Tree Crown Volume (BKV)

Greening is playing an ever greater role in both urban and rural areas. With the introduction of the European Nature Restoration Law in 2030, authorities and project developers will be required to create more space for greenery. In the Netherlands, this takes shape in the National Tree Standard, which comes into force from May 2024. Where the number of trees used to be the benchmark, the focus is now on tree crown volume (BKV).

BKV refers to the total volume of tree crowns that contributes to a healthy and liveable climate. This is not determined by the number of trees, but by their combined effect on shade, cooling and biodiversity. Scientific research, including that of Professor Cecil Konijnendijk, supports this approach with the 3-30-300 rule:

At least 3 trees should be visible from a home.
A neighbourhood should have at least 30% tree canopy cover.
Everyone should have access to a green space within 300 metres.

Studies show that 30% canopy cover is a threshold at which the positive effects of greenery on health, cooling and biodiversity become measurable. Many Dutch cities have not yet reached this standard, which means there is still ground to make up.

BKV in practice: a more efficient approach to greening

For a long time, the focus was on the number of trees planted, but the National Tree Standard introduces a different approach: steering greening by tree crown volume. The larger the BKV, the sooner a tree delivers functional value for its surroundings.

An example:

A Platanus hispanica measuring eight metres in height with a trunk girth of 30 to 35 centimetres at planting already has a crown volume of 35 cubic metres. To achieve the same volume, eight young trees with a trunk girth of 14 to 16 centimetres would be needed.

So larger trees deliver returns more quickly: more shade and faster CO₂ storage. In addition, young trees, although they may seem cheaper to buy, require more maintenance in the long term. Mature trees are more robust and need less management, which saves costs over time.

For a site of five thousand square metres, the National Tree Standard requires a total tree crown volume of eleven thousand cubic metres. That means:

With young trees (fourteen to sixteen centimetres trunk girth, BKV: five cubic metres per tree), two thousand two hundred trees are needed.
With mature trees (thirty to thirty-five centimetres trunk girth, BKV: thirty-five cubic metres per tree), three hundred and fifteen trees are sufficient.

Alongside the numbers, space and cost savings also play a role. Young trees take up a lot of space and require intensive maintenance. Larger trees deliver the desired effect from day one and need less management, which means maintenance and replacement costs are significantly lower in the long term.

Choose balance

Large trees provide rapid cooling and air purification, but smaller species are important too. A healthy mix creates a tree stock that is resilient and ecologically valuable for the future.

View our trees

Balancing large and smaller tree species

The National Tree Standard emphasises tree crown volume because larger trees contribute directly to cooling, water retention and air purification. Even so, smaller tree species also have an important role to play. Greening that stands the test of time calls for a varied tree population, in which both large and smaller species have their place. The right balance is crucial: choose trees with a large crown volume wherever possible, but also take account of sites where smaller species are a better fit and ecologically valuable. First-size trees deliver a large BKV more quickly, but second- and third-size trees contribute as well, especially when planted in a semi-mature form. It is also important to opt for a mixed planting of both native and non-native species that will remain resilient in the changing Dutch climate.

How Van den Berk Boomkwekerijen helps deliver BKV

Successful greening is about more than planting trees. The right tree selection and planting area design determine long-term success. At Van den Berk Boomkwekerijen, we help with:

BKV calculations based on the project requirements, so it is clear how much tree crown volume is needed and how this can be achieved efficiently.
Supply of large trees that contribute immediately to a greener environment.
Advice on planting sites, tailored to soil, rooting space and water management.

By working together early in the design process, the available space is used to best effect and the result is a green scheme that meets the standard straight away and remains effective in the long term.

Need tailored advice? Get in touch for personal guidance or a bespoke calculation. Together, we can create greening that is ready for the future.