Abstract
Ornamental tree planting and establishment in cities is a great challenge because urban soil physical properties are unfavourable to the development of root systems. Our objectives were to measure (i) the effects of organic matter on soil physical properties and tree development, and (ii) the effects of ensuing root development on soil physical properties. Using twenty-four 600-L planted or bare soil containers, we monitored physical properties such as dry bulk density, aggregate stability and near-saturated hydraulic conductivity of our reconstituted soils over a 5.5-year period. A 28-cm thick top layer of sandy loam amended with 40% (v/v) sphagnum peat or organic composts was laid on top of a 28-cm thick layer of sandy loam. Bare-root Ostrya carpinifolia trees were planted in half of the 24 containers, and we monitored shoot development and root biomass and distribution. After 5.5 years, trunk diameter had increased from 59 mm for the control soil to 66 mm for soil mixed with green waste compost, and 74 mm for soil mixed with co-compost of sewage sludge and wood chips. After 4.5 years, trunk diameter was strongly correlated with the total number of axes (r = 0.94) and fine root length density (r = 0.98), and was confirmed as a good indicator of tree development. Fine root development increased stable aggregate formation in all treatments as compared to bare soil. After 4.5 years after planting, the tree root system induced by a high organic matter input had significantly improved near-saturated hydraulic conductivity and was fit to support fertile urban soils.
Highlights
Ornamental trees in urban areas are a major societal issue
Between May 2005 and May 2006, the relative diameter growth rate was low for control soil (CO) and green-waste compost (GW) (0.24 and 0.36 mm year-1, respectively) and high for sludge/woodchip compost (SW) and sphagnum peat (SP) (0.56 and 0.52 mm year-1, respectively)
In May 2010, after five growth seasons, the Ftirge. 2eEgvorloutwionnovienr 5S.5WyearhsaofdOtsthryea cgarrpeinaitfoelisattrdunikadmiameteeterr 1(m73abomvemthe, sFoiilgli-ne iun rthee c2on)t,rovla(CluOe, s )f,osoril+thsluedgter/eweoosdcghripocwomnpoisnt (SGWW, ▲a),nsdoil+SgPreewn-ewraestesciommpio-st (GW, ), and soil+sphagnum peat (SP, ) containers lar (66 and 64 mm, respectively) and the value for the tree grown in CO was the smallest (59 mm)
Summary
Ornamental trees in urban areas are a major societal issue. The average lifespan of urban street trees was estimated to be only seven years (Moll, 1989) or 13 years (Skiera and Moll, 1992), with for example 39% of mortality over a fiveyear period after planting in Liverpool (Gilbertson and Bradshaw, 1990). Roman and Scatena (2011) conducted a meta-analysis of US studies on the survival of urban trees. They showed that the average lifespan was longer (19 to 28 years) than specified in previous studies (7 to 13 years). The reduction of annual urban tree mortality during the first years after planting depends on (i) quick root system development to promote efficient water and nutrient
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