Biochar for Restoration in the Boreal Forest of Northwestern Ontario, Canada
Bieser, J. M. H. . 2023. M.Sc. ΔUniversity of Toronto
Abstract
Pyrolyzed organic material, or biochar, has been proposed as an effective soil amendment for
reforestation and mine reclamation due to its capacity to retain soil nutrients and water,
immobilize toxic metals, and its recalcitrance to mineralization. Potential sources of biochar in
remote northern sites are high-carbon wood ash from wood waste gasification, and natural
charcoals generated by wildfire. My thesis examines the effects of biochar application on boreal
species growth and establishment in three study systems: (1) the effects of a poplar wood biochar
and a mixed-feedstock high-carbon wood ash biochar on soil and vegetation in a 3-year field
experiment in NW Ontario, Canada; (2) the effects of a 'natural' biochar and mixed-feedstock
high-carbon wood ash biochar on mine tailings reclamation in a 2-year field experiment at a gold
mine in northern Ontario, Canada; and, (3) the potential for biochars to sorb allelochemicals and
mitigate allelopathic effects on seed germination and early seedling development in three
common invasive plants in Canada, garlic mustard (Alliaria petiolata), tree of heaven (Ailanthus
altissima) and yellow sweetgrass (Melilotus officinalis). I found that biochars improved soil
conditions and enhanced growth of native plant species, resulting in large increases in substrate
C, reduced substrate bulk density, and up to a 4.5-fold increase in planted native grass biomass.
Biochar additions also enhanced availability of the plant nutrients P, K, Mg, and Zn; high-carbon wood ash biochar increased spot measurements of soil moisture, but also increased levels of Cu,
Mn, and Pb. Natural biochar and mixed-feedstock high-carbon wood ash biochar reduced cover
of Melilotus spp., an abundant invasive and allelopathic taxon. Amendments had large effects on
plant community composition, generally favoring native species. Addition of high-carbon wood
ash resulted in declines in growth performance of planted white spruce (Picea glauca); a path
analysis suggests this was due to effects of toxic elements rather than indirect effects of
competition with non-tree vegetation. I conclude that while there are large differences in plant
species responses to biochars, and potential for toxicity effects and indirect effects mediated by
plant competition, overall, results suggest some benefits of biochars, including high-carbon wood
ash biochars, for forest regeneration and mine reclamation in northern environments.
