Figure 22.27 Changing tree distribution following the retreat of glaciers. As the glaciers began retreating in North America 18,000 years ago, the trees began moving north to colonize the newly exposed habitats.
Data from G. L. Jacobson et al., in W. F. Ruddiman and H. E. Wright, Jr. (eds.), North America During Deglaciation (Geological Society of America, 1987), pp. 277–288.