This study investigates how changes in forest canopy density, measured through leaf area index (LAI), influence microclimate, air quality, and soil moisture during the autumn leaf-fall period in temperate deciduous forests at the University of Toronto Mississauga. As foliage declines, increased canopy openness alters local energy balance, moisture retention, and the capacity of vegetation to intercept airborne pollutants. To quantify these effects, meteorological stations positioned beneath the canopy continuously recording temperature, precipitation, wind, radiation and fine particulate matter (PM2.5) , while LAI, and soil moisture are measured weekly in autumn. By integrating microclimate and environmental monitoring with canopy structure data, this project examines how seasonal canopy transitions regulate air filtration, hydrological exchange, and microclimate stability in temperate ecosystems. Preliminary results show pronounced contrasts among forested, grassland, and open reference sites. Mean PM2.5 concentrations at the open site were approximately 90% higher than beneath the forest canopy and 93% higher than in the grassland. Wind gusts beneath the forest canopy were roughly 36% lower than at the open site and 30% lower compared to the grassland, indicating strong canopy-driven wind attenuation. Incoming shortwave radiation at the grassland was approximately 77% higher than the forest. The forested site exhibited 29% lower soil moisture content on average. These trends become more pronounced when examined alongside seasonal declines in LAI, highlighting the role of autumn canopy loss. These findings demonstrate the importance of high LAI in urban settings and clarify autumn’s role in regulating ecosystem processes.