Tree clearing is a topical issue world over. The high rates of clearing in Queensland take place to increase pasture production. The present research evaluates the impact of clearing on some soil biological properties i.e. total soil respiration, root respiration, microbial respiration and microbial biomass (C and N). Paired cleared and uncleared (intact) pasture systems were selected to represent three major tree communities of the region i.e. Eucalyptus populnea, E. melanophloia and Acacia harpophylla. The cleared sites were chosen to represent three different time-since-clearing durations (5, 11-13 and 33 years) to determine the temporal impact of clearing on soil biological properties. Soil respiration responses to change in temperature (for different seasons of a year) and moisture (during rainy season) were also examined in the field.

There was no significant difference (P<0.05) in rate of total soil respiration between cleared and uncleared sites, whatever the time-since-clearing. The average rate of CO₂ emissions was 964 g CO₂ m^-2 yr^-1. Microbial respiration and microbial biomass were greater at uncleared compared to those at cleared sites. The Q₁₀ value of 1.42 (measured for different seasons over a year) suggested a little response of soil respiration to soil temperature possibly due to the limited availability of soil moisture or organic matter. Results indicate that it is likely that with rising ambient temperature and consequently soil temperature, soil respiration in cleared pastures will increase faster than that in uncleared pastures for the following reasons:
1. since root biomass (herbaceous roots) was greater at the cleared than uncleared sites, and
2. since root respiration is considered more sensitive to temperature change than total soil respiration.