Maximizing biodiversity: Top 10 tips from the field

This post is adapted from a talk given at the Grey 2 Green Cascadia symposium in November 2023 by GRIN board member, Ryan Vasseur. Ryan is the Manager of Living Architecture Ecosystems at Architek, a company focused on green roofs, trellises, living walls, and more. He is passionate about the ability for green roofs to mimic healthy ecosystems that benefit pollinators, beneficial insects, birds, and more.

This post features my Top 10 methods to maximize biodiversity on green roofs, which I’ve been experimenting with for the last 7 years.

The potential to increase biodiversity on green roofs is enormous. It can be done with an array of green roof types from intensive roof gardens to simple sedum roofs. Biodiversity can be enhanced at any stage of the green roof lifecycle, from design to installation, right through to maintenance activities. We can enhance these ecosystems to create habitat, forage, and security for diverse species of bees, beneficial insects, and birds.

It’s important to note that many green roofs in coastal BC are currently designed with sedum monocultures, which limits opportunities for biodiversity. While some designers seem to love pre-grown sedum mats and tiles, the plastic webbing and geotextile layers significantly limit any diversification of substrate (depth, composition) or vegetation. My team and I have found ways around this, for example, planting appropriate perennials in the spaces between mats or tiles.

My Top 10 methods are given below, divided according to the different points of time in a green roof project: Design, Installation and Maintenance.

DESIGN

1. Work closely with designers early in the green roof life cycle. Communicate that the best green roofs are built with diversity in mind (right from the start).

2. Seeing is believing! Showing designers photos and video examples of the differences between biodiverse green roofs and monocultures has an impact, whether via lunch & learns or green roof tours. This is why GRIN is so committed to green roof tours followed by happy hour! Join our mailing list to hear about our 2024 offerings and get first dibs on registering for a spot.

INSTALL

3. Hydroseeding or hand broadcasting wildflower seed mixes is a cost-effective way to spread biodiversity on a green roof. Ensure that you customize your seed blend with a high diversity of native species. I’ve found a couple seed suppliers that allow me to customize my blend such as Satinflower Nurseries. Be sure to check the species composition and avoid blends with invasive or aggressive non-native species!

4. During construction, add a thin layer of biologically active compost above the growing media to ensure good plant and soil health. Premium Soils is a local supplier that makes healthy compost. I advocate taking it one step further, by inoculating the soil with mycorrhizal fungi. This must be done before the plants go in, however, as these fungi require contact with plant roots. We have worked with Jo Tobias at RootShoot Soils to test and apply amendments such as compost extract that increase fungal content and other markers of biological soil health.

MAINTENANCE

5. Record species of bees and beneficial insects that are visiting your green roofs. You can record your observations on a range of citizen science platforms, which helps our collective understanding of populations. For example, check out iNaturalist and Bee Tracker, a project of the Native Bee Society of BC.  

6. Augment biodiversity on sedum green roofs by adding native species (flowers, grasses) in the post-install maintenance period. My top 5 are coreopsis, nodding onion (Allium cernuum), goldenrod, lupine, and yarrow. These species are excellent for native pollinators and the wildflowers cooperate well with the sedums. Experiment and observe which native species thrive on sedum rooftops in your region. Let us know what you discover in the comments below!

The sedum meadow of the Vancouver House green roof features purple coneflower, yarrow, camas, nodding onion and much more.

7. Assess, evaluate, and add soil microbes. Biodiversity starts in the soil, and the maintenance period is a great time to add compost extract rich in microorganisms. Note that some projects have loading constraints on adding more material, so make sure to clear this with the building owner or project manager first.

The microbial soil community (e.g., fungi, bacteria, microbes), are essential for healthy plants and soils, including green roof growing media. If you’re able, I highly recommend examining your amendments under a microscope or consult with a soil biologist. This knowledge functions in reverse, too: an underperforming green roof can be improved by adjusting the microbial community, often the proportional balance of fungi and bacteria. 

Lastly, don’t panic if you see mushrooms pop up on your roof! This is a sign of mycelial networks working between the plant roots.

8. Add amendments to enhance plant and soil health. I like using seaweed, humic acids, and other organic amendments, which I get from Organic Gardener’s Pantry in Victoria, BC.

9. For green roofs with meadow character, consider using a European scythe instead of an electric or gas-powered weed eater. They are much less disruptive to wildlife than machinery. The image below shows one of my colleagues scything the Arbutus Residences’ green roof meadow last fall.

10. During the maintenance period, consider leaving beneficial native volunteer plants that pop up on the roof such as fireweed, lupin, goldenrod, and more.

Let us know what you think. Please use the comment box for any questions, experiences or resources you’d like to share that relate to biodiversity on green roofs. Feel free to email us and/ or join our mailing list here.

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