A Framework for Multi-Dimensional Assessment of Wildfire Disturbance Severity from Remotely Sensed Ecosystem Functioning Attributes

Abstract

Wildfire disturbances can cause modifications in different dimensions of ecosystem functioning, i.e., the flows of matter and energy. There is an increasing need for methods to assess such changes, as functional approaches offer advantages over those focused solely on structural or compositional attributes. In this regard, remote sensing can support indicators for estimating a wide variety of effects of fire on ecosystem functioning, beyond burn severity assessment. These indicators can be described using intra-annual metrics of quantity, seasonality, and timing, called Ecosystem Functioning Attributes (EFAs). Here, we propose a satellite-based framework to evaluate the impacts, at short to medium term (i.e., from the year of fire to the second year after), of wildfires on four dimensions of ecosystem functioning: (i) primary productivity, (ii) vegetation water content, (iii) albedo, and (iv) sensible heat. We illustrated our approach by comparing inter-annual anomalies in satellite-based EFAs in the northwest of the Iberian Peninsula, from 2000 to 2018. Random Forest models were used to assess the ability of EFAs to discriminate burned vs. unburned areas and to rank the predictive importance of EFAs. Together with effect sizes, this ranking was used to select a parsimonious set of indicators for analyzing the main effects of wildfire disturbances on ecosystem functioning, for both the whole study area (i.e., regional scale), as well as for four selected burned patches with different environmental conditions (i.e., local scale). With both high accuracies (area under the receiver operating characteristic curve (AUC) > 0.98) and effect sizes (Cohen’s |d| > 0.8), we found important effects on all four dimensions, especially on primary productivity and sensible heat, with the best performance for quantity metrics. Different spatiotemporal patterns of wildfire severity across the selected burned patches for different dimensions further highlighted the importance of considering the multi-dimensional effects of wildfire disturbances on key aspects of ecosystem functioning at different timeframes, which allowed us to diagnose both abrupt and lagged effects. Finally, we discuss the applicability as well as the potential advantages of the proposed approach for more comprehensive assessments of fire severity.

Analysing How Pre-Fire Habitat Legacy and Post-Fire Management Influence the Resilience of Reptiles to Fire

“…The NDVI has been used to monitor post-fire habitat dynamics [46,67], and it is considered as a reliable predictor of habitat recovery after fire for many ecosystem components [68]. Our results support this conclusion as we detected a general reduction of the NDVI index in all burnt areas one year after the fire.…”

Resilience of reptiles to megafires

“…Reptile responses were modeled with fire history, as well as climate and remotely sensed environmental variables. These satellite‐based variables translated different dimensions of ecosystem functioning linked to energy–matter flows (Alcaraz et al, 2006; Cabello et al, 2012), which recovered with distinct trajectories and speeds after a fire (Marcos et al, 2021; Torres et al, 2018) therefore potentially improving the assessment of reptile responses to megafires. Finding a reptile decline pattern toward the center of the burnt area would suggest that colonization is the main process; the lack of such a pattern may suggest local extinction (if they are absent) or fire survival (if reptiles are present); the latter would support reptile persistence after megafires.…”

A satellite-based multi-dimensional approach to identify potential post-fire regime shifts in ecosystem functioning

“…To that end, approaches based on ecosystem functioning offer an integrative view of ecosystem responses to wildfire-induced changes, since fire can cause rapid modifications in key aspects of matter and energy flows in ecosystems (B. Marcos et al, 2021;Petropoulos et al, 2009). Furthermore, ecosystem functioning provides quicker, quantifiable responses to disturbances than structure or composition, and are more directly connected to ecosystem services (Alcaraz-Segura et al, 2008).…”

“…Moreover, the utility of SRS to evaluate ecosystem functioning resilience, and to anticipate potential regime shiftsthrough the translation of spectral indices into meaningful, informative ecosystem variablesis still largely under-explored (B. Marcos et al, 2021).…”