Increased fire activity under high atmospheric oxygen concentrations is compatible with the presence of forests

Abstract

Throughout Earth’s history, the abundance of oxygen in our atmosphere has varied, but by how much remains debated. Previously, an upper limit for atmospheric oxygen has been bounded by assumptions made regarding the fire window: atmospheric oxygen concentrations higher than 30–40% would threaten the regeneration of forests in the present world. Here we have tested these assumptions by adapting a Dynamic Global Vegetation Model to run over high atmospheric oxygen concentrations. Our results show that whilst global tree cover is significantly reduced under high O2 concentrations, forests persist in the wettest parts of the low and high latitudes and fire is more dependent on fuel moisture than O2 levels. This implies that the effect of fire on suppressing global vegetation under high O2 may be lower than previously assumed and questions our understanding of the mechanisms involved in regulating the abundance of oxygen in our atmosphere, with moisture as a potentially important factor.

Functional traits of fossil plants

“…Ancient ecosystems have been reconstructed using plant traits and included in models that make fire behavior predictions for time periods such as the Permian (He et al ., 2016), the Triassic–Jurassic (Belcher et al ., 2010; Belcher, 2016; Baker et al ., 2022), the Cretaceous (Belcher & Hudspith, 2017), and the Miocene (Boulton & Belcher, 2019). More recently, global dynamic vegetation models have been used to answer deep‐time questions regarding atmospheric oxygen that rely on consideration of plant functional types (Vitali et al ., 2022). Therefore, the study of fossil plant traits has a significant potential to inform novel understanding of paleo wildfires and their effects, and we have scored this trait highly as a paleo‐functional trait (7) accordingly (Table S1).…”

Smoldering behavior of peat fire

“…The results of research obtained the range of smoldering combustion temperature of 500-700℃ which is lower than the flaming combustion (1500-1800℃) [6]. In the study of the effect of moisture and organic content as well as observed trends of smoldering combustion that could spread further and deeper laterally into the ground, revealed that fire activity would be greatly suppressed below 18.5% O2, completely switched off below 16% O2, and rapidly enhanced between 19-22% O2 [7]. There was significant influence of moisture content on the probability of smoldering combustion and the propagation rate of the tropical peat sample [8].…”