Grazing

Effects of grazing on the habitat, microclimate and food supply of soil biota:

• Heavy grazing results in low plant litter levels. Litter provides both a living-space for soil animals as well as forming organic residues in the soil as food for soil biota.
• Litter protects the soil environment against climatic extremes. In pastures at Tamworth, in northern NSW, Australia, summer temperatures at 5 cm depth in overgrazed, bare pastures can reach 50°C. However, the soil temperature can be < 25°C at the same depth in lightly grazed pastures with a good litter layer.
• Litter layers slow the evaporation of moisture from soil from 10 mm/day to <2 mm/day in summer in the same pastures.
• Trampling by high numbers of large herbivores such as sheep and cattle can compact the soil, squeezing the pores and making them smaller. It is then difficult for small soil animals to access the soil as they cannot form their own tunnels. In addition, compacted soil is hard for the tunneling animals such as earthworms to move through.
• Soil nutrients and organic matter (in the form of dung) are concentrated into stock camps on higher ground or in corners of paddocks, where stock congregate to rest. This aggregation occurs at the expense of nutrients and organic matter over the rest of the paddock.

Overgrazing affects the soil biota in following ways:

• Reduces the numbers and biomass of soil mesofauna and macrofauna
• Soil microbial activity is higher in the stock camps than over the general paddock
• Diversity of some species of soil biota declines (e.g. springtails).