Drought-stressed trees face race to adapt

CNN: Scientists have known for some time that climate change and the impacts of longer droughts and higher temperatures could pose a problem for forests. But many thought it would only affect a minority of trees, perhaps just those in extremely arid regions.

However, new research is showing that a large majority of tree species around the world are operating on the brink of collapse. If the predicted pace of climate change continues, many may not be able to adapt in time and large numbers could die-off.

The authors of the study, whose findings were published in the scientific journal Nature, looked at 226 different tree species from 81 sites around the world, covering the full range of climatic conditions, from Mediterranean-type arid to the tropical Amazon rainforest.

They found that 70% of the trees studied adapt closely to the local environment, whether arid or tropical, absorbing just enough water in order to survive, but leaving them highly vulnerable to minor shifts in rainfall and drought stress.

"We thought that in the dry areas, plants would have adapted to survive more than ones growing in the wet, but we found they were all equally vulnerable. It was a big surprise," says Steven Jansen, from Germany's Ulm University and co-author of the study.

In periods of drought, the vascular network (xylem) distributing water and nutrients around the tree develops air bubbles which hinder the passage of water. As drought stress increases, these blockages, or "embolisms," accumulate eventually causing the tree to dry out and die....

Tree rings shot by Arpingstone, public domain