Compost improves soil properties and tree establishment along highway roadsides

Abstract Highway roadside landscapes can be used to increase urban canopy cover by way of tree planting and successful tree establishment. Soil compaction and topsoil removal resulting from construction activities along roadside sites, contributes toward extensive and prolonged transplant stress; limiting the survival and effective establishment of planted trees. The current study sought to evaluate the efficacy of soil restoration as an intervention tool for facilitating the long term success of tree plantings on two unmaintained highway roadside sites. Soil level impacts immediately following and 5 years post restoration were therefore characterized. Restoration methods included mechanical de-compaction with and without the addition of increasing rates of organic amendment (0 %, 10 %, 25 % and 50 % v/v municipal food and yard waste) to improve the key soil properties (Db and SOM) influencing tree survival and establishment. At 5 years post restoration, total survivorship ranged from 46 to 92 % according to treatment, while the greatest cumulative tree growth as demonstrated by the cumulative change in tree height and trunk diameter was found to occur across trees planted into the 25 % v/v treatments. Average Db and SOM for the 25 % v/v treatments, although not the most improved of all treatments, was consistently and significantly improved as compared to compacted, amended and de-compacted, un-amended controls over the course of the trial. The results of the current study demonstrate the inadequacy of survivorship as a sole measure of planting success. Findings pertaining to individual tree and soil level impacts support the incorporation of moderate volumes of stabilized, high quality organic amendment prior to planting as an effective method for providing immediate and sustained improvements to Db and SOM. These improvements are found to coincide with improved tree establishment as demonstrated by cumulative tree growth, across the otherwise unfavourable soil conditions that are characteristic of post-construction, naturalization planting sites.