Accounting for Nature: Assessing habitats in the UK countryside
4.   Boundary and Linear Features

Stock and change

4.12 Table 4.2 shows the stock and change of Linear Landscape Features for England and Wales, and Scotland recorded by CS2000. The results for Northern Ireland are presented in Box 4.2. The total length of these features in the UK is over 1.8 million km, two thirds of which are in England and Wales, a fifth in Scotland and an eighth in Northern Ireland. The density of Linear Landscape Features is highest in Northern Ireland and lowest in Scotland. The stock of Linear Landscape Features in the six Environmental Zones in Great Britain is illustrated in Figure 4.1.

4.13 In England and Wales as a whole, hedges (449,000 km) and remnant hedges (52,000 km) were the dominant Linear Landscape Feature. No significant difference was detected in the total stocks of hedges and walls in 1990 and 1998, but the length of remnant hedges declined by about 14,000 km (21%). The length of the two categories of lines of trees and shrubs totalled some 153,000km in 1998, a net increase of about 35,000 km 31%). Fences had an estimated length of 423,000 km in 1998, an increase of 26,000 km (7%).

Figure 4.1: Stock (‘000 km) of linear landscape features by Environmental Zone in Great Britain in 1998. The greatest stock of linear features is found in the lowlands of England and Wales (EZ1 & 2) where hedges and fences are the dominant features. In the uplands of England and Wales (EZ3) and the lowlands of Scotland (EZ4) walls are more significant features than hedges. The stock of linear features is lowest in the marginal uplands and uplands in Scotland (EZ5 & 6) where fences and walls dominate. See Figure 1.5 for description of Environmental Zones.

[Click on the graph to reveal the underlying data]

4.14 In Scotland, the dominant Linear Landscape Features were fences (234,000 km) and walls (87,000 km). Neither showed a significant change in net length, though the estimated stock of fences had increased and walls decreased. Hedges and remnant hedges were much less widespread in Scotland and showed no significant changes in net length. As in England and Wales, the length of both categories of lines of trees and shrubs increased, by about 4,000 km (18%), to a total of 24,000 km in 1998.

4.15 Although there was no net change for hedges in England and Wales over the full period from 1990 to 1998, there is some evidence from the interim survey of hedges in 1993³that net losses, recorded in the first part of this period, 1990-93, were reversed in the latter part. The apparent increase in hedges between 1993 and 1998 needs to be confirmed by a more detailed analysis of the data for 1993, and comparison with other sources of information on hedgerow planting within agri-environment schemes.

4.16 The results of CS2000 indicate that the declines in length of hedges and walls reported for the 1980s have been halted, and in the case of hedges in England and Wales, there is some evidence that losses in the early 1990s have been reversed. However, when making a judgement about these data, it is important to note that the calculation of net change may obscure large transfers into and out of each category. If these transfers tend to balance each other out, the stock of a given feature may appear stable when it is actually in a state of flux. Newly created or restored features may not have the same value in terms of ecology, landscape and historical significance as long-established features. Consequently even if the total is unchanged, the ‘value’ of the resource may change over time depending on the patterns of removal, recruitment, restoration and management.

4.17 Figure 4.2 illustrates the complex interchanges between different woody Linear Landscape Features in England and Wales between 1990 and 1998. All the transfers are estimates based on the sample survey and should be interpreted as an indication of the magnitude and direction of trends rather than an accurate measurement.

Figure 4.2: Transfers between woody linear landscape features in England and Wales, 1990 to 1998. The weight of arrow is proportional to the size of the transfer. Numbers are length of feature in '000 km.

4.18 The total stock of hedges was maintained by a balance between the various losses and gains. About 10,000 km (2%) of hedges were removed and a similar amount planted. The amount of hedges degenerating into remnant or relict features (15,900 km) exceeded the restoration of such woody boundaries into hedges (12,800 km). However, more hedges were planted beside other boundary types (16,900 km), mainly fences, than were replaced by these features (14,400 km).

4.19 The net losses to remnant hedges in England and Wales are a consequence of further degeneration into lines of trees and shrubs (6,200 km) and removal or replacement by fences or other boundaries (11,100 km). However, a substantial amount (8,500 km) of the stock that was recorded as remnant in 1990, was restored to a hedge in 1998.

4.20 The net gains in lines of trees and shrubs/relict hedges have come from three main sources. The largest part of this increase (about 17,000 km) was accounted for by ‘new’ features in 1998. A further amount (9,400 km) was derived from existing fences and banks. The analysis of results so far does not permit the definite distinction of new lines of trees and shrubs from pre-existing features recorded for the first time in 1998. However, it is likely that much of the increase is a consequence of reclassification of existing features. The third source of the increase (16,000 km) was, as we have seen above, through the management neglect of hedges and remnant hedges. A small amount (2,200 km) of the lines of trees and relict hedges recorded for 1990 were removed.

4.21 This analysis of transfers between woody Linear Landscape Features in England and Wales shows that, while the net loss of hedges may have been reversed during the last decade, this is because a delicate balance has been achieved between planting and removal, degeneration and restoration. Comparison with the 1984-90 period⁴ shows that rates of hedge planting are similar but rates of removal have fallen by a factor of seven. There is evidence for a gradual degeneration of woody linear features as some hedges become remnant hedges and some of these in turn become lines of trees or shrubs. But, unlike the 1980s and early 1990s, restoration and management has largely counteracted these trends.

4.22 The patterns of transfer observed in Scotland were similar to those in England and Wales, except that they were smaller.

4.23 The losses of managed hedges, reported in Countryside Survey 1990 and the interim survey in 1993, appear to have been reversed in the mid-1990s. However, although the net length of hedges now appears stable or possibly increasing this does not necessarily imply that the value of the resource is stable as newly planted or restored hedges may not compensate in all respects for the older features which have been lost. Evidence of changes in the ecological condition of the hedgerow stock is reported below.

4.24 There was no statistically significant change detected in net length of walls for England and Wales, and Scotland. However, there was a small but significant net loss of 1,600 km (13%) of walls in the easterly lowlands of England and Wales (Environmental Zone 1). Compared to hedges, walls showed few transfers with other features. The survey estimates that slightly more (4,700 km) of the stock of walls had been removed than had been constructed (3,200 km) in Great Britain as whole between 1990 and 1998, with similar trends in Scotland, and England and Wales. Overall rates of wall removal were reduced by a factor of five from the 1984-90 period. Widespread losses in walls reported for the 1980s therefore appear to have been slowed or halted. The loss of walls in Environmental Zone 1 may be a localised effect and deserves further investigation.

4.25 There was no significant change in net length of banks and grass strips. Fences, on the other hand, showed marked increases everywhere.

3 Hedgerow Survey 1993 was limited to 108 sample squares containing hedges in England and Wales. The survey estimated a net loss of 13% of hedges between 1990 and 1993, mostly attributed to management neglect. The differences in sample size and field methods mean that further work is required in order to compare the results of the survey directly with Countryside Survey 2000. However, losses in the early 1990s must have been reversed between 1993 and 1998 for there to have been no net change over the 1990-98 period as a whole. Reference: Barr, C.J., Bunce, Gillespie, M.K. and Howard, D.C. (1994) Hedgerow Survey 1993, Contract report to DOE by Institute of Terrestrial Ecology.
4 Barr, C.J., Bunce, R.G.H., Clarke, R.T., Furse, M.T., Gillespie, M.K., Groom, G.B., Hallam, C.J., Hornung, M., Howard, D.C. and Ness, M.J. (1993), Countryside Survey 1990, Main Report, DOE London.