The impact of soil disturbance on root development in woodland communities in Western Australia

Abstract

The impact of soil disturbance of the Banksia woodland soil profile and particularly the effect of different reconstructed soil profiles (overburden profile, white profile and yellow profile) and soil ripping within rehabilitation sites, was investigated in terms of root development and architecture for eight species that are key structural elements in Banksia woodland. The aim was to determine the soil environment best suited for root development and architecture likely to contribute to high seedling survival in post-mined sites.

Root development and architecture differed significantly between native woodland, and rehabilitation sites. In general, roots were longer in native woodland with low lateral root production (for all species studied) compared to rehabilitation sites where the roots were shorter, tended to divide or lose geotrophy and consisted of numerous laterals. When comparing the different soil profiles in the rehabilitation sites, the commonly reconstructed profile of ‘topsoil over overburden’ (overburden profile) was the least favourable for root development and architecture. Ripping of the soil to 80 cm depth had a positive effect on root growth.

There were differences between native woodland and rehabilitation sites, in soil impedance, soil bulk density, soil moisture percentage and organic carbon content. In general, reconstructed soils in rehabilitation sites have (1) soil impedance and soil bulk density values likely to seriously impede root development and architecture, (2) soil moisture percentages higher than those in undisturbed woodland during all months of monitoring and at most depths down to 40 cm and (3) lower organic carbon content than native woodland. When comparing the different soil profiles in rehabilitation sites, the overburden profile (a) had the highest impedance values, (b) was one of the profiles with the highest bulk density values and (c) had the highest soil moisture percentages during most months and at most depths examined. Ripping the soil decreased soil impedance and soil moisture contents.

The major conclusion from this study is that soil impedance, which influences water movement, is a key characteristic of soil conditions that are not conducive to the development of deep penetrating root systems. These deep root systems may be directly linked to survival.