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Transforming our urban forests into landscapes with various tree species is in our best interest as diversity helps make our cities more livable. Planting a variety of trees can improve wildlife habitat, help build resiliency and support various benefits that nature provides to humans.


Biodiversity refers to a variety of living organisms which can include plants, animals, insects and fungi. Planting a diverse range of trees can be very beneficial in an urban setting where there are often fewer trees, so each individual tree is very important. Tree diversity can also enhance the many social and environmental benefits that the urban forest provides. These become increasingly important as much of the world’s population shifts to “city-living.”

Check out "Montana Diversification"

Why is Tree Diversity Important?

To Improve Wildlife Habitat

Planting a variety of tree species can help support a variety of wildlife. For example, the hackberry tree produces fruit and seeds eaten by small mammals and birds and is a specific host for the hackberry butterfly. The sugar maple is great for nesting birds such as chickadees and woodpeckers. The Ohio buckeye produces large spring flowers that attract hummingbirds and fruits that are often eaten by squirrels. The white spruce produces seeds that are a great winter food source for chickadees and nuthatches. These are just some examples of how planting different trees can attract a wider range of wildlife species year-round. This is important since wildlife tends to have more difficulty sourcing food, water and shelter in an urban setting than they would in a natural forest.

Improve Urban Forest Resilience

Urban trees are often faced with many stresses such as air pollutants, invasive pests, road salts, high winds and drought-like conditions. Some trees are more equipped to handle these urban stresses than others. For example, when the invasive emerald ash borer (EAB) beetle was introduced to Ontario in 2002, many ash trees were lost. In years prior, a lot of ash trees were planted as street trees, so cities faced major tree/canopy cover loss in those areas. This can be avoided in the future by diversifying the types of trees that are planted.

Supports Ecosystem Services

Ecosystem services refer to the benefits that nature can provide to humans (and other living organisms). A healthy, diverse, urban ecosystem can help absorb air pollutants, promote physical and mental well-being, generate more environmental interest, improve water quality and improve soil quality. Monocultures (the planting of only one species) might be able to achieve some of these in the short-term but are not sustainable long-term. Not only does planting a wide range of species help the environment, but it can make cities more beautiful! A variety of trees means a variety of leaf shapes, canopy shapes, flowering/blooming times and fall colour.

For those that aren't familiar, the 10-20-30 rule is a guideline to reduce the risk of catastrophic tree loss due to pests. The rule suggests an urban tree population should include no more than 10% of any one species, 20% of any one genus, or 30% of any family.

Submitted by Adriana Rezai-S... on May 21, 2021

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