4.1.1 On Origin of Fire and Fire-Adapted Species

Across aeons most ancient, the primordial Earth was cloaked in darkness, but for the light of the Sun, lightening, and occasional geological fireworks in the form of volcanic eruptions. Its landscapes bare, exposing naked rock, deep in its oceans, microscopic alchemists were at work. Life was emerging, and upon doing so, it was slowly, but surely repurposing the planet.

An exothermic oxidation reaction [28], there are three essential elements to the existence of fire, of which one, a heat source, was available prior to the arrival of life. The second element, oxygen, was of insufficient quantity in the Earth’s early atmosphere to support fire; studies illustrate that a minimum atmospheric concentration of between 13% (Bowman et al, 2009) and 16% [29] (Belcher et al, 2010) is required.

However, a by-product of photosynthesis, oxygen reached above adequate supply [an est. 20%] in the early Paleozoic, some 540 million years ago [mya] (Pausas and Keeley, 2009; Holland, 2006). However, not until 420 mya, with the advent of combustible hydrocarbons in the form of terrestrial plants, did the third element, fuel, drop into place (Bowman et al. 2009; Wellman et al, 2003). Fusain (fossilised charcoal) deposits suggest that it was during the period towards the end of the Silurian, 419.2 mya, and the beginning of the Carboniferous, 358.9 mya that herbaceous plants colonised land in sufficient volume to carry fire (Rimmer et al, 2015; Pyne, 2012; Glasspool et al, 2004) [Fig. 7]. The latter the tinder, the kindling was soon to arrive; the earliest known tree is believed to date to the Middle Devonian, c. 385 mya (Stein et al, 2007), and by 370 mya woody vascular plants had evolved in the form of Lycopsida, Cladoxylopsida, and Progymnospermospsida [progymnosperms] (Berner, 2005; Meyer-Berthaud, 2000; Meyer-Berthaud et al, 1990). The evolutionary equivalent of the Olympic flame, these early forests mark the advent of biomes comprised sufficient biomass, therein fuel, to sustain fire over broad spatial scales (He and Lamont, 2017). Thus, as life colonised continents, so too did fire, and upon doing so it left behind its molecular signature; therein a geological record as documents its history (Jasper et al, 2013; Brooxwn et al, 2012; Glasspool and Scott, 2010).

In supplying two of the three elements necessary for fire, therein completing the seminal ‘fire triangle’ [Fig. 8], biota had birthed a “biophysical perturbation” (Pyne, 2012, p.15) that enables the cycling of nutrients, therein the continual renewal and reconfiguration of terrestrial biomass. Put succinctly, by virtue of its accidental alchemy, life had created a catalyst for evolution, which, from the outset, would become fundamental to its spatiotemporal organisation. Life had not merely evolved in and of itself; life, coevolved with its habitat, engulfing the Earth in a potent chemical concoction, which, over a period of epochs transformed it into an “intrinsically flammable planet” (Bowman et al, 2009, p.482).

Today, atmospheric oxygen is at 21% (Pausas and Keeley, 2009). However, historically, this figure has risen and fallen in line with global plant productivity. During the Carboniferous atmospheric oxygen peaked somewhere between 31-35% (Beerling, 2007, 1998; Berner, 2006; Bergman et al, 2004), just over 160% of the current level. Experiments undertaken during the course of the past four decades have established that as oxygen levels rise so too does the combustibility of plants with higher moisture contents (Glasspool et al, 2015; Watson and Lovelock, 2013; Cope and Chaloner, 1980; Watson et al, 1978). Additionally, higher oxygen concentrations have evidenced a general correlation with shorter ignition times, increased peak heat flux [30] and rate of flame spread (Belcher et al, 2010; Berner et al, 2003; Babrauskas, 2003; Tewarson 2000). Thus, both in temperate and tropical regions, the forests of some 300 to 350 mya were immersed in a gaseous cocktail so very combustible as to spark conflagrations of colossal proportions (Falcon-Lang, 2000). Indeed, biomass burned on a scale so great as would have laden the atmosphere with suffice solid and liquid particulates and gases as to more or less permanently tint the sky a yellow- brown (Ward, 2006).

The combustible Carboniferous incubated the earliest incarnations of the cone-bearing vascular land plants Pinophyta, more commonly known as conifers (He et al, 2012). Their cones carrying a cargo of seeds [Figs. 9, 10, 11], conifers are thus gymnosperms, they being plants of which the offspring can be transported near or far, and by a variety of mechanisms, including wind dispersal [Fig. 12]. By the end of the Mesozoic era [66 mya] conifers had evolved the reproductive systems that have served them to the present day. Much like modern-day tree rings, fossil records of gymnosperms, together with those of their now extinct spore-bearing antecedents progymnosperms, evidence aspects of the environmental conditions in which they had lived. We thus know, as remains the case today, that these early plant communities evolved in and with a diversity of fire conditions (Pausas and Keeley, 2009). Furthermore, the paleobiological record is testament to the ‘work in progress’ nature of evolution. Like the Carboniferous, the mid to late Cretaceous [140 – 94 mya] was highly combustible (Belcher et al, 2013); a combination of evaluated atmospheric oxygen and carbon dioxide, and warmer than present day temperatures, together with abundant biomass (Spicer, 2003) which fuelled frequent and intense fires, which in turn, stoked physiological changes in biota, including the evolution of angiosperms [flowering plants] circa 124.6 mya (He and Lamont, 2017; Bond, 2010; Sun et al, 2002). In other words, fire was the original ‘flower power’.

>Continue to Chapter 4.1.2 here.

Footnotes

[28] A form of chemical reaction, an exothermic oxidation reaction releases energy in the form of heat or light to its surroundings.

[29] Belcher et al hypothesised that a minimum 16% atmospheric O2 is required for biotic matter to ignite (Belcher et al, 2010). However, Bowman et al’s earlier estimate of 13% appears valid (Bowman, 2009).

[30] Heat flows to its surroundings, the direction headed hot toward cold. In gases and liquids the process is called convection, in solids conduction, and in electromagnetic waves radiation. Whatsoever the carrier medium, heat flux is the term applied to the process, peak indicative of the maximum speed of flow.

The thesis is also available in PDF format, downloadable in several parts on Academia and Researchgate.

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Citation: Sterry, M. L., (2018) Panarchistic Architecture: Building Wildland-Urban Interface Resilience to Wildfire through Design Thinking, Practice and Building Codes Modelled on Ecological Systems Theory. PhD Thesis, Advanced Virtual and Technological Architecture Research [AVATAR] group, University of Greenwich, London.