The restoration of neglected hedges: a comparison of management treatments
Introduction
As the farming industry in the UK became more specialised during the latter half of the last century many mixed farms began to specialise in arable production. This change in practice contributed to the loss of approximately half of Britain's hedgerows (Barr and Parr, 1994), many of which were grubbed out to facilitate the use of large machinery and to increase the area of productivity. The length of hedgerows now appears to be more stable with results from Countryside Survey 2000 (CS2000) indicating that there was no net change in the total length of hedgerows between 1990 and 1998. However, over the same period of time the linear features categorised as lines of trees/shrubs and relict hedges increased by about 35,000 km (31%) (Haines-Young et al., 2000) suggesting that hedgerows were still being lost over time through neglect rather than by removal. During the inter-war years almost half of hedgerows were layed and approximately 70% of farms cut less than half their hedges each year with most of this management being carried out between November and February (Bright and MacPherson, 2002). This would clearly produce a very different hedgerow habitat than the annual post-harvest flailing that is the common practice today (Britt et al., 2000). The UK is in the fortunate position of still having an estimated 190,000 km of species rich and/or ancient hedgerows (Anon., 1995), i.e. those that contain five or more native woody species per 30 m length and were in existence before the 18th century Enclosure Acts (Anon., 1994). The historical, cultural and biological importance of these hedges led them to be designated as a priority habitat in the national Biodiversity Action Plans (Anon., 1994) and to be protected by legislation under the Hedgerow Regulations of 1997 (Anon., 1997). As the function of stock containment had become redundant so the objectives of hedgerow management in arable areas changed. The regular and intensive post-harvest flailing undertaken in the interest of tidiness and shade reduction has resulted in some hedges becoming very reduced, and sometimes shorter than the oilseed rape crops they surround. At the other extreme some hedges were neglected and allowed to become tall and gappy (Macdonald and Johnson, 2000) and were best described as lines of trees. In order to maintain their status and function it is important that these neglected hedgerows receive the correct restoration treatment.
As one of the few remaining areas of semi-natural, uncultivated land in the modern farmed landscape hedgerows are important for a variety of groups as providers of food resources (Croxton and Sparks, 2002), potential movement corridors (Bright and MacPherson, 2002) and both nesting and roosting sites. The species richness and structural diversity in hedgerow flora is reflected in the diversity of other groups associated with hedgerows such as birds (Hinsley and Bellamy, 2000), small mammals (Kotzageorgis and Mason, 1997), butterflies (Dover and Sparks, 2000) and other invertebrates (Maudsley, 2000, Maudsley et al., 2002). The presence of mammals such as muntjac deer Muntiacus reevesi (Ogilby), hares Lepus europaeus (Pallas), rabbits Oryctolagus cuniculus (L), and grey squirrel Sciurus carolinensis (Gmelin) however, may have detrimental effects on the floristic diversity and structure of hedgerows if there is excessive pressure through the browsing, grazing and bark stripping activities that has been shown to occur in woodlands (Kenward & Parish, 1986, Cooke, 1995, Gill, 2000).
If hedgerows are to retain their structural integrity then some management is required (Barr & Gillespie, 2000, Baudry et al., 2000), with a lack of management appearing to be as detrimental as the over-management of hedges (Garbutt and Sparks, 2002). There is also an increasing recognition that both the timing of management and the techniques employed play an important role in the wildlife value of hedgerows (Maudsley, 2000, Croxton & Sparks, 2002). More information is needed on the structural elements of hedgerows in order to maintain and optimise their value especially for the wide range of species that use them as primary habitat; this includes 47 species of conservation concern in the UK, 13 of which are globally threatened or rapidly declining (Anon., 1995).
In 1963 a series of hedges were planted at the Monks Wood research station with four replicates of 11 hedgerow types incorporating the major hedgerow types in the UK. Following initial studies these hedges had remained unmanaged for some 20 years, although unfortunately some of the plots had been grubbed out. In 1998 a decision was made to re-examine the hedges and to make further use of this valuable resource (Downing and Sparks, 1999). During the period of neglect the hedges had grown into lines of trees between 5 and 8 m tall with girths between 30 and 62 cm at 20 cm above ground level. Some species had produced many suckers from the roots and were beginning to form wide, dense thickets. Between the winters of 1998/9 and 2001/2 a programme of coppicing and pollarding was introduced to restore the hedges to a conventional hedgerow shape. The size of the trees was too great to allow the evaluation of laying as a restoration treatment.
This paper describes the preliminary results following the reinstatement of the management regime and compares the two methods of restoration and their suitability for a range of hedgerow types.
Section snippets
Materials and methods
The mixed hedge experiment at Monks Wood was originally planted as double rows, 30 cm apart with 60 cm between plants, in plots ca. 27 m (90 feet) long. As some of the original plots had been lost over time this study compared nine hedgerow types (listed, with scientific names following Stace (1997), in Table 1, Table 2), in 17 of the surviving 25 plots, i.e. those with at least one year's regrowth, 12 plots were composed of single species, two were a mixture of hawthorn and beech, two were a
Survivorship
The results for the single species plots are summarised in Table 1. There are clear differences in species survivorship rates between the coppicing and the pollarding treatments. The most tolerant of the single species hedges to cutting were field maple, hazel and elm, with some plots having complete survivorship of the ten stools under both the coppicing and pollarding regimes. One replicate of hawthorn and the blackthorn plot both had good survival. The two replicates of coppiced hornbeam had
Discussion
Experimental manipulation of hedgerows is fraught with difficulties related to the scale of the management regime required and this study is no exception. The reader is reminded that the plots described here were cut in different years and low counts of some species occurred in some plots. Despite this the results of initial regrowth reported in this study illustrate the regenerative power of some hedgerow tree and shrub species to the extent that they will recover rapidly even when cut back
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