Switzerland: Forestry Climate Change: Trees Have an Ecological Memory

Irrigated Scots pines in the dry Pfyn Forest (canton of Valais) had their water supply turned off after 11 years. The trees' response surprised the international research group as it suggests that tree growth is also influenced by past conditions. Trees, you might say, do not forget.

Birmensdorf/Switzerland — Climate change is leading to drier conditions in Valais. For around two decades now, many Scots pines in the canton have been dying, in some cases over large areas. The Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) is conducting an irrigation experiment to investigate the growth of Scots pines in the Pfyn Forest. Since 2003, it has been irrigating a number of plots within the forest to illustrate the dependency of pine growth on an adequate water supply.

The trees, which were first drought-stressed and then irrigated, grew very well for over a decade, developing thicker crowns and stems than their non-irrigated neighbours. At the end of 2013, the water supply was turned off in some parts of the site. The question was whether the trees could benefit from the 'years of plenty' or whether the long period of irrigation had made them less well adapted to the new drier conditions. The answer is multifaceted, as different tree organs responded in different ways. It is clear, however, that pine growth is influenced by past conditions, as the results published by a WSL-led international research group in the journal New Phytologist now illustrate.