Global patterns of Mediterranean ecosystems recovery from recurrent fires

Over the past two decades wildfires have been increasingly disturbing many ecosystems worldwide. Among them, the Mediterranean-like climate regions have been strongly affected by recurrent events, as widely seen during the fire seasons of 2003, 2005, 2017 and 2022 in Portugal and northern Spain, as well as in Greece and southern Italy in 2007, 2021 and 2023. Additionally, Chile experienced significant fire seasons in 2015 and 2017, California faced destructive wildfires in 2018, 2020 and 2021, and Australia was affected by severe wildfires during 2019-2020.

Even though there is an observed increase of fire frequency over fire-prone regions, the Mediterranean ecosystems are in general well adapted to fire through several mechanisms to tolerate exposure to extreme conditions and recover from fire. However, climate change has been exacerbating the frequency and severity of climate extreme events, so that the pace of recovery of ecosystems from fires may be impaired, enhancing the potential of irreversible changes in vegetation communities. 

Here we assess the recovery of global Mediterranean vegetation after recurrent fires over the past two decades based on Enhanced Vegetation Index (EVI) retrieved from the MODIS sensor. To do so, we apply a statistical model to assess the recovery rate of vegetation repeatedly burned across different land cover types. Moreover, we study how fire severity, pre-fire state of vegetation and post-fire climate conditions modulate the recovery rates. Our results show a significant influence of fire severity on vegetation recovery rates globally across all Mediterranean regions, suggesting that higher severity levels may trigger the activation of the ecosystem's recovery mechanisms. Nevertheless, we also find a modulating effect of post-fire climate conditions, particularly air temperature and precipitation, on the recovery rates of burned vegetation, which highlights how compounding effects of changing disturbance regimes and climate change might destabilize ecosystems.

This study was supported by the doctoral Grant PRT/BD/154296/2022 financed by FCT under the MIT Portugal Program and was performed under the framework of DHEFEUS project, funded by Portuguese Fundação para a Ciência e a Tecnologia (FCT) (https://doi.org/10.54499/2022.09185.PTDC). The work was also funded by the FCT I.P./MCTES through national funds (PIDDAC) UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). A.R. is supported by the FCT through national funds from the MCTES within the Faculty of Sciences of University of Lisbon, through https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006.