Toronto biochar street tree Experiment
In collaboration with the City of Toronto, the Thomas Lab is currently testing the effects of biochar on City-managed street trees. This research will assess the effects of biochar soil amendments on the four most common species planted on "hard surface" sites in Toronto, including hackberry (Celtis occidentalis), honey locust (Gleditsia triacanthos), elm (Ulmus spp., mainly U. americana hybrids), and Kentucky coffeetree (Gymnocladus dioicus). The biochar in use for this project is created through pyrolysis of wood waste material, and has been provided by industry partners Titan Clean Energy Projects and Haliburton Biochar. This study represents the first large-scale designed experiment of biochar effects on street trees globally. More than 200 street trees in Toronto's downtown core are involved in the study.
What is Biochar?
Biochar refers to a type of charcoal created by the pyrolysis of organic waste materials and intended for use as a soil amendment. It's different from cooking charcoal in that the energy-rich bio-oils are removed, leaving a highly porous solid material. Biochar is analogous to fire residues from natural wildfire, so many plants and other organisms are pre-adapted to biochar.
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Benefits of Biochar
Street trees in Toronto face numerous anthropogenic stresses. Soil compaction greatly reduces the aeration of the soil and its water holding capacity. Salts applied during the wintertime often enter the soil around trees, having direct toxic effects and reducing nutrient availability. Biochar increases soil water and nutrient retention and also helps remove sodium ions from the soil solution, combating the effects of high soil salinity. A particular advantage to biochar is its resistance to decomposition, which allows biochar to maintain soil porosity and resist soil compaction in the long term. In other systems biochar also enhances soil microbial activity and diversity. We thus expect biochar to be particularly beneficial for street trees.
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Overall Goals of the Study
Biochar provides an opportunity to divert urban wood waste into a sustainable resource that promotes the growth and health of street trees in urban areas. Additional project components include evaluating the use of urban wood waste as a biochar feedstock, conducting life-cycle analysis and economic evaluations of biochar use and production in urban forestry, greenhouse gas emissions associated with urban forest waste, and the potential broad-scale benefits to urban forest ecosystem function. Parallel projects are also underway in Québec City and Edmonton, enabling a broader evaluation of the potential for biochar in urban forestry across Canada.
