Kama Paudel

Urban sustainability, until very recently, has concentrated on built structures; only afterthought has been given to the protection and enhancement of natural spaces within cities. This situation has led to the degradation of soil conditions necessary to support mature trees in many urban areas. This study was conducted to investigate the potential for park naturalization to improve soil quality in a forested portion of Kew Gardens Park, Toronto. It was designed to compare and contrast soil conditions in a 6-year naturalization enclosure with those found in adjacent managed parkland. Soil compaction, bulk density, texture, moisture, pH, electrical conductivity, and soil-available nitrogen measurements were collected at 104 sample sites and analyzed using the geostatistical approach of ordinary kriging. Log normalization was applied to soil data exhibiting highly skewed data distributions, which included compaction, water infiltration, electrical conductivity, and nitrate. Prediction maps, and associated standard error surfaces, were generated for each soil variable. Results showed that elevated soil compaction (>2000 kPa) and bulk density (>1.8 g/cm3) were spatially correlated with locations of high pedestrian traffic, and with corridors used by park maintenance vehicles. Such elevated values are known to restrict tree root growth and respiration, as well as impair soil water infiltration; this contrasted with no compaction or bulk density measurements above a root restrictive threshold in the naturalization area. Soil pH was found to be slightly acidic in the naturalized area, and within the range necessary for optimal plant-nutrient absorption. Alkaline soil was encountered in the north and northeastern portions of the managed park; similar locations were found to have higher electrical conductivity and nitrogen readings. Overall, this research found that park naturalization was highly spatially correlated with physical and chemical soil conditions more favorable for plant growth.