The Value of Hedgerows

Discover why hedgerows are important to carbon sequestration, biodiversity, and farming.

The Value of Hedgerows

Most of Ireland’s hedgerows were planted during the 1700 and 1800s when Acts of Parliament obligated landowners to plant proper permanent boundaries between their properties (Teagasc, 2022). However, some date back to medieval times and even as early as the Neolithic and Bronze ages (Teagasc, 2022). In 2010, the Teagasc Hedge Map indicated an area of 482,000 hectares or 6.9% of the total land area in Ireland is held by hedgerows, which included scrub and non-woodland trees (Black et al., 2022). The 2017 National Forest Inventory later used a different methodology to calculate that the national hedgerow and non-forest other wooded land is estimated to occupy 347,690 ha (Black et al., 2022). Hedgerows are multi-functional habitats and were previously planted to mark townland boundaries and enclose livestock in fields, however, they are now recognised to also have many ecosystem service benefits. For example, they sequester carbon, provide wildlife habitat, control flooding, improve water quality, and improve the scenic appearance of our landscape.

Carbon Sequestration

Hedgerow and non-forest woodlands have the potential to sequester 0.66–3.3 t CO2/ha/year (EPA, 2014). Hedgerow-bordered fields also hold greater soil organic carbon stocks due to the increased soil moisture and reduced temperature under the hedgerow (Van Den Berg et al., 2021). This microclimate results in slower carbon decomposition compared to adjacent fields not bordered by hedgerows (Van Den Berg et al., 2021). Conversely, the removal of hedgerows reduces this soil organic carbon storage capacity and releases carbon into the air due to soil compaction and disturbance, particularly when heavy machinery is used (Van Den Berg et al., 2021). Other factors relating to soil organic carbon are that tree-dominated hedgerows hold greater stocks than shrub-dominated hedgerows, and that hedgerows have extensive root systems and leaf litter (Dexler et al., 2021). The structure of hedgerows (their width, density, and connectivity) also determines both the carbon and biodiversity profile of hedgerows (Teagasc, 2022).

Biodiversity

The biodiversity profile of hedgerows refers to how well they provide food, nest sites, and hibernation sites to Ireland’s wildlife. The Countryside Bird Survey has previously recorded that 55 of 110 regularly recorded bird species utilise hedgerows, with 35 of these using larger hedgerows (1.4m high and 1.2m wide) as nest sites (Teagasc, 2022). Hedgerow trees and fruiting shrubs, such as blackberries on bramble, also provide perching posts and food sources for birds, respectively (Teagasc, 2022). In terms of the species structure of a hedgerow, mature trees (for example, those with interior cavities formed from fallen branches) provide roosts for bats, whilst a hedgerow’s dense base allows small birds and mammals, such as hedgehogs, to escape predation (Teagasc, 2022). Hedgerows also facilitate greater insect abundance due to their bare earth and higher soil organic carbon (Montgomery et al., 2020). For example, beetle abundance declined with agricultural intensification but remained relatively stable in hedgerows (Montgomery et al., 2020). These primary consumers further attract bird species due to increased food availability.

Hedge laying is a vital management tool for the biodiversity of hedgerows as it increases the density of the base—woody and leafy density along with new growth are beneficial for shelter, connectivity, and food resources (Graham et al., 2018). Habitat heterogeneity during hedge laying (done in small sections over a series of years) is preferred because it maintains tall sections, which are preferred by bats, while allowing herbaceous plants and some farmland birds to flourish in shorter, laid sections (Graham et al., 2018). The availability of berries and flowers is also essential, particularly for invertebrates (Graham et al., 2018). This cautions against overly frequent and extensive flailing or hedge-cutting, as this limits fruiting in the following year. In turn, it supports the use of hedge-laying approaches which produce a greater abundance of detritivores, herbivores, and predators when compared to circular saw methods (Amy et al., 2015).

Farmland Benefits

Besides their carbon and biodiversity benefits, hedgerows also benefit the farming landscape through shelter, flooding, and water quality. Hedgerows provide a wind-break and physical shelter for livestock during periods of wet, windy weather, as well as shade during sunny spells (Teagasc, 2022). Hedgerows help to prevent flooding during heavy rainfall events because of their dense vegetation base and less compacted soil compared to adjacent fields (Holden et al., 2019). This helps to slow water movement and allows the excess overland flow to infiltrate and percolate into the soil (Holden et al., 2019). Increased infiltration and percolation also improve our freshwater quality by trapping surface sediments and nutrients, therefore blocking their swift entry to surface water bodies such as rivers and lakes (Holden et al., 2019). A debt is owed here to the soil invertebrates whose greater abundance in hedgerow soils impacts hydrological functioning (Holden et al., 2019). For example, earthworms bury through the soil, mixing it up and creating networks of pores that increase permeability (Holden et al., 2019). Besides, the shelter and hydrological benefits of hedgerows to farmland, they also improve the farm’s scenic appearance (Teagasc, 2022). They are a part of our cultural, historical, and archaeological heritage, which means that every hedgerow is deeply rooted in Ireland’s past and confers a sense of character to the farm (Teagasc, 2022).

You can learn more in our reference list below, or by listening back to Teagasc’s Signpost Series Webinar “The Nature of Irish Hedgerows”. Search it on YouTube or click here to open the video. The Irish Hedgerows: Networks for Nature publication is also an incredibly valuable resource, click here to read it. 

References

  • Amy et al. (2015) Hedgerow rejuvenation management affects invertebrate communities through changes to habitat structure – https://doi.org/10.1016/j.baae.2015.04.002
  • Black et al. (2022) Pre-print: Biomass pools in intensively managed hedgerows can be a net emission of carbon dioxide – https://doi.org/10.21203/rs.3.rs-1761627/v1
  • Dexler et al. (2021) Regional Environmental Change: Carbon sequestration in hedgerow biomass and soil in the temperate climate zone – https://doi.org/10.1007/s10113-021-01798-8
  • EPA (2014) Carbon Sequestration by Hedgerows in the Irish Landscape Towards a National Hedgerow Biomass Inventory for the LULUCF Sector Using LiDAR Remote Sensing, EPA Climate Change Research Programme 2007–2013 – https://www.epa.ie/publications/research/climate-change/ccrp-32-for-webFINAL.pdf
  • Graham et al. (2018) The influence of hedgerow structural condition on wildlife habitat provision in farmed landscapes – https://doi.org/10.1016/j.biocon.2018.02.017
  • Holden et al. (2019) The role of hedgerows in soil functioning within agricultural landscapes – https://doi.org/10.1016/j.agee.2018.11.027
  • Teagasc (2022) – https://www.teagasc.ie/environment/biodiversity–countryside/farmland-habitats/value-of-hedgerows/
  • Teagasc (2022) – https://www.teagasc.ie/news–events/daily/environment/the-state-of-irelands-hedgerows.php
  • Van Den Berg et al. (2021) Agroforestry Systems: Soil carbon of hedgerows and ‘ghost’ hedgerows – https://doi.org/10.1007/s10457-021-00634-6