Biodiversity Index for Urban Trees: 105 Species at a Glance
The 2021 Biodiversity Index for urban trees rates 105 tree species and cultivars by their ecological value for insects, birds, and small animals, on a scale from 0 to around 6. It comes from SWILD on behalf of Grün Stadt Zürich (final report 09.12.2021) and has been used since 2026 in the BAFU Adapt+ funding programme as a prioritisation criterion for tree planting: values above 2 in settlement areas, or 3 or above outside them, are considered eligible for funding.
- Number of species/cultivars rated
- 105
- Publication
- SWILD / Grün Stadt Zürich, final report 09.12.2021, Table 9
- Adapt+ threshold, settlement area
- > 2 (exclusive)
- Adapt+ threshold, outside settlement area
- ≥ 3 (inclusive)
- Highest index value in the dataset
- Field maple (Acer campestre), 4.3
- As of
- 26.08.2026
What the index measures
The Biodiversity Index rates how much ecological value a tree species provides to its surroundings — in particular as a food source and habitat for insects, which in turn feed birds and other small animals. The publication distinguishes two base values per species: a street-tree index (excluding crown volume, more conservative) and a park-tree index (including crown volume, usually higher).
Native and long-naturalised species with a complex crown structure tend to score higher than exotic ornamental trees that offer little food for local insect species.
Where the index has an effect today
BAFU communication UV-2554 on the Adapt+ funding programme (29.01.2026) requires, in chapter 5.3.1, that tree species selection prioritise species with a Biodiversity Index above 2 in settlement areas, or at least 3 outside them. This has turned an originally purely scientific index into a funding criterion with direct financial relevance.
Two corrected typos from the original publication
When importing the table, two typos in the publication itself were corrected — not introduced by us: "Junglans regia" was corrected to Juglans regia (walnut), and "Pterocarva fraxinifolia" to Pterocarya fraxinifolia (Caucasian wingnut). The original misspelling remains resolvable as an alias in our database, in case someone searches for it exactly.
For your business
If you are preparing an Adapt+ application for a municipality or compiling a planting list, a species' index value is an objective, source-backed argument to use with commissioning authorities — regardless of whether you work with Gardinova.
For the commissioning authority
The index comes from an independent scientific publication, not from a software vendor — it can be cited directly as evidence in a tender or funding application, without any vendor tie-in.
What this does not mean
- The index is a 2021 scientific publication, not a legal norm — a future revision by BAFU or a successor publication could change individual values.
- For 3 unnamed Ulmus hybrid cultivars there is no established common English or German name — we have not invented one; the field is intentionally left blank.
- The index rates a species' general ecological performance, not its suitability for a specific site (soil conditions, climate zone, and space requirements still need to be assessed separately).
Frequently asked questions
- What does a Biodiversity Index of 2.9 mean?
- A value of 2.9 sits just below the Adapt+ threshold for settlement areas (which requires an exclusive "> 2", so 2.9 satisfies it) and below the "≥ 3" threshold for locations outside settlement areas — here it is decisive whether the street-tree or the park-tree value is used, since the two base values can differ.
- Which tree species has the highest index value in the dataset?
- Field maple (Acer campestre) reaches 4.3, one of the highest values in the entire 105-species dataset.
- Is the Biodiversity Index legally binding?
- No. It is a scientific publication. It only becomes binding indirectly, when a funding programme such as Adapt+ explicitly adopts it as a criterion in its guidelines.