The biodiversity indicator in the Takoma Park Native Tree Selection Guide provides a measure of how much a tree species will potentially contribute to ecosystem biodiversity through the food web.
When selecting a tree to maximize the contribution to ecosystem biodiversity, this indicator has the advantage of being easy to understand, available for a large number of tree species, and based on a growing body of scientific study.
But is it the only indicator that people should consider?
Below, Dr. Erwin points out the usefulness of multiple indicators and of certain ones specific to urban trees.
Dr. Erwin is a horticulturalist and professor at the University of Maryland College Park, where he is also Chair of the Department of Plant Science and Landscape Architecture. Dr. Erwin served for eight years as a Minneapolis Park and Recreation Commissioner, adding to his practical insights about urban forest management.
What do you think of biodiversity indicator presented in the Takoma Park Native Tree Selection Guide?
I think it’s fine but one could have many more indicators. Suppose someone wants a tree with yellow flowers. There’s nothing wrong with that. If you provide another indicator on flower color, that would be great.
Urban trees, particularly street trees, face stresses that shorten their lives by two-thirds compared to growing in a forest. Indicators about how various tree species can handle these stresses are useful.
What sort of urban tree indicators would you suggest?
One type would be indicators of how well the roots and leaves of different species tolerate extreme temperatures, heat waves, and drought, which are likely to increase due to climate change. It would be particularly useful if such indicators could be combined into an index for species resilience in difficult urban sites.
An indicator of how susceptible a tree species is to storm blow down could help in selecting less hazardous species. Even something as simple as how much shade a tree species provides could be a useful indicator when reducing the heat island effect is a goal.
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