Interim guidance on site selection and good practice now available
News from Forest Research: April 2009
Concerns about climate change and fossil fuel shortages are encouraging interest in alternative energy sources. As a result, there is increasing demand in Britain for forest biomass to supply power plants. As around 25% of the mass of a tree is in its stump and roots, attention has turned to the possibilities of stump harvesting as an additional source of biomass.
However, the removal of stumps and roots may have an adverse impact on soil and water, including a loss of soil carbon. It is therefore important that these risks are carefully managed to ensure that the potential disadvantages do not outweigh the benefits of harvesting stumps for biomass.
Forest Research has identified the main risks of stump harvesting as:
- Increased soil damage leading to erosion and reduced stream water quality
- Removal of essential nutrients, leading to lower soil fertility
- Removal of base cations (calcium, magnesium, sodium and potassium) leading to soil and stream water acidification
- Increased carbon loss from disturbed soil.
These risks have now been assessed for all soil types based on expert judgement and practical experience of managing forest soils. High-risk soils have been identified, for which stump harvesting is not recommended, and measures have been developed to minimise the impact on medium and low risk soils.
Interim guidance on site selection and good practice for stump harvesting has been released. Experiments starting this summer in south Scotland will test the guidance and provide data on the long-term effects of stump harvesting on soil condition, site nutrition, water quality and soil carbon.