This part of the site covers the research and survey work that members of the Hedgelink partnership have commissioned or supported by in recent years. It also contains information on, and links to, other research and surveys related to hedgerows.
If you would like your research or survey work to be placed on this site, or signposted from it, please send us a message through the Contact and Feedback page.
A wide range of hedgerow research has been undertaken. In the early part of the last century this focussed on the agriculture impacts. Then, from the mid-1960s onwards, the focus began to shift to the wildlife value of hedgerows. In the last two decades, a substantial amount of research has been undertaken to support agri-environment schemes, such as Environmental Stewardship.
To maintain the shape of an hedge, ongoing management is required to prevent it from turning into a line of trees. This management can incorporate a wide variety of practices, such as flailing, laying and pollarding. Which technique is used and when is undertaken can have a big influence on the diversity of the hedge; for example the number of berries it produces or its suitability to provide nesting habitat for birds. Much of the recent hedgerow research has been used to fine-tune these techniques to maximise the benefits that hedgerows can offer.
The frequency and timing of when a hedge is trimmed has an influence on the berries produced. Defra research project BD2102 showed that more berries are produced on second-year growth of woody species.
BD2114 Effects of hedgerow management and restoration on biodiversity is currently underway (2009-2017) and is investigating the effect of the timing, frequency and severity of trimming on the quality and quantity of wildlife habitat, and food resources in hedgerows. The project also aims to identify, develop and test low-cost practical options for hedgerow restoration.
The project is being undertaken by the Centre for Ecology and Hydrology and includes three experiments;
Experiment 1: Long-term effects of timing and frequency of cutting on resource provision for wildlife
Ongoing treatments manipulating the frequency (once every 1, 2 vs. three years) and timing (autumn vs. winter) of cutting have been applied to hawthorn-dominated hedgerow plots since 2006, at a site in Cambridgeshire (Monks Wood).
Experiment 2: Timing, intensity and frequency of hedgerow cutting A randomised block experiment at five sites (Marsh Gibbon, Oxfordshire; Woburn, Buckinghamshire; Waddesdon Estate, Oxfordshire (two sites); and Yarcombe, Devon) is being used to investigate effects of the following hedge management treatments on flower production, berry yield, utilisation of flowers by pollinating insects, invertebrate abundance and structure:
- Time of cutting (early autumn vs. late winter);
- Intensity of cutting (standard cut back to old cut line vs. incrementally raising the cutter bar by approximately 10 cm each time the hedge is cut. Thus over the course of the current experiment annual incremental cutting has allowed a 1 m hedge to increase to approximately 1.4 m, incremental cutting every two years has resulted in a 1.2 m tall hedge and incremental cutting every three years in a 1.1 m tall hedge);
- Frequency of cutting (one, two and three year cycles).
Monitoring of the experiment included; vegetation composition, flower counts, berry availability over winter, pollination visitation rates, invertebrates and hedge structure.
Experiment 3: Rejuvenation of hedgerows
Several rejuvenation treatments have been applied to 24m long contiguous hedgerow plots including; Midland hedgelaying; conservation hedgelaying, wildlife hedgelaying; re-shaping with a circular saw and coppicing. Monitoring of the experiment included; vegetation composition, cost and speed, regrowth, dead foliage cover, hedge structure and berry availability over winter.
BD2108 highlights extensive research that mixed species planting, rather than single species, is better for wildlife. This study also found evidence that hawthorn selected by local provenance had better survival and growth rates. BD2018 also showed the difficulty in balancing the need to suppress weed growth in the early years of hedge establishment, with that of developing ground flora for the benefits of wildlife. It was concluded that the suppression of ground flora should stop by the fourth growing season.
Hedgerow tree population
Research commissioned in 2008 by Defra from Forest Research on behalf of Hedgelink has shown that to stabilise the hedgerow tree population 45% of trees should be under 20cm in diameter. Currently this figure is only 19% which explains why Countryside Survey 2007 reported a significant 3.9% fall in hedgerow tree numbers in Britain between 1998 and 2007. To maintain the current population of 1.67 million trees 30,000 new trees need to be recruited to the population each year, whereas in fact only between 10,000 and 15,000 are. Urgent action is needed to address this shortfall if we are not to lose most of our hedgerow trees in the next few decades.
Here you can read the full report.
Hedge Shape, Dimensions and Density
BD2108 identifies research showing that coppicing every 8 to 20 years is a low cost maintenance operation for hedgerows used throughout Europe. BD2106 showed that woody hedges should encourage the greatest number of birds on farmland in winter. Hedge laying has been found to significantly increase insect numbers (BD2108).
More information can be found in the hedgerow management section of this website.
Adjacent Land Use
Adjacent land use can have a big influence of the hedge and its associated species. For example, project BD2106 found that hedges next to stubbles held greater numbers of reed bunting and yellowhammers and hedges next to grass held greater numbers of thrush species.
Hedgerow Management and Wildlife
Plants and hedgerows
A hedgerow’s vegetation can depend on its previous history, for example whether it was formed during the clearance of ancient woodland or deliberately planted. Hooper’s Rule suggests that planted hedgerows will become more species rich by one species every 30 yards every 30 years. There is much scepticism about whether this rule can be applied and it is generally accepted that there is at least a regional variation. Research can pick up long term trends. When a resurvey of Dorset’s hedgebanks was undertaken some 70 years later it found that they had dramatically deteriorated both floristically and structurally (BD2107). Research (BD2102) has also shown that reducing the fertiliser contamination in the bottom of a hedge can help maintain plant diversity.
The herbaceous flora that grows alongside and under the hedge itself is an important habitat but its plant species diversity has declined in the last 20 years. Project BD5301 identified six distinct types of herbaceous vegetation that will need different approaches to restoration.
All hedgerows will need to be protected from fertiliser contamination, herbicide drift and severe disturbance. Vegetation that already contains species typical of woodland or species-rich grassland can be maintained by low intensity cutting or grazing. Rank, grassy vegetation will be difficult to restore on fertile sites but on some it might be possible to increase woodland, grassland or tall herb species by extensive management over a long period.
Disturbed, species-poor pasture may require re-establishment of perennial vegetation by reseeding but only on less fertile sites and where heavy grazing and trampling can be avoided. Disturbed arable vegetation would also require reseeding, although establishing a grass margin will often be the only realistic option. Heavily shaded, sparse vegetation might require reduction of the canopy by more regular hedge management but this would need to be balanced against other environmental objectives.
The project also identified a need for further research on hedgerow soils and to test restoration options.
For more information, you can download the full report (PDF, 1MB).
Birds and hedgerows
Hedgerows provide important nesting habitat for birds and, as project BD2108 recognised, the degree of management undertaken influences the nesting of birds. As highlighted in the hedge management section, cutting hedges every second year will encourage a large berry crop for birds to feed on. Project BD2102 also showed that mixed species hedgerows provide a more consistent berry supply. As well as berries, birds also rely on the invertebrates that hedgerows support. Research on this area is provided in the invertebrate section below. Defra project BD2106 identified that there was a relationship between the size and structure of the hedge and which species would be most to be present.
Mammals and hedgerows
Hedgerows have been shown to provide an important habitat for a number of species that include bats, shrews, voles, harvest mice and dormice etc. (BD2108). Focusing on dormice, BD2108 highlighted evidence that hedgerows were found to be dormice’s second most important habitat after woodland, and also that they acted as corridors for dispersal. Key management guidelines to emerge from managing hedgerows for mammals are to allow the hedge to grow as tall and wide as possible with a dense hedge bottom, and to trim in late winter to maximise autumn fruit production.
Invertebrates and hedgerows
Hedgerows provide habitat for a range of invertebrates from butterflies to spiders. Defra project BD2102 found invertebrate groups response to the hedge being cut in either winter or spring was complex, with different taxa responding in different ways. It also found that hedge laying can increase provide a diverse range and high abundance of invertebrates as the hedge grows. BD2108 highlights several research conclusions for enhancing invertebrate diversity in hedgerows. One of the most important methods is to maximise floral diversity in a hedgerow. Other findings include planting and retaining hedge trees and minimising fertiliser inputs close to hedgerows.
Amphibians, reptiles and hedgerows
Little research has been undertaken to look at the direct relationships between hedgerows and amphibians and reptiles. BD2108 suggests that hedgerows with dry banks and dense ground flora are likely to be most beneficial. For amphibians the hedgerow should be located within 2km of a pond.
More information about how hedgerows support wildlife can be found in the “wildlife and hedges” section of this website.
Hedgerows and climate change
Hedgerows have been widely suggested as facilitating species movement along corridors by acting as wildlife corridors. Though this is more accepted for animals and birds (CR0389), analysis of Countryside Survey data in BD2108 has shown that this assumption is questionable for plant species. Defra report BD2302 looks at the contribution hedgerow options in agri-environment schemes make to capturing carbon and therefore mitigating the effects of climate change.
Contractor and farmer attitudes to hedges
Research on attitudes to hedges by those who maintain them is important to help understand why management decisions are made. A major piece of research (BD2103) was undertaken in the late 1990s and a follow up study was completed in 2011 (BD2117). Both research projects were funded by Defra and provide information on what period of the year hedges are cut and why, and the reasons for the method, style and frequency of cutting.
BD2103 Final Report (PDF)
“BD2117 FINAL REPORT – Hedgerow Management: A survey of land managers, and contractors’ practices and attitudes”: (PDF)
APPENDIX 1 Farmer Questionnaire (PDF)
APPENDIX 2 Contractor Questionnaire (PDF)
APPENDIX 3 Follow-up Questionnaire (PDF)
APPENDIX 4 Field Survey Form (PDF)
Socio-economic research examines the relationship between the activity of hedgerow management and the social impact, such as the employment of those who maintain and restore hedges, supply of goods and services e.g. firewood etc. Little research has been carried out in this area, but a study based in Devon, undertaken for the Countryside Agency, predicted several outputs including numbers of jobs created and local goods purchased. It showed a positive multiplier effect because both hedge contractors and materials are largely locally sourced.
The UK Biodiversity Action Plan (BAP) Steering Group will continue to examine which areas are a priority for future research. If you know of any other relevant hedgerow research, please contact us.