Tyfiant Coed — Growth Modelling of Sitka Spruce and Birch as Decision Support System for Continuous Cover Forestry

Britain has a relatively short history of state-organised forest management. The formation of a state forest service, the Forestry Commission, in 1919 was the reaction to a severe shortage of timber during the First World War. The primary objective of the Forestry Commission was to build up a strategic reserve of timber for the nation. This gave rise to the establishment of coniferous plantations dominated by even-aged stands of Sitka spruce managed by patch clearfelling. In the 1990's an international movement towards more natural forest management, the Rio-Helsinki process, and the requirements of certification began to stir up concerns about this type of forest management in Britain. Devolution has provided further impetus for new and distinctive agendas for the woodlands of the three nations in Great Britain with emphasis on alternatives to clearfelling. The Welsh woodland strategy launched in 2001 contains the strongest commitment to what can be generally termed continuous cover forestry (CCF). The "Woodlands for Wales" strategy aims "to convert at least half of the National Assembly woodlands to continuous cover... and encourage conversion in similar private sector woodlands" (Forestry Commission, 2001, p. 25). This political decision, the outcome of a long consultation process involving a wide range of interest groups including representatives of local communities, meets a rather unprepared forestry sector, and the consequences of this large-scale change of forest management are largely unknown. The necessary transformation of even-aged, single species plantations faces several problems which need to be taken into account such as climatic conditions of high rainfall and high exposure, and deer and squirrel browsing. Experience with this management type among woodland managers is very limited (Hart, 1995), and silviculturists have recognised the need to compensate for the lack of practical experience with scientific tools, producing management guidelines and corresponding financial scenarios (see e.g. O'Hara and Valappil, 1999; Twery et al., 2000; Lexer et al., 2000).

In order to facilitate the uptake of CCF the School of Agricultural and Forest Sciences of the University of Wales and the Forestry Commission Wales successfully joined up to launch an Objective One project, Tyfiant Coed, which started in September 2001 and finished in October 2004. Its aim was to develop a decision support system for continuous cover forestry with Sitka spruce and birch which produces alternative silvicultural scenarios for specific forest stands and delivers accurate forecasts in terms of yield, economics and ecological consequences. Tyfiant Coed is Welsh and means forest or tree growth. The project was partly funded by the European Union and FC Wales with the sum of £419,101.

Tyfiant Coed project staff established a total of 10 permanent experimental plots, which provide detailed information on stand structure and tree growth under CCF scenarios, and also serve as management demonstration sites. Various thinning experiments were carried out on several of these plots in order to design appropriate CCF techniques for the specific environmental conditions in North Wales. Data were also collected from five temporary plots. Foundations were laid for the development of an individual tree-based growth model. This includes the overall model theory as well as vital work on several aspects of growth modelling, such as parameters for increment functions, allometric relations, site dependent modelling and crown shape modelling. Much emphasis has been placed on the modelling of spatial forest structures. Forest structure analysis software was developed which forms the first completed part of the envisaged decision support system.

During the second phase of Tyfiant Coed, which started in March 2005, the objectives are to continue with the collection, processing and analysis of data on stand structure and tree growth under CCF scenarios, and to disseminate the findings of Phase One among forest managers and planners throughout Wales.

Arne Pommerening, July 2005