Effects of hedgerow management and restoration on biodiversity

Staley, J.T, ORCID: https://orcid.org/0000-0001-6467-3712; Adams, N.P.; Amy, S.R.; Botham, M.S. ORCID: https://orcid.org/0000-0002-5276-1405; Chapman, R.E.; Hulmes, L.; Hulmes, S.; Dean, H.J.; McCracken, M. ORCID: https://orcid.org/0000-0002-8298-8838; Mitschunas, N.; Peyton, J.M.; Savage, J.; Ridding, L.E.; Baldock, K.S.; Pywell, R.F. ORCID: https://orcid.org/0000-0001-6431-9959. 2018 Effects of hedgerow management and restoration on biodiversity. Defra, 93pp. (Defra Project no. BD2114, CEH Project no. 03658)

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Abstract/Summary

Hedgerows can provide key semi-natural habitat within intensively farmed landscapes, and can deliver habitat and resources for a range of important wildlife, in addition to supporting ecosystem services. The value of hedgerows in supporting wildlife varies, depending on the management applied. Hedgerow management options have high uptake within agri-environment schemes (AES), both historically in Environmental Stewardship (ES) and in the current Countryside Stewardship (CS) scheme, including the Hedgerow and Boundaries grant. Previous studies on hedgerow management have shown substantial potential effects of hedgerow management regimes on the provision of resources for overwintering wildlife (Sparks and Croxton, 2007), and some indication of benefits for wildlife (Maudsley et al. 2000), but have not been quantified or rigorously tested. Here, results from three large-scale manipulative field experiments are presented, to assess different hedgerow management and rejuvenation methods in relation to the provision of resources for wildlife, and the response of invertebrates. The aims of this study were: 1) To examine the effects of simple hedgerow cutting regimes promoted by CS and ES, and the potential for cutting to allow incremental growth, on the quality and quantity of wildlife habitat, and food resources in hedgerows. 2) To identify, develop and test low-cost, practical options for hedgerow restoration and rejuvenation applicable at the large-scale under both CS and ES. Methods Two experiments were conducted to assess hedgerow cutting treatments. Experiment 1 consisted of replicated cutting frequency (every year vs. every two years vs. every three years) and timing (autumn vs. late winter) treatments, applied to replicate sections of hawthorn-dominated hedgerow at a single site in Cambridgeshire. Experiment 1 pre-dated this research project, and so it provided initial findings on these cutting regimes early in the project, which informed the revision of ES hedgerow options in 2012. Experiment 2 was run at five sites in lowland England over seven years (2010 – 2016), on hedgerows dominated by hawthorn (two sites), blackthorn (one site) or a mixture of woody species (two sites). In addition to testing the same cutting treatments as Experiment 1 on a wider range of hedgerow types and locations, Experiment 2 was designed to test the effect of cutting intensity, in order to assess a new hedgerow management option that might be included in future AES. A second multi-site experiment was conducted at five separate lowland sites in England, to compare traditional forms of hedgerow rejuvenation (Midlands style hedge-laying, coppicing) with alternative methods (conservation hedging, wildlife hedging, reshaping with a circular saw). Woody species composition varied between rejuvenation sites, further details below (Section 2.2). Rejuvenation methods were applied to replicate sections of hedgerows, and assessed immediately following implementation in terms of their cost and the time to apply each method. In addition, ongoing management (cut twice in five years as per current ES guidance) was applied to half of each rejuvenated plot, in a split-plot design. The other half was left unmanaged following the rejuvenation. Regrowth, hedgerow structure and berry provision were assessed over three years following the hedgerow rejuvenation. Key findings Hedgerow management (frequency, timing and intensity of cutting) • Cutting once every three years (a current AES hedgerow option) had clear benefits, compared with cutting once every year, which is the current standard practice for hedgerows outside AES schemes. Hedgerow plots cut once every three years had more flowers from two woody hedgerow species (hawthorn and blackthorn), which were shown to be linked to enhanced utilisation of these floral resources by pollinating invertebrates. • More berries were available for overwintering wildlife from four woody species (hawthorn, blackthorn, bramble and dog-rose) on plots cut once every three years. At some sites the increase in hawthorn and blackthorn berries were limited to plots cut in winter. • More Lepidoptera (butterfly and moth) caterpillars and pupae were present on plots cut once every three years, and there was a greater species richness on these plots. More eggs of brown hairstreak butterfly, a conservation priority species, were found on plots cut once every three years in autumn. • There was weaker evidence for the benefits of cutting once every two years. Plots cut once every two years had more hawthorn flowers at some sites and in some years, but flowers were not increased across multiple woody species. More berries were available over winter from four woody species (at some sites) on those plots cut once every two years in winter, but not on plots cut every two years in autumn. • Cutting to allow incremental growth (retaining around 10 cm recent growth when a hedge is cut, so the height and width gradually increases) forms part of the management advice for the current CS hedgerow option, but is not included as a compulsory management prescription. Results from this project provide strong support for the inclusion of this reduced, incremental trimming intensity in future AES hedgerow management prescriptions. • Cutting at a reduced intensity to allow incremental growth resulted in substantially more hawthorn and blackthorn flowers and berries, leading to increased utilisation of these plots by pollinating invertebrates. Lepidoptera diversity was also increased under this reduced intensity cutting treatment, as were the number of brown hairstreak butterfly eggs. Regrowth following incremental cutting was reduced for both blackthorn and field maple, compared to standard cutting intensity. • The benefits of an incremental cutting intensity were not dependent on the timing of cutting, unlike some benefits of the reduced cutting frequency treatments. On land where access for hedge cutting is limited to some times of year (e.g. on land too wet to access with a tractor and flail in late winter), this reduced intensity cutting will provide a range of benefits for wildlife. • The timing of cutting affected the Lepidoptera community using the hedgerows. Plots cut in winter had a greater overall abundance of larvae and pupae than those cut in early autumn, but fewer brown hairstreak butterfly eggs, a priority species for conservation. Timing of cutting should be tailored to the requirements of species present at particular sites. To achieve this, AES hedgerow option prescriptions should include some flexibility about the timing of cutting. Current hedgerow options within ES and CS do contain this flexibility. • Visitation rates of pollinating invertebrates to woody hedgerow flowers were strongly linked to floral abundance, within each species. Pollinating invertebrates made relatively more visits to blackthorn and bramble than hawthorn, perhaps because alternative floral resources are scarcer when blackthorn and bramble are flowering. • There was no evidence to support the assertion that cutting frequency can alter the woody structure of hedgerows, over the six years of this experiment. There was some weak evidence that maximum gap size in the base of hedgerows may be slightly smaller under an incremental trimming intensity, compared with plots cut back to a standard height and width. • Regrowth of hawthorn was largely unaffected by the timing and intensity of cutting. This suggests that the effort required for cutting hawthorn hedges under regimes that differ in timing and intensity should be about equal. In contrast, regrowth of blackthorn and field maple was reduced under the incremental cutting intensity treatment. Hedgerow rejuvenation methods • Of the three layed rejuvenation methods (Midlands hedge-laying, conservation hedging and wildlife hedging; see Section 2.2 for details), wildlife hedging was far quicker to apply than the other two methods (on average less than 1 minute vs. 12 and 33 minutes). However, it cost 62% of the price of conservation hedging and 33% that of Midlands hedge-laying. Wildlife hedging requires three people and heavy machinery, which may be why the time it took was reduced more than price. • Differences between the three layed rejuvenation methods in regrowth and berry provision were greatest in the two years immediately following rejuvenation. Berry provision was not reduced immediately following rejuvenation for wildlife and conservation hedging, but was for Midlands hedge-laying. However, by the third year there was no difference. Canopy regrowth in the second growth season following rejuvenation was less vigorous following wildlife hedging, though this difference was no longer apparent by the third season. • Regrowth from basal stools also differed between layed treatments, as wildlife hedging resulted in taller shoots and fewer basal stems with shoots. There were differences in the basal hedge structure between these three methods, as the wildlife hedging plots had a greater woody area and smaller maximum gaps than the other two layed treatments. • The conservation hedging was twice as quick to apply and about half the cost of Midlands hedge-laying. The conservation hedging plots had slightly lower rates of canopy regrowth in 2012 and a heavier berry weight in 2010-2012, but by 2013 did not differ from plots rejuvenated using Midlands hedge-laying in terms of regrowth, structure or berry provision. Conservation hedging has similar medium-term benefits as more traditional hedge-laying styles, and thus could provide a cost-effective rejuvenation alternative under AES such as Higher Level Stewardship, or the Higher Tier of the current CS scheme. • Coppicing was the second cheapest rejuvenation method tested if fencing was not required, and showed the most vigorous basal regrowth following rejuvenation. Coppice affected hedges over a longer time-scale than the other methods tested, shown by differences in regrowth, structure and berry provision that were still apparent three to four years later. Coppiced hedgerow sections had the most vigorous basal regrowth following rejuvenation. • Reshaping with a circular saw was the cheapest rejuvenation method tested, and had longer term effects on canopy regrowth and berry provision than the three layed methods. Circular saw plots continued to produce greater canopy regrowth compared with the unmanaged control plots three years after rejuvenation, and still had reduced berry weights four years later. The structure of circular saw plots was more similar to that of control plots than the other rejuvenation methods, as the density of woody material in the hedge base was not increased. • Reshaping with a circular saw and coppicing have benefits as cost-effective methods by which to encourage canopy and basal regrowth respectively. Both methods reduced berry provision even four winters following rejuvenation, compared to unmanaged plots. In addition, reshaping with a circular saw did not increase the density of hedge bases, and immediately following rejuvenation coppiced plots also had little basal woody material. Both methods may provide less shelter for mammals and invertebrates than the three layed rejuvenation methods, over the four year timescale tested in this project, and potentially longer. Summary The findings of this project provide support for some existing AES hedgerow management options, within both the ES and CS schemes, in terms of the provision of resources for wildlife and the invertebrate communities that utilise hedgerows. New management techniques have been shown by this project to have potentially more substantial and consistent benefits; reduced intensity cutting to allow incremental growth; and conservation hedging as an alternative to traditional hedge-laying. Early results from this project were used to inform the revision of hedgerow AES options in 2012, and through peer-reviewed papers, knowledge transfer events and resources, the findings of this project have been and continue to be widely communicated.

Item Type:	Publication - Report (Project Report)
Programmes:	CEH Topics & Objectives 2009 - 2012 > Biodiversity > BD Topic 2 - Ecological Processes in the Environment > BD - 2.4 - Estimate the impact of the main drivers and pressures on biodiversity ...
UKCEH and CEH Sections/Science Areas:	Biodiversity (Science Area 2017-)
Funders/Sponsors:	Defra
Additional Information. Not used in RCUK Gateway to Research.:	Official URL link provides further project information and full-text links.
NORA Subject Terms:	Ecology and Environment Biology and Microbiology
Date made live:	09 Aug 2022 13:55 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/532938

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