Forests of the future: what, when and how will trees get their water?

The earth’s atmosphere is changing, with increasing CO2 concentrations changing the way the planet looks through its impact on vegetation. The earth is getting greener in some places, and trees all over the earth appear to be changing the way they use water (refs). These changes will impact forests and water resources globally, but until now we have not had a way to test how trees will actually respond to higher CO2 in the future. This project will help fill this important gap by using a globally unique experimental facility that is artificially enhancing the CO2 concentrations of an old growth oak forest in central UK (BIFoR FACE).

In terms of changes to tree water use, this may decrease because stomata will open less frequently, or alternatively the canopy leaf area may increase (‘CO2 fertilization effect’), creating higher overall transpiration rates. These questions over “how much” are important, but there is also the critical, and as yet overlooked, question of “which” water is being taken up and used by trees. This project will utilise δ2H and δ18O stable isotopes as a method to trace the water being used by trees over the growing season at the BIFoR CO2 enrichment experiment (FACE) to gain the first mechanistic insights into which water the forest of the future will use.

This work will have important implications that will directly inform how we think about forests and catchments of the future. Forest regeneration efforts are expanding globally and are widely recognised as providing many beneficial ecosystem services, but how resilient these forests of the future will be with changing water and climate dynamics is highly uncertain. This project will provide critical insights into how they might respond to water stress, how we might think about their planting and management. Finally, this work will also inform catchment water management by examining whether how the results might apply at larger scales, specifically how the water being used by trees in turn changes the water available for soils and rivers and hence the supply of water resources downstream. These forest and water resource implications will be worked on directly with project partners and collaborators in the Environment Agency, as well as other partners in the forestry sector, allowing the student to also translate research into policy practice.