Ecosystem services delivery by urban hedges

RHS project team

Tijana Blanusa

Partners

University of Reading

Start date

01/10/2015 00:00:00

End date

01/01/2021 21:00:00

The problem

Hedges are a relatively simple and cheap natural barrier capable of providing a spectrum of benefits. They capture air pollutants, reduce risks of localised flooding (through intercepting rainfall), cool the proximate air, support wildlife and much more. 

Despite all these benefits they’re increasingly being removed or omitted from gardens, as homeowners prioritise space for car parking.

Where hedges do still exist, species choice and plant management can significantly affect the extent of benefits they provide so, it’s important to understand the benefits offered by different species and how to care for the plant to get the most impact.

Approach

Through experiments in the glasshouse and field research facilities at University of Reading - as well as several other locations nearby - we are recording the ecosystem services provided by a range of popular hedge species. 


The ecosystem services we’re looking out for include: 

• delaying rainfall and runoff volumes, 
• capturing pollution particles 
• cooling localised air.

We are testing both deciduous and evergreen species:

• Ligustrum ovalifolium cv ‘Argenteum’ (privet)
• Ligustrum ovalifolium cv ‘Aureum’ (privet)
• Cotoneaster franchetii
• Photinia fraseri ‘Red Robin’
• Taxus baccata (yew)
• Thuja plicata (Western red cedar)
• Crataegus monogyna (hawthorn)
• Fagus sylvatica (beech)

We are measuring parameters such as:

• plant water use,
• leaf stomatal conductance and net photosynthetic activity (as an indicator of a plant’s physiological activity), 
• leaf and ambient temperatures,
• leaf areas,
• canopy size,
• number, size and weight of particles deposited on leaf surfaces 

We are carrying out well-replicated experiments with:

• individual plants in containers, 
• model hedges in large troughs
• hedges in situ.

Benefits to gardeners

We will be able to identify which plant traits can be linked with the provision of environmental benefits. This will enable RHS scientists and advisors to provide advice to members, and green space planners and managers, on the best planting options to achieve maximum environmental gains.

Summary of results

Our findings (Blanusa and Haldey, 2019) suggest that – after three days between rainfall events - species such as Cotoneaster and Crataegus with larger and wide canopies, and with high evapo-transpiration / water use rates, delayed the start of rainfall runoff (by as much to 10-15 minutes compared to bare substrate) as well reduced the volume of rainfall runoff. For example, <5% of the applied rainfall had runoff with Cotoneaster and Crataegus, compared with >40% in bare substrate.

Our extensive review of literature (Blanusa et al., 2019) also revealed that a number of common hedge species can demonstrate high levels of ecosystem services delivery, including Fagus sylvatica, Crataegus monogyna, Ilex aquifolium and Rosa rugosa. No species surveyed had an entirely negative association with ecosystem services, and most provide at least some benefits (e.g. Viburnum tinus, Laurus nobilis).

Further information

Read our summary guide on choosing hedges that provide environmental benefits in urban settings

References

Blanusa, T., Hadley, J., Hunt, L., Alexander, P. and Hobbs, K. (2017) Provision of ecosystem services by hedges in urban domestic gardens: focus on rainfall mitigation. Acta Horticulturae, 1189. pp. 519-523. ISSN 2406-6168 doi:

Blanusa T, Garratt M, Cathcart-James M, Hunt L, Cameron RWF (2019) Urban hedges: A review of plant species and cultivars for ecosystem service delivery in north-west Europe. Urban Forestry & Urban Greening: in press. doi:https://doi.org/10.1016/j.ufug.2019.126391 –https://www.sciencedirect.com/science/article/pii/S1618866718306848

Blanusa T, Hadley JG (2019) Impact of plant choice on rainfall runoff delay and reduction by hedge species. Landscape and Ecological Engineering: in press