Diversitree is an interactive web-based visualization tool, research paper (published in Urban Forestry and Urban Greening) and open-source project repository (GitHub) exploring the diversity of species, genera and family in street tree inventories within — and across — eight cities internationally.

We measure street tree networks against the long-standing “10/20/30 rule”, which suggests an urban forest should be no more than 10% of one species, 20% of one genus, and 30% of one family. We also use diversity indices — the Shannon Index and Simpson Index — to account for the abundance and evenness of the species present in the city. These two measures provide a snapshot view of how dominant any single species, genus, or family is within a city, and a glimpse into the diversity of the street tree network as a whole.

Of course, how species adapt to local conditions is more important than diversity in and of itself. Street tree diversity should always seek to fulfill a range of community forest objectives, rather than adherence to numerical standards alone. Those numerical standards, however, can show us places where street tree diversity has room to grow.