Plants

THE ANCIENT GREEKS were the first to identify a relationship between climate and plants. Following this insight, other naturalists recognized that fossilized plants revealed the climate in prehistory. Plants colonized the land 410 million years ago, shaping the climate as they spread throughout the globe. By absorbing carbon dioxide, plants have the potential to cool the climate. By releasing water vapor into the atmosphere, plants have the potential to warm the climate by trapping heat, or to cool the climate by forming clouds. Rooted to the ground, plants must either adapt to the climate or die. Sudden climate changes threaten some species with extinction, whereas hardier species survive. From equator to pole, climate determines what plants grow at given latitudes.

History of the Relationship between Climate and Plants

Theophrastus, a pupil of Aristotle and the founder of botany, may have been the first to ponder the relationship between plants and climate. He understood that each species of plant is adapted to a particular climate, and that in a foreign climate a plant will not thrive and may not survive. Plants are thus an indicator of climate. The mangrove, for example, is an indictor of a climate wet enough to form swamps. With the work of Theophrastus, the promising synthesis of botany and the study of climate was in its infancy, but the Romans did not bring this synthesis to maturity. The Romans were a practical people, with no interest in the theoretical relationship between plants and climate. The Middle Ages were no better for the study of the relationship between plants and climate. The emphasis on theology undercut any progress in science.

Microbiologist Kevin Schmder examines a culture of green algae (Selenastrum capricornutum).

In 1876, Norwegian botanist Axel Blytt revived Theophrastuss notion that plants are an indicator of climate. Working on prehistoric climates, Blytt identified fossils of trees that no longer grew in Denmark. From this observation, he posited that the climate in Denmark had once been suitable for these species of trees, but was no longer. The climate was not therefore a static, unchanging entity. Rather, the climate has changed over time. Working in a similar vein, Swedish [Page 792]geologist Ernst Von Post identified fossils of Alnus, a genus of tree, in the strata of rocks throughout Europe. Alnus is adapted to a warm wet climate, and Von Post tracked the tree fossils as they migrated from southern to northern Europe at the end of the Cenozoic Ice Age. As the glaciers retreated, Alnus rooted itself in the warm wetlands that followed the ice age.