Earthworms in some Tasmanian forest soils in relation to bioturbation and soil texture profile

Abstract

Soil properties and earthworm population density were examined for 5 forest soils derived from Silurian-Devonian sandstones (Mathinna Beds) in north-eastern Tasmania. The soils occur along gradients of altitude, rainfall, and forest type; they include 2 with texture-contrast and 3 with gradational soil profile types. The density and biomass of the most abundant earthworm species Megascolex montisarthuri, and of all earthworm species combined, were found to be greater in gradational than in texture-contrast soils. A greater proportion of the earthworms in gradational soils than in texture-contrast soils was found to occur at soil depths exceeding 10 cm. The contrast was most pronounced between the 2 texture-contrast soils and the single gradational soil that occur under dry eucalypt forest. This paper explores the hypothesis that bioturbation of surface and subsurface layers by earthworms is an important mixing process that in gradational soils outweighs the counter tendency for soil particles to sort and thus form texture-contrast profiles.

The role of fire and nutrient loss in the genesis of the forest soils of Tasmania and southern New Zealand

“…These are: (1) greater nutrient cycling and organic matter cycling and carbon accumulation under the greater biomass of wet forests compared to dry forests; (2) more soil mixing by soil fauna (particularly earthworms) in the moister wet forest soils (Laffan and Kingston, 1997) compared to dry forest soils; and (3) stabilisation of clay by humusclay-cation linkages (Muneer and Oades, 1989;Percival et al, 2000;Clough and Skjemstad, 2000;Ahmed et al, 2002a,b) which is likely to be more significant in the more organic matter rich and higher quality (lower C/N ratio; Table 12) organic matter of gradational soils under wet forest. Conversely, destruction of stable organic matter-clay linkages, changes of clay mineralogy to relatively inert clays, and coarsening of soil texture after hot fires (Ketterings et al, 2000;Sertsu and Sánchez, 1978), together with litter and organic matter destruction that creates an inimical soil environment for earthworms and mixing fauna (Laffan and Kingston, 1997) is likely to favour clay eluviation and formation of texture-contrast soils. We point out that repeated heating of the mineral soil, even if it is only to 1 mm depth in any one fire, will cumulatively tend to destroy clay-organic matter linkages, and local burning and heating to greater depth undoubtedly occurs ( Fig.…”

“…There appear to be three reasons why this association occurs: (1) the soil parent material is nutrient-and clay-rich and therefore less prone to clay eluviation (for example, Holloway and Bream soils in dolerite; Tables 11 and 12); (2) a relatively short history of fire-enough to induce dry forest but not enough to induce texture-contrast profiles (see for example the Wurrawa profile under dry forest; ; and (3) bioturbation by earthworms in moister soils having impeded drainage (Laffan and Kingston, 1997). The converse association of wet forest with texture-contrast soils also sometimes occurs (e.g.…”

Fire intensity, slopewash and bio‐transfer of sediment in eucalypt forest, Australia

“…Ant mounding may not only provide a sediment supply for erosion, but also affect particle size distribution in soils. Considerable quantities of sediment are subject to redistribution by ants and other animals (Humphreys and Mitchell, 1983), and bioturbation involving burrowing organisms like earthworms is often associated with gradational soil profiles as a result of particle size mixing (Laffan and Kingston, 1997). The sediment in ant mounds is derived from surface and near-surface soil and, as soil profiles at Faulconbridge are uniform or gradational rather than texture-contrast, ant activity cannot be altering current particle size distribution.…”