Forest hydrology

 

A key criterion of the Governments policy on sustainable forest management is safeguarding the quality and quantity of water.

Forests and forestry management practices can have profound effects on the freshwater environment.  The main water quality issues are recognised as being: increased turbidity and siltation resulting from the soil disturbance accompanying cultivation, drainage, road building and harvesting operations; the impact of aerial fertiliser applications, in particular of phosphate and urea, on the nutrient status of receiving waters; and the enhanced capture of acid deposition by forest canopies leading to further surface water acidification.  The effect of lowland pine forests on nitrate concentrations within groundwaters is an emerging issue in parts of lowland England.  Water quantity issues include the threat posed by the expansion of conifer forests and to a lesser extent broadleaved forests to future groundwater supplies in drought prone regions and the impact of forestry on both winter floods and summer low flows.  The effect of riparian forest management on the freshwater environment and the potential for the riparian clearance of upland conifers to aid the recovery of acidified waters are also receiving increasing attention.  Finally, the recent flooding in England and Wales has renewed interest in the role of floodplain forests in controlling flood flows and mitigating the effects of floods.

This programme addresses the effect of lowland forestry on the quality and quantity of groundwater recharge, the impact of forests and silvicultural practices on winter floods and summer low flows, the effect of riparian forest management on the freshwater environment, the impact of forestry on surface water acidification, the demonstration of sustainable forestry to protect water quality and aquatic biodiversity, and the role of floodplain forests in flood defence and sediment control. Uncertainty over future rainfall patterns and quantities, as well as the influence of climate change on tree growth, make long term assessments a major challenge. The Water Framework Directive has increased emphasis on understanding these relationships at a catchment scale and in relation to other land uses. Consequently partnership working remains an important approach. Regular liaison with the water regulatory authorities and other interest groups will ensure that new problems are rapidly identified and addressed by further work and improvements in guidance. Expert advice is provided to national and international groups on the effects of forestry on water quality and quantity.

Following the publication of the 4th edition of Forests and Water Guidelines, particular issues will be explored in more detail in information notes, including one on water use of trees.  The scientific evidence underpinning advice and guidance will be ensured through regular papers in peer-reviewed journals.  A notable output will be contributions to a special issue of the journal Hydrology and Earth System Sciences entitled ‘The Sustainability of UK forestry: contemporary issues for the protection of freshwaters’. A report has recently been produced on the hydraulic impact of floodplain woodland. The programme supports a substantial advisory function to Forestry Commission staff, the forestry industry and government.

Commissioned reports

No reports available at this time