risk of abrupt change. Second, some climates are likely to disappear regionally and even globally. Ecosystems of such climates will be unsustainable under any circumstances. Third, novel climates will appear in many regions, yielding ecosystems that are difficult to anticipate with our current modeling tools. Finally, ecological surprises are likely in view of the nature of future climate change and its interactions with invasive species, pests and pathogens, and human land-use and other activities. Integration of paleoecological studies with modeling, monitoring, and experimental studies will help assess risks, identify trends, and devise effective strategies for adaptation and mitigation.