Toronto biochar tree Experiment

In collaboration with the City of Toronto, the Thomas Lab is currently testing the effects of biochar on city-managed trees. This research will assess the effects of biofertilizer and biochar soil amendments on tree establishment, in addition to soil and tree health. The five most common species planted on "hard surface" and “soft surface” sites in Toronto are integrated into this project, including hackberry (Celtis occidentalis), honey locust (Gleditsia triacanthos), Freeman maple (Acer x freemanii), elm (Ulmus spp., mainly U. americana hybrids), and Kentucky coffeetree (Gymnocladus dioicus). The biochar in use for this project is created through the pyrolysis of wood waste material, and has been provided by industry partners Titan Clean Energy Projects and Haliburton Biochar. For the soft surface Toronto tree planting trials, deactivated brewer’s yeast (Saccharomyces cerevisiae) was selected as the biofertilizer of choice, as it is a ubiquitous, nutrient-rich by-product of the beer brewing industry with little market value, and is widely available for urban soil fertilizer applications. If trial results are successful, this waste product has great potential

to contribute to a circular economy. This study represents the first large-scale designed experiment of biochar effects on street trees and soft surface tree plantings globally, with ~500 Toronto street trees included 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 wildfires, so many plants and other organisms are pre-adapted to

biochar.

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 of 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.

What is Bio Fertilizer?

Biofertilizer refers to an organic fertilizer derived from microbial organisms. Main types of biofertilizers include nitrogen-fixing bacteria, phosphorus biofertilizers, compost, mycorrhizal fungi, and yeast.

What are the benefits of bio fertilizer?

Biofertilizers promote plant growth through the introduction of organic materials with high plant nutrient content to revitalize soil microbial communities. Deactivated brewers' yeast (Saccharomyces cerevisiae) has been shown to enhance soil health by increasing microbial diversity, enhancing nutrient availability in soils, and improving overall plant biomass. Since deactivated brewers' yeast is an organic material, it offers a sustainable alternative to chemically synthesized fertilizers.

Overall Goals of the Study

Biochar and biofertilizer provide an opportunity to divert food and 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.

How will the amendment be applied to trees?

Treatments will be applied as a top-dressing in the top 0-15 cm soil depth by light raking. The doses are either 3 kg or 6 kg per tree for typical tree root zones. Biofertiliser treatments will be added as a solution onto the base of trees at the beginning of the growing season.
What kind of measurements will be conducted, and how often?

Measurements will be taken 2-3 times per year after treatments are applied. Measurements include: Responses of soil to amendment additions, including soil pH, nutrient status, microbial activity and elemental composition. Responses of soil greenhouse gas flux to biochar additions (CO2, CH4, N2O). Response of tree growth and health status to amendment additions such as tree height, diameter at breast height (DBH), leaf pigments, and crown height/extension.
What instruments will be used during measurements?

The following instruments will be used during data collection: Soil & leaf gas flux analyzer (carbon dioxide, methane, and nitrous oxide measurements) Optical Leaf Clip Meter (chlorophyll and leaf pigment data) Soil moisture meters
How long will this study last?

Measurements are planned to be continuously collected through 2027, however, longer-term monitoring of tree growth and mortality is planned.
Are the amendments natural, organic, or synthetic?

All amendments used in the study are organic.The biochar soil amendment we are using is certified organic by Seeds Canada Centre for Systems Integration (CSI). The inactivated brewer’s yeast (Saccharomyces cerevisiae) biofertilizer is a waste product that is not yet widely commercialized, so has not yet been formally certified as organic. However, brewer’s yeast is a common nutritional supplement and the inactivated form is a natural by-product of bread and beer production processes.
How often do treatments need to be applied?

Since biochar is resistant to decomposition, it requires a singular treatment. Once incorporated, biochar will remain in the soil.
Will the results of the study be available to the public?

The results of the study will be made available to the public via progress reports in 2026 and 2027. Exact dates are to be determined. A peer-reviewed published scientific article outlining the comprehensive project may come at a later date.
Are there any environmental or health risks associated with the soil amendment applications?

The application of biochar materials to street trees as a soil amendment carries very low risk as it is an inert substance and is applied in a coarse particle size to reduce dust. Once the biochar has been applied below the mulch, there is little risk of coarse biochar breaking down via wind and water erosion. There are no associated health or environmental risks associated with applying biofertilizer as a soil amendment.

For further information or to report concerns regarding this project, please contact 311 or refer to the City of Toronto website: www.toronto.ca/trees/