The post-fire stability index; a new approach to monitoring post-fire recovery by satellite imagery

Ecological resilience is the capacity of a system to maintain function following disturbance. With the frequency and severity of wildfire activity increasing due to warmer and drier global climate conditions, there are increasing reports of declines in ecological resilience and ecosystems at risk of collapse due to post-fire recovery failure. Observational monitoring of post-fire recovery at the landscape scale is important to understand drivers, identify vulnerable ecosystems and prioritize management intervention to support resilience. Defining a suitably representative baseline condition to compare post-fire recovery states against can be challenging, particularly in broad-scale remote sensing approaches. Here, we introduce a new approach to monitoring post-fire recovery by satellite imagery, the post-fire stability index. The method is based on the concept that a disturbed system state will be reflected by increasing or decreasing rates of system change, while undisturbed or recovered system states are characterised by near-zero rates of change. This reflects the typical pattern of diminishing rate of change in post-fire recovery trajectories. We demonstrate strong performance and suitability of the post-fire stability index in comparison to alternative approaches through time series analyses, and independent validation from post-fire vegetation surveys taken at one-year post-fire. The post-fire stability index was consistently the best performing model across all field measures of vegetative response following the fire event. In ecosystems which exhibit post-fire resprouting, higher values in the post-fire stability index were associated with higher levels of field-based measures of foliage projective cover and canopy cover (+/− resprouting), and with lower levels of basal and no resprouting. The post-fire stability index provides a relatively simple and practical solution for consistent broad-scale monitoring post-fire recovery with satellite imagery, which together with standardised fire severity mapping, provide extensive opportunities for further fire and landscape ecology research. • The post-fire stability index examines the rate of change in the years after fire. • The post-fire stability index consistently out-performed pre-fire baseline methods. • Pre-fire baseline definitions changed the spectral recovery by up to 56%. • Years of stability may be interspersed with years of increase or decrease. • Fire severity data enhanced understanding of post-fire recovery dynamics.