Open Collections

Cheung, Chi Hung

University of British Columbia

Urbanization and limited supply of natural soils have led to widespread use of human-made soils in urban landscapes. In Canada, soil blends composed primarily of sands and compost are now commonly used as growing media throughout cities and are codified in the Canadian Landscape Standard. In Vancouver, about 40 percent of land is pervious surface. As land is developed or redeveloped, soil blends are increasingly replacing existing topsoil in these areas. Consequently, their impact on urban vegetation, including trees, will be significant, particularly as cities face extreme precipitation and drought events due to climate change. However, urban soil blends have received limited research attention. Although they are essentially structureless at installation due to mechanized screening of the components, little is known about their ability to develop soil aggregates, accumulate carbon over time, and maintain balanced water dynamics across vegetation types. These characteristics are closely linked to key soil physical properties, which we assessed through soil sampling and measurements of in situ saturated hydraulic conductivity and soil depth at 88 sites on the University of British Columbia campus that had been redeveloped with soil blends over the last 30 years. Sites were vegetated with one of four landscape types: grass, trees with grass, shrubs, or trees with shrubs. Analyses included aggregate size, carbon content, particle size distribution and plant-available water. Soils under grass, whether alone or with trees, were shallower (averaging 23 cm) than under non-grass landscapes, while soils under trees with shrubs had the deepest average depth at 42 cm. Soil aggregate mean weight diameter was overall low, but greater in older soils, which were also relatively finer textured. This suggests that the differences in aggregation were primarily due to changes in the specifications of the soil blends over time, with newer soils containing higher sand content and fewer fine particles. Nevertheless, total soil carbon content was similar, regardless of soil age. All soils had very high saturated hydraulic conductivity but low plant available water, likely due to extremely high sand contents. These findings highlight soil blend limitations and inform urban soil management to enhance vegetation and ecosystem services.

Text

2025-05-13

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/91121

Forestry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/