Balance™ methodology – converting carbon finance to biodiversity creation

ABSTRACT

This paper addresses two interlinked problems in sustainable development and suggests a methodology to resolve them. The first is the reduction of atmospheric greenhouse gas emissions, especially carbon dioxide. The second is the maintenance of biodiversity. Current carbon financing and environmental stewardship mechanisms underwhelm, often diluting intended positive effects. Most existing carbon credits do not have protection after 40 years, placing projects substantially beneath the C02 radiative forcing cycle. This paper presents the ‘Balance’ approach to sustainable development, including contractual principles ensuring C02 reduction, biodiversity enhancement and financial accountability. We describe two novel measures: a carbon calculator for commercial entities, and a new metric, the Balance Unit, combining biodiversity creation with carbon credits. A case study, spanning over 20 years at the Forest of Marston Vale, is then presented. It finds an increase in tree cover, CO2 sequestration, reduction in agricultural GHG emissions, sulphur dioxide and particulate matter absorption, and annual local economic benefits totalling £UK12.83 million. Expository detail regarding the ‘Planting Principles’ practised at Marston Vale is also provided. We argue that the Balance methodology, especially the Balance Unit, enables greater measurement reliability and long-term efficacy for maintaining biodiversity and reducing GHG emissions than current carbon financing approaches.

KEYWORDS:

• Sustainability
• biodiversity
• carbon
• forestry
• environment
• balance

1. Introduction

1.1. Reforestation

1.1.1. Ecological considerations for planting locations

Reforestation planting areas, comprising afforestation or reforestation efforts aimed at carbon offsetting, account for 7 percent, which is equivalent to 264 million hectares, of the global forest cover. The area of such reforestation is expanding quickly as plantations become increasingly relied upon for wood-based products, carbon management, soil and water conservation, and the rehabilitation and diversification of impoverished landscapes (Ghazoul, Bugalho, and Keenan 2019). This has collectively led to a significant anthropogenic influence on the composition of forests (Barsoum et al. 2016, 4, FAO 2010; Pawson et al. 2013). It is also important to note that afforestation might not be a viable long-term adaptation solution in some regions. Tree planting can be especially problematic in native non-forest ecosystems (Veldman et al. 2015), that are often overlooked by restoration and conservation policies. Balance therefore does not encourage planting trees in non-forest ecosystems.

In some areas, scientific research increasingly suggests that allowing forest regeneration to occur naturally can deliver a wider range of climate change adaptation services with fewer trade-offs than plantations. Several of these ‘rewilding’ projects have led to the return of open woody habitats once grazing pressure from domestic livestock is reduced, creating some notable successes in restoring rare wildlife (Tree 2018). Naturally-established forests can also be more cost and resource efficient because they rely on less costly and labour-intensive human interventions. They can also accumulate carbon rapidly once sufficient trees have colonised a site and tend to be more biodiverse than plantations (Cook-Patton et al. 2020).

Forestry plantations have often come at the expense of naturally occurring ecosystems, such as natural grasslands and peatlands (Veldman et al. 2015), which may be more resilient to climate change impacts and may lack diversity entirely. In the Balance process, it is important to define whether a target area was historically covered by forests, as this can be a key indicator of the suitability of the land for reforestation. Planted areas, generally, are beneficial where natural biodiversity is low, and where the land is suitable for forest regrowth, particularly on lands which were previously forested, as non-forested lands like grasslands or wetlands already contribute to carbon capture, so should be avoided (Tan et al. 2020). Selecting an area that is already in use for agriculture could result in further deforestation elsewhere, resulting in carbon leakage and potential loss to biodiversity. Finally, the number of trees planted in a given plantation area should be as close to the maximum as possible.

Forestry of all types has employed mixed and native species in line with national commitments to forest and landscape restoration, yet there are still many projects which fall short in terms of biodiversity, resilience and ecosystem services provision (Chausson et al. 2020). The Balance methodology presented in this paper integrates the lessons learned from past carbon offsetting, using current evidence of the most effective and sustainable carbon offset projects through the lens of NbS (Gómez Martín et al. 2020; Seddon et al. 2020). Each of the outlined points are included within the first motion of the five-point Planting Partner Contract. Balance stresses the necessity to consider the exact types of trees for the location and geographical context of the project, and the importance of planting indigenous species while considering forest composition, while allowing the inclusion of exotic species for certain benefits, though in the right context and quantity to minimise negative ecological consequences. It is important to note that while these principles are relevant to current and future afforestation strategies, they are particularly relevant to carbon offset reforestation initiatives.

1.1.2. Selecting native species

Balance specifies, as an obligation, that native species should be the first consideration in any tree planting project. A few key species of local provenance are picked to enhance local biodiversity development and ecosystem services, while space for exotic species should not be discarded at the outset. In Europe, according to Barsoum et al. (2016), 29 percent of forests are composed of a single tree species, and many of these are plantations composed of a single non-native species, with serious implications for biodiversity. It is important to note that, given the current warming scenario, the selection of ‘indigenous’ species may be reconsidered with a view to the future, so that species derived from warmer conditions, but as close to the location of the project as possible (from where the species would be migrating), are included.

1.1.3. Soil and topography

Large-scale reforestation initiatives increasingly utilise multidisciplinary studies such as remote sensing and mapping of soils, topography, tree and forest cover, as well as other biophysical variables, to prioritise and choose species for specific planting locations, and to decide whether tree-planting is the correct solution for local conditions.

The characteristics of soils, including their fertility, texture, colour, depth, acidity, and water retention capacity, exhibit significant variation. Different soil types develop unique horizons (or layers), resulting in a distinctive soil profile. In contrast to agricultural soils, which are frequently disturbed by ploughing, forest soils are typically undisturbed, allowing them to retain their natural profiles. Soil horizons exhibit variation in properties such as ‘colour, quantity of organic matter (i.e. dead flora and fauna), size and proportions of soil particles, acidity, and nutrient availability for plant growth’ (Greenbelt Consulting N.A., Bender and van der Heijden 2015). Amongst the six basic soil types (clay, sandy, silty, loamy, chalky and peaty), each are favoured by a number of common tree species. Many species are capable of growing with a variety of variable soil types.

Soil is also a significant carbon sink (Broadmeadow and Matthews 2003). While this is not yet specifically accounted for in our calculation methodology, the selection and growth of diverse species is certainly beneficial to carbon sequestration in soils, thus elevating the potential benefits of planting based upon soil types, and further promoting the benefits of biodiversity-based planting (Seddon et al. 2016). The provision of semi-permanent land cover, for example, creates physical shelter to minimise soil disturbance and thus reduces erosion. It also aids in the reduction of soil contamination by avoiding the high inputs of fertilisers and pesticides associated with many forms of agriculture, and restores organic content to soils through organic decomposition and heightened presence of biotic matter. Similarly, woodlands indirectly aid in reducing the incidence of landslides through the shelter of soils and the reduction of grazing pressures. As Philip Lymbery reminds us:

‘Soil fertility could be turbo-boosted by that rotational symphony of plants and animals working in harmony with underground ecosystems. Huge amounts of carbon could be locked up in the ground.’ (Lymbery 2022)

1.1.4. Forest composition and ecosystem services

The ability of forests to deliver ecosystem services and the various co-benefits depends on biodiversity and necessary focus on the ecosystem as a whole, not just the trees. In fact, trees represent less than a third of the plant species across a range of forest types (Spicer, Mellor, and Carson 2020). Forests host a diverse range of plants, animals, fungi and microbes that form symbiotic relationships that are critical to forest recovery (Alvarez et al. 2019). The explicit consideration of the natural composition of locally-situated ancient forests is therefore particularly useful, taking into account stand diversity and composition, as well as understorey vegetation such as shrubs and herbs (Behera et al. 2017; Lewis et al. 2019; Luyssaert et al. 2008; Sullivan, Sullivan, and Lindgren 2001; The Woodland Trust 2018).

Current forestry policy advocates a diversification of forest stands to achieve both more productivity and sustainability, favouring mixed age structures and polycultures over single-aged monocultures. Canopy phenology, defined as the timing of recurring the biological regrowth of the canopy, relies on biotic and abiotic forces and the interrelation among phases of the same or different species (Dieler et al. 2017). It is also important to widen forest species diversity due to the diversification of traits between species (Barsoum et al. 2016, Osuri et al. 2020).

The creation of forests with ‘contrasting’ traits can ‘neutralise’ the influence of specific tree identities on the composition of understorey vegetation, which allows for the proliferation of ground plant species that are often suppressed or excluded in a monoculture plantation due to the presence of a limited number of species identity influences (Liang et al. 2016). Monoculture stands generally have poor nutrient retention. Mixed stands thus reduce the abundance of species that would otherwise tend to dominate and limit the growth of ground vegetation communities in a monoculture.

Understorey vegetation impacts nutrient cycling and disturbance mediation; it also plays an important role in the provisioning of habitat and foraging material (e.g. pollen, nectar, foliage) for many species. Ground vegetation, in turn, is strongly influenced by the composition and structure of the overstorey, responding to differences in temperatures and the availability of light, water and soil nutrients at the forest floor level.

Also important are forest management cycles which allow healthy growth of selected species, whereby trees are planted, allowed to grow, then certain trees are ‘thinned’ (a proportion cut and harvested), allowing space for the remaining trees to grow larger and more effectively and for new growth to be accelerated through cyclical procedure. This process takes decades, which makes effective and thorough planning of the management cycles for biodiversity development and native species essential.

The creation of woodlands also plays a role in natural flood management, particularly with reforestation of hill slopes and gullies and the restoration of wetlands, floodplains and river channel meanders. Woodland can increase hydraulic ‘roughness’ by slowing down and reducing run-off as water storage is increased and drainage to streams is delayed, which can help to desynchronise multiple flood peaks within a catchment and decrease the overall geographic scale, depth and frequency of floods (Scottish Forestry 2019).

1.2. Resilience and longevity

1.2.1. Resilience

Resilience is the capability of a forest to withstand external pressures and, in time, to recover from disturbances, which may involve returning to its pre-disturbance state so as to retain the same function, structure, identity and feedbacks (Cavers and Cottrell 2015). It is the extent of perturbation that a system can experience before it undergoes a shift to an alternative state; in other words, a system’s ability to maintain elasticity and avoid reaching a state of malleability.

There are two types of nature-based solutions (NBS) carbon credits: avoidance and removal. The Balance methodology only focuses on removal credits. Avoidance credits, although extremely valuable in protecting longstanding forest with significant existing biodiversity benefits, need to prove that the forest will be felled if the carbon finances are not received. This may cause corruption issues, for instance, with organisations that may choose not to accurately or fully report their potential felling of forests, in order to receive carbon finance.

‘When viewed over an appropriate time span, a resilient forest ecosystem is able to maintain its “identity” in terms of taxonomic composition, structure, ecological functions, and process rates’ (Secretariat, CBD., 28). Based on current scientific evidence, it can be firmly asserted that forest resilience is significantly influenced by biodiversity at various levels, and that maintaining or restoring biodiversity in forests is pivotal to promoting their resilience to different types of external pressure. Biodiversity, crucially, should be considered at all scales, from ecosystem level to individual stands or trees, and in terms of all elements, whether that be genes, communities or species (Thompson et al. 2009; Brancalion and Holl 2020).

1.2.2. Adaptation to climate change

The high level of uncertainty regarding whether locations that are currently climatically suitable for forests will remain so in the future is a major concern. ‘Climate change may threaten woodlands by increasing the frequency of disturbance events that kill trees. Unlike other sectors, adaptive measures for forestry need to account for long time lags between tree establishment and maturity’ (Dunn et al. 2021, 28). The importance of biodiverse forests is paramount in the context of climate change and more extreme climate events. Regional impacts of events such as droughts, fires, and hurricanes might be sufficient to overcome the resilience of even some large areas of primary forests, pushing them into a permanently changed state. Balance therefore requires planting partners to display their consideration of the impacts of climate change upon forest locations, and the necessary alterations to the considered tree species for planting.

Knowing exactly how the climate will change in the near future is impossible, but projects should work under the assumption that we will continue to experience a warming scenario, and choose species accordingly (Hickling et al. 2006). The inclusion of species which are more resilient to higher temperatures, even if not native to the specific locale in which a project is located, seems worthwhile, as long as exotic species do not become dominant species. As local climate evolves, the types of forest species able to be planted should be under continuous review.

The Forestry Commission in the UK recommends including species and provenances with more southerly origins (DEFRA 2014). FC England, similarly, advises that at least one-third of the plant material should be local, but consideration should be given to including plants from southern areas of origin, especially from 2 to 5 latitudes further south (Cavers and Cottrell 2015, 22) than the project location, with the exception of Eastern European sources in the UK due to a lack of suitability. Although provenances from farther south may be well adapted to the warmer weather expected by climate change, they are not always well suited to other conditions at British locations. As a consequence, this may merely lead to the substitution of one sort of maladaptation risk for another (Cavers and Cottrell 2015, 22). It is necessary, then, to display to Balance that the project has carried out careful planning for any inclusion of exotic species and their potential risks even in cases where they might be potentially suited to climatic conditions in the near future. Please see Appendix B for additional local considerations regarding planting, including forest structure, accounting for diseases, and invasive species.

1.3. Biodiversity

1.3.1. Biodiversity and its impact on resilience

Species-rich ecosystems are typically more resilient because different species respond differently to stressors, thereby buffering the system as a whole (Dunn et al. 2021; Isbell et al. 2015; Jucker et al. 2014). The cultivation of native tree species in environments that meet their climatic and abiotic requirements fosters intra-species genetic diversity, thereby enhancing prospects for climate adaptation and bolstering resilience. Accordingly, future woodland creation initiatives geared towards conservation of biodiversity would do well to prioritise the inclusion of natural regeneration and locally sourced seed as fundamental components (Dunn et al. 2021; Ennos et al. 2019). Practices which select only certain types of trees for harvesting should be avoided in all cases.

Depending on whether ecosystem resilience or species resilience is being considered, stability may depend on either diversity of species throughout an ecosystem or intraspecific genetic diversity, respectively, and the processes governing their maintenance. Studies show that the level of genetic diversity within an individual species is important for delivering the potential for ‘evolutionary rescue’; that is, to adapt and change to different abiotic circumstances.

The mechanism of evolutionary rescue involves initial population decline followed by recovery as genotypes adapted to the new conditions prosper via natural selection. Trees, generally, maintain high levels of genetic diversity and are typically effective at gene dispersal, particularly in northern temperate forests. Many tree species are also capable of adapting genetically to local environments, although the degree and geographic scale over which they are distributed may vary depending on the heterogeneity of the landscape conditions. With the threats presented to forests now and in the future, individual tree species with optimised resilience through variants of genes or gene combinations, as well as particular forest compositions typically conferred by high biodiversity, will prove most resistant.

Generally, the larger and less fragmented a forest is, the better. Also, large tree species are important ‘drivers’ in an ecosystem, particularly in northern temperate forests such as the UK which are typically species-poor. The ideal circumstance is that intended large tree species are suitably resilient to potential threats. Thus, planning for optimal resilience of the primary tree species in any forest is essential. To do this, forest planting projects should plant with varying compositions based upon a variety of species, while prioritising one or two main tree species with intraspecific genetic diversity. The mode and scale of dispersal of species, as well as particular threats to certain species, must be accounted for.

1.3.2. Biodiversity for carbon sequestration

Many studies have explored the trade-offs of planning for biodiversity and carbon sequestration but have failed to provide any detailed guidelines on what to plant and how to manage these plantings, and many more studies which have found positive correlations in the past have been conducted in non-forest landscapes such as grasslands. Addressing this issue requires deciphering to what extent forest biodiversity and carbon sequestration influence each other. Few empirical or modelling studies address the trade-offs and synergies that can occur between biodiversity and carbon sequestration in forests, and even fewer have identified any potential mechanisms which facilitate that relationship.

Another stumbling block has been the heterogeneity and lack of regulation (as well as ambiguous categorisation) of carbon sequestration monitoring and quantification. This is because outcomes strongly depend on how the boundaries of the analysis are drawn and which aspects are incorporated, i.e. developments solely within the forest ecosystem itself, or inclusive of wood products and emission substitution effects (Biber et al. 2020). Clearer insights might be achieved if the multidimensional outcomes and factors of biodiversity are condensed and made uniform so that a single robust indicator is used, and the same is done with carbon sequestration.

Carbon is sequestered in forests through a mix of several ecosystem processes, of which photosynthesis is key, though respiration and decomposition subsequently play their part. Carbon can be stored as soil organic carbon (SOC), and as carbonates, the latter of which are created over thousands of years when carbon dioxide dissolves in water and percolates the soil, combining with calcium and magnesium minerals, forming ‘caliche’ in desert and arid soil. Temperature and moisture levels in the soil are the most important climatic factors that influence photosynthesis, decomposition, and respiration rates. For instance, high levels of SOC occur when photosynthesis outpaces decomposition in cold, wet northern latitudes (Habumuremyi 2019, 9; Ontl and Schulte 2012), while temperate ecosystems, the likes of which exist in the UK, are likely to have high productivity in the summer with high temperature and sufficient moisture levels.

Because soil organic matter (SOM) is composed of compounds that are highly enriched in carbon, high levels of SOM typically allow for increased sequestration of carbon (SOC) for several decades. SOM is made up of a heterogeneous mixture of materials that range in stage of decomposition and include soil microbes like bacteria and fungi, decaying material from once-living organisms like plant and animal tissues, faecal material, and products formed from their decomposition. SOC levels do not change in any way when carbon inputs and outputs in a forest are in equilibrium. SOC levels rise over time when photosynthesis adds more carbon than it takes out (Habumuremyi 2019, 8). This, of course, is achieved in planting projects, but can be optimised amongst those which directly benefit biodiversity.

One method by which soil can be optimised for carbon sequestration and health is through continuous improvement by a type of charcoal which we now know as ‘biochar’, a rich, black, fertile earth which can be made from all sorts of organic material including agricultural waste, tree trimmings, manure, and rice husks. It offers many agricultural benefits, improving fertility without the need for synthetic fertilisers, supporting healthy soil by providing a home for armies of microbes and mycorrhizal fungi, and increasing the soil’s ability to hold water, mitigating the effects of flooding and improving drought resistance (Crummett 2023). But biochar’s biggest benefit is enduring carbon sequestration, removing carbon from the atmosphere and holding it as an inert substance over the very long term (Li et al. 2016; Wang et al. 2023).

In all soil types, the benefits of biodiversity can work to ensure that SOM is more abundant and that this process occurs to store carbon at greater capacities and for longer periods. Similarly, with biodiversity enhancing the resilience of forests, carbon is stored for longer and the release of carbon into the atmosphere when the plants die is less frequent.

Primary native forests, particularly in the tropics, are most effective in storing carbon, as they hold the largest carbon pools of any forest habitats in the world (Busch et al. 2019; Houghton, Byers, and Nassikas 2015). However, a great variation exists in the carbon stock estimates for different types of forests, and can even vary widely among the same forest types.

More recently, synergies between species richness and diversity and carbon storage have been found among various forest types all over the world (Fraser et al. 2015). For example, Biber et al. (2020) argue that, though difficult to analyse, win-win situations for carbon sequestration and biodiversity and forest landscapes across Europe have been shown. Vayreda et al. (2012) found that species richness and structural richness variables are better predictors of C accumulation than climatic and local site variables in Western Mediterranean region. Poorter et al. found that diversity of species is strongly related to carbon storage at smaller scales, while structural attributes of forests are more related to carbon storage at larger scales, though are relevant at all scales. Liu et al. (2018) found that tree species richness enhances ecosystem-level C storage in the subtropical forests of China. Kothandaraman et al. (2020) used tropical forests in India as an example of forests rich in biodiversity proving hugely beneficial for carbon storage by estimating ecosystem-level carbon stock with data from 70 forest plots in three major forest types. Considerable quantities of carbon per hectare were found in the more biodiverse tropical evergreen forests, with an average of 336. Mg C/ha, of which just under a third of the carbon was stored in understorey, litter, deadwood and soil respectively (with the majority stored in trees). Among the forest types, the tropical evergreen forest type, the most biodiverse of the studied forest types, had the highest average carbon stocks when compared to semi-evergreen forests and dry deciduous forests.

Within the tropical evergreen forests, 14.5 percent of carbon was stored in the understorey, raising the overall carbon sequestration per unit area, while the average contribution of understorey over every other forest type is only 2.2 percent. Pichancourt et al. (2014) found that the type of forest, the landscape context and climate are all significant. Therefore, since there is no ‘one size fits all’ solution, the best management solutions must include complex planning.

In addition to their role in enhancing biodiversity, larger trees should also be prioritised for their carbon sequestering capabilities. Lutz et al. (2018) reported that large-sized trees account for nearly 41 percent of carbon storage in forests on a global level. Tree species richness is widely known to increase tree size inequality among and within species, creating varied and diverse structures with a larger number of large trees, thus enhancing overall carbon stocks in a forest. Tree species evenness, monoculture planting or excessive logging for timber, on the other hand, is known to have a negative effect on average large tree size, structural diversity and overall carbon storage (Kothandaraman et al. 2020).

The extent to which soil carbon storage is influenced by either species diversity or specific species identity is another crucial factor in being able to analyse how to approach planting for biodiversity. Historically, offsetting and conservation initiatives that have been mainly focused on carbon storage failed to protect many species that exist in species-rich, biodiverse forests, and positive relationships between diversity and carbon sequestration have not been well captured by global carbon models. Today, forests are often planted to maximise a single prime objective, whether that be biodiversity or carbon sequestration, often using just a single metric to determine success, rather than maximising the two objectives concurrently. Ironically, this has damaged the stocks of carbon found in the whole ecosystem, in favour of fast-growing, monoculture tree species, as well as the long-term ability of many projects to sequester carbon by reducing the forests’ resilience. The potential tonnage of carbon available for sequestration if intensive agriculture is converted into agroforestry, therefore, is enormous (Lamb et al. 2016).

1.3.3. Transpiration

The benefits of transpiration are well-researched and shall be described briefly here. When water is absorbed by trees predominately through osmosis, it moves vertically upwards through the inner bark’s xylem through capillary action (enabled by the phenomenon of surface tension against the force of gravity). Once water reaches the leaves, it evaporates into water vapour through the stomata (pores), and if this process occurs more than the rate at which water vapour returns to a liquid state on the surface of the leaves, there is net evaporation (Kumagai 2011). In this context, large quantities of water vapour can be emitted by trees, and larger trees, of course, incur more transpiration. This evaporation causes a decreasing effect on immediate surrounding temperature, as considerable energy is required to vaporise each gram of water. A mature oak tree, for example, transpires more than 400 litres of water on one hot summers’ day, and each gram of water transformed into water vapour removes heat. If one imagines this process carried out amongst every tree and plant across an entire forest, it causes a significant cooling impact on the surrounding area. Water also evaporates from soil, so the total output of water vapour into the air from a forest or any ecosystem is called evapotranspiration.

The benefits of transpiration are not limited to the cooling effect on temperatures, they also cause humidifying benefits across a widespread system of air currents, preventing desertification. The evapotranspiration from rainforests, other forests, fields, and yards adds water to the atmosphere in the form of clouds and general humidity. Most of these clouds release the water right back onto the local areas. In simplified but strongly evidenced terms, forests are barriers to desiccation, a process which can spiral into a cycle of aridification and forest destruction whereby both phenomena positively influence each other, while also promoting susceptibility to pests and diseases. Stressed trees, in drier atmospheres and higher temperatures, are also more susceptible to fire, which adds to the cyclical process of destruction (IPCC 2019). In the Amazon rainforest, for example, ‘flying rivers’, air currents which carry the precipitation from the forest, are critical for the transport of moisture across the continent of South America, and even beyond. Widespread deforestation, through its destructive impacts upon evapotranspiration, contributes significantly to potentially irreversible tipping points.

1.4. The current state of forests and forestry in the United Kingdom

1.4.1. Forestry in the UK

The current land-cover of forests in the UK (13 percent) is small compared to that of other European countries. It is, however, larger than the forest land cover which existed at the end of the First World War in 1918, when, it is thought, it was only 5 percent. Existing forests at the time were a combination of native woodlands and commercial forests of mostly native species, though a new regime of forest creation through afforestation created intensively managed monoculture forests, typically involving exotic species. Historically, clear-cutting practices were widespread, involving the harvesting of exotic tree species at economic intervals of between 40 and 70 years, after which replanting of comparable exotic species ensued. Subsequently, governmental administrations incentivized the afforestation of non-indigenous conifers, with Sitka spruce and select other conifer species being acknowledged as capable of yielding significantly larger volumes of merchantable timber than native woodlands. This facilitated the development of a rural industry that currently employs more than 43,000 individuals in forest management and primary wood processing, providing the country with a domestic supply of timber and wood products, thereby decreasing the nation's reliance on imports (Dunn et al. 2021). Levels of woodland creation across the UK are generally low at present, however, with woodland creation targets of 30,000 hectares per year to aid in meeting the Net Zero by 2050 mission proving particularly challenging.

Many tree planting initiatives have consisted of monoculture forests or mixed forests prioritising exotic species under the guise of tree planting as environmentally and economically beneficial. This has been a longstanding issue; in the 1980s, peatlands, bogs and moorlands were planted with conifer, with environmentally damaging results, because planting trees on peatland dries out the soil, whereas peat in its natural state can act as a powerful carbon sink (Drinan et al. 2013). The promise of planting native broadleaf species and mixed composition forests in place of the more typical monoculture conifer species of past forests is considerable. In terms of adaptive capacity, native tree populations in the UK typically show a degree of adaptation to environmental and topographical conditions in Britain to a far greater degree than those from mainland Europe. In provenance trials with Scots pine, silver birch, sessile oak and alder, for instance, British provenances outperformed continental European ones in terms of growth and survival in 90 percent of cases (Cavers and Cottrell 2015, 19; Gerber et al. 2014). Also, native mixed-species planting in the UK which leads to oaks dominance also results in more durable carbon stores than achievable by conifer forests. Local provenances are typically, therefore, best adapted to current climatic and abiotic conditions in Britain, and thus should be prioritised in tree planting programmes in the UK.

Planting practice in the UK has increasingly come to acknowledge the necessity for native species. Multiple guidelines within the UK today recommend the use of local provenances for planting of primarily native species, yet monoculture forests with tree species or exotic origins are still selected, particularly for forests intended for timber production.

Today, according to Cavers and Cottrell (2015), British forests consist of roughly half conifer, 32 percent broadleaf and 8 percent broadleaf/conifer mixtures. Most of the conifer species are of exotic provenance; Scots pine, which is endemic to the area, Sitka spruce and Lodgepole pine (both USA/Canada), Larch (Central Europe or Japan), North-Central European Norway spruce, Southern European Corsican pine, and American/Canadian Douglas fir are the main species grown (Cavers and Cottrell 2015, 14). Sitka spruce is the most abundant species, and covers half of the area of commercial conifer forests. The only native conifer species, Scots pine, represents only 18 percent of planted species. Oak, beech, sycamore, ash, and birch are the most common broadleaf species. Of all the broadleaf species in Britain, oak and ash account for 30 and 14 percent of the standing volume, respectively (Anon 2013; Cavers and Cottrell 2015). Unfortunately, in most cases, studies of genetic diversity in British tree species are few, despite the role that this would play in understanding how forest resilience may be increased. This is because most British species have distributions that extend to mainland Europe and so studies have been carried out across a broad geographic scale with little consideration of the British context.

The UK’s forests are under particular threat from new pests and diseases of exotic provenance. At least 28 known pests and diseases are thought to have the potential to significantly harm British trees if they entered the country. There are numerous instances in which introduced pathogens have resulted in the widespread extinction of tree species elsewhere in the world, such as in North America with chestnut blight and white pine blister rust (Cavers and Cottrell 2015, 13).

Current recommendations advise that large-scale tree planting programmes should steer clear of ecologically important regions, such as peatlands, highly productive agricultural lands, and habitats with elevated conservation value. Instead, emphasis should be placed on repurposing underutilised grazing lands, given their abundant availability and potential to satisfy governmental commitments for afforestation. It is cautioned that afforestation of high-quality arable land must be avoided, unless accompanied by strategic compensation measures, as it would further impede the UK's capacity to produce food, culminating in greater reliance on imported food products, which are often associated with tropical deforestation. Moreover, it is critical to note that open habitats of high conservation value or ‘priority habitats’, including lowland heathlands and species-rich grasslands, are susceptible to being compromised by the establishment of woodlands, and should be avoided (Dunn et al. 2021).

Planting on peat that is deeper than 50 cm is now outlawed under the UK Forestry Standard, but planting on shallow peat continues, supported by evidence that these forests can sequester carbon over the production cycle if the productivity is high enough. However, modelling suggests that peats should be avoided altogether to avoid damaging the soil, and new forests should be created in low-grade agricultural land instead. In all, policies regarding the establishment of woodlands on carbon-rich soils need further refinement if evidence emerges of adverse effects on the large stocks of carbon held below ground.

In order to maximise the potential for large-scale afforestation in the UK, forests ought to be planted on lands with low species diversity, particularly grasslands. The Forestry Commission has identified a vast expanse of ‘low risk’ land, measuring five million hectares, that could potentially be utilised for this purpose. However, Friends of the Earth have excluded grasslands that are species-rich and have been designated as priority habitat for conservation, narrowing their estimate to 1.4 million hectares (Dunn et al. 2021; Friends of the Earth, n.d.).

Encouragingly, political frameworks have increasingly begun to incorporate the concepts of forest resilience, native species, and biodiversity. The UK Forestry Standard serves as a framework ‘for more sustainable forestry, discouraging geometric plantings of single species in large even-aged blocks in favour of mixed systems including native species (at least five per cent)’ (Dunn et al. 2021, 31).

1.4.2. Forestry in Scotland

Scotland is considered the most advanced in its modernisation of forestry techniques and renewing targets set for forest creation with incorporation of biodiversity and native species restoration. Although regimented monoculture forests of conifer, which are managed primarily for timber, can still be seen on a large scale in Scotland, recent efforts have been made to redress this issue by building a vision for Scottish woodlands in line with modern consensus on the necessary ecological, environmental, social and economic concerns when planting forests. Forests in Scotland, on the whole, are now far more diverse in structure, with forest certification and political readdressing of forestry in Scotland as one of the most important drivers for this change in approach.

Habitat Action Plan Targets for native woods in Scotland were revised as early as 2006 along with the rest of the UK with the wide review of UK Biodiversity Action Plan targets. At that time, conifer constituted 39,741 hectares of the total 59,057, or 67 percent, of planted woodland sites in Scotland. Targeted for their replacement were ancient broadleaved woods and Scots pine in areas suitable to their proliferation, with ambitious targets of 51 percent potential expansion area for 1 km woodland networks, and 43 percent for 250 m woodland networks, citing that these native species should be able to disperse freely, and attract more investment as success is evidenced.

Unfortunately, in the decade since this report, such progress has been limited. As outlined by the Forestry Commission Scotland (2019), a report aimed to provide government advice to planning authorities on planning for forestry and woodlands, much more still needs to be done to expand native woodland cover. The major drivers for native reforestation outlined in the report are to aid Scotland in mitigating climate change, to heighten Scotland’s timber productivity, support sustainable economic growth, support community development, improve quality of life and wellbeing, improve health through greater access to woodlands, conserve and enhance Scotland’s biodiversity, and protect ecosystem services. Those ecosystem services include improving water quality, reduction of wind erosion and sedimentation of water courses, reduction of run-off, increased entry of rainwater into soil, maintaining soil health, minimising soil disturbance, managing floods, and providing shelter for farmland and riparian habitats (Cao et al. 2016). The development and enhancement of native woodlands is also supported for its help in developing forest habitat networks, as part of integrated habitat networks, to enhance habitat interconnectivity and resilience to climate pressures.

The vision set out in Scotland is to increase woodland cover to 25 percent of land area by 2050, focusing on native species and the maximisation of the delivery of multiple benefits from Scottish woodlands, including the restoration of lost habitats and climate mitigation through the increased effectiveness of carbon sequestration in native forests. Scotland’s native woodlands support a disproportionately high proportion (36 percent) of threatened species in Scotland, as well as 7 UK priority habitat types, and are a key element of Scotland’s landscape and cultural heritage; conserving this is central to the Scottish Government’s new Scottish Biodiversity Strategy. Nevertheless, despite the promising nature of the suggested outcomes of their renewed forestry strategies, the Scottish government has not entirely shifted their priorities to native, mixed forests, but has instead included four main types of woodland envisaged as the future of Scotland’s forests:

1. native woodlands.

2. mixed woodlands.

3. softwood forests.

4. energy forests.

Native woodlands are thus positioned on equal terms of importance as ‘energy forests’, which are explicitly monoculture forests for the primary purpose of energy generation, and, tangentially, timber production. As long as ‘energy forests’ are still included in long-term plans for national forestry strategies, the positive impacts of biodiverse forests cannot be optimised on a scale that would see widespread impacts.

1.5. The woodland carbon code

1.5.1. The woodland carbon code

Afforestation-centred carbon offset initiatives are limited in number and scope within the UK context, because many are located in developing regions of the Global South. Nevertheless, promising examples of successful forests aligned with the principles established in this methodology do exist, one of which is the Forest of Marston Vale, a forest through which Balance operates, and the primary case study presented in this paper.

The Woodland Carbon Code (WCC), a voluntary standard for woodland creation projects in the UK, is based on an early carbon methodology established by Daniel Morrell and Richard Tipper in the 1990s, which today offers offsetting projects the greatest opportunity for tangible verification and validity based upon a number of integrated considerations. Other voluntary carbon standards, such as the UK Peatland Code, Verra’s Verified Carbon Standard, the Gold Standard, and Plan Vivo all operate for organisations within the UK, yet the WCC has seen endorsement and promotion accelerate under governmental decree in recent years when compared with the other standards.

In the most basic sense, the WCC encourages a much-needed consistency and uniformity among approaches to woodland offsetting projects, while providing validation and independent verification to projects based upon sustainable management to national standards, reliable estimation and monitoring of the amount of carbon sequestered, and adherence to transparent criteria and standards to ensure that benefits are delivered. To meet the requirements of the code, projects must demonstrate additionality, scalability and guaranteed maintenance for their duration, use standardised methods for estimating sequestered carbon, and have integrated long-term management plans to ensure project sustainability. The code accounts for most types of forest growth or regeneration and associated carbon sequestration and emissions reductions, including woodland created by planting and natural regeneration, multiple types of management regimes from frequent clear felling to minimum intervention woodland, and even emissions outside the woodland boundary which result from the project. The code does not, however, account for additional carbon sequestration due to changes to the management of existing woodland, or carbon stored in forest products.

The WCC ensures comprehensive planning and managing, including an outline of the necessary inputs and resources including a full financial analysis, a summary of operational techniques, consideration of species selection for current and future benefits, consideration of longevity and resilience in created forests, maps of the areas being planted, and a chronological plan of all key project operations to be established at the outset of the project. The code ensures that the management plan is updated regularly with renewed longer-term management targets and intentions beyond the project duration.

The WCC operates by allocating WCUs to organisations and individuals based on projects within the UK. WCUs are voluntary offset units and thus cannot be used in the compliance market, and cannot currently be used for emissions made outside the UK, thus are restricted purely to the voluntary market for organisations based primarily within the UK. They are acquired upon the verification of a project, but before that the units are called Pending Issuance Units (PIUs), the purpose of which is to demonstrate the quantity of potential future sequestration at the outset of the project, which can be assigned to buyers but cannot yet be used or retired until they are transferred into WCUs, which can be used as full carbon credits. All units are assigned a vintage, which is the period in which their delivery is anticipated, as determined by monitoring and verification schedules.

When the vintage has ended, the quantity of PIUs assigned to it is automatically converted into WCUs, and only verified WCUs can be used or retired to help compensate for an organisation’s emissions. All retirements are shown on the public view of the UK Land Carbon Registry, prior to using WCUs in any reports. This process helps to ensure the validity of all carbon units sold, with each unit designed to represent real and tangible carbon sequestration, and that carbon units cannot be resold to create further carbon leakage through excess emissions which are ‘compensated for’ elsewhere.

The designation of WCUs is achieved through determining the project’s net carbon sequestration, which is the total amount of carbon sequestered by the project which can be converted into carbon units. These are divided between the proportion that will contribute to the shared WCC buffer and the claimable carbon sequestration which is the amount the project can sell or claim. The net carbon sequestration is derived from the simple, REDD+ compliant (Secretariat of the Convention on Biological Diversity 2011), equation: (1) $\mathrm{N}\mathrm{e}\mathrm{t}\mathrm{C}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n}\mathrm{S}\mathrm{e}\mathrm{q}\mathrm{u}\mathrm{e}\mathrm{s}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}=\mathrm{P}\mathrm{r}\mathrm{o}\mathrm{j}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{C}\mathrm{a}\mathrm{r}\mathrm{b}\mathrm{o}\mathrm{n}+\mathrm{L}\mathrm{e}\mathrm{a}\mathrm{k}\mathrm{a}\mathrm{g}\mathrm{e}\text{–}\mathrm{B}\mathrm{a}\mathrm{s}\mathrm{e}\mathrm{l}\mathrm{i}\mathrm{n}\mathrm{e}$(1) By this, the predicted number of carbon units is identified in accordance with the project’s verification schedule, and will then be divided into the claimable carbon sequestration units, WCUs, and the contribution to the WCC buffer. Offset value is only delivered when the offsetting has actually taken place. Monitoring of the carbon sequestered at 5 years into the project is based on the projected carbon sequestration established at the outset of the project, but from year 15 onwards (at intervals of 10 years), it is based upon field survey measurements.

Developers are required to describe the original condition of the location, including details about vegetation cover, soil type and carbon content, through which they are to estimate the baseline for the carbon quantities at the site for the duration of the project in the hypothetical absence of the project’s activities. The WCC’s conservative approach to baseline construction means project activities must be more effective to accrue additional benefits, so only the most efficient carbon sequestering woodlands create a significant number of WCUs. Included in the baseline are carbon pools made up from tree biomass, soil, non-tree biomass and litter and deadwood, and measuring can be achieved with reference to any photographs, maps, field survey results or remotely-sensed images which indicate the condition of the vegetation and soil before project commencement. For tree biomass in the baseline scenario, which is most often the largest carbon pool prior to the start of a project, assessment can be done by determining the density of the trees and their current age, converting this to an equivalent area of woodland of a given age and using Carbon Lookup Tables to estimate the likely changes to that stock over time. The inclusion of non-tree biomass and litter and deadwood in the baseline scenario encourages the growth of biodiverse forests which facilitate understory development as well as mixed stand structure and tree age, which, as discussed, enhances the resilience of the forest and its capability to sequester carbon. Also significant is that all units are expressly publicly visible in regard to their current status and owner, providing clarity and transparency of carbon owners and claims that are made, and avoiding duplicity or ‘double counting’ (Cames et al. 2016).

Considerations of carbon leakage are taken into account by the WCC; small projects (of equal to or less than 5 hectares in planting area) are assumed to produce no leakage due to UK legislation which is designed to protect semi-natural habitats from threats such as deforestation, while standard projects (of 5 hectares or more in planting area) should account for any significant GHG emissions through land use changes in other areas over the project duration..

Additionality is also accounted for by the WCC. In order to assess additionally, the project must pass legal and carbon finance tests. If both are passed, an investment test is used to confirm a project’s additionality, but if that is not passed, a barrier test may be used. The legal test is the assessment that there are no laws, regulations, orders, agreement or any legally binding agreement which requires the implementation of the project, and the carbon finance test is used to show the significance of income from carbon units; projects must demonstrate that income from the sale of carbon units over the project lifetime, equates to at least 15 percent of their planting and establishment costs up to and including year 10. The investment test is used to prove that carbon finance is crucial to making woodland creation economically attractive in the given circumstances, i.e. the net value of woodland creation is positive only with the support of investment. If the investment test is not passed, proof of other economic, environmental or social barriers which stop a project from going ahead with the absence of carbon finance is sufficient to demonstrate additionality.

Through the comprehensive list of WCC regulations, any project operating through the code is far more likely to provide the benefits which carbon offset projects are supposed to supply, while ensuring that invalid initiatives do not slip through the cracks. This makes the WCC a valuable contributor to a global effort to reinvent carbon offsetting and ensure that it contributes to climate mitigation as efficiently as possible, and aligns with the Balance ethos as established in this methodology.

2. Methods

2.1. The balance methodology and ‘balance unit’

Voluntary carbon credits can create a number of benefits, provided they adhere to a sound methodology (ICVCM 2023). These should include the following benefits: biodiversity protection, rewilding and reforestation, emissions reduction, physical and mental health improvements in the general public, new jobs, and a variety of ecosystem services. To achieve long-term emissions reductions in line with the UNFCCC Paris Climate Agreement, the Sustainable Development Goal 15 of the 2030 Agenda for Sustainable Development. Balance’s methodology aims to repurpose biodiversity in line with the Kunming-Montreal Global Biodiversity Framework and the UN’s Sustainable Development Goal 15 of the 2030 Agenda for Sustainable Development as the key differentiator in addressing the global biodiversity and climate crises.

Balance represents the synthesis of carbon and biodiversity. A tonne of carbon, produced in the balance process, does not solely represent a particular quantity of trees; it's also the land mass required for the biodiverse forest to store a tonne of carbon, a quantity which varies depending upon the land’s capability to store carbon both in its soil and the planted biomass. This approach indirectly also addresses the huge problem of topsoil loss which, as Philip Lymbery (2022) argues, may mean we have only sixty harvests remaining.

The ‘Balance Unit’ is a combination of biodiversity credits and carbon credits. Unlike credit-based systems, it emphasises measurable constraints that ensure long-term compliance to standards that hold a greater likelihood of biodiversity stability and greenhouse gas reduction, such as the duration of forestry protection, instead of shorter term credit-by-credit evaluations. The Balance methodology assumes a stable rate of emission reduction and biodiversity maintenance (and, when applicable, increases) applied to developments mandated to last for at least 50 years beyond the contractual expiration of most credit-based systems. Through Balance we develop a new, more robust and interlinked marketplace for carbon credits, with the intention of improving compliance, especially of participating commercial businesses. In this hypothetical marketplace, the Balance Unit as a carbon-denominated instrument has a multiplier attached to it due to its additional values, which include higher quality, integrity, and the creation of natural capital. Balance Units fit with the evolving understanding of biodiversity credits that commercial entities purchase as part of their commitment to sustainable environmental practice.

The Balance Unit is unlike credit systems in its being assessed qualitatively, with awareness of annual biodiversity and emissions data, as well as more specific estimates generated by the Balance Calculator for individual entities. Rather than focusing on species-by-species data at individual development sites, as with biodiversity credits for instance, the Balance methodology uses evidence-based principles that require sites to conform to practices known to preserve biodiversity and reduce emissions. This simplifies the measurement and required data reporting for individual entities, increasing the likelihood that more conform to the long-term sustainable development guidelines discussed previously. While the specified measurement of biodiversity and emissions reduction are necessary for the ongoing study of management practises at sites in different locations–featuring changing levels of ecosystem complexity, natural disturbances, soil conditions, and other measurable climate conditions, for example–the balance methodology comprises adherence to a long-term contractual obligation, following the practises outlined here and specifying long-term sustainability targets instead of credit-based tracking alone. This includes less easily measured variables, such as the probability that entities conform to agreed-upon targets when funding sustainable development sites and the long-term social benefits to local communities. Entities that do so in line with the Balance methodology are herein shown to be more likely than those solely tracking credit-based systems to conform to required practices and continue doing so in line with sustainable development targets (see ‘Case Study: The Forest of Marston Vale’, sections 4.1 and 4.2).

Each tonne of carbon is allocated to a Balance credit. In the UK, for example, following the Woodland Carbon Code, Woodland Carbon Units (WCUs) can be assigned. Each WCU represents a tonne of CO₂e which has been sequestered in a WCC-verified woodland. The WCU has been independently verified, is guaranteed to be present, and can be used by companies to report against UK-based emissions audits or to support claims of carbon neutrality or compliance with Net Zero emissions goals. WCUs are acquired upon the verification of a project, after Pending Issuance Units (PIUs) have vested over a 10-to-30-year interval. There is a one-to-one relationship between PIUs and WCUs because a PIU is effectively a promise to deliver a Woodland Carbon Unit in the future based on the predicted level of carbon sequestration performed when the involved trees have matured. PIUs help demonstrate the volume of potential future sequestration at the outset of the project. As planning tools and data points, PIUs can be assigned to buyers but not used or retired until they are transferred into WCUs, which can be used as full carbon credits.

Balance clients create biodiversity and natural mechanisms for carbon sequestration, the Balance methodology mitigates a year’s worth of emissions by ensuring that carbon sequestration over 20 or 30 years will effectively negate the impact of those emissions. While tree growth determines the 10–30-year window over which PIUs convert to WCUs in the United Kingdom and delivered PIUs are eligible for conversion into WCUs after 10 years, it’s also important to note that Balance Eco Limited and its planting partners hold land under contract for 99 years. This longer interval significantly increases the carbon sequestration capacity of the woodlands involved. The 99-year land lease in Balance contracts also guarantees that sequestration calculations underestimate the restorative impact of employing the Balance methodology. Professor Peter Cox, Professor of Climate System Dynamics at the University of Exeter (in Exeter, Devon, United Kingdom), helped quantify and validate the positive impact of the 99-year timeframe that Balance contracts support, which is a net gain of more than 10 percent.

The Balance methodology's 99-year contractual obligation for forest protection is in harmony with the 100-year GWP (Global Warming Potential) used by IPCC and Oxford Net Zero. This commitment acknowledges the necessity of addressing the CO2 100 years radiative forcing cycle; this 99 years time frame covers both short-term and long-term warming mitigation, highlighting the projects’ role in meeting climate targets; this timeframe also is sufficient time for biodiversity enhancing natural practices to take place, such as deadwood for insects and birds to nest in (Fankhauser et al. 2022). In contrast, most existing carbon credits have no protection after 40 years. Carbon credits lacking the 99 years of protection may inadequately counter the lasting warming effects of emissions, hindering their efficacy in climate mitigation.

The lack of retirement, which has long been a factor of the compliance market attracted negative attention for permitting excess emissions elsewhere, or ‘carbon leakage.’ Retirement of offset credits avoids double counting and non-additional credits being resold on the carbon market. This is a ‘live’ issue in present climate negotiations as we move to carbon markets.

Prioritisation of indigenous species and the planting of a variety of species adapted to the local abiotic context, is another aspect of the Balance methodology. Established forests in accordance with the UKFS (UK Forestry Standard), are verified through the UK Woodland Carbon Registry, the public registry of the Woodland Carbon Code, and validated by a certification body accredited by the UK Accreditation Service.

Within the carbon credit trading landscape, another disconcerting practice has emerged where resellers acquire impactful high-optic carbon credits, only to channel a significant portion of the offset into blended, low-cost credits. This concerning trend involves reallocating credits from failed forestry projects to inexpensive methane amelioration without client awareness or consent, distorting their intended support for nature-based solutions. This manoeuvre serves as a cost-effective means of evading reforestation obligations. Despite recent systems buffering credits in case of project failure and the nascent emergence of insurance measures, the troubling practice of blending avoidance and the mingling of high-cost and detrimental projects persists. In direct contrast, the Balance methodology firmly eschews blending, aligning each ton of balance unit carbon with a distinct project, coupled with the addition of an extra tree in a non-carbon monitored forest near the client, ensuring direct financial allocation to chosen initiatives with transparency and active engagement. This avoids the failures of Nature based solutions (NBS) forestry projects which, for example, swap out cheap methane CO2e GHG equivalence for failed projects, in some instances, may do so without consultation to the buyer (Keith et al. 2021). This transformative approach emphasises the conversion of existing carbon credits into tailored balance units, uniquely primed for resilience creation, supported by a trusted and transparent framework.

Please see Appendix A for a summary of the Balance methodology’s recommended guidelines for planting, addressing some of the problems raised here.

2.2. Measures

2.2.1. The Balance Calculator for individual entities

The Balance Calculator allows greater accessibility to a wider range of carbon emitting companies or individuals. The Balance CO2 Estimation Methodology outlines the calculations through which estimates of required carbon offsets are achieved. Historically, the concept of generating an effective general calculator for measuring GHG has been hindered by complexity and inaccuracies. To address this problem, researchers introduced sector specific calculators. Sector specific calculators, for example, have been used to model a city’s emissions (Lin et al. 2014) and even predict the future emission levels of an entire country (Nieves et al. 2019).

The Balance methodology includes the development of equations leading to a calculator that uses sector-based analysis based upon national GDP, estimating the share of GHG for businesses based on their specific sector/sub-sector and their current GDP proportion to the sector/sub-sector GDP. This provides individual-level estimation more simply than other methods, encouraging more continuous reporting by organisations.. The calculator compares company turnover with government GDP data and DEFRA data on emissions broken down by 720 sectors; this can then estimate a company’s emissions by pro-rating the emissions on the basis of their share of sector GDP, thus establishing how much their footprint within the sector is proportionate to their turnover. The company need only provide annual turnover and its industry sector (SIC) code, via a simple, searchable interface. This intends to improve company compliance by lessening the likelihood that organisations opt-out of tracking to avoid providing more sensitive data, such as specific emissions-related expenditures. A country’s GDP and emission factors are typically in the public domain, and published by the IPCC.

The Balance Calculator estimates the value of Sector Turnover based on the GDP Fraction. This is a conservative estimate used to calculate the proportion of GHG for a company based on company turnover. Subsequently, the sector turnover estimation uses a curve-fitting process to predict Sector Turnover (ST) based on the GDP Fraction (GDP). In this process, 98 different sectors with known GDP-F help develop the equation. The equation is developed in the following steps:

1.	Identifying the conversion rate (CR) based on CR =
2.	Based on the value of CR, sectors are grouped (G) as displayed in Figure 1:

Figure 1. Table of sector group categories based on CR value.

In the table presented in Figure 1, a category is assigned for every few CR values in the same range. The gap between ranges is not considered here but has been taken care of in step 4. Also, the adjustment process has been done later in step 4 to modify categories for higher accuracy. The number of categories provided is based on the heuristic of performing a test on several scenarios, but in general, increasing the number of categories increases the accuracy in the equation.

3.	In the next step, a simple arithmetic progression based on the G and GDP is used to calculate CR.
4.	The category value of sectors has been modified to increase the accuracy of curve fitting. The first and final values of categories are listed in Figure 2.
5.	The final accuracy review shows an average accuracy of 97.78 percent, with a standard deviation of 1.90 percent. This is the accuracy of predicting Sector Turnover based on the GDP Fraction.
6.	The final step calculates the proportion of GHG for a company based on the Sector Turnover (ST) and the Company Turnover (CT) to measure the Balance value, using the Balance™ Equations (Equations (2) and (3)): (2) $\mathrm{B}\mathrm{a}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}=\mathrm{o}\mathrm{r}\mathrm{g}\mathrm{T}\mathrm{u}\mathrm{r}\mathrm{n}\mathrm{o}\mathrm{v}\mathrm{e}\mathrm{r}\ast {\displaystyle \frac{\left({\displaystyle \frac{\mathrm{s}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{C}\mathrm{O}2\mathrm{e}\ast 1000}{\mathrm{u}\mathrm{k}\mathrm{G}\mathrm{D}\mathrm{P}\ast \mathrm{s}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{W}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{h}\mathrm{t}}}\right)}{1000}}$(2) (3) $\mathrm{B}\mathrm{a}\mathrm{l}\mathrm{a}\mathrm{n}\mathrm{c}\mathrm{e}=\left(\left({\displaystyle \frac{\mathrm{o}\mathrm{r}\mathrm{g}\mathrm{T}\mathrm{u}\mathrm{r}\mathrm{n}\mathrm{o}\mathrm{v}\mathrm{e}\mathrm{r}}{\mathrm{s}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{T}\mathrm{u}\mathrm{r}\mathrm{n}\mathrm{o}\mathrm{v}\mathrm{e}\mathrm{r}}}\right)\ast \mathrm{s}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{C}\mathrm{O}2\mathrm{e}\ast 1000\right)$(3)

The GHG emissions quantity is translated into the amount of carbon required to offset emissions through our metric system, which equates one Balance Unit to one tonne of CO2e, allowing participants to view their quantifiable contribution to biodiversity easily, and compensate for their emissions in a way that creates more lasting benefits than comparable systems. The concept of a Balance Tonne guarantees that at least a tonne of carbon will be taken out of the atmosphere as a direct result of its acquisition. Because all ‘additionality’ is mitigated, a Balance Tonne results in genuine carbon reduction rather than being attached to planting that might have happened anyway.

Figure 2. Table displaying primary and final values of categories, with increased accuracy to curve fitting.

Individual consumers using the above-derived Balance calculator can view how many tonnes of CO2e they generate. Afterward, the turnover and sector-based calculations translate this into the tonnage of carbon required to offset emissions. Some additional considerations regarding its use are listed below:

1. When using this methodology, no improvement in results will be seen due to sustainability performance improvements made individually, because the results are based on the industry average.

2. To track actual results, trends and improvements requires a more in-depth GHG assessment of individual business or consumer operations.

3. The sector-based calculator accounts for in-country scope 1 and 2 emissions only, not scope 3, and is reviewed to be 97.8 percent accurate in all instances to Government data. If everybody in a company’s supply chain were balanced, scope 3 emissions would go away. BALANCE® encourages sector base calculator clients to ask that their supply chain become Balanced to spread the cost of scope 3.

3. Case study: the forest of Marston vale

3.1. The project

The Forest of Marston Vale is a group project consisting of ten sites, covering 61 square miles between Milton Keynes and Bedford in Bedford Borough and central Bedfordshire, providing a home for newly-grown forest ecosystems. The Forest is one of Balance’s major planting partners. The project began in 1991 when the Government designated this area as one of 12 Community Forests across England, and the Forest of Marston Vale Trust was created by the founding partnership of Natural England, the Forestry Commission and local authorities. The individual planting projects in the scheme are managed by the Trust. Historically, the site upon which a considerable portion of the Forest has been planted had been damaged by industrial processes such as brick making and refuse sites over many decades. At the start of the project, the Forest area had just 3 percent tree cover.

Today, Marston Vale is home to an expanding range of forests which have increased overall tree cover to 15 percent, and have incorporated the key concepts of biodiversity, forest resilience and carbon sequestration to considerable success, with a key target of increasing tree cover to over 30 percent playing a central role in driving the project. Millions of trees have been planted with the participation of local communities and businesses, boosting the local economy and aiding in potential future growth. The site is home to some pre-existing semi-natural ancient woodlands, which help to connect and buffer the created forests. The site conforms to all Balance methodology guidelines specified in this paper.

Woodlands vary between the different sites of the Forest, but generally they include plant protection (with fencing or the use of tree shelters), ground cultivation, and sward establishment using a ‘pollen and nectar’ grass and wildflower mix to form the understorey. Trees are planted with higher spatial density than found in ancient forests in the same region. Whereas the typical ancient woodland would have trees 8 m apart, the Forest of Marston Vale project plants trees at 2 m apart, in an attempt to acquire the same benefits from ecosystem services and carbon sequestration as found in ancient woodlands. This is because trees today are considered light-dependent; that is, they need to grow higher quicker to get the light they need to survive, and thus need to be closer together.

Importantly, roughly three quarters of the landscape is planted with native species found on site or locally, creating a largely unhindered ancient woodland character comprised of oak, pine and maple woods, with particular consideration for resilience in the context of climate change by the inclusion of oak and hornbeam tree species which are projected to fare better with local temperature rises and climatic extremes in the near future. The provenance and sourcing of seedlings is most often exclusive to the UK, from nurseries and contractors located in the UK, thus avoiding importation while selecting species most suited to the heavy clay soil found at the site’s location in Bedfordshire. Amongst all the woodlands created in the project, forest composition normally incorporates an intermix of dominant UK native species and fewer exotic species which comprise a core of 2 or 3 species, as well as minor native species, which work to simultaneously create functioning biodiverse ecosystems while preparing the forests for future threats. Similarly, the inclusion of species from 2 to 5 degrees south to suit projected climate shifts, as recommended by forestry experts, is in line with the Forestry Commission and the Forest of Marston Vale’s targets. Mitigation of the threat of diseases is also considered as part of the project with the explicit avoidance of creating monoculture forests, which are more likely to be seriously impacted by diseases. The focus on native species and creating forest ecosystems which resemble ancient forests that exist on the site increases overall biodiversity, which elevates the forest’s overall resilience to pests and diseases. If any one of the species succumbs wholly to disease, the woodland should be able to repair itself.

Investment has been plentiful, with an average of 15 partnerships with public and private sector organisations per year. These have helped to secure a total inward investment of over £UK22.8 m, so far. The recreational benefits of creating the forest have helped the visitor economy in the area, bringing an estimated £UK6.91 million in outside revenue per year.

3.2. Results and discussion

An academic report published by the Forest of Marston Vale highlights the various achievements of the project over its 20-year lifespan, and makes an effort to quantify the social, environmental and economic impacts of the project. Thus far, tree cover has increased from just 3.6 percent in 1995 to more than 15 percent in 2015, and has created over 1,150 hectares of new woodland, more than trebling woodland cover. Overall economic benefits are valued annually at £UK12.83 million, which equates to benefits with a net present value of £UK339 million, and, according to the study, £UK11 of social, economic and environmental benefits for every £UK1. In terms of employment, the report estimates that the project has supported an additional 167 jobs per year for residents, which includes both direct employment in the project, to service industry positions and contractors. The local economy has been especially supported by the preferential use of local goods and services by the project. In turn, these local businesses provide local jobs and boost local incomes.

Economic benefits, though useful for attracting investment, are only a small part of the story, however. The advantages to health and wellbeing of the forest are numerous; the majority of the new woodlands are close to residential areas, which enhances access and recreational opportunities, with public footpaths crossing many of the sites. Using both visitor data and research on how physical activity outdoors can reduce hospital visits and increase life expectancy, the value of the physical health benefits through the provision of recreational space for exercise and contact with nature provided by the Forest was estimated at £UK4.95 per annum (Forest of Marston Vale 2018). This does not include the benefits to mental health and wellbeing, which, although not quantified, if comprehensive studies from around the world on forests and mental health issues such as stress and anxiety are to be believed, are likely substantial. Less quantifiable social impacts, such as the facilitation and fostering of social cohesion and a new sense of place, as well as the benefits derived from increased understanding of natural and ecological processes, may also be present.

The Forest has long sold the carbon stored in the woodlands as a voluntary carbon offset initiative, with buyers allocated carbon offset units on the Markit Registry. Today, the Forest operates by the Woodland Carbon Code, and the overall benefits to carbon sequestration, forest resilience and biodiversity as transferred through the various requirements for WCC verification are embodied by the nature of the planting process. Total carbon sequestration of the involved trees has been estimated at 4,917 tonnes of CO2 annually, and has potential for creating an even larger carbon pool with the planting of more trees. Biomass carbon, including below ground root mass, and SOC, are considered in carbon sequestration models.

Environmental benefits and ecosystem services of the project besides the storing of carbon have been numerous. Air pollution, for example, has been significantly reduced; it is estimated that the new woodland thus far created has been able to absorb 0.65 tonnes of sulphur dioxide (SO2) and 65 tonnes of particulate matter. While agriculture remains the primary land use within the Forest area, the shift in land use to woodlands has resulted in reduction of impacts such as GHG emissions from fertilisers and machinery, which are common with modern intensive agriculture, and has significantly benefited soil health and reduced soil erosion. To date, it is estimated, the creation of the Forest has reduced agricultural GHG emissions by 1,747 tonnes CO2e per annum, which is additional to the increased size of the carbon pool as a result of forest creation. Water quality has also been imp roved, and flood risk reduced, due to the slowing of the flow of water; the quantity of woodland created in the Forest so far is estimated to reduce peak flood flows by 5 percent.

The core target of increasing tree cover up to 30 percent from today requires the planting of around 5 million more trees by 2031. With the currently active adoption of the Woodland Carbon Code, the future of the Forest of Marston Vale is extremely promising, as is its continuous adherence to the Balance methodology outlined here.

3.2.1. Co-benefits of balance units

Biodiverse land offers a multitude of co-benefits, each playing a significant role in fostering a harmonious relationship between nature and society. These co-benefits encompass various approaches to land management, contributing to ecological vitality, community welfare, and lasting sustainability (Perrings and Madhav 2003).

The concept of Balance units is a powerful approach to fostering biodiversity, resulting in mutual benefits for both the environment and the human population. By engaging with suggested co-benefits, we can achieve a biophilic connection, leading to a transformation in people's mindsets and generating additional income that contributes to sustainable long-term environmental practices. Human involvement in protecting ecosystems is crucial to fostering biodiversity and ensuring a healthy environment (Cardinale et al. 2012). The relationship between people and biodiversity is symbiotic, each supporting and enhancing the other (Aerts, Honnay, and Van Nieuwenhuyse 2018).

In regions where locals gain income from their land through co-benefits, such as agroforestry, permaculture, apiary, water catchment enhancement, forest products, sustainable firewood management, and bioChar, they can invest in essential services like schools, hospitals, and infrastructure (Brown et al. 2011; Browder et al. 2019). This financial stability can mitigate the need for climate migration, creating a more resilient community. The effects of each co-benefit are detailed, here:

1. Agroforestry: Agroforestry harmonises agriculture and forestry by integrating trees, crops, and livestock. This practice enhances ecosystem resilience, augments biodiversity, improves soil fertility, and establishes sustainable livelihoods (Brown et al. 2018).

2. Permaculture: A design philosophy inspired by natural ecosystems, creates landscapes for self-sufficiency and sustainability. It minimises waste, optimises resource use, eliminates the need for external food purchases, and yields marketable products, contributing to the local market (Vovk and Buheji 2018).

3. Apiary: Cultivates bee colonies for pollination and bee-related products like honey and beeswax. Besides sustaining local economies, apiary contributes to ecosystem health, enhances food production through pollination assistance, and generates additional community income by offering marketable products (Etxegarai-Legarreta and Sanchez-Famoso 2022).

4. Water Catchment Enhancement: Improves water quality and availability. By reforesting, conserving soil, and implementing efficient land management, these practices boost water storage and reduce flooding risks. Forestation on hillsides further enhances downstream water catchment, curbing flooding and promoting river flow, which can lead to additional income from fisheries (Shah, Nisbet, and Broadmeadow 2021).

5. Forest Products: Encompass a wide array of goods from forests, spanning timber and non-timber products such as furniture, fencing-like fruits, nuts, and medicinal plants (Zhang et al. 2023).

6. Sustainable Firewood Management: The responsible utilisation of forest resources to fulfil energy requirements while ensuring the preservation of forest ecosystems. By averting deforestation and minimising environmental repercussions, this approach safeguards the welfare of both humans and the environment. Furthermore, this practice involves the removal of combustible materials from forests as a proactive fire mitigation measure (Zhang et al. 2023).

7. Biochar Production: involves converting organic biomass into charcoal through controlled pyrolysis. When applied to soil, biochar enhances fertility, retains nutrients, and sequesters carbon, making vital contributions to sustainable agriculture and climate mitigation.

Biochar kilns can be developed at an exceptionally low cost, making large-scale production feasible. This presents a cost-effective alternative to expensive air scrubbing systems that can only remove a small tonnage of carbon annually. Embracing biochar production, with its ability to absorb gigatons of CO2 each year, and integrating it into carbon forestry on an industrial scale, establishes a straightforward and effective approach to carbon capture. This approach not only combats climate change but also aids in the mitigation of forest fires by removing dry combustible materials (Zhang et al. 2023).

4. Conclusion

The Forest of Marston Vale is just one example of the type of reforestation which the Balance methodology has successfully facilitated through its focus on biodiversity and ecosystem creation. Future study is planned to investigate challenges unique to each planting location, especially regarding appropriate forest composition, local topography and climate. Planting shall always occur on previously low-diversity lands, and avoid peatlands or high diversity grasslands or other productive biomes, in order to avoid carbon leakage and negative impacts on biodiversity. Selected planting partners for future research, as a matter of both priority and necessity, should strictly follow the planting principle obligations set out in this methodology. This ensures that future studies are able to replicate the conditions provided here and control for any additional variables under consideration.

Biodiversity is the key factor in implementing the Balance methodology through forest creation. When focusing on biodiversity in selecting and planting species, a positive feedback loop encourages both tree and non-tree species diversity. This in turn promotes forest resilience, carbon sequestration and ecosystem services, as well as the various social, economic and environmental benefits associated with biodiverse forests. Ultimately, Balance targets the creation of large, connected forest ecosystems, with varying stand age and size, complimented by the prioritisation of large native tree species. The mitigation of the threat of diseases and serious climate related threats is simultaneously achieved through the creation of biodiversity and avoidance of monoculture planting.

Through the novel concept of Balance Units and measurement using the formulae composing the Balance Calculator, a simple summation of carbon equivalent emissions is offered to the consumer, offering the share of GHG for businesses based on their specific sector/sub-sector and their current GDP proportion to the sector/sub-sector GDP, which works to provide an estimation in a much simpler way compared to other methods, improving compliance and ensuring all targets match those needed to effectively pursue climate change offsetting goals.

Acknowledgements

The authors would like to thank Oliver Rieche (Balance Eco Ltd.), Jessica Hunter (Balance Eco Ltd.) and JohnMichael Jurgensen (The University of Chicago) for their assistance with the early drafts of this manuscript and subsequent review.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available in the Balance Methodology dataset at: https://osf.io/ak3y8/?view_only=6adcbf7661c242728628f06ce1d2b263. These data were derived from the following resources, all of which are available in the public domain:

• https://www.ons.gov.uk/economy/environmentalaccounts/datasets/ukenvironmentalaccountsatmosphericemissionsgreenhousegasemissionsbyeconomicsectorandgasunitedkingdom/current

• https://www.ons.gov.uk/aboutus/transparencyandgovernance/freedomofinformationfoi/publicandprivatesectoremployeescontributiontogdp

• https://www.ons.gov.uk/economy/grossdomesticproductgdp/datasets/gdpodatasourcescatalogue

• https://www.ons.gov.uk/aboutus/transparencyandgovernance/freedomofinformationfoi/annualturnoverbyindustryforallsicindustriesfrom1998to2015