Abstract: At the beginning of the twentieth century, the forest cover of Great Britain (i.e. the countries of England, Scotland and Wales) had declined to about four per cent of the land area following centuries of mismanagement and unsustainable exploitation of the natural forests. A major objective of national forestry policy from 1919 onwards has been to increase the forest area by means of a sustained programme of afforestation. From the 1960’s to date the expansion of woodland cover has been concentrated on land that was marginal for agriculture, particularly in the upland zones of Scotland. As a consequence of this policy, in 2002 there were over 2.7 million ha of forests in Britain comprising about 11.6 per cent of the land area. There are substantial differences between the three countries with Scotland having the highest forest cover at 17 per cent and England the lowest at only 8.5 per cent. This expansion represents one of the major changes in the rural landscape of Britain in recorded history. Because of this history, the forest area in Scotland has some unusual features compared to the rest of Europe and other parts of the Temperate Zone. Plantations established with timber production as their primary function are the dominant forest type. These plantations are mostly composed of species of non-native origin so that Sitka spruce (Picea sitchensis), which was first introduced in 1851, now makes up 47 per cent of the forests with other introduced conifers accounting for a further 25 per cent. Native species such as Scots pine (Pinus sylvestris) and various broadleaves (e.g. Quercus petraea, Q. robur, Betula pendula, B. pubescens, and Fraxinus excelsior) comprise the remainder. Many of the plantations are due to reach rotation age in the next 10-20 years, thus offering increased silvicultural opportunities for changing the structure and composition of the forests. Over the last 25 years forest policy objectives have changed to give much greater emphasis to establishing and managing forests to provide multifunctional objectives. Afforestation using non-native conifers and silvicultural practices that sought to maximise timber yields per unit area proved increasingly controversial in the 1980’s, particularly on sites with nature conservation value. As a result from the early 1990’s, much greater emphasis has been given to the use of native species in afforestation. In addition, people have begun to question whether patch clearfelling with regeneration through planting, the dominant silvicultural system used in plantations, was necessarily the best way to provide for a range of non-market benefits such as landscape amenity and recreation. This has resulted in increasing interest being shown in the use of a range of alternative silvicultural systems to clearfelling, generally known as Continuous Cover Forestry. Silvicultural practices in Scottish forests have therefore had to evolve to meet changing policy objectives. The emphasis during the major periods of afforestation was on establishing productive stands that would provide a national timber supply in case of emergencies. Conifer species were the main species used in plantation establishment because of their faster growth rates and their greater tolerance of difficult site conditions during plantation establishment. Non-native conifers such as Sitka spruce, lodgepole pine (Pinus contorta), Corsican pine (Pinus nigra var maritima), larches (Larix spp.) and Douglas fir (Pseudotsuga menziesii) were extensively planted because Scots pine, the only timber producing native conifer, proved more sensitive to site conditions and relatively slow growing. With improved understanding of site factors influencing establishment and early growth, it proved possible to develop highly productive plantations of these non-native species even on the most inhospitable of sites. As a consequence, these conifer plantations are highly productive in European terms with average growth rates of about 14 m3 ha-1 year-1. Thinning occurs in less than 50 per cent of conifer stands because of the risks of windthrow in an oceanic climate. Rotation age is between 35 and 60 years depending upon species and site. Forest design plans are used to ensure that extensive uniform areas are restructured during the felling process to increase structural and species diversity, while care is taken to increase the amount of native species, to protect special habitats and to enhance biodiversity. Because the conifer stands are comparatively young with around 80 per cent being 50 years or less of age, softwood timber production is anticipated to double over the next decade. The wood and fibre qualities of Sitka spruce, the dominant element of this increase in production, are attractive for a range of end-uses and the forest resource is conveniently located for major markets in southern Britain and northern Europe. As a consequence of devolution, in 1997 forestry policy and its implementation in Scotland was devolved to the restored Scottish Parliament (an equivalent process took place in England and Wales). In 2000, the first Scottish Forestry Strategy was published with an overarching principle of contributing to national sustainability through sustainable forest management (SFM), and associated principles of integrating forestry with other rural land uses, of contributing to the well being of the people of Scotland, of implementing management practices that enjoyed public support, and of respecting diversity in forest types. Five strategic priorities were defined: · to maximise the value of the Scottish wood resource, · to create a diverse forest resource for the future, · to make a positive contribution to the environment, · to create opportunities for the enjoyment of trees, woods, and forests, · to help communities benefit from their forests. A further aspiration was to increase the forest area to around 25 per cent forest cover by 2050. The aims of the strategy are promoted in private forests (65 per cent of the forest area) through grant subsidy and through Forestry Commission management in the public forests. At present, much of the Scottish forest estate lies either in the ‘stand initiation’ or ‘stem exclusion’ phases of forest stand dynamics (terminology follows that of Oliver and Larson). Despite the regular structure of many plantation forests, substantial progress has been made towards implementation of SFM with over 45 per cent of Scottish forests (including all Forestry Commission managed areas) having achieved certification under the United Kingdom Woodland Assurance Standard, which is FSC accredited. The forests are valued for recreation and recent studies have shown them to make a substantial contribution to biodiversity objectives. However, it is also clear that provision of most non-market benefits will be enhanced if the forests are managed to increase the representation of the ‘understorey reinitiation’ and even ‘old growth’ stand structures. Achieving the transition from the simple stands characteristic of our plantation forests to the more complex and diverse structures necessary to meet current policy needs requires us to rethink many of the precepts on which our silvicultural practices are founded. For instance, we need to acquire greater knowledge about aspects such thinning mature stands to promote and manage natural regeneration which have not formed part of Scottish silviculture for over a century. This development of ‘new’ silvicultural practices must consider the potential impact of climate change, for instance the potential for greater storm intensities and consequential risks of wind damage to forests. However, we also need to consider the need to maintain a flow of quality timber production to ensure that Scottish forests continue to contribute to the development of our rural economy. The extent to which these changes can be accommodated without undermining the value of the existing Scottish wood resource is critically dependent upon our ability to understand and predict the interaction between site, species, silviculture, and wood quality which underpins profitable forest management. In this paper, I illustrate changing practice in Scottish silviculture using results from a few, selected forest experiments and trials, some of which have been monitored for over 70 years. These are: a species trial which explains why so much use has been made of non-native conifers in developing the Scottish forest estate; an establishment experiment which illustrates some errors that can be made in extrapolating from early results to long-term stand development; a mixtures experiment whose results were a major stimulus to controversial afforestation in the 1980’s; an experiment in management of native Scots pine woodland which is influencing our thinking on the naturalisation of plantation forests; and a recent experiment examining processes relevant to the wider use of Continuous Cover Forestry in Scotland. I conclude by emphasising the continuing need for creating and maintaining well designed long-term forest experiments to provide the ecological and site based silvicultural knowledge that will be key to developing the varied and productive forests that are an ultimate objective of modern forest policy.
Citazione: Mason B (2005). The lessons of 25 years of change in the silviculture of Scottish forests; from conflict to synergy . 5° Congresso Nazionale SISEF, Grugliasco (TO), 27 – 29 Set 2005, Contributo no. #c5.6.4