The role of fire in global forest loss dynamics.

Dave Van Wees,Guido R Van Der Werf,Niels Andela,Yang Chen,James T Randerson,Douglas C Morton

doi:10.1111/gcb.15591

Abstract

Fires, among other forms of natural and anthropogenic disturbance, play a central role in regulating the location, composition and biomass of forests. Understanding the role of fire in global forest loss is crucial in constraining land‐use change emissions and the global carbon cycle. We analysed the relationship between forest loss and fire at 500 m resolution based on satellite‐derived data for the 2003–2018 period. Satellite fire data included burned area and active fire detections, to best account for large and small fires, respectively. We found that, on average, 38 ± 9% (± range) of global forest loss was associated with fire, and this fraction remained relatively stable throughout the study period. However, the fraction of fire‐related forest loss varied substantially on a regional basis, and showed statistically significant trends in key tropical forest areas. Decreases in the fraction of fire‐related forest loss were found where deforestation peaked early in our study period, including the Amazon and Indonesia while increases were found for tropical forests in Africa. The inclusion of active fire detections accounted for 41%, on average, of the total fire‐related forest loss, with larger contributions in small clearings in interior tropical forests and human‐dominated landscapes. Comparison to higher‐resolution fire data with resolutions of 375 and 20 m indicated that commission errors due to coarse resolution fire data largely balanced out omission errors due to missed small fire detections for regional to continental‐scale estimates of fire‐related forest loss. Besides an improved understanding of forest dynamics, these findings may help to refine and separate fire‐related and non‐fire‐related land‐use change emissions in forested ecosystems.

Highlights

Forests play a crucial role in the climate system and are integrally linked to biodiversity, biogeochemical and hydrological cycling, and the Earth's radiation budget (Foley et al, 2005)
We include forest loss that is the direct result of fire, such as in wildfires, and indirect fire-use during land conversion practices such as slash burning as part of commodity-driven deforestation and shifting agriculture
In contrast to previous studies by Curtis et al (2018) and Tyukavina et al (2018), we focus on quantifying the fraction of forest loss that is related to fire, regardless of what driving mechanism is at play

Summary

| INTRODUCTION

Forests play a crucial role in the climate system and are integrally linked to biodiversity, biogeochemical and hydrological cycling, and the Earth's radiation budget (Foley et al, 2005). Commodity-d riven deforestation for the development of pasture or cropland is the main driver of permanent forest loss in the humid tropics (Kim et al, 2015; Morton et al, 2008) This process typically involves mechanical felling of all standing vegetation, followed by repeated burning of the resulting slash (Carvalho et al, 1995; Kauffman et al, 1995). We aim to improve this understanding using a novel approach for estimating the fraction of gross (permanent and non- permanent) forest loss that involves fire on a global scale, which we refer to as fire-related forest loss In this estimate, we include forest loss that is the direct result of fire, such as in wildfires, and indirect fire-use during land conversion practices such as slash burning as part of commodity-driven deforestation and shifting agriculture. | 2379 and 20 m resolution burned area from the Sentinel-2 Multispectral Instrument (MSI; Roteta et al, 2019), to test the validity of the coarser-resolution approach

| METHODS

| RESULTS

Findings

| DISCUSSION