Landscape composition is a key driver of biodiversity at a local level, especially in rural areas [1].

 Hedgerows are a dominant form of field boundary across farmed landscapes worldwide, ranging from western Europe, to as far as north and south America, Australia, and China [2]. By broad definition, hedgerows are linear rows of woody shrubs, trees and herbaceous understory vegetation that form continuous networks across agricultural landscapes [3]. Hedgerows were originally constructed in Europe during the deforestation of Neolithic settlements and were employed with the aim of protecting and segregating livestock and crops [4] [5]. That said, the original function of hedgerows became less common from the mid-twentieth century onwards, primarily owing to the vast availability, low cost, and low maintenance of fencing alternatives, which also acted as a practical solution to maximising the space of agricultural lands [6]

Field boundaries, such as hedgerows, comprise fundamental habitats and refuges for various forms of Irish biodiversity – especially birds. Specific attributes of hedgerows determine the composition of bird species within a region, not to mention the land use adjacent to it [7]. That said, hedge size (incorporating the height, width, and volume) and the presence/ abundance of tree habitats are the primary determinants of species richness and abundance regarding breeding birds [8]. Larger hedgerows made up of both trees and shrubs also function as valuable ecological corridors, therefore they provide a means of connectivity to facilitate the movement of birds, in addition to bats [9]. Where extant, hedgerows continue to provide the services they were originally intended for, and have been additionally seen to provide co-benefits, not only in relation to bird species. That said, due to changes to traditional farming methods in addition to intensified landscape management, farm birds in particular have been susceptible to population declines [10].

Seeing as the majority of bird populations reside in rural areas, good conservation measures and management must be in place to meet such protection requirements [8]. Hedgerows are typically cut for their long-term well-being. If not managed sustainably, however, there is potential to negatively impact hedgerows and the animal populations that rely on their services. In Ireland, hedgerow cutting is prohibited between the 1st of March and the 31st of August each year. Such restrictions are laid out under Section 40 of the Wildlife Act 1976, which was more recently amended by the Wildlife Act 2000 and Heritage Act 2018 [11]. Exceptions exist, however, in the interest of road safety where local authorities may trim hedges during the prohibited period at their discretion.

Why do birds need hedgerows?

Due to the variable habitat composition of European farmland, birds associated with hedgerows consist of both farmland and woodland species [13]. This has resulted in different birds having their own preferences regarding the specific type/ structure of hedgerow habitat they require in order to optimise their success in the wild.

The primary uses of hedgerows for birds are nesting and foraging. Others include using hedges for song perches and perching posts. In Ireland, approximately 55 out of the 110 species recorded in the Countryside Bird Survey utilise hedgerows in one way or another. Of these 55 species, 35 nest in hedgerows [12]. The vegetation structure at the base of a hedgerow is a key determinant regarding nest site selection, and the nesting success of a species in general [8]. Ground nesting bird species require dense vegetation in order to also act as a refuge from predators. The wren (Troglodytes troglodytes) is an example of a species that tends to nest deep down in hedgerows as they tuck themselves away in vegetation [12] [13]. The robin (Erithacus rubecula) also opts for nesting low down in hedgerows as a way to stay secluded.

The nest of the once-common yellowhammer (Emberiza citronella) is also generally confined to hedgerows themselves, or strategically located on the ground in various ditches and grassy field margins. This is due to the availability of invertebrate prey in the chick-rearing phase [10]. This bird requires a variety of other farmland habitats for their continued survival, including that of border tillage field boundaries where they also feed on tillage and cereals.

Wider hedgerows are known to support species such as the blackbird (Turdus merdula) [13] [14]. The blackbird is common across Ireland and use wider hedges for protection and shelter, while they also provide a plentiful supply of worms below the hedge [12]. Many bird species opt for nesting in dense hedgerows, as chick survival is lower when nests are open and accessible due to predation by corvids [15].

The selection/ abundance of food and other foraging opportunities is also a key factor in determining where birds set up their nests. Berries are one of the most commonly associated foods with Ireland’s birds. Blackberries on bramble are a prime example of this, as well as elderberries [12]. Hedgerows are also rich in insect prey, which feeds various bird species such as blue tits, for example. Birds, as mentioned, also feed on snails, slugs, and worms which are often abundant under hedgerows in damp conditions.

Beyond birds: Why should we save our hedgerows?

Hedgerows serve many forms of biodiversity, including, but not limited to birds. From the examples above, this is primarily through their provision of shelter, foraging opportunities, wildlife corridors, and breeding sites. In addition to the ecosystem services mentioned, hedgerows offer other functions attributing to their continued importance in rural landscapes globally in a much broader sense regarding the surrounding environment. Just some of these additional co-benefits as outlined in Collier (2021) [6] include:

  • Snow drift prevention;
  • Improved soil drainage;
  • Providing shelter and shade to livestock;
  • Buffering flood and soil erosion;
  • Supporting pollinating invertebrates;
  • Prevention of wetland pollution from run-off;
  • Limiting evapotranspiration.

The idea has been put forward that hedgerows have a role to play in mitigating the impacts of anthropogenic change as the earliest nature-based solution, and even in the larger context of mitigating the impacts of climate change [6]. A nature-based solution is one defined by the International Union for the Conservation of Nature (IUCN) as ‘actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human wellbeing and biodiversity benefits[16].

Due to their already proven and continued importance, hedgerows are being replanted across Europe, this time as a nature-based solution, and not only as a means to segregate field boundaries and livestock. This is a way of addressing contemporary issues that have emerged in recent decades. Some of these problems include crop and animal exposure, poor soil stabilization, nutrient and spray drift, and a decline in pollinator repositories [6]. Additionally, alterations to the Common Agricultural Policy (CAP) in Ireland required farmers to replace hedgerows that were once lost [17].

In more recent times, hedgerows are even being planted in more urbanised settings, not only rural, as well as along motorways. This is a way of intercepting particulate matter, chemicals, and noise. The contribution of hedgerows to attaining net-zero targets remains to be unclear at this point in time, however studies are emerging with the aim of quantifying carbon sequestration rates linked to the planting of hedgerows [18]. This in turn can be used as a mitigation measure to tackle various environmental pressures, and even those that are human health related.

References

  1. Lecoq, L., Ernoult, A., Mony, C. (2021). Past landscape structure drives the functional assemblages of plants and birds. Scientific Reports, 11, 3443.
  2. Baudry, J., Bunce, R.G.H., Burel, F. (2000). Hedgerows: An international perspective on their origin, function and management. Journal of Environmental Management, 60, 7-22.
  3. Hannon, L.E., Sisk, T.D. (2009). Hedgerows in an agri-natural landscape: Potential habitat value for native bees. Biological Conservation, 142, 2140-2154.
  4. The Heritage Council. (n.d.). Conserving Hedgerows. Available at: Layout 1 (heritagecouncil.ie) [Accessed 19 March 2022]. 
  5. Montgomery, I., Caruso, T., Reid, N. (2020). Hedgerows as Ecosystems: Service Delivery, Management, and Restoration. Annual Review of Ecology, Evolution, and Systematics, 51, 81 – 102.
  6. Collier, M.J. (2021). Are field boundary hedgerows the earliest example of a nature-based solution? Environmental Science and Policy, 120, 73-80.
  7. McMahon, B.J., Whelan, J. (2006). Individual field boundary evaluation and grading system attributes and Irish farmland birds. Tearmann: Irish journal of agri-environmental research, 5, 29-42.
  8. Hinsley, S,A. Bellamy, P.E. (2000). The influence of hedge structure, management and landscape context on the value of hedgerows to birds: A review. Journal of Environmental Management, 60, 33-49.
  9. Forman, R.T.T., Baudry, J. (1984). Hedgerows and hedgerow networks in landscape ecology. Environmental Management, 8, 495-510.
  10. Finch, D., Moore, P., Lusby, J. (2022). Breeding densities and habitat associations of Yellowhammer Emberiza citrinella in their core range in an arable landscape in east Cork. Irish Birds, 44,45-54.
  11. National Parks and Wildlife Service. (n.d). Restrictions on Cutting Hedgerows and Burning. Available at: Restrictions on Cutting Hedgerows and Burning | National Parks & Wildlife Service (npws.ie) [Accessed 27 February 2023] 
  12. Teagasc. (2020). How birds use hedges. Available at: Environment – How birds use hedges – Teagasc | Agriculture and Food Development Authority [Accessed 27 February 2023]
  13. Graham, L., Gaulton, R., Gerard, F., Staley, J.T. (2018). The influence of hedgerow structural condition on wildlife habitat provision in farmed landscapes. Biological Conservation, 220, 122-131.
  14. Green, R.E., Osborne, P.E., Sears, E.J. (1994). The distribution of passerine birds in hedgerows during the breeding season in relation to characteristics of the hedgerow and adjacent farmland. Journal of Applied Ecology, 31, 677–692.
  15. Dunn, J.C., Gruar, D., Stoate, C., Szczur, J., Peach, W.J. (2016). Can hedgerow management mitigate the impacts of predation on songbird nest survival? Journal of Environmental Management, 184, 353–544.
  16. Walters, Gretchen Marie. (2016). Nature-Based Solutions to Address Global Societal Challenges. Nature-Based Solutions to Address Global Societal Challenges. https://doi.org/10.2305/iucn.ch.2016.13.en
  17. Thompson, L. (2021). Hedgerows offer route to increased carbon sequestration on farms. The Irish Times. Available at: Hedgerows offer route to increased carbon sequestration on farms – The Irish Times [Accessed 27 February 2023]

Biffi, S., Chapman, P.J., Grayson, R.P., Ziv, G. (2022). Soil carbon sequestration potential of planting hedgerows in agricultural landscapes. Journal of Environmental Management, 307, 114484.