Mechanical and hydrological impacts of tree removal on a clay fill railway embankment

et al. 2016

Géotechnique

107

Plant evapotranspiration is recognised to affect soil suction of slopes and landfill covers. Previous work has focused on evapotranspiration-induced suction by a single plant, with little attention paid to the effects of planting density. The aim of this study is to quantify any changes in tree growth and tree-induced suction during evapotranspiration and rainfall under different planting densities for non-mixed-species plantations. A tree species, Schefflera heptaphylla, which is commonly found in Asia, was planted in silty sand at spacings of 60, 120 and 180 mm, representing three different planting densities. For each case, three replicates were tested to consider tree variability. In total, the responses of suction for 297 seedlings subjected to drying and a rainfall event with a 10-year return period were measured. The test results show that reducing the tree spacing from 180 to 60 mm induced greater tree-tree competition for water, as indicated by a 364% increase in peak suction upon evapotranspiration. Such tree-tree interaction led to: (a) a 19-35% reduction in the leaf area index; (b) a 17-36% decrease in root length; and (c) an obvious decay of roots. Upon the rainfall event, the infiltration rate for vegetated soil with trees planted at a spacing of 60 mm was up to 247% higher than those for soil with a wider tree spacing, where mainly fresh roots were found. Although most suction within the root zone (i.e. top 100 mm) was lost due to increased infiltration at 60 mm spacing, suctions in deeper depths below root zone were largely preserved.

Section: Discussionsupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Effects of planting density on tree growth and induced soil suction

et al. 2016

Géotechnique

107

“…Grass that has relatively shallow root system may be effective for soil erosion control, while tree has relatively stronger and deeper root system which may be used for mechanical soil stabilisation. Despite of rather different root systems, transpiration would happen for both types of species, causing a change in matric suction (Pollen-bankhead and Simon 2010; Garg et al 2015b; Leung et al 2015b;Ng et al 2013Ng et al , 2014Ng et al , 2016a and consequently the soil hydrology (Simon and Collison 2002;Smethurst et al 2015;Ng et al 2016c). The increase in matric suction due to plant transpiration would result in a decrease in soil hydraulic conductivity (Ng and Leung 2012) and also an increase in soil shear strength (Ng and Menzies 2007).…”

Section: Introductionmentioning

confidence: 99%

Investigation of plant growth and transpiration-induced matric suction under mixed grass–tree conditions

et al. 2017

Can. Geotech. J.

Investigation of plant growth and transpiration-induced matric suction under mixed grass-tree conditions Ni, J. J.; Leung, Anthony; Ng, C. W. W.; So, P. S. General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain.• You may freely distribute the URL identifying the publication in the public portal. Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractAlthough evapotranspiration-induced matric suction for single species has been widely studied, little is known about how mixed-species planting would affect the plant growth and induced matric suction. This study aims to explore the effects of grass-tree interaction on their growth and induced matric suction during evapotranspiration (ET) and rainfalls. Field monitoring was carried out to measure matric suction responses in compacted soil that was vegetated with (i) single tree species, Schefflera heptaphylla and (ii) mixed species of the trees and a grass species, Cynodon dactylon. In each condition, three tree spacings (120, 180 and 240 mm) were planted. When tree spacing increased from 120 to 240 mm, the peak tree root area index (RAI, for fine roots with diameter < 2 mm) decreased by 16%, but the peak grass RAI increased by 29%. At mixed planting plots, the ET-induced peak matric suction for tree spacing of 240 mm was 20% higher than that for spacing of 180 mm because of increased contribution of grass root-water uptake as the trees were more widely spaced. Without grass, a reverse trend was observed as tree-tree interaction reduced at wide spacings. The peak ET-induced matric suction had a significant linear correlation with RAI. During rainfalls, the highest matric suction was preserved for the case of 240 mm spacing due to the greatest reduction of soil hydraulic conductivity by roots.

“…Vegetation is known to affect the hydrology and hence stability of earth infrastructure such as man-made slopes (Osman & Barakbah, 2011;Smethurst et al, 2015). Plant roots cause changes in soil matric suction (Simon & Collison, 2002;Veylon et al, 2015;Ng et al, 2016a;Ni et al, 2017) through evapotranspiration and soil hydraulic properties, including soil water retention curve (SWRC) and soil hydraulic conductivity function (SHCF).…”

Section: Introductionmentioning

confidence: 99%

Unsaturated hydraulic properties of vegetated soil under single and mixed planting conditions

2019

Géotechnique

Unsaturated hydraulic properties of vegetated soil under single and mixed planting conditions Ni, J. J .; Leung, Anthony; Ng, C. W. W. Published in: Géotechnique DOI:10.1680/jgeot.17.t.044 Publication date: 2018 Document Version Peer reviewed version Link to publication in Discovery Research Portal Citation for published version (APA):Ni, J. J. ., Leung, A., & Ng, C. W. W. (2018). Unsaturated hydraulic properties of vegetated soil under single and mixed planting conditions. Géotechnique. https://doi.org/10.1680/jgeot.17.t.044 General rightsCopyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain.• You may freely distribute the URL identifying the publication in the public portal. Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Accepted manuscript doi:10.1680/jgeot.17.t.044 Accepted manuscriptAs a service to our authors and readers, we are putting peer-reviewed accepted manuscripts (AM) online, in the Ahead of Print section of each journal web page, shortly after acceptance. DisclaimerThe AM is yet to be copyedited and formatted in journal house style but can still be read and referenced by quoting its unique reference number, the digital object identifier (DOI). Once the AM has been typeset, an 'uncorrected proof' PDF will replace the 'accepted manuscript' PDF. These formatted articles may still be corrected by the authors. During the Production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. Version of recordThe final edited article will be published in PDF and HTML and will contain all author corrections and is considered the version of record. Authors wishing to reference an article published Ahead of Print should quote its DOI. When an issue becomes available, queuing Ahead of Print articles will move to that issue's AbstractEffects of plant roots on changes of soil hydraulic properties, including soil water retention curves (SWRC) and soil hydraulic conductivity functions (SHCF), are not well understood, especially when soil is unsaturated and vegetated with multiple plant species. This note aims to quantify the root effects on both SWRC and SHCF of silty sand using the instantaneous profile method. Four types of vegetated soil, namely bare, grass-only, tree-only and mixed tree-grass soils, were subjected to a controlled drying-wetting cycle in a plant room. Plant roots affect the air-entry value, saturated hydrau...