High-resolution data reveal a surge of biomass loss from temperate and Atlantic pine forests, contextualizing the 2022 fire season distinctiveness in France

Abstract

Abstract. The frequency and intensity of summer droughts and heat waves in Western Europe have been increasing, raising concerns about the emergence of fire hazard in less fire-prone areas. This exposure of old-growth forests hosting unadapted tree species may cause disproportionately large biomass losses compared to those observed in frequently burned Mediterranean ecosystems. Therefore, analyzing fire seasons from the perspective of exposed burned areas alone is insufficient; we must also consider impacts on biomass loss. In this study, we focus on the exceptional 2022 summer fire season in France and use very high-resolution (10 m) satellite data to calculate the burned area, tree height at the national level, and subsequent ecological impact based on biomass loss during fires. Our high-resolution semi-automated detection estimated 42 520 ha of burned area, compared to the 66 393 ha estimated by the European automated remote sensing detection system (EFFIS), including 48 330 ha actually occurring in forests. We show that Mediterranean forests had a lower biomass loss than in previous years, whereas there was a drastic increase in burned area and biomass loss over the Atlantic pine forests and temperate forests. High biomass losses in the Atlantic pine forests were driven by the large burned area (28 600 ha in 2022 vs. 494 ha yr−1 in 2006–2021 period) but mitigated by a low exposed tree biomass mostly located on intensive management areas. Conversely, biomass loss in temperate forests was abnormally high due to both a 15-fold increase in burned area compared to previous years (3300 ha in 2022 vs. 216 ha in the 2006–2021 period) and a high tree biomass of the forests which burned. Overall, the biomass loss (i.e., wood biomass dry weight) was 0.25 Mt in Mediterranean forests and shrublands, 1.74 Mt in the Atlantic pine forest, and 0.57 Mt in temperate forests, amounting to a total loss of 2.553 Mt, equivalent to a 17 % increase of the average natural mortality of all French forests, as reported by the national inventory. A comparison of biomass loss between our estimates and global biomass/burned areas data indicates that higher resolution improves the identification of small fire patches, reduces the commission errors with a more accurate delineation of the perimeter of each fire, and increases the biomass affected. This study paves the way for the development of low-latency, high-accuracy assessment of biomass losses and fire patch contours to deliver a more informative impact-based characterization of each fire year.

40-Year Fire History Reconstruction from Landsat Data in a Mediterranean Area of North Africa Following International Standards

“…The validation of the 2017 EFFIS BA map showed that the latter presented the highest omissions of all the assessed BA products, which resulted in a considerable underestimation of the total BA, plus a smoothing effect on fire perimeters that roughly delineated the burned patches. These inconsistencies have been previously reported in [40,91,92], and are attributed mainly to the 250-m coarse-resolution input data from MODIS used to generate the EFFIS product. On the other hand, GABAM is, to date, the only available global high-resolution BA product to provide BA mapping at finer spatial resolution to reliably detect smaller burned patches [32].…”

Temperature extremes of 2022 reduced carbon uptake by forests in Europe

“…An assessment of these fires in France, based on Sentinel-2 observations of burned area at a 10m resolution and a 10 m map of impacted biomass density derived from Global Ecosystem Dynamics Investigation (GEDI) height and French National forest inventory (NFI) plot data was produced by Vallet et al 60 . In their study they did not calculate emissions, but biomass lost from fires.…”

“…In their study they did not calculate emissions, but biomass lost from fires. Emissions of carbon gases and aerosols to the atmosphere should represent at most 50% of the biomass lost 60 , given typical combustion completeness factors. Our best estimate of biomass loss derived from this study is of 0.5 Tg C y −1 .…”

Assessment of Pinus halepensis Forests’ Vulnerability Using the Temporal Dynamics of Carbon Stocks and Fire Traits in Tunisia

“…With the increased resolution of and precision in measuring tree height [43] and the tree crown area [44] at the regional scale with remote sensing, local allometric relationships will allow for landscape-scale applications of tree compartment assessments [45]. From this information, at a fine resolution and over extended areas, Fire 2024, 7, 204 12 of 17 regional impacts [15] and ecosystem vulnerabilities to fires could then be easily evaluated to drive post-fire management and restoration plans.…”

“…Availability of fruits (cones) can delay regeneration, and low crown base height can increase new crown fire likelihood. Although fine resolution remote sensing now allows for large scale biomass potential loss assessments [15], some key aspects of the amount of biomass within organs and resistance/regeneration potentials based on bark thickness or seed mass are hardly ever assessed or are only derived from generic allometric equations. Numerous studies have been conducted to estimate the pine aboveground biomass in Mediterranean countries, such as Pinus pinea in Italy [16], Pinus brutia in Turkey [17], or Pinus halepensis and Pinus nigra in Spain [18], among others.…”