Photo 19. Tree in front of house facade (photo by Benjamin Suomela).

5. Conclusions and recommendations

Overall project results

The Yggdrasil – The Living Nordic city had as its aims to:

Evaluate the 3+30+300 principle’s effectiveness in enhancing public health, climate change, and biological diversity, with a specific focus on native tree species.
Guide the Nordic Countries in their implementation of the Kunming-Montreal Global Biodiversity Framework Target 12 on green cities (Target 12 (cbd.int)) and support their work on Target 8 and 11 on climate change, nature-based solutions and ecosystem services (Target 8 and 11 (cbd.int)).
Establish a collaborative network among Nordic cities, fostering the preservation and expansion of local tree populations.
In countries where the 3+30+300 principle might not be relevant to implement (e.g. Faroe Islands, Iceland, and Greenland) due to the lack of native tree species and the difficulty in reaching high tree canopy levels, the aim is to assess realistic steps towards 3+30+300 and recommend alternative ways of urban greening based e.g., on native vegetation.

As this report has documented, comprehensive information and analysis has been provided on the current implementation of the 3+30+300-principle in the Nordic Region. Findings include, among others, an overview of the overall status of urban forests and green spaces according to this principle in all Nordic countries, showing that most countries and municipalities score well when it comes to 3+30+300 compliance. However, in particular, the gap analysis for the participating municipalities has shown there are opportunities for further improvement. The results presented in this report also highlight the links of 3+30+300 with public health, climate change, and biodiversity considerations.

The work carried out by the Yggdrasil team provides an important contribution to the wider fulfilment of green space, biodiversity, and nature-based solutions policies and targets at different levels, including the Kunming-Montreal Global Biodiversity Framework Target 11. Concrete ways of integration 3+30+300 in policies and plans are provided in this report, based on experiences from Nordic countries and cities, as well as those elsewhere. One example of a relevant policy framework is that of urban forestry master plans but as the example of several Swedish cities shows, 3+30+300 can even be included in municipal comprehensive plans. The principle has the potential to be an important delivery mechanism and metric for the wider implementation of nature-based solutions, also in a more equitable way.

The Yggdrasil project has created a network of organisations and municipalities that can help advance 3+30+300 implementation and the efforts to enhance biodiversity, public health, and climate action, e.g., through wider implementation of nature-based solutions in Nordic municipalities. Important knowledge and experience sharing has taken place within this network.

Although most Nordic countries and municipalities are well placed to implement 3+30+300, it is important to work context-specific and recognise that starting conditions and needs will differ. Trees and green spaces are important for climate adaptation and health promotion, and even countries and regions with lower tree and forest covers like the Faroe Islands and Iceland show that 3+30+300 can be a useful tool to enhance urban and other built-up areas. But obviously the local landscape and biodiversity concerns need to be considered. This report also shows the role of biodiversity and native trees in meeting policy objectives related to liveable and resilient cities, while highlighting the importance of diverse and resilient urban forests that also include non-natives.

Recommendations

Based on the work within Yggdrasil, several recommendations can be provided, both for the wider greening of Nordic municipalities and the implementation of nature-based solutions and specifically for implementing the 3+30+300 principle.

Overall recommendations

Policies and planning

Nordic cities and other municipalities have a long tradition of urban greening. In the face of urban densification, climate change, and biodiversity loss, this tradition is under threat, however, as there is a risk that urban areas can become less green and with that also more vulnerable and less liveable and healthy. Awareness about this risk needs to be raised and actions have to be taken to counteract it.
Linked to the above, it is important to ensure that green space and trees are not removed in urban regeneration programs or densification strategies that are implemented to create higher urban attractivity and to support security in socio-economic vulnerable areas.
Sufficient canopy cover and green spaces need to be provided in new developments to avoid creating the vulnerable neighbourhoods of the future. Climate change and predicted warmer, dryer and wetter climate, and a higher extreme weather will affect our Nordic cities and areas without trees and green space will be more exposed and vulnerable.
To maximise their socio-economic benefits, trees need to be integrated into broader urban planning and development policies. Tree-planting initiatives should be aligned with housing, transportation, and public health strategies for greater impact.
Children, the elderly, the sick, or otherwise vulnerable are particularly in need of green infrastructure and proximity to high-quality public green spaces, partly because they are more sensitive to the effects of air pollution and heat, and partly because they often spend a large proportion of their time close to their homes or various institutional settings. It has to be noted, however, that Nordic cities often do not show the usual link between higher level of neighbourhood vulnerability and lower levels of greenness.
Implementation of the 3+30+300 principle should be seen within the wider international and national policy context. The new Nature Restoration Law of the European Union, for example, sets minimum requirements for urban tree canopy cover and share of public green space.

Funding and investment

Public investment in urban forestry, as well as incentives for private landowners to plant and maintain trees, are crucial. Cities may implement tax breaks or grants for greening efforts. Although funding and investment were not specifically addressed by the project, there is no doubt that sound urban forestry and urban greening programs require sufficient funds, including for longer-term management.

Tree protection and management

We need to retain and care for existing trees in the urban landscape, rather than putting too much emphasis on planting new trees. This is especially important for older trees since they provide more ecosystem services than smaller trees.
Protective measures should be taken for street and city trees near construction, both above and below ground, so that trees can get older and provide more ecosystem services. Important trees that are in need of, and suitable for, root zone renovation in order to improve growing conditions for existing city trees should be identified and properly cared for.
Nordic municipalities should allocate more resources into surveying and monitoring their tree populations. The more data collected the better policies regarding tree diversity they could produce and implicate.

Tree selection and planting

Just planting as many trees as possible, no matter where, no matter what species, should be avoided. It is important to consider, for example, future climate conditions and biodiversity concerns.
You are in this for the long run, plant trees with ample space to become a large tree. Better a few good trees that have a real chance to grow older and larger than many smaller ones.
Make sure you plant a variety of species for a sustainable and resilient urban forest cover.

Tree diversity, including the use of native and exotic species

Striving for a more diverse tree population is important for climate change mitigation and adaptation. Not all Nordic municipalities currently have a sufficiently diverse urban forest and thus become vulnerable to climate change, current and emergent pests and diseases, and the like. Tree diversity can be increased by planting new species instead of the more common species within the city, for example based on species suitability under future climate scenarios. Further, within tree species, diversity makes the populations less vulnerable to changes in the environment and increases their adaptive potential. Diversity also relates to a good age distribution in the urban forest, so that a healthy canopy can be maintained. In parks and woodland, the presence of dead wood can also support biodiversity. age of trees, a diverse population of younger and older trees, including dead trees supports biodiversity.
Diversity is also important to mitigate ecosystem disservices like pollen allergens and tree diversity is positive for the diversity of flora, fauna, and fungi dependent on different species. Moreover, tree selection should include both the positive and more challenging characteristics of trees, also in the longer term.
It should be ensured that new trees are chosen not only for the existing climate, but for the future climate as well.
The number of trees planted solely for ornamental purposes should, in many cases, be reduced in favour of trees intended to provide shade, as temperature regulation and other climate-related benefits of trees have become a priority
The use of exotic trees should be conducted with much care. There is a great need for being cautious regarding the risk of invasive species being introduced where they can spread and compete with local flora and habitats. Using non-native plants can also affect pollinator communities. Therefore, it is important to follow the respective country's recommendations to avoid the use of invasive species.

Community engagement

Engaging local communities in urban tree initiatives fosters a sense of ownership and ensures that tree-planting projects are aligned with community needs. Participation in local greening projects can empower residents and ensure long-term success.

3+30+300-specific recommendations

Overall, 3+30+300 approach and implementation

It is essential to formulate a clear, long-term vision for the trees and green spaces in the municipality (or at a different scale) and then see how 3+30+300 can help you deliver this vision.
This principle is a great starting point, as it has a decent evidence base, is increasingly tested and implemented, and serves as an international benchmark. Moreover, it provides a simple metric or guideline that combines the importance of visible green, surrounding green, and recreational green.
One needs to always integrate the 3+30+300 principle in a wider policy and planning context, with other guidelines, metrics, etc. 3+30+300 is not only for tree and green space plans and policies. Try to integrate into plans and policies for health, climate action, biodiversity, social justice, education, etc. However, work context-specific and see what is realistic and desirable.
Consider how appropriate 3+30+300 implementation is to local contexts. In some cases, adding more trees to areas can be seen as less appropriate and conflicting e.g., with local habitats.
Don’t forget local communities and their wishes. Find ways to engage them in 3+30+300 implementation.
Do not request a new development to be 3+30+300-compliant from the start, as this is impossible Do not request a new development to be 3+30+300-compliant from the start, as this is impossible (unless the development is in an area where substantial existing vegetation can be maintained). Trees take time to grow. An alternative might be that you request it to be 3+30+300-compliant in 20 years for instance.
Learn from others, as more and more municipalities - also in the Nordic region - are gaining experience with implementing the principle.
Undertake gap analyses and set priorities for 3+30+300 implementation where needs are highest, for example in the vicinity of kindergartens, schools, care facilities, and other types of social institutions, as well as in areas with a high proportion of children and elderly people.

Assessment and monitoring

It is important to carry out an initial 3+30+300 assessment of your municipality, neighbourhood, or other area.
You can overlay 3+30+300 maps with other relevant maps, such as the socio-demographic neighbourhood characteristics and climate maps shown in this report, but also for example, mobility maps, presence of underground infrastructure, and the like.
A gap analysis tells you where to prioritise and start first, given limited budgets. A gap analysis can take different forms and can focus on the municipality as a whole but also on specific neighbourhoods as well as land-use or building types (for example, schools, hospitals, and elderly homes).
The individual 3, 30 and 300 components allow you to know if your effort should go into creating a park, creating more street trees or creating better support/policy for trees on private territory.
As a follow-up: through time you could monitor if your efforts have been effective. Moreover, you can link the monitoring of your 3+30+300 scores to (changes in) different ecosystem services, such as cooling and public health gains. Various assessment tools, including i-Tree, can assist with this and sometimes also provide insights into economic costs and benefits.
Important to note is that 3+30+300 should be seen as a minimum level. This is especially important in the Nordic context as the cities here in general score high on one or several of the parts of the rule. Our good conditions and long history of preserving and safeguarding urban green space is a strength and should not be taken for granted.
Don’t get discouraged by a drop in one of the three components. There could be good reasons for that, for example a replacement of certain tree species by others that are more climate-resilient or functional (and which can lead to e.g., a temporary drop in canopy cover).

Key messages

Four key messages result from the project and crystalise its main findings and recommendations. These messages can be used when implementing the 3+30+300 rule and developing greener municipalities throughout the Nordic region, in collaboration with different stakeholders.

Let’s keep our Nordic cities green as they grow and transform.

Although Nordic cities are small and green, rapid transformations are at risk of changing that due to lack of tools and policies to preserve and develop new green space as cities are growing and densifying.
The Nordic cities generally score high on the 3+30+300 principle, but the further north we get the fewer trees can grow (although climate change could lead to an expansion of the tree palette). We have nature around the corner, but we cannot take our trees and green spaces for granted. As new neighbourhoods need to be planned and developed, and existing neighbourhoods have to be transformed, trees and green space should be an integral component so that these areas can be healthy, resilient, and biodiverse.
Human-caused climate change poses challenging conditions for both humans and trees. Trees, shrubs, and other green spaces are crucial in adapting to climate change and mitigating the effects of a wetter, dryer, and warmer climate.

Use 3+30+300 to assess, promote, and celebrate the possibilities of urban trees.

The narrative on trees and urban green space needs to be shifted from a two-dimensional, abstract, and placeless understanding of greenery, to that of a narrative of trees and other vegetation that are living, physical, and multi-dimensional.
Trees need to be viewed both as individuals and as important components of green networks for humans and non-humans. Due to the specific Nordic context, shrubs and ground vegetation also need to be included in a holistic understanding of the urban green space.
The 3+30+300 principle is a powerful communication tool for decision-makers, civil servants, different professions, and residents to rally around.

The city is an unnatural habitat for trees - and thus specific actions are needed to still make trees thrive and contribute to better cities.

Understanding the properties, needs, and characteristics of both native and introduced (exotic) species is crucial in a changing Nordic climate. Climate change is pushing climate zones and changing conditions for both existing urban trees and those that are being planted today.
The use of native species influences legibility, place attachment, and sense of place as well as contributing to local gene pools. Thus, native species are important, but it is important to realise that they are not native to the city.
Urban conditions for trees are often challenging, affecting the lifespan and viability of trees highlighting the complexity of species choice and selection.

Relationships between socio-economic vulnerability, trees, and green space have a specific Nordic dimension.

The relationship between tree canopy cover, green space access, and socio-economic status in Nordic cities differs from what the literature from North America and elsewhere suggests, as neighbourhoods with more vulnerable communities are not necessarily less green. The definition of socio-economic vulnerability also differs widely between the Nordic cities.
Access to green space and the presence of trees in connection to vulnerable groups such as children, the elderly, and the health-challenged remains an important planning challenge.
While green space is often available, safety and seasonal challenges need to be addressed in areas of socio-economic vulnerability.