A new study published in Ecolgy Letters by a team of researchers from the University of Stirling shows that forests around the world are at risk because of global drought. Not surprisingly, the results found that increased frequency and severity of drought cause trees to die - a result quite expected as forests continue to be deprived of an essential resource for consistently longer periods of time.
The researchers looked at trees across many different biomes and geographic regions where drought has been present. By performing a global meta-analysis of 58 studies of drought-induced forest mortality and modeling mortality rates as a function of drought, temperature, biomes, phylogenetic and functional groups and functional traits, they arrived to the conclusion that no matter where on Earth, trees react similarly to lack of water. The study states: “We found no significant differences in the magnitude of the response depending on forest biomes or between angiosperms and gymnosperms or evergreen and deciduous tree species.”
Dr Sarah Greenwood, Postdoctoral Researcher in Stirling's Faculty of Natural Sciences, said: "We can see that the death of trees caused by drought is consistent across different environments around the world. So, a thirsty tree growing in a tropical forest and one in a temperate forest, such as those we find throughout Europe, will have largely the same response to drought and will inevitably suffer as a result of rising temperatures and changes in rainfall patterns on Earth."
Of course, certain trees are more fit to survive throughout droughts. According to the study, species with denser wood and smaller, thicker leaves usually do better during prolonged, unusually-dry periods. The study reports that these functional traits increased from 30 to 37% when wood density and specific leaf area were included.
So what does this trend mean on a larger scale? Unfortunately the implications aren’t all that optimistic.
Stirling co-author and Professor of Ecology, Alastair Jump, said: "By pinpointing specific traits in trees that determine how at risk they are from drought, we can better understand global patterns of tree mortality and how the world's forests are reacting to rising temperatures and reduced rainfall. As the temperature of the planet continues to climb, mass tree mortality will hit more forests than ever before. Forests store a substantial amount of the world's carbon and increased tree death will only propel future global warming. This has very significant implications for fully understanding the impact of climate change on our planet."
One important take-away point from this study could be a suggestion for forest management. Knowing now that certain characteristics are more hardy to drought, arborists can incorporate more of these species into forest diversification plans. Because of previous evidence suggesting that plants communicate and support each other through chemical networks, the survival of these more resistant species could help other more vulnerable species as well.