Suofei Li

This project investigates the effect of organic mulch on one of the important conditions necessary for tree growth in cities – moderation of soil temperature in the near-surface rooting zone. It is one component of a broader research collaboration between Ryerson University‟s Urban Forest Research & Ecological Disturbance (UFRED) Group and Bruce Tree Expert Company that is working on identifying management approaches that can protect and enhance the growing medium for city trees. The study area for this project is an urban park on the Exhibition Place grounds in Toronto, Canada. Intensive soil temperature sampling (collection of in-situ data using and offset grid sampling design) was performed from June through August 2011. Spatial variation in near-surface soil temperature was measured under mulch ring treatments with different radii (0.75, 1, and 1.5 m), and in adjacent soil covered with turf grass. Ordinary kriging was used for interpolation of point data (soil temperature measurements) to a surface. Cross-validation statistics and visual inspection of temperature prediction surfaces were used to select optimal parameters for inclusion in the ordinary kriging procedure. This study reports the findings of five temperature prediction surfaces produced for each of two contiguous sections of urban parkland. Overall, results show that the spatial pattern of near-surface soil temperature changed dramatically following the application of mulch. Soil was coolest nearest to the main stem of trees where mulch was applied. The extent of temperature moderation was positively associated with the size of the mulch ring, where this study found that a ring of radius 1.5 m was most effective at maintaining optimal temperatures in the rooting zone. Overall, this project demonstrates that larger diameter mulching treatments have the potential to reduce heat stress for city trees and are, therefore, recommended as an urban forest management strategy.