Dr Alexander Waller – Written evidence (NSD0005)


Hedging our bets or betting on hedges?


This is a synopsis of a paper delivered at the 21st Asian Bioethics Conference online 29 August 2021


There are a plethora of terms relating to and definitions of what constitutes Nature-based Solutions (NbS) but for this article it will used as defined by the IUCN being:


“actions to protect, sustainably manage, and restore natural or modified ecosystems, that address societal challenges effectively and adaptively, simultaneously providing human well-being and biodiversity benefits”.


According to the UNEP present challenges of climate change, biodiversity loss and human health are likely to be met at lower cost over the longer term by employing NbS rather than using conventional technical approaches. The UNEP is so committed to promoting NbS that it has produced free MOOCs that have already been successfully rolled out in over one hundred universities and to hundreds of thousands of learners worldwide. There are many examples of NbS that are advantageous for increased carbon capture such as:


One simple example of NbS for decarbonising our world whilst simultaneously securing habitats, reducing soil degradation, and limiting some needs for pesticide and fertilizer applications in addition to contributing to cooling urban heat islands is through conserving and establishing increasing lengths, volumes and diversity in our hedgerows in urban and rural settings. Considering all of the applications and benefits listed above, in the light of increasing global temperatures induced by anthropogenic activities, can we truly risk gambling on decarbonizing our future without employing NbS? If we don’t reduce greenhouse gas levels in the atmosphere the world will continue to suffer from the increasing effects of climate change. Employing the photosynthetic potential of hedgerow plants requires less investment than many highly technical solutions, has relatively straightforward management and monitoring requirements and yet pay out dividends in its capacity for storing carbon above and below ground. There is the added potential for harvesting some hedgerows for biofuels to be used in electricity generation or as feedstock in pyrolysis plants.


Hedging a bet?

A land sparing approach would tend to a series of safe oases or islands of security for nature, but as potential isolated between each other these would not be stable for an unlimited future. Adopting the land sharing approach by giving hedgerow development and management special legal conservation status would assist in preserving pathways between isolated patches or nature reserves.


Establishing and maintaining both rural and urban hedges is just one example of how NbS can be an affordable low tech approach that not only increases carbon capture through photosynthesis but simultaneously provides many other benefits both to human health and also nature as a whole. Although hedgerows are not an ecosystem as such they do provide vital habitats and support many ecosystem services. Hedgerows contribute to providing functions including promoting soil health and reducing water runoff, habitats and food for a diverse range of species including pollinators provision of field boundaries whilst acting as pathways or green corridors, food, material, shelter from wind that also reduces soil erosion and organic carbon storage. Both coppice managed and unmanaged hedgerows have significant potential for carbon sequestration. Hedgerow benefits are being promoted across the globe from research into reducing runoff in Kenya, nitrogen fixation through alley cropping in Jamaica to estimations of carbon sequestration rates in Indian contour hedging.


It must be kept in mind, if the main objective of planting hedgerows and other NbS is to promote carbon capture, that there are many other ecosystem services and functions that could be co-benefits. The significance of such benefits adds value which may assist in funding applications or overcoming prices. However the co-productivity of these functions must not be assumed, for example planting forestry monocultures for carbon capture will reduce biodiversity. Likewise the degree to which co-benefits are achieved must be determined. As Nemitz et al. (2020) say regarding the use of NbS to reduce urban pollution:


Even large-scale conversion of half of existing open urban greenspace to forest would lower urban PM2.5 by only another 1%, suggesting that the effect on air quality needs to be considered in the context of the wider benefits of urban tree planting, e.g. on physical and mental health.


It is this wider, holistic overview of synergistic benefits that must be considered when planning for and deciding whether to allocate funding to found NbS. Alvarado (2020) argues that:


Growing urban populations are facing numerous environmental, socioeconomic and public health challenges that significantly impact the liveability of cities. Lately, there has been growing acknowledgment of the role that nature-based solutions (NBS) can play in addressing these societal challenges while simultaneously providing a range of long-term benefits to human well-being and biodiversity. Yet the unceasing, large-scale loss of natural areas in cities implies that local authorities are failing to consider the benefits of NBS, and thus incorporate their value, into urban spatial planning decisions.


The Convention on Biological Diversity (CBD) guidelines for EbA list 10 principles, one of which is to maximise synergies in achieving multiple benefits, including for biodiversity, conservation, sustainable development, gender equality, health, adaptation, and risk reduction, UNDRR (2021). This synergy is neatly illustrated in diagram of nested circles for the SDGs with goals related to wellbeing at the centre but all goals being subsets of those directly related to nature. That is to say goals 13, 14 and 15, which are targeted at addressing climate change, and conservation of terrestrial and marine ecosystems respectively.


Health Benefits

Many writers connect mental health and wellbeing with immersion in nature although it may not be so clear in exactly what way nature improves a sense psychological wellbeing, there is stronger evidence to show that higher levels of mental health have associated physical and public health benefits In urban places both green and blue spaces provide areas for physical activity, stress relief, and social interaction. Shading and evapotranspiration by plants provide cooling that reduces the impact of the urban heat islands during hotter seasons. There is also some evidence that vegetation may improve air quality by removing air pollutants. All these functions contribute to public health and wellbeing. This wellbeing is not just a matter of pleasure or feeling good, but also good functioning through resilience and positivity.


Conversely, reductions in the amount of greenspace in cities have been shown to have negative health consequences. For example, very high temperatures in cities during increasingly extreme and frequent heat waves aggravated by urban heat island effects are likely to result in heat-stress-related health problems, including heat stroke, dehydration and heat exhaustion; some of which impact mortality and morbidity rates. There are also psychological and behavioural health issues linked with heat stress such as aggression, criminal behaviour, suicides, mood disorders and dementia. So greening of urban spaces through rooftops schemes and hedging initiatives could all have additional benefits to carbon capture.


Ecological Benefits

Carbon sequestration in hedgerows has comparable potential to that of forests according to a meta-analysis study by Drexler et al. (2021), who found variable capacity for average increases soil organic carbon after the establishment of hedgerows on cropland and a hedgerow biomass carbon stock of 92 ±40 Mg C ha1. According to Jones et al. (2019) existing UK urban woodland removes 0.7 kt PM2.5 yr1, reducing the health burden from PM2.5 by about 1900 life years lost/year. How much more potential reduction in costs could be achieved by increasing the amount of urban green space. Both some urban and rural hedges could be managed through coppicing and the harvest used as directly as biofuel or feedstock for secondary fuels. This, working in conjunction with e-Fuel[1] use, would assist in the transition from fossil fuels in some hard to decarbonise industries such as electricity generation.


Furthermore hedgerows contribute to many ecosystem services and other functions such as:


Managing hedgerows for NbS

It is not beyond our reach to green cities with more hedgerows; already some cities such as Toronto, Basel and Portland, Oregon have compulsory regulations to include green roofing in new urban developments. NbS has the potential to reduce social-ecological vulnerability. This involves decreasing ecosystem sensitivity by increasing adaptive capacity which is determined by the diversity and connectedness within the system. Monitoring, reporting and verification systems for carbon sequestrations in soils and hedgerows in developing countries must use be affordable and use accessible technology. Sampling for this can be carried out by non-specialists. Summarising research involving citizen science contributors that compared urban and rural hedges in the UK Gosling et al (2016) said;


Utilising the manpower of the general public enables scientists some additional capacity to study hedge habitats. Furthermore, educating the public about hedges and the plants and animals that use them can help to protect their future. Encouraging people to develop a passion for the natural world and recording, monitoring and protecting it is perhaps one of the best future-proofing techniques against further habitat loss that scientists can provide.


Some interesting developments in this area include the use of new technologies such as Black et al (2014) who demonstrated the possibility of developing a cost-effective and efficient national hedgerow carbon inventory for Ireland using Light Detection And Ranging (LiDAR) remote sensing and terrestrial laser scanning (TLS) technologies. Katie Jane Parsons and Josh Wolstenholme (2021), both of the University of Hull propose developing a project that “has been engaging with youth organisations to enhance their environmental and digital knowledge, whilst combining their input with state-of-the-art artificial-intelligence approaches.


When establishing new hedgerows with the aim of gaining maximum co-benefits of supporting a diversity of birds and other species it is important to consider which endemic species will thrive best in local conditions. Many governments have agricultural or rural information offices to help advise land owners with lists of species such as that provided by Pirie (2020) for the Scottish Farm Advisory Service. There is also a government funding scheme, which is followed up with inspections to ensure that new hedgerows meet minimum width and planting densities along with, apart from the exception of beech hedges, they must include a diversity of at least three endemic species such as hawthorn, blackthorn, dog rose, holly or elder. This incentive was available for a few years, but to really make any traction with NbS to assist in decarbonisation then governments and other funding bodies must show commitment for the long term.


24 August 2021

[1] E-Fuels are produced using electrolysis of water, using electricity from renewable sources, and the resulting hydrogen can be combined with carbon monoxide, derived from atmospheric carbon dioxide, via Fischer-Tropsch synthesis reactions. These e-Fuels such as methanol can supplelement or be substituted for traditional fuels.