What About the Willow?
“As the Tree grows, the river flows
and life continues to thrive….” -Debra J. Stiles
by Arden Bonokovski
So Mark asked me if I knew anything about how the wonderful willow is able to clean up so many of our messes in nature….
Here is what I have found out. Willows are an excellent candidate for this work as they have deeper root systems that the typical grassy plants used in eco-restoration, so they are able to detoxify much deeper soil than the typical species. Willows are able to do so because they are resistant to heavy metals such as cadmium, copper, zinc, nickel, lead and iron. They are also desirable candidates as the vastness of the genus means that different species of willow are native to most continents, making it easy to find a species of willow suitable for any area. So far it is known that willows are able to detoxify environments in four ways: phytoremediation, phytodegradation, phytostabilization, and rhizofiltration.
Phytoremediation is the extraction of heavy metals from soil through the uptake of the toxin by the roots of the willow followed by the translocation of the toxin to the above ground organs of the plant. The high biomass of a willow tree or shrub allows for a large uptake of the heavy metals.
Phytodegradation is the accumulation and degradation of toxins by plants. A study by Thompson in volume 8 of the Landscape Architects journal (1998) entitled Botanical remedies showed that the Prairie cascade willow was able to cleanse soil contaminated with oil, by stimulating oil degrading microbes that reside tin it’s root system.
Phytostabilization is the dehydration of toxins and the prevention of transportation by run off. This is most commonly used by industries that produce toxic waste. By planting willows on top of landfills for example, they absorb all of the water in the waste to prevent toxins from seeping into and contaminating the surrounding area. Willows can also be planted around landfills where they absorb any run off before it reaches the surrounding area
Rhizofiltration is the uptake of toxins in water through the roots. Willows are good at this because they are very tolerant to flood conditions. I found a very exciting study by Corseuil & Moreno, published in volume 35 of the journal of water restoration (2001) entitled Phytoremediation Potential of Willow Trees for Aquifers Contaminated with Ethanol Blended Gasoline. This study discovered that the weeping willow was able to reduce the concentration of ethanol and benzene in water by more than 99% in less that one week!
So the willow is a great tool to use to reduce the toxins in our soil and water. In all of my reading the only caution I found in using willows for any one of these processed was that wildlife had to be kept away from the willows, as they contain high levels of heavy metals that could be ingested by herbivores.
Now we know that the willow really is wonderful.
