Global Warming

Spring foliage appearing early in the Alps

Because of global warming, trees in the Alps are coming into leaf earlier than they used to – which could have negative consequences for forest ecosystems.

In the early 1960s, spring came to the mountains about five weeks after arriving in the lowlands – as observed by the appearance of leaves on the trees. Today, that delay is only about three weeks, says the Swiss Federal Research Station for Forest, Snow and Landscape in a report published on Monday.

Researchers came to this conclusion after assessing more than 20,000 observations recorded by volunteers and collected over the past six decades by MeteoSwiss, the Federal Office for Meteorology and Climatology. The data set pertains to beech, spruce, larch and walnut trees.

Premature leaf and needle development is even more pronounced at higher altitudes, meaning that those trees sprout foliage much faster after a warm winter.

The researchers explain the phenomenon in part by how long the trees are exposed to temperatures of 0-8°C (32-46°F) at the end of winter. The trees need this frost-free cold phase so that the buds can awake from their hibernation and develop normally in spring.

According to the study, this in turn has consequences for the structure and functioning of forest ecosystems, especially the interactions between plants and animals.