As climate change progresses, identifying climate outliers in a living collection can contribute to the resilience of the collection and provide unexpected opportunities for plant conservation and public education.
The methodology, based on a process developed at The Morton Arboretum and outlined in its guide, A Methodology for Identifying Climatic Outliers in Living Collections, provides a framework for other institutions to find climate outliers that may be in their own collections to guide climate adaptation and species selection planning efforts.
From July through December 2024, The Morton Arboretum Collections and Horticulture department conducted a survey of its living collections to determine which plants were “climatic outliers,” plants with an expected USDA Hardiness Zone higher than the Arboretum’s zones 5b and 6. The USDA Hardiness Zone map shows average annual temperature lows that can be used to determine where plant species are most likely to perform well, based on cold tolerance.
The Arboretum’s survey found 18 plant species with an expected hardiness of 7 and three plant species with an expected hardiness of 8 growing on its site. These findings will inform the Arboretum’s curation and plant collection practices moving forward.
Using this methodology, public gardens and other institutions with plant collections can identify species already within their collections that may be particularly resilient to climate change. This can supplement ongoing research, such as plant trials and breeding plants for heat and drought tolerance.
Climatic outliers also provide an opportunity to discuss climate change and plant adaptations for public education.
