During the advance and retreat of the glaciers, temperatures where changing rapidly enough to reassemble ecological communities in a time span of thousands of years. It has been forecasted that mean temperature changes similar to those which separated the ice ages are expected to occur in a much shorter time span, hundreds of years. This could result in major ecological changes occurring throughout the life span of individual trees, rather than over several generations.
Therefore, will the behavior of species during the last glaciation provide any indication of the types of vegetation changes which may occur in future climate change? This of course, is not known.
It is clear though than any vegetation migration that might take place in the future will have many obstacles to over come. Migration which occurred in the geological past took place through pristine ecosystems. Today, there are numerous anthropogenic barriers, such as agriculture and urbanization, which will disable many species from moving out of their current refuges.