Short-Term Recovery of the Aboveground Carbon Stock in Iberian Shrublands at the Extremes of an Environmental Gradient and as a Function of Burn Severity

José Manuel Fernández-Guisuraga,Paulo M Fernandes,Leonor Calvo,Susana Suárez-Seoane

doi:10.3390/f13020145

José Manuel Fernández-Guisuraga, Paulo M Fernandes + Show 2 more

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https://doi.org/10.3390/f13020145

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Abstract

The degree to which burn severity influences the recovery of aboveground carbon density (ACD) of live pools in shrublands remains unclear. Multitemporal LiDAR data was used to evaluate ACD recovery three years after fire in shrubland ecosystems as a function of burn severity immediately after fire across an environmental and productivity gradient in the western Mediterranean Basin. Two large mixed-severity wildfires were assessed: an Atlantic site, dominated by resprouter shrubs and located at the most productive extreme of the gradient, and a Mediterranean site, dominated by obligate seeders and located at the less productive extreme. Initial assessment of burn severity was performed using the differenced Normalized Burn Ratio index computed from Landsat imagery. Thresholds for low and high burn severity categories were established using the Composite Burn Index (CBI). LiDAR canopy metrics were calibrated with field measurements of mean shrub height and cover at plot level in a post-fire situation. Pre-fire and post-fire ACD estimates, and their ratio (ACDr) to calculate carbon stock recovery, were computed from the predictions of LiDAR grid metrics at landscape level using shrubland allometric relationships. Overall, ACDr decreased both with high burn severity and low productivity, although the burn severity impact was not homogeneous within the gradient. In the Atlantic site, ACDr was similar under low and high burn severity, whereas it decreased with burn severity in the Mediterranean site. These results suggest that carbon cycling models could be biased by not accounting for both fire severity and species composition of shrublands under different environmental conditions.

Highlights

Shrubland ecosystems store about half of the global terrestrial carbon [1,2] and their potential feedback with the atmosphere, associated with changes in carbon stocks, has significant implications for global carbon cycling [3]
Post-fire shrub height measured in the field at plot level was best correlated to the mean height of Light Detection and Ranging (LiDAR) 1st returns metric, both in the Atlantic (R2 = 0.69; root-meansquared error (RMSE) = 0.20 m) and Mediterranean (R2 = 0.74; RMSE = 0.15 m) sites (Figure 4)
The quantification of carbon stocks through remote sensing techniques is crucial for understanding wildfire impacts at large spatial scales in shrubland ecosystems

Summary

Introduction

Shrubland ecosystems store about half of the global terrestrial carbon [1,2] and their potential feedback with the atmosphere, associated with changes in carbon stocks, has significant implications for global carbon cycling [3]. The biomass per unit area might be relatively small in shrubland ecosystems, land degradation due to wildfires represents a significant change in live aboveground carbon pools in this region [7]. Wildfire disturbance causes direct pyrogenic carbon release of the aboveground and belowground pools to the atmosphere through combustion and modifies the distribution of live and dead aboveground carbon stocks and their associated fluxes through mortality and regeneration [8,9,10,11,12,13,14]. Post-fire mortality and regeneration in shrublands are the processes playing a key role in carbon transfer between aboveground pools

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