Burn severity metrics in fire-prone pine ecosystems along a climatic gradient using Landsat imagery

Abstract

Multispectral imagery is a widely used source of information to address post-fire ecosystem management. The aim of this study is to evaluate the ability of remotely sensed indices derived from Landsat 8 OLI/TIRS to assess initial burn severity (overall, on vegetation and on soil) in fire-prone pine forests along the Mediterranean-Transition-Oceanic climatic gradient in the Mediterranean Basin. We selected four large wildfires which affected pine forests in a climatic gradient within the Iberian Peninsula. In each wildfire we established CBI plots to obtain field values of three burn severity metrics: site, vegetation and soil burn severity. The ability of 13 spectral indices to match these three field burn severity metrics was compared and their transferability along the climatic gradient assessed using linear regression models. Specifically, we analysed the performance of 12 indices previously used for burn severity assessments (8 reflective, 2 thermal, 2 mixed) and a new reflective index (dNBR-EVI). The results showed that Landsat spectral indices have a greater ability to determine site and vegetation burn severity than soil burn severity. We found large differences in indices performances among the three different climatic regions, since most indices performed better in the Mediterranean and Transition regions than in the Oceanic one. In general, the dNBR-EVI showed the best fit to site, vegetation and soil burn severity in the three regions, demonstrating broad transferability along the entire climatic gradient.

Mean Composite Fire Severity Metrics Computed with Google Earth Engine Offer Improved Accuracy and Expanded Mapping Potential

“…The degree of fire-induced ecological change, or fire severity, has been the focus of countless studies across the globe [1][2][3][4][5]. These studies often rely on gridded metrics that use pre-and post-fire imagery to estimate the amount of fire-induced change; the most common metrics are the delta normalized burn ratio (dNBR) [6], the relativized delta normalized burn ratio (RdNBR) [7], and the relativized burn ratio (RBR) [8].…”

“…The fire severity datasets produced by the MTBS program have clearly advanced wildland fire research in the US. Although some studies involving the trends, drivers, and distribution of satellite-inferred fire severity are evident outside of the US [4,5,15,29,30], the number and breadth of such studies are relatively scarce and restricted compared to those conducted in the US. We suggest that, if spatially and temporally comprehensive satellite-inferred severity metrics were more widely available in other countries or regions, opportunities for fire severity monitoring and research would increase substantially.…”

Do Fire Regime Attributes Affect Soil Biochemical Properties in the Same Way under Different Environmental Conditions?

“…Further studies are necessary to better understand the underlying factors responsible for the different effects of fire frequency and severity on soil biochemical properties along climatic gradients. We also encourage future research to characterize fire regimes using field-based methods, as they could be suitable (i) for characterizing fire frequency for longer periods, (ii) and obtaining accurate burn severity measurements, as remote sensing methods have a limited capacity to quantify soil burn severity [49].…”

“…This index is a standard measurement of burn severity and its performance has been largely validated in many ecosystems worldwide. In pine forests of the Iberian Peninsula, models relating dNBR and field measurements of burn severity (Composite Burn Index) have shown R 2 values ranging from 0.68 to 0.88 [49]. Landsat 7 scenes from 22 August 2011 (pre-fire) and from 25 August 2012 (post-fire) were used to calculate the dNBR at the Mediterranean site; Landsat 7 scenes from 20 September 2011 (pre-fire) and 6 September 2012 (post-fire) were used to calculate the dNBR at the Transition site; and Landsat 8 scenes from 30 August 2013 (pre-fire) and 15 September 2013 (post-fire) were used to calculate the dNBR at the Oceanic site.…”

“…In order to focus field sampling in areas with a heterogeneous fire frequency and severity, we developed maps for each study area ( Figure 1) that combined frequency (one to three fires) and severity (low and high severity; using the dNBR value 0.55 as the threshold, with this value representing moderate severity, according to [17,18,48,49]) categories. At the Mediterranean and Transition sites, we focused on a study frame of 3000 ha, and at the Oceanic site, we selected the entire wildfire (2500 ha) ( Figure 1).…”