Written evidence submitted by Dr Jill Edmondson, Dr Karl Evans, Dr Holly Croft,
Dr Stuart Campbell and Prof. Jonathan Leake (UGS0044)
Inquiry into Urban Green Spaces
Written evidence submitted to the Environment, Food and Rural Affairs committee by Dr Jill Edmondson, Dr Karl Evans, Dr Holly Croft, Dr Stuart Campbell and Prof. Jonathan Leake
Dr Jill Edmondson, Dr Karl Evans, Dr Holly Croft, Dr Stuart Campbell and Prof. Jonathan Leake are based in the School of Biosciences at the University of Sheffield. Our submission provides research-based evidence, co-designed with urban green space stakeholders, showing the importance of urban green spaces in the delivery of ecosystem services. Crucially, it highlights the importance of providing high quality green spaces in order to optimise the benefits provided to UK urban communities, and reduce the impact of urban areas on the wider environment. The research presented herein was supported by UKRI funding from EPSRC, NERC and BBSRC.
Executive summary
Urban green spaces are interwoven throughout the built-up fabric of cities and towns, providing essential ecosystem service benefits to city dwellers. However, they are highly heterogeneous, varying in size, quality and composition. They range from large urban parks and woodlands down to small patches of roadside verge or individual street trees. The quality, size and connectedness of these green spaces will affect their ability to deliver their benefits to people that city dwellers rely on. It is therefore crucial to consider the quality of urban green spaces not just the overall amount. For example, urban street trees or hedges provide the crucial ecosystem service of mitigating urban air pollution by removing particulates from the atmosphere, preventing respiratory harm, but they must be co-located alongside busy roads where particulate pollution is high and provide a continuous connected network along that road in order to provide that benefit. In terms of quality, mown amenity grassland may provide an important resource for certain types of recreation, which was particularly important during the covid 19 pandemic, but it is relatively poor in terms of its an ability to support other key environmental benefits, e.g. biodiversity across a wide range of taxa, urban heat island mitigation, and human well-being benefits. With more than 80% of the UK population living in cities and towns, the perception by urban inhabitants of the quality of urban green space is also crucial.
1. How successfully are the Government and Local Authorities protecting and increasing urban green spaces, and what trends can be seen in the extent and quality of those spaces?
Our research has shown that green spaces in UK cities typically cover about 50% of the urban area (Edmondson et al, 2014 a; Edmondson et al 2020 a), with greenspace cover increasing as urban intensity decreases. Approximately half the urban green space, by area, in UK towns and cities is located in private gardens (Edmondson et al, 2014 a). These, especially front gardens, are declining in quality (trends towards simpler vegetation structure) and extent (conversion to hard surfaces for alternative land-uses). There is starting to be some discussion of the potential for local authorities to provide incentives to slow or reverse these trends through council tax reductions (Cameron, 2023).
Another key trend is the decline in the provision of allotment green space, designated specifically for urban horticultural production, we found that since peak provision in the mid-twentieth century allotment land had declined by >60% with the greatest loss occurring in more deprived urban areas (Dobson et al, 2020 a). Although nearly half of this land is now built infrastructure, 25% remains as greenspace (Dobson et al, 2020 a). Our research, and that of others, has demonstrated that in terms of quality allotment land is really important, providing a habitat for biodiversity, supporting sustainable soils, providing food, and mitigated extremes of the urban environment (see section 2.5 for detail). Here, we should seek to understand the quality of the resource that remains as green space and where possible provide support to ensure that these green spaces are managed to optimise ecosystem service provision, including provision of space to grow food, targeting green spaces in deprived communities.
2. What environmental challenges are urban areas facing, and how could wider access and inclusion to green spaces (including dog-friendly spaces) address these challenges? Areas to consider but not limited to:
Key recommendations:
For individual recommendations related to each area of interest please see below.
Urban green spaces can provide key ecosystem service benefits that can mitigate some of the pressures that are created by the trend of increased urbanisation. In the UK more than 80% of the population live in cities and towns, relying on the benefits provided by the green spaces interwoven across the urban landscape. The list of potential areas of interest listed by the enquiry might benefit from wider access to, and inclusion of green spaces, but a key challenge not detailed in the enquiry is the differing ability of different forms of green spaces, or vegetation land cover (e.g. amenity grassland or trees) to deliver these services. Below, we provide evidence of the role of different forms of green spaces in supporting delivery of these different areas of interest
2.1 Increased temperatures and the ‘urban heat island’ effect
The urban heat island effect and high temperatures within the urban environment are a growing threat in the UK. For example, at present it is estimated that extreme heat is responsible for 2,500 deaths annually (PHE, 2020), with the majority of these deaths occurring in urban areas, but, with climate change it is likely that the frequency and severity of extreme heat events are likely to increase. There is a global body of research demonstrating the ability of green spaces to mitigate the urban heat island effect, but, our research has demonstrated that even within urban green spaces the urban heat island effect is still detectable, with soil surface temperatures in green spaces 1.4-1.5oC higher in the city centre of the study city (Leicester) compared to the suburbs (Edmondson et al, 2016). However, our research also demonstrated that soil surface temperatures beneath amenity grasslands were 3oC higher than beneath trees and shrubs on average during the summer months. Recent research has also found that trees located in parks, gardens and on streets within Sheffield are inequitably distributed across the city, which has profound effects on land surface temperatures across the urban area. An integrated set of solutions that includes nature based solutions is essential for effective mitigation of urban heat islands (Lin et al, 2021).
Whilst our research, and that of others, has demonstrated the key role of trees in urban areas for urban heat island mitigation, it is also important at a smaller scale to consider that tree species, size and structure will all affect the cooling provided. Our ongoing research at the University of Sheffield Urban Tree Observatory, using a network of trees instrumented with sensors that monitor water movement and tree structure every 15 minutes across Sheffield, is monitoring the cooling potential of different tree species at different locations across the city. This research has been co-designed with Sheffield City Council to build an evidence base to support decision making in future tree planting strategies (Edmondson et al, in review).
Recommendation: Urban green spaces can provide crucial urban cooling, but, to maximise the benefit provided by urban green spaces policy should focus on the expansion of tree and woody vegetation cover, focussing on equity of provision across the urban area for all communities.
2.2 Flooding risks and water quality in urban watercourses
The high proportion of grey space and built infrastructure in cities and towns means they are extremely vulnerable to flooding, and this problem will be exacerbated by the increased frequency of extreme rainfall events that come with climate change. Green spaces, and engineered green infrastructure such as sustainable drainage systems and green roofs and walls, can slow the flow and soak up rainwater, decreasing runoff onto grey infrastructure such as roads, and reducing the likelihood of flooding and the pressure on urban sewage systems.
Sustainable drainage systems (SuDS) are designed specifically to reduce flood risk and are becoming an important feature of cities and towns, particularly in urban centres where urban green spaces are limited in extent. They present a key opportunity to retrofit functional green spaces into grey deserts in city centres that can also, if well designed, support other key environmental and socio-cultural benefits to urban dwellers. For example, the Grey to Green scheme is a 1.6 km long SuDs in Sheffield city centre on the site of a former four lane road. This award winning scheme was designed to provide multiple benefits, for example, incorporating large trees to provide urban cooling and promote biodiversity.
In contrast to the engineered SuDS that have soils specifically designed to support flood mitigation, the prevailing assumption has been that soils in urban green spaces are of poor quality and unable to support many of the key functions we rely on them for in rural ecosystems. However, our research and that of others has overturned these assumptions and demonstrated that in general urban soils are of good quality (Edmondson et al 2011, Edmondson et al 2014 a, Edmondson et al, 2016, Dobson et al 2021 a). For example, it is often assumed that urban soils are compacted, this would limit their ability to mitigate flooding as they would have reduced capacity to soak up rainwater. Our research, using soil bulk density as an indicator of compaction, demonstrated that urban soils are significantly less compacted than agricultural soils and had similar bulk densities to equivalent semi-natural ecosystems in the rural environment (Edmondson et al 2011). In addition, we found that soils beneath urban trees and woody vegetation were significantly less compacted than those beneath urban amenity grasslands (Edmondson et al 2011).
Recommendations: Schemes should be developed to support the retrofit of multifunctional SuDS into urban centres for flood mitigation but also to support regeneration of dense areas of built infrastructure.
In urban green spaces attention should be focussed on the development of high quality green space, preserving urban soil quality and increase tree cover.
2.3 Carbon storage
Our research has demonstrated that urban greenspaces hold considerable stocks of carbon that are often significantly greater on a per unit area basis than the agricultural areas surrounding most UK cities (Davies et al, 2011, Edmondson et al 2012, Edmondson et al 2014a, Edmondson et al 2014b, Edmondson et al, 2016, Dobson et al 2021). We found that 82% of this carbon is stored below-ground in urban soils (Edmondson et al 2012), but as with heat and flood mitigation, the vegetation in urban greenspaces is important in driving both storage in plants and in soils. For example, we found that garden soils beneath trees and shrubs held significantly more carbon than found beneath amenity grasslands and even trees within public greenspaces (Edmondson et al 2014 a).
Within public land, we also found important species specific effects of urban trees, with common ash and trees from the maple genus (e.g. sycamore), storing more carbon below ground than oak trees and patches of mixed urban woodland (Edmondson et al, 2014 b). However, the major effect of trees on urban carbon storage is in their biomass, we found that >97% of carbon stored in urban vegetation is in trees, with the majority held in large mature trees (Davies et al, 2011). As a consequence, vegetation in gardens, which typically contain smaller trees, contributed just 4% of total garden carbon storage, whereas in non-domestic greenspaces vegetation contributed 23% to the total stock (Edmondson et al, 2012).
Understanding the stocks of carbon in urban green space is important, as signatories to the Kyoto Protocol we are required to keep accurate accounts of carbon stored in terrestrial ecosystems to enable monitoring of changes to carbon stocks associated with land-use change. At present the UK does not accurately account for carbon stored in urban areas, assuming that cities and towns store little or no carbon, however our research demonstrates that far from being carbon deserts, urban areas hold nationally important stocks of carbon that need accounting for in order to protect this resource and further enhance carbon storage in cities and towns (Edmondson et al, 2015).
Recommendations: The UK should account for urban carbon in national inventories so that this important resource can be protected.
To enhance urban carbon storage policy should focus on increased tree cover within urban greenspaces.
2.4 Pressures on biodiversity and ecosystems in urban centres
Many species decline in local population densities as housing densities, or other measures of urbanisation ‘intensity’ increase (Tratalos et al, 2007). Even species that are generally regarded as able to cope with urbanisation, such as the blackbird (Turdus merula) exhibit these patterns. One key factor contributing to this is reduced breeding success, with experimental data demonstrating that urban areas need to contain at least 2.5 times more caterpillars than currently for great tits (Parus major) to have similar breeding success in urban areas as forests (Seres et al, 2020). This requires increasing the quality of urban green space, for example converting mown amenity grassland to more complex vegetation structures and increasing the abundance of native vegetation which supports greater numbers of herbivorous insects that form a core part of avian diets during the breeding season (Narango et al, 2018).
Green space quality and urban intensity is also important for invertebrates. For example, we recorded a negative effect of urban intensity on the range of plant species visited by two key pollinator communities, bees and moths, in urban allotments (Ellis et al, 2023). In an experimental study in urban allotments across Leeds we found that tomato pollination increased with urban density (Ellis et al., in review), suggesting that invertebrates are concentrated into allotments as they are high quality greenspaces with high floral resource and greater vegetation structural complexity.
Recommendation: To reduce the negative effects of urban intensity on biodiversity management of the existing greenspace resource and creation of new green spaces should focus on quality of provision, including introducing structural complexity and a diverse range of plant species within dense urban areas.
2.5 Local food security
Urban horticulture, the production of fruits and vegetables within cities and towns, has historically been an important contributor to local food security, for example, in the Dig for Victory Campaign during World War Two people grew approximately 18% of the UKs fruit and vegetables in green spaces (Defra 2015). We recently presented written and oral evidence at the Environmental Audit Committee enquiry into Environmental Change and Food Security and oral evidence at the House of Lords Horticulture Select Committee enquiry into the future of the Horticultural Sector on the potential of urban horticulture to contribute to food security and provide wider environmental and socio-cultural benefits. In brief, our research has demonstrated that food production in urban allotments, green spaces designated specifically for food production, currently grow enough fruits and vegetables to feed 3% of the population of Leicester and Sheffield (Edmondson et al 2020 a and b). We found that if the area of land used for urban horticulture was increased by 10% it could provide enough fruit and vegetables to feed 15% of the urban population on their five a day recommended diet (Edmondson et al, 2020 b).
But urban horticultural greenspaces should be valued for more than just food production; our research has demonstrated that urban horticulture provides health and wellbeing benefits, supports community cohesion (Dobson et al 2020 b), they eat 70% more and waste 95% less fruit and vegetables than the national average (Gulyas and Edmondson, 2023). In addition, we found that urban growers manage their greenspaces sustainably (Dobson et al 2021 b) and are consequently are able to maintain soil quality, and similar to other urban green spaces store considerable carbon stocks, without the degradation associated with conventional horticulture (Dobson et al 2021 a). At a time when there is increased interest in urban horticulture, evidence by the growing waiting lists for allotment plots in the UK, future plans for green spaces should include land designated specifically for fruit and vegetable production.
Recommendation: National government and local authorities should support the expansion of land available for urban horticulture as this could make an important contribution to local food security, improved diets, the health and wellbeing of the urban population and the sustainability of the supply of fruit and vegetable crops.
2.6 Climate change impacts on urban green spaces
Whilst we have demonstrated that urban green spaces provide crucial environmental and socio-cultural benefits, which could potentially be enhanced by expansion of urban green spaces or changes in green space management, for example by increasing tree cover, there are important questions about how green spaces will themselves respond to the changing climate. Urban green spaces already experience a range of pressures created by the urban environment, in the same way that we do, for example extreme weather events, or air pollution could affect the ability of green spaces to deliver the environmental and socio-cultural benefits that we rely on. These pressures are likely to interact with and be exacerbated by the extremes of climate change. Understanding how to manage green spaces now to be resilient to future climate change is crucial to ensure they are sustainable and resilient in the future. This should be a research priority in the UK. For example, in the Urban Tree Observatory at the University of Sheffield, we are exploring which tree species are likely to be vulnerable to the changing climate and which species are likely to thrive, continuing to support delivery of environmental benefits (Edmondson et al, in review).
Recommendation: The government should prioritise research that focusses on understanding how to develop resilient urban green spaces able to maintain or increase delivery of ecosystem services in a changing climate.
3. To what extent will Government initiatives such as the Green Infrastructure Framework, the levelling up parks fund and urban tree challenge fund adequately address the issues associated with a lack of green space in towns and cities?
In combination the Green Infrastructure Framework, the Urban Tree Challenge Fund and the Levelling Up Parks Fund provide a good pathway for improving access too and the quality of urban green spaces. As highlighted above, quality of green space is crucial for delivery of all ecosystem services and a key component of this is the provision of urban trees across the landscape. However, in many areas local authorities are running out of space to plant more trees, and opportunities must be explored to increase tree cover in privately managed urban areas and to provide investment to retrofit trees into dense urban centres which can often be costly.
Recommendation: The government should incentivise the provision quality greenspaces in private land to improve provision of ecosystem services across the urban landscape.
4. Will the Government achieve its aims to increase the amount of green cover to 40% in urban residential areas? What other additional measures should the Government take to increase green urban space?
Our research has shown that green spaces in UK cities typically cover about 50% of the urban area (Edmondson et al, 2014 a; Edmondson et al 2020 a), with greenspace cover increasing as urban intensity decreases. Approximately half the urban green space, by area, in UK towns and cities is located in private gardens (Edmondson et al, 2014 a). These, especially front gardens, are declining in quality (trends towards simpler vegetation structure) and extent (conversion to hard surfaces for alternative land-uses). There is starting to be some discussion of the potential for local authorities to provide incentives to slow or reverse these trends through council tax reductions (Cameron, 2023).
Preventing loss of, or increasing cover of green spaces is not just a physical challenge – finding the space to expand the green resource – it must also focus on the challenge of engaging local communities in areas where green resources are proposed. All individuals, communities, private sector, third sector organisations and public bodies who interact with the urban green spaces are its stakeholders. Thus, management by, or for, any stakeholder is challenging when there are competing goals and drivers. For example, integrating trees into an unvegetated street by a local authority may help to meet objectives set by national governments but the local residents may view the trees as an obstruction to parking. Consultation with local stakeholders is the only way to ensure successful integration new green spaces or changes to the structure of existing green spaces in the urban landscape.
Recommendations: National and local government should incentivise schemes to prevent loss of garden green space and encourage creation of green space on private land in UK cities.
Changes to green space management or increase in green space cover must be taken in consultation with local stakeholders to ensure success and acceptance.
References
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