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Siltation
Siltation principally results from soil disturbance associated with ground cultivation,
drainage, road construction and maintenance, and harvesting operations. It is
best managed at the site level and good site planning is an essential part of any
forest operation. The Guidelines require a methodological approach, which involves
consideration of available techniques and resources, the potential environmental
impacts of the work, and early consultation with appropriate bodies to assess the
sensitivity of the area. Usually there will be a need for a detailed site assessment and
the production of a well-annotated map (site plan) showing pertinent information,
particularly site constraints. Common aspects are:
• the need for meticulous planning and supervision of operations;
• the adoption of less disruptive practices;
• the careful matching of machinery to site conditions;
• varying the scale and timing of operations according to site sensitivity;
• the use of a wide range of protective measures; and
• the preparation of a contingency plan in case of the accidental spillage of
chemicals or oils.
Effectiveness of the Forests and Water Guidelines
Research and monitoring have played a key role in assessing the effectiveness of
best management practices (Nisbet, 2001). The preferred approach has been to form
a partnership with the water regulatory authorities and others in undertaking this
work. In general, sensitive catchments and large-scale treatments were selected to
provide good test cases. Where possible both water quality and biology are examined.
Results are published, often in peer-reviewed scientific literature, for general scrutiny.
Examples relevant to afforestation are Nisbet et al. (1995), Nisbet (1997) and Nisbet
et al. (2002). The effects of fertiliser applications are described in Nisbet and Stonard
(1995) and Lees and Tervet (1994). Road construction, harvesting and restocking
impacts are written up by Pratt et al. (1996), Neal and Reynolds (1998), and Nisbet et
al. (2002). These studies confirm the effectiveness of the Guidelines in controlling the
threat of diffuse pollution from forestry. Demonstration studies such as the EU LIFE
UK182 Project in Galloway (CVCWT, 2004) have also played a vital part in promoting
and communicating the success of best practice for protecting the freshwater
environment.
THE USE OF WOODLANDS IN AGRICULTURAL LANDSCAPES
The success of the Guidelines has resulted in attention shifting from viewing forestry
as a threat to exploring how it can be used to improve the ecological status of water
bodies. In particular, opportunities exist for forestry to help tackle diffuse pollution
from more intensive land uses such as agriculture. One example is the use of riparian
woodland buffers to retain sediments, nutrients and pesticides in waters draining
from adjacent farmland. Investigations of the use of forestry in largely agricultural
catchments are beginning to demonstrate the potential value of woodlands. Work
in the upper reaches of the Severn within the Pontbren catchment showed that
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