Analyzing spatial and temporal variability in short-term rates of post-fire vegetation return from Landsat time series

The disturbance and recovery cycles of Canadian boreal forests result in highly dynamic landscapes, requiring continued monitoring to observe and characterize environmental change over time. Well-established remote sensing methods capture change over forested ecosystems, however the return of forest vegetation in disturbed locations is infrequently documented and not well understood. Landsat time-series data allows for both the capture of the initial disturbance and the ability to monitor the subsequent vegetation regeneration with spectral vegetation indices. In this research, we used three spectral recovery metrics derived from an annual Landsat-based per-pixel Normalized Burn Ratio time series to determine trends in the short-term rates of spectral recovery for areas disturbed by wildfire (1986-2006), as assessed using a series of 5-year post-disturbance windows to observe forest recovery trends. Our results indicated that rates of spectral forest recovery vary over time and space in the Taiga and Boreal Shield ecozones. We found evidence that post-fire spectral forest recovery rates have accelerated over time in both the East and West Taiga Shield ecozones, with a consistent, positive, and significant trend measured using a Mann-Kendall test for monotonicity and Theil-Sen slope estimation. Over the analysis period (1986-2011), relative rates of spectral forest recovery increased by 18% in the Taiga Shield East and 9% in the Taiga Shield West. In contrast, spectral forest recovery rates in the Boreal Shield varied temporally, and were not consistently positive or negative. These results demonstrate that post-fire spectral recovery rates are not fixed over time and that spectral trends are dependent upon spatial location in the Canadian boreal. This retrospective baseline information on trends in spectral recovery rates highlights the value of, and continued need for detailed monitoring of vegetation regeneration in boreal forest ecosystems, particularly in the context of a changing climate.