Pre-War research, complemented by improved cultivation machinery (Zehetmayr 1960), had provided foresters with a robust set of silvicultural techniques to establish conifer plantations on a range of sites that had been considered unplantable at the beginning of the 20th century. The focus upon maximum wood production at least cost (Malcolm 1997) resulted in the use of intensive site manipulation to reduce the stand initiation phase so that canopy closure was achieved as quickly as possible (Davies 1979). Fast growing species with high volume production such as Sitka Spruce were preferred wherever possible so that the resulting forests had little species diversity. Increasing awareness of the risks of wind damage to plantations on shallow soils in exposed upland areas led to the progressive adoption of no-thinning regimes in many areas (Quine et al. 1995). This strategy proved an attractive option in difficult market conditions and/or in forests remote from end-users. The lack of thinning prolonged the stem exclusion phase where the limited light below the canopy (Hale 2005) would restrict both regeneration and understorey vegetation. The main silvicultural system employed in nearly all British conifer forests for much of the last century was one of ‘patch clear-felling’ (Matthews 1989) stands when the trees had reached economic maturity followed by replanting. Discounted cash flow techniques and stand yield tables (Johnston et al. 1967, Edwards & Christie 1981) were used to determine felling ages, which for most conifer species tended to be in the region of 40–60 years, depending upon growth rate and the risk of windthrow.
Hibberd (1985) described the application of the patch clear-felling system in the spruce-dominated forests of the English–Scottish border, where the main concessions to other objectives were reducing the size of the felled area in more conspicuous areas and the introduction of a percentage of broadleaves into the restocking. This system did create greater variation at a landscape scale through the ‘restructuring’ process whereby extensive areas of single aged stands were broken up through felling into smaller units of different ages, so increasing between-stand variation. However, there were few structural features such as large veteran trees, gaps, and standing and fallen deadwood which are beneficial to biodiversity and attractive to visitors (Peterken et al. 1992, Humphrey et al. 2003). The ultimate consequence was the creation of simple forests largely composed of stands in the stand initiation and stem exclusion phases with little within-stand structural diversity.
By the early 1990s, several factors had combined to make the use of alternative silvicultural systems more interesting to managers. These included the increasing maturity of many conifer stands resulting in greater frequency of natural regeneration (Malcolm 1997), which offered the chance of reducing costs involved in restocking. There was also greater awareness of the negative visual impact of even well-designed clear felling, and a desire to maintain mature conifer woodland habitat that was attractive to the public, especially in areas used for recreation. Managers began to recognize that a different system to patch clear felling might be better suited to meeting objectives, especially in locations where non-market aspects such as landscape and amenity were important. This led to increasing interest in the CCF approach, which involves a number of principles such as avoidance of clear felling, working with natural processes such as natural regeneration, and development of mixed stands of irregular structure (Mason et al. 1999, Pommerening & Murphy 2004). These principles can be implemented using alternative silvicultural systems described in Europe for nearly two centuries (Matthews 1989), but largely ignored in Britain for much of the post-War period (Hart 1995). All are characterized by the progressive thinning of a mature stand coupled with retention of some overstorey trees to act as a seed source for natural regeneration and also to provide an element of shelter for the regenerated seedlings. Thus, successful implementation of these systems involves the movement of a stand from the stem exclusion phase to that of understorey reinitiation with a consequent increase in structural diversity. In some methods, like various seed tree and shelterwood systems, the mature trees are normally felled once the regeneration is satisfactorily established, so that the resulting stand is essentially regular and even-aged. However, it is possible to retain some of the mature trees for another rotation to provide greater structural diversity. These systems were used on some scale on private estates in the eastern native pinewoods of Scotland in the first part of the last century, as is evident from descriptions and photographs in Steven and Carlisle (1959). They appear to have been abandoned in the 1950s, partly because the 1953 storm removed large numbers of retained trees and thus eliminated the seed source, but also because the system was deemed too complicated to fit within the constraints imposed by the woodland grant schemes of the time (D.B. Paterson pers. comm.).
Other alternative systems, often termed selection or group selection, are based upon the approaches developed in the mixed irregular forests of the mountains and foothills of central Europe dominated by beech, Norway Spruce Picea abies, and European Silver Fir Abies alba (Matthews 1989). These species are all shade bearers and regenerate under the mature canopy, so that the natural structure is one of stands containing trees of all sizes, and ages, in an intimate mixture and with several storeys within the one stand. Silviculture of such forests gives less attention to the establishment of regeneration, provided adequate seedling numbers are present, and concentrates on fostering a structure where all tree sizes are present in a desired ratio. The nature and utility of this ratio is much discussed in the forestry literature (Kerr & O’Hara 2000 and references therein) but the spatial structure of selection stands managed according to such ratios is very different from the regular patterns characteristic of plantation forests (Pommerening & Murphy 2004). The selection systems also differ in that a greater range of product sizes are harvested at any one time, and that there is an explicit focus upon the production of large diameter trees of high timber quality. Anderson (1960) first proposed the possibility of transforming conifer plantation forests in Britain by the adoption of selection systems, but the approach found little favour at a time when conifer afforestation was at its height.
Uptake of CCF was given further stimulus by the certification process (see earlier) and especially the requirement of the UKWAS protocol that ‘in windfirm conifer plantations, lower impact silvicultural systems are increasingly favoured’ (UKWAS 2000). This has resulted in an almost ten-fold increase in the area of Scottish conifer forests designated for CCF management (Mason 2003). A feature of CCF forests compared with many plantations, especially those managed on non-thin regimes, is that regular thinning is essential to develop a more stable stand structure and a suitable environment for the development of regeneration (Malcolm et al. 2001). As a consequence CCF stands are characterized by a wider range of tree sizes including more big trees with deeper crowns and there is greater diversity of vertical and horizontal structure than in a regular stand. Such variation might also be expected to provide wider biodiversity benefits (Kerr 1999), although the evidence for this is still limited (Quine et al. 2004). Furthermore, greater use of CCF will still take several decades to achieve substantial alteration in forest structure. For instance, the trial at Glentress forest near Peebles that was started by Anderson in the 1950s has not yet completed the transformation to the desired irregular condition after 50 years (Wilson et al. 1999).
Evans (1997), in a review of developments in British broadleaved silviculture, referred both to the poor quality of many broadleaved woodlands in the pre- and immediate post-War periods and to a lack of interest in these species that continued at least until the early 1970s. This period also saw the planting of conifers in many broadleaved woodlands as part of an attempt to increase their productivity and to convert their structure to conform to the prevailing plantation silviculture ‘paradigm’ (Rackham 2003). The collapse of markets for small dimension roundwood discussed earlier saw a progressive abandonment of coppice management with a loss of the ‘woodmanship’ skills that had supported traditional broadleaved forestry (Rackham 2003). The patch clear-felling system has also been the main one employed in broadleaved high forests, the major difference from conifer forests being the much smaller size of the felled area (Evans 1984). Planting has traditionally been used to restock felled broadleaved woodlands given that natural regeneration has proved difficult, in part because of weed competition on more fertile soils often compounded by heavy browsing by deer (Harmer 2001).
The renewed interest in broadleaved management that followed the adoption of the broadleaves policy in the 1980s (Richards 2003) has seen appreciable increases in the proportion of broadleaved planting enhanced by the adoption of improved protection methods, such as treeshelters (Potter 1991), and more effective weed control regimes and increased grant aid. However, arguably the tending of stands that have closed canopy (stem exclusion phase) has not advanced, partially as a consequence of the bark stripping damage that can be caused to broadleaves by the Grey Squirrel Sciurus carolinensis (Mountford 1997), but also because of ongoing difficulties in marketing small sized timber. There have been some attempts to develop methods of more dynamic tending of broadleaved stands such as ‘free-growth’ regimes in oak (Kerr 1996), but these do not appear to have been widely adopted, and the general impression is one of less frequent thinnings in broadleaved woodlands in the last 10–15 years. The low levels of recent management recorded by Kirby et al. (2005) in a repeat survey of broadleaved woodlands provide support for this argument.
Although Hart (1995) cites some examples of the use of CCF systems in broadleaved woodlands, these appear to be less systematic both in approach and in scale than recent initiatives in the conifer forests. This may partly reflect perceived difficulties in obtaining natural regeneration (Harmer 1994), but also the browsing pressure exerted by rabbits Oryctolagus cuniculus, deer and other small mammals upon any seedlings that emerge. Arguably greater use of the thinning regimes designed to favour selected stems which are an integral part of CCF silviculture (Bruciamacchie & Turckheim 2005) could help improve stand quality and the financial attractiveness of greater management of broadleaved woodlands. There has been some revival of coppice management in the last 20 years or so, especially in woods managed for conservation purposes (Rackham 2003). However, it seems unlikely that this traditional system will ever be used on the scale of the pre-War period and earlier centuries unless a new bulk market is developed which can absorb substantial volumes of small dimension timber.