All around the Arctic circle, the tree line is moving north as the climate warms. In Norway, birch and pine are moving poleward. In Alaska, spruce are taking over from lichen and moss. Globally, current research indicates forests are expanding along two-thirds of Earth’s 12,000 kilometer long northern tree line.
Forest gains are not only confined to the far north. At lower latitudes, some warmer, arid regions are also seeing an increase in trees, partly because increasing concentrations of carbon dioxide are enabling plants to use water more efficiently and thrive in drier soils. Also, the fertilizing effects of CO2 are enabling existing forests to add more leaves and wood, increasing their biomass.
It is a startling contrast from what is happening in the tropics, where hundreds of thousands of hectares of forest are lost each year to chainsaws and fire, and climate change is stressing the remaining trees. But these tropical losses could be more than offset by gains elsewhere, some studies predict, leading in the coming decades to a world with more and faster growing trees.
That could be surprisingly good news for curbing global warming. Forests often have a cooling effect, releasing water vapor and organic compounds that promote the formation of clouds. And more, faster growing trees would absorb more atmospheric carbon and store it away in wood.