Fire resilience analysis: Using high temporal and spatial satellite imagery for rehabilitated landscapes

Abstract

The progressive rehabilitation of open-cut coal mines and the demonstration of a sustainable post-mining land use is required prior to mine closure in many parts of the world. There is a general belief that the risk of rehabilitation failure following mine closure due to disturbance events such as fire is minimal, based largely on the assumed resilience of rehabilitated pastures and the assumption that rehabilitated pastures will respond analogous to unmined pastures following fire. However, there is little scientific evidence to support this notion, and additional knowledge gaps on the resilience of rehabilitation age classes and appropriate methods for land managers to measure and demonstrate rehabilitation resilience. We used Sentinel-2 and Landsat-8 time-series and assessed the impact and vegetation response to eight fire events in rehabilitation and five fires in unmined analogues in central and southeast Queensland, Australia. Using the Soil Adjusted Vegetation Index (SAVI), we aimed to compare rehabilitated and unmined areas using three resilience metrics: i) percent impact, ii) recovery time and iii) recovery rate. Compared with unmined pastures, post-mine rehabilitation recorded higher mean impact (52–65 % vs 67–79 % respectively), longer recovery times (38–117 vs 144–245 days respectively) and a slower rate of recovery (2.5–5.7 % vs 0.9–1.7 % per day respectively). Younger age-classes (<10 y/o and 10–15 y/o) recorded reduced resilience compared to mature rehabilitation (≥ 16 y/o). We compared three different baseline indices and showed that the choice of baseline index yielded significantly different results for the same fires, indicating the importance of standardised approaches to resilience monitoring.