Gwenzi, W, Veneklaas, EJ, Phillips, I, Bleby, TM & Hinz, C 2009, 'Spatial distribution of fine roots on a rehabilitated bauxite residue disposal area in Western Australia', in AB Fourie & M Tibbett (eds), Mine Closure 2009: Proceedings of the Fourth International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 317-327, https://doi.org/10.36487/ACG_repo/908_24
(https://papers.acg.uwa.edu.au/p/908_24_Gwenzi/)
Abstract: Root spatial distribution controls water and nutrient uptake, and is a key input in ecohydrological and 
biogeochemical models. In particular, fine roots are responsible for resource acquisition and represent the 
most dynamic component of root biomass. While root distribution on natural and agro-ecosystems is 
relatively well documented, few studies have investigated root spatial distribution on rehabilitated mined 
ecosystems, where adverse physical and chemical conditions may limit root growth. The authors investigated 
the spatial distribution of fine roots (< 4.5 mm diameter) on a rehabilitated bauxite residue disposal area 
under Mediterranean conditions. The objectives of this study were:  to determine the vertical and horizontal 
spatial variability of fine roots at plot scale; to develop a spatial model for root distribution for use in 
ecohydrological modelling and other numerical applications; and to compare observed results to those 
reported in literature for natural ecosystems under similar climatic conditions.  
A 20 × 20 cm grid sampling scheme was used to collect 226 core samples (10 cm diameter and 10 cm 
height) from a 700 cm long and 150 cm deep trench. Samples were analysed for root length (L), root 
diameter (D), root length density (RLD) and root biomass density (RBD). Soil dry bulk density, pH and 
electrical conductivity (EC) were used as indicators of soil physical and chemical constraints to root growth. 
Root characteristics showed high spatial variability with coefficient of variation (CV) ranging from  
51–200%. The top 20 cm had the highest mean RLD (8.4 cm cm-3) and root mass density (RMD) (1 g cm-3) 
which decreased with depth according to a power function (RLD = 2474 × (SD)-1.8, r2 = 0.92). About 80% of 
the total root length and biomass were in the top 40 cm, while the remainder was in the deeper layers (40–
140 cm). At all depths, very fine roots (≤ 1.5 mm in diameter) constituted about 95% of the total root length, 
suggesting a root system adapted for water uptake in the dry season when soil moisture is limited. Soil EC 
values were generally low (mean 1.1 dS m-1), but showed high spatial variability (CV = 91%) probably due 
to non-uniform incorporation of chemical amendments. For 19 out of the 24 samples, EC values were below 
2.5 dS m-1, considered the upper limit for normal plant growth. Soil pH was slightly alkaline (mean of 8.2), 
and showed low spatial variability (CV = 4%). In all cases, bulk densities (mean = 1.3 g cm-3) were below 
the critical value for restricted root growth (1.6 g cm-3). Correlation analysis suggested that root distribution 
was not limited by soil dry bulk density, pH and EC. Accordingly, the depth distribution of cumulative RLD 
and RMD closely agreed (r2 = 0.93) with the general root depth distribution models for natural vegetation 
ecosystems in Mediterranean climates. The results are discussed in the context of vegetation water uptake on 
rehabilitated mined ecosystems.