Trees for bioswales

Climate change is bringing more frequent extreme weather. Drought and water shortages are a problem, but so are heavy rainfall and flooding. The impact is felt in nature, agriculture, and our living environment. Think of dried-out natural areas, falling groundwater levels, but also flooding and saturated soils that can no longer absorb water fast enough.

One smart way to manage rainwater better is to build bioswales. These are natural water retention systems that temporarily hold rainwater and let it infiltrate into the soil slowly. Bioswales help reduce flooding, recharge groundwater, and increase biodiversity.

What is a bioswale?

A bioswale is a depression in the landscape where rainwater is temporarily collected and gradually infiltrates the soil. This helps prevent flooding, relieves pressure on the sewer system, and helps maintain groundwater levels. A bioswale also contributes to a greener, cooler urban climate and can function as a recreational green space.

Benefits of bioswales

Bioswales are being used more and more in urban areas and infrastructure projects. The benefits are significant.
• Better stormwater management: Bioswales slow the runoff of rainwater, so sewers are less likely to become overloaded and flooding is reduced.
• Groundwater recharge: The captured water slowly infiltrates the soil, replenishing groundwater. That benefits plants, wildlife, and our drinking water supply.
• Greater biodiversity: Bioswales provide habitat for plants and animals that naturally occur in wet areas.
• Cooler surroundings: Water and planting in a bioswale help lower the ambient temperature, which is especially welcome in cities.
• More attractive outdoor space: A well-designed bioswale creates a greener, more pleasant living environment.

Why plant trees in bioswales?

Trees play an important role in the bioswale ecosystem. They do more than support water management; they also make the surroundings more comfortable. Here are a few reasons to plant trees around bioswales:
• Water uptake: Trees help absorb and transpire water, so the soil becomes saturated less quickly and flooding is reduced.
• Soil stabilization: Tree roots improve soil structure and reduce erosion.
• Shade and cooling: Trees provide shade, which helps lower temperatures and reduces water evaporation.
• More biodiversity: Trees attract birds, insects, and other wildlife, strengthening the ecosystem around the bioswale.
• Improved air quality: Trees filter harmful pollutants from the air and contribute to a healthier environment.

Which trees and plants are suitable for bioswales?

Trees and plants in a bioswale must tolerate both dry and wet periods. Below are some suitable species:
Trees for bioswales:
• Alnus – Performs well in soils that alternate between wet and dry and improves the soil.
• Fraxinus – Tolerates moist conditions well and has a strong root system.
• Salix – Takes up large amounts of water and is ideal for wet soils.
• Populus – A fast-growing tree that can handle both wet and drier soils.
• Quercus – A strong tree that tolerates both dry and wet conditions.
• Taxodium distichum – Prefers wet soils, but also grows in drier locations.
• Nyssa sylvatica – Naturally a swamp tree, but it also grows well in less moist soils.

There are many more species suitable for bioswales. Would you like advice on which trees are the best fit for your site? Contact our advisors. We’ll be happy to help you make the right choice for a green, climate-resilient environment!

Did you know: The word wadi originally comes from Arabic and means “valley” or “riverbed,” but in Dutch it has also been turned into an acronym: Water Afvoer Drainage en Infiltratie. A wadi is basically a depression in the landscape or your garden where excess water flows and infiltrates into the soil.

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