The amount of water that a forest uses remains an important subject of debate around the world. Trees and forests have the ability to use more water than shorter types of vegetation. This has led to concerns that major afforestation schemes could reduce water supplies, leading to water shortages and increased costs.
Much research has been undertaken to quantify the water use by different tree species or forest types, including in the UK. Unfortunately, there is no simple answer to the question of how much water forests use and research continues to improve our ability to predict the impact of forestry on water supplies.
To improve our ability to quantify the amount of water used by trees through a range of process, field-catchment and modelling studies.
Much of our knowledge of the impact of forestry on water supplies has been gained through a number of collaborative and external catchment studies. The main sites are:
- Coalburn:Coalburn in the north of England is Britain's longest running forest hydrology research catchment, providing a unique 50-year record of the long-term effects of conifer afforestation on upland water supplies.
- The long-term water balance (1972- 2004) of upland forestry and grassland at Plynlimon, mid-Wales
- Plynlimon water balance 1969-1995: the impact of forest and moorland vegetation on evaporation and streamflow in upland catchments
- Black Wood:
- Soil water changes below beech woodland and grass on chalk sites in Hampshire
- Evaporation estimates from sensible heat flux measurements over beech woodland and grass on chalk sites in Hampshire
- The results from Black Wood and Bridgets Farm compared with those from other woodland and grassland sites