
TY  - JOUR
A1  - Hamilton, SD 
A1  - Lawrie, AC 
A1  - Hopmans, P 
A1  - Leonard, BV 
T1  - Effects of Fuel-Reduction Burning on a <I>Eucalyptus obliqua</I> Forest Ecosystem in Victoria
JF  - Australian Journal of Botany
JO  - Aust. J. Bot.
Y1  - 1991
VL  - 39
IS  - 3
SP  - 203
EP  - 217
KW  - 
UR  - https://doi.org/10.1071/BT9910203 
N2  - An autumn fuel-reduction burn of low intensity (200-250 kW m-1) was performed in a Eucalyptus obliqua forest near Gembrook, Victoria. The aim of the study was to evaluate the effect of a single burn on floristics, biomass, N content and N2 fixation. The fire burnt 50% of the area in a mosaic pattern, significantly reducing understorey vegetation cover (by 90%) and plant density (by 70%) in burnt areas immediately after the fire. Understorey cover was restored to 40% of the original value 1 year later, but 33% of the understorey species were still absent from burnt areas. In the whole site mosaic, biomass declined by 30 t ha-1 (3 kg m-2) (10%) and N content by 100 kg ha-1 (10 g m-2) (18% excluding soil N, 2% including soil N). These losses were due to significant losses of biomass and N from the understorey only (88%, 85%), standing dead trees (57%, 62%), fallen wood (73%, 60%) and litter (69%, 70%). One year later, there was no significant increase in either biomass or N content. Burnt areas had five times the total nitrogenase activity of unburnt areas, owing to significantly greater specific nitrogenase (C2H2 reduction) activity, three times the nodule weight and 20 times the plant density of unburnt areas for the dominant legume (Pultenaea scabra). Using a calibration ratio for C2H2:N2 of 2.68 :1 derived from glasshouse growth studies, N2 fixation for P. scabra was estimated as 15 g ha-1 year-1 in burnt areas and 3 g ha-1 year-1 in unburnt areas, with a mean of 9 g ha-1 year-' for the whole site mosaic. Adding superphosphate to burnt areas increased estimated N2 fixation significantly by 14%, mainly by increasing nodulation. Losses of N due to the burn (100 kg ha-1) were considerably greater than gains from increases in N2 fixation (6 g ha-1 year-1) one year after the burn. Even allowing for N2 fixation by other, infrequent legumes and greater N2 fixation in subsequent years, these data suggest that the N lost in the burn is more likely to be replaced by inputs from soil reserves and rainwater than from N2 fixation by legumes. 
ER  -

