Soil compaction at tree-planting sites in urban Hong Kong

Various soil limitations commonly influence the performance of landscape plants in cities, with physical problems often neglected. This study evaluates the compaction of soils at tree sites in urban Hong Kong at both roadside and park habitats. Field and the laboratory studies evaluated selected physical properties of 100 samples, including structure, texture, consistence, bulk density, and porosity. A large proportion of the soils are excessively coarse textured and stony, with widespread structural degradation and compaction. Two-fifths of the samples have bulk densities above the 1.6 Mg/m³ threshold, with some exceeding 2Mg/m³. An increase in particle packing results in collapse of interstitial voids and shifts in pore-size distribution. The causes and consequences of compaction are discussed in relation to tree growth. The findings indicate an association between soil texture and compaction, with the sandy nature of the soils checking the extent of compaction and its negative impacts on root development. The results yield useful management implications for adoption in the local urban tree program. Copyright © 1998 International Society of Arboriculture.