The effects wildfire on water yield and its relationship with vegetation response

The response of vegetation regrowth and water yield after a wildfire is dependent on factors such as fire intensity, climate and vegetation type. Australian woody vegetation species have evolved two mechanisms for surviving fire disturbance; i) seed germination (obligate seeders) and ii) resprouting from dormant vegetative buds and/or lignotubers (obligate resprouters). The majority of post wildfire vegetation response studies have been conducted in Victoria, Australia and have been in obligate seeder dominant communities. These studies have found that there is a significant delay in vegetation regrowth as they rely on the seed bank, whilst also finding there is a significant change in water yield post-wildfire. Those studies are not representative of the vegetation in the Sydney Basin, which is dominated by obligate resprouter species. This study examines vegetation recovery and its potential effects on water yield in a burnt subcatchment of the Nattai River, which was affected by wildfire in 2001/02. The study used was designed to detect i) changes in vegetation growth during recovery and ii) establish if these changes corresponded with changes in water yield. The first approach used an 18 year time series of Landsat data to assess annual vegetation 10 years pre-wildfire and 8 years post-wildfire. Several vegetation indices were compared to assess the health and integrity of eucalypt forests and woodlands (NDVI, NDVIc and NBR). The second approach used weekly rainfall, water yield and temperature data over an 18 year time series. A generalised additive model (GAM) was used to create a water yield model and change in water yield was detected through the use of prediction intervals and error plots. Results show that there was no significant impact on vegetation or water yield following wildfire as both recovered within 8 years.

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