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The vital role soil mapping plays in the sustainable management of the nation’s forests

Culbin forest (c) James Hutton Institute
"Forestry in the UK is now more focused than ever on woodlands delivering multiple benefits, notably those related to human health and wellbeing, water protection and enhanced landscape quality, as well as timber production.

Dr Andrew Nolan, Environmental and Biochemical Sciences, James Hutton Institute, and Bill Rayner, Forest Research, Forestry Commission

Site-specific knowledge of soil resources is essential to understanding their potential contribution to the management of the nation’s forests.  Indeed, soil mapping may be seen as an imperative in the inventory, modelling and management of sustainable forest areas.  This is particularly important in the UK where there is great diversity of climate, geology, landscapes and soil forming processes within a relatively small area. In terms of human influence, the land has been subject to a long history of settlement, deforestation, agriculture, and management of the vegetation by fire and grazing animals. This led to a gradual reduction in forest cover, to a minimum of around 5% by the end of the nineteenth century. Following a review of this scarcity of timber resources, a strategic and very largely state-owned forest estate was created following an Act of Parliament, commencing in 1919 with extensive plantings on lowland and upland areas of grassland, dwarf-shrub heath and peatlands previously managed as grazing land. The goal of re-establishing woodland cover was seen as a national priority and while the original impetus may have been the wartime scarcity of timber, this perception has been greatly expanded with the recognition of the role forests play in recreation, human wellbeing and their contribution to biodiversity.

An important prerequisite in re-establishing forest cover and the choice of tree species is the carrying out of pre-planting surveys to map the distribution of different soil types and identify site and soil characteristics likely to be of significance in forest management. These include the underlying rock type and the depth of soil overlying bedrock, the presence or absence of ironpans or hardpans, soil texture and whether there are any peat deposits present.  The existing vegetation can also give vital clues as to the patterns and variability in soil types underlying any particular area. From the early days of land acquisition and plantings, a Forestry Commission soil classification was devised for mapping soil resources in considerable detail, generally at a scale of 1:10,000, focussing on the main soil groups, notably Brown Earths, Podzols, Ironpan soils, Gleys, Rankers and Peatland soil types.  Further detail is specified by invoking soil phases where appropriate to the main soil coding specifically related to forest management, for instance soil depth, stoniness and drainage.

Information is gathered in the field by digging small soil inspection pits and by the use of soil augers, with the frequency of records determined by the complexity, variability and predictability of soil patterns.  Rates of progress vary accordingly but an experienced surveyor may cover up to 50 hectares per day. Mapping is carried out on aerial images with boundary lines drawn to show the extent of different soil types.  Soil complexes of up to three component soil types are used where different soils occur in close association, often related to specific topographic patterns such as glacially-deposited moraine, or where rock ridges are close to the surface.  Along with an assessment of soil moisture regime, such information contributes to the overall ecological site classification of any particular forest area.

With developments in digital technology, geographic information systems and modelling, there is a greater awareness by forest managers of the need for detailed soil and site type information to be incorporated into decision support systems. Such GIS-based management tools are a vital component of modern forest management at the individual forest block and compartment level. They incorporate data from many sources ranging from climate, topography, nature conservation designations, services and hazards, as well as information on soil types. These data, notably on rootable depth and soil wetness, are a key aspect of the assessment of windthrow hazard or tree snap, which is vital in the determination of efficient rotation length, stand age and the height of trees on harvesting. This soil information also plays a key role in the plans for restocking of forests.  With the increased likelihood of greater variations in climate in future decades, the implications for forest management are of some concern and appropriate resource assessments are seen as a key component of an efficient forest management system for the future.

Soil survey skills in the UK were in danger of being lost but a new emphasis on upgrading the resolution of soils data in forest management models has raised the awareness of this and facilitated the training and mentoring of a younger generation of surveyors and the passing on of such skills and expertise. At present extensive and detailed soil mapping is being carried out notably on areas not previously mapped in detail but where the first or second rotation tree crop is nearing felling.

Forestry in the UK is now more focused than ever on woodlands delivering multiple benefits, notably those related to human health and wellbeing, water protection and enhanced landscape quality, as well as timber production. Soil is a key determinant of how these aspirations might be best achieved from our woodlands and the detailed mapping and interpretation of soil resources plays a vital role in the sustainable management of the nation’s forests.

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The James Hutton Research Institute is the result of the merger in April 2011 of MLURI and SCRI. This merger formed a new powerhouse for research into food, land use, and climate change.