top of page

Medicine from Bark, Shrubs to Mitigate Pollution, and Trees on Roofs: 6 months of learning

A picture of bark shavings on a towel, with recently whittled prunings nearby
Bark being prepared for medicine-making

Well, originally these were supposed to be separate blog posts, but I never got around to it, which is something that happens while working and parenting in a pandemic. But! Here's three of the coolest things I learned about trees about trees and shrubs over the last six months:

  1. You can make herbal medicine from whittling prunings.

I was lucky enough to get to take a course with Juliette Abigail Carr from Old Ways Herbal up in Vermont. We learned about all of the amazing compounds plants make to protect themselves from various pathogens, and how some of them work for people, too! For some reason, I had always thought bark harvesting involved 'fancy trunk stuff', but I'm here to tell you that it doesn't. You just shave the bark and cambium off of normal prunings, like are pictured above. Incredible! You can use these pruning shavings to make syrups, salves, and weight-to-volume tinctures. Another way in which prunings are an amazing and often under-utilized resource.

2. Trees and shrubs capture a LOT of particulate heavy-metal pollution from the air, but some are a LOT better than others.

I was able to attend the International Society of Arboriculture (ISA) conference in 2021, and hear Dr. Francesco Ferrini from Lucca, Italy, describe his research into this. The city of Lucca is twice as polluted as New York City, and an estimated 56,000 people die because of pollution in Italy every year according to his research. 1 square centimeter of leaf area adsorbs 10-70 micrograms of particulate matter every year, but broad-leaved trees adsorb more than conifers and evergreens more than deciduous. And the more complex, big, and hairy the leaves the better. Even on a genus level adsorption varies, for example sycamore maple retains far more particulate matter than Norway maple. My main takeaway from this talk? In our current New England climate, we have relatively few winter-hardy broadleaved evergreens. Rhododendron is one example, so if you're planting trees as a roadside pollution barrier, maybe consider those. Prune for shrubbiness and increased leaf area and density if you're going for a pollution barrier--this could mean intensive or minimal pruning depending on the species. Be wary of roadside foraging! Leaves are adsorbing a lot. Check out these slides from the Ferrini lab for more information.

3. Green roofs have come a looooooonnng way!

Also at the ISA conference, I was able to hear Jason Lubar and Laura Hansplant talking about growing and anchoring trees on elevated structures, specifically on roofs. There's really impressive engineered soil available for rooftop growing these days that's a lot lighter than normal soil: 65-90lbs/cubic foot compared to regular soil that's normally more in the range of 110./140 lbs/cubic foot. While there's still a lot to think about and learn in terms of anchoring trees (rootball vs higher up, the need for slack in systems to allow trees to build their own strength), inoculating rooftop soils with beneficial fungi, and engineering buildings to support the weight of saturated soils and mature trees, the foundation is there and it IS possible to grow shade trees on roofs. Very cool.

That's a wrap. Always happy to chat about anything tree-related and nerdy at --have you learned anything cool about trees or wood or wood products lately?


bottom of page