the boreal forest is one of the most extensive biomes in canada at an estimated 2.7 million ha. the requirement for a growing agricultural sector, along with a currently warming climate, has accelerated the conversion of boreal forest to agriculture. the resulting more intensive soil use may have a significant impact on the soil ecosystem, potentially degrading some ecosystem services, such as carbon sequestration, water purification, climate regulation, nutrient cycling, flood regulation, habitat for organisms, climate control, and the provision of food, fibre, and fuel. analysis of soil health using a structured synthesis of physical, chemical, and biological indicators can provide information on the sustainability of soil use. soil health as a metric of soil change can inform farm managers and policy-makers of the status of soil and increase awareness of sustainable farm practices in a region. in this dissertation, i assessed the impact of land conversion from boreal forest to agriculture near thunder bay, ontario, canada. i found that land conversion created declines mainly in biological soil health indicators, along with total nitrogen and carbon. soil health indicators related to soil carbon were the most informative to land disturbance in plots < 10 years since land conversion; indicators associated with forage cropping systems on thunder bay dairy farms. carbon and nitrogen mineralization increased with time since conversion from forest. archaeal and fungal abundance increased after land conversion. in addition, land conversion altered the microbial functions related to carbon, nitrogen, and phosphorus cycling. new knowledge about the effects of land conversion in the boreal forest will play a critical role in developing and implementing environmental and agricultural policies supporting canada’s soil sustainability and soil health.