Green infrastructure has a lot of benefits: nature can improve people’s mental and physical health; vegetation helps reduce building energy use by providing insulation and cooling; and plants and soils store carbon.

The problem is there’s no way of evaluating whether green infrastructure projects really live up to their promises. How much carbon does a street tree actually sequester? And what’s the greenhouse gas impact of growing seedlings in nurseries, assembling the raw matterials for potting soil, and transporting mulch to where it needs to go?

The solution, according to a group of researchers in Finland: develop carbon footprint standards (known as Environmental Product Declarations or EPDs) for plants, soils, and mulches similar to those that already exist for building materials. This would provide an objective check of cities’ and developers’ claims about the environmental benefits of green infrastructure projects, and help landscape designers plan, construct, and maintain green spaces in the most climate-friendly way.

“Landscape designers will need to know how much carbon typical plants and growing media can sequester. This should be seen as basic product information that enables us to mitigate climate change,” says study team member Matti Kuittinen, adjunct professor of architecture at the University of Aalto in Finland.

But that basic information isn’t so simple to assemble. As a first step to developing such standards, Kuittinen and his colleagues analyzed how carbon flows through plants, soils, and mulches in different phases of their life cycle. Based on this analysis, it’s clear that standard methods for assessing the carbon footprint of building materials will need to be tweaked when applied to components of green infrastructure, the researchers report in the International Journal of Life Cycle Assessment.

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