4.2.1 Fire Regimes: Biomes as Biotic and Abiotic Assemblages

As one might expect of a relatively young science, there are several fire regime classification systems in use in North America alone, and as yet, no general consensus on which system to use in ecological literature. The seminal classification system was published in the proceedings of the 1972 annual meeting of The Ecological Society of America (Wright and Heinselman, 1973). Documenting studies of the role of fire in conifer forests, the paper gave precedence to fire frequency and intensity whereupon identifying fire regimes, specifying the following variants: Long-interval crown-fire regimes; Short-interval crown-fire regimes; Long-interval surface-fire regimes; Short- interval surface-fire regimes, and “all possible combinations of the above” (Ibidem, p.11). The authors identified fire as the over-arching ecological organiser within the study areas, while also acknowledging the complexity of the symbiosis between the abiotic and biotic elements involved. Their paper stressed the matter that not “anywhere in the world” was research underway to document fire regimes in their totality (Ibidem, p.5). In the absence of the technological advances that have occurred between then and now, Wright and Heinselman estimated it would take “centuries” to complete the task (Ibidem, p.5). However, the pair were part of a growing ecological school of thought that recognised the role of disturbance as imperative to ecosystem integrity and functioning, whereupon in the absence thereof not merely would many species generally demise, but go extinct. The very same year that the above paper went to print, fellow ecologist C. S. Holling published his seminal paper on resilience and stability of ecological systems (Holling, 1973), which though a work apart, evidenced the same general thinking around the role of disturbance in ecosystems [Fig. 21]. Collectively, Wright, Heinselman, and Holling understood the need for a shift from a principally quantitative interrogation of the natural world, to a qualitative approach. The parties also recognised that whereupon a disturbance becomes manifest within an ecosystem, it may align to not merely one successional trajectory, but to one of several, which, at that time, was a veritable ecological epiphany.

In the intervening years since the publication of Wright and Heinselman’s paper, various authors have added or subtracted to the number of regime types described, while also editing the defining characteristics of the schemata (Barrett et al, 2010; Morgan, 2001; Smith and Brown, 2000; Frost, 2000; Hardy, 1998a, 1998b; Agee, 1993; Crutzen and Goldammer, 1993; Pickett and White 1985; Kilgore, 1981). Differences of opinion with regard to the significance of the many variables in shaping fire regimes underpin the variances in the several classification systems. Whereas Heinselman’s system is principally shaped by the fire frequencies and intensities (Heinselman, 1973) later studies have placed emphasis on biotic assemblages (Davis et al, 2001), or on fire severity (Agee, 1993; Quigley et al, 1996; Hardy et al, 2001). Furthermore, whereas some classification systems are born primarily of ecological observations, others bring greater emphasis to anthropogenic factors. Therein, the classification system adopted tends relate to the end-purposes of the study concerned.

On the whole, the authors of the several hundred fire ecology journal papers, articles, and books reviewed for the purposes of this study employed a tri-part classification system in which fire regimes are described as being low-severity, mixed-severity, or high-severity in type. In some instances, authors added moderate-severity to this trio, thus engaging a quadri-part descriptive system, but more commonly ‘moderate’ is used interchangeably with ‘mixed’, (Agree, n.d). Occasionally authors utilised the Fire Regime Groups [FRG] specified by the LANDFIRE Program, which is one of a suite of more than twenty products delivered as part of a partnership between the U.S Department of Interior, the U.S Forest Service, and the Nature Conservancy, FRG harnesses the rich and varied quantitative data sets produced by Earth satellite and terrestrial observation ICT infrastructure.

Launched in 2001, in such fashion as one might expect of a software program, LANDFIRE and its various assets, have so far been updated on five occasions, in each instance by means of integrating new insights and technological capabilities. At the time of writing LF 2014 [LF_1.4.0] is the latest ‘update’ (LANDFIRE, 2014, 2016). FRG, as was Wright and Heinselman’s, is a 5-part fire regime classification system born of analysis of vegetation dynamics, fire spread, fire effects, and spatial context, that utilises empirical data, but within a qualitative approach. However, whereas Wright and Heinselman’s system featured two long-term [35-200 years] fire return intervals, two short-term [<35 years] fire return intervals, and “all” combinations thereof, FRG replaces the latter with a yet longer [>200 years] fire return interval of “any” severity. A further variation of the 5-class fire regime system retains the same duration for the short-term return interval [0-35 years], but reduces the term of the long-term interval [35-100 years], together with that of the fifth class [100> years] (Agee, 2005). A yet more recent study likewise concurs that whereupon datasets spanning fire size, frequency, intensity, season, and extent are analysed, fire regimes align to one of five classifications. Furthermore, the study demonstrates fundamental constraints within each of the five regime variants, wherein only certain combinations of fire characteristics are possible, described as akin to the ecological trade-offs found in plant physiology (Archibald et al, 2013). Technically, the LANDFIRE fire regime classification system is the most rigorous and fit for future purpose, given that its overall design schematic can accommodate for advances in Earth observation systems and analysis, the latter of which are subject to rapid and ongoing technological advances (Asner et al, 2012; Saatchi et al, 2011; Shugart et al, 2010; Lefsky et al, 2010; Running et al, 2009). However, a “stochastic, spatially complex disturbance process” (Morgan et al, 2001) wildfire manifests with such great variability as to render both FRG, and all the above classification systems unable to quantify fire regimes in absolute terms. Given that most of the fire ecology literature reviewed in this study aligned to the tri-part ‘low, mixed, or high’ severity system, it is this to which the fire ecology case studies, and the wildland urban interface theoretical design works born thereof, are ascribed in this thesis. The method utilizes the fire severity trio as an organising paradigm through which we can interrogate the systemic nature of wildfire (Agee, 1998).

>Continue to Chapter 4.2.2 here.

Footnotes

[56] Broadly corresponding with a climatic region, “biome” describes the largest biogeographical region (Allaby, 2012).

[57] Covering 22.9 million square kilometres, the Neoarctic is a biogeographic region extending from North America to Central Mexico (Escalante et al, 2010) that was first delimited in the 19th Century by Sclater (1858), and Wallace (1876). The latter delineated the region into four subdivisions, of which he stated, though “pretty clearly indicated by physical features and peculiarities of climate and vegetation”, zoologically, “while the species of several sub-regions are in most cases different”, at the taxonomic level of genus, “even the vast range of the Rocky Mountains has not been an effectual barrier against this wide dispersal of the same forms of life”. Following in Wallace’s footsteps, the WWF also divides the Neoarctic into four bioregions having applied a similar methodology (Ricketts et al, 1999).

[58] ‘Biogeographic realm’ is the broadest delineation of taxonomic composition. First introduced by Miklos Udvardy in a paper for UNESCO’s Man and the Biosphere Programme (Udvardy, 1975), the classification system was adopted by WWF in its Global 200 scheme in the 1990s, employing the same general methodological approach (Olson and Dinerstein, 1998). Udvardy’s system defined 8 categories of biogeographic province, with a further 193 subcategories characterized by one of 14 biome types. Whereas, WWF’s system is more detailed, specifying 8 forest types and 867 ecoregions (Olson et al, 2001).

[59] An ‘ecoregion’ designates a “large unit of land or water containing a geographically distinct assemblage of species, natural communities, and environmental conditions” (WWF, n.d).

[60] Some several hundred definitions for ‘forest’ exist worldwide (United Nations, 2010). However, within the research domain of dendrology a ‘forest’ is defined as an area greater than 0.5ha of land featuring trees of 5m or more in height, of which the density is at least suffice to meet a minimum of 10% canopy cover (FOA, 2005).

[61] The term necromass describes “any quantitative estimate” of the sum of the mass of dead organisms p/unit area or volume within a specified time (Lincoln, Boxhall, and Clark, 1998).

[62] Quantified on a scale of 0-100, albedo describes the percentage of the Sun’s energy (radiation) reflected back into space from the Earth’s surface. On average, Earth’s surfaces have an albedo of .31. However, forests have a relatively low albedo, averaging between .08 and .15 (ESSEA, 2017).

[63] In 1584 Elizabeth I chartered Sir Walter Raleigh to explore and colonise “remote, heathen and barbarous lands, countries, and territories, not actually possessed of any Christian Prince or inhabited by Christian People” (Lillian Goldman Law Library, 2008). However, attempts at the colonisation of North America were unsuccessful until 1606, when King James I chartered the London Company to establish colonial settlements, of which Jamestown, Virginia, established in 1607, was the first.

[64] Graminoids refers to plants of the order Poales (Poaceae), more commonly known as the grass family (Allaby, 2012).

[65] Functional traits are described as the “morphological, biochemical, physiological, structural, phenological or behavioural characteristics of organisms that influence performance or fitness” (Nock, Vogt, and Beisner, 2016).

[66] Phylogenetics pertains to the evolutionary history of a taxonomic group of any rank [Domain, Kingdom, Phylum, Class, Order, Family, Genus, or Species] (Lincoln, Boxshall, and Clark, 1998).

[67] The term basal area (BA) describes ‘the cross-sectional area of a tree stem when measured at breast-height’, and it is calculated using the formula BA (m 2) = pi * DBH (cm) 2 / 40000, (Erdle, 2012).

[68] Shrubland is a biome type comprised evergreen sclerophyll shrubs, which comprised hard leaves, are woody plants that grow to less than 10m tall.

[69] Snag refers to standing dead tree, or part thereof (NOAA, 2016).

[70] Whereupon its tissues are damaged by fire, a tree develops physical and chemical boundaries at the injury site: a process that helps to reduce the probability of infection. As in humans, this process is called ‘scarring’, and in the record thereof helps dendrologists to establish information about the timing and possibly intensity of an historical fire (USDA, 2016).

[71] Topkill refers to mortality of aerial biomass, which may, or may not recover by resprouting in the aftermath of a fire).

[72] Course woody debris is described as “dead woody materials in various stages of decomposition, including sound and rotting logs, snags, and large branches” (Enrong, Xihua, and Jianjun, 2006).

[73] Stand refers to a biotic unit comprised a single species that is homogeneous both in composition and age (Lincoln, Boxshall, and Clark, 1998).

[74 /75] The finer the fuel, the higher the surface area to volume ratio, i.e. whereas a blade of grass might have a ratio of 1:3,000, a log might have a ratio of 1:6 (TDA, 2002).

[76] Pyrolysis refers to an irreversible thermochemical decomposition that occurs in carbon-based [organic] matter whereupon exposed to high temperatures in the absence or near absence of oxygen. The process turns organic matter into its gaseous components, leaving a solid residue in the form of carbon, ash, and pyrolytic oil (Boslaugh, 2017).

[77] Systema Naturæ per ignem regnis [Nature System by means of the three kingdoms of fire] is a reference to the title of the 10th edition of Caroli Linnæi’s publication of Systema Naturæ, which published in 1758, had the extended title Systema Naturæ per regna tria naturæ, Secundum Classes, Ordines, Genera, Species, Cum Characteribus, differentiis, synonymis, locis.

[78] Ecologist Richard Vogl thought the concept of successional stages of limited in fire ecology. He considered it more useful to conceive of species through the lens of a 5-part functional group comprised increasers, decreasers, neutrals, invaders, or retreaters (Vogl, 1974).

[79] Serotiny refers to a functional trait, which found in some flora species, enables the retention of seeds in resistant structures, including cones and pods, whereupon dispersal follows a major environmental disturbance (Lincoln, Boxshall and Clark, 2003).

[80] Perennial refers to plants of which the lifespan exceeds 24 months. 81 Ephemerals may be described as flora that lives fleetingly.

[82] Occurring at temperatures of 500 °C and above, flashover refers to the near-simultaneous ignition of organic matter within an enclosed area.

[83] Mesophytes are plants adapted to environments where precipitation is not scarce or excessive.

[84] Autecology is the study of how individual organisms or single species interact with both living and nonliving entities within their environment.

[85] On the Tendency of Species to form Resilience is a reference to a joint presentation made by Alfred Wallace and Charles Darwin at the Linnaen Society of London on July 1st 1858 to announce their theory of evolution by natural selection.

[86] A method of molecular systematics, which resides within field of phylogeny, Molecular phylogenetics involves the analysis of hereditary molecular differences by means of establishing the evolutionary relationships between species (Brown, 2002).

[87] The Bayesian method enables calculation of the probability that an unknown organism belongs to a specified taxonomic lineage (Lincoln, Boxshall and Clark, 2003).

[88] Imbibition is a diffusion process, which in seeds involves the absorption of water.

[89] Meristematic tissue is comprised “unprogrammed” living cells that are yet to be “assigned a role” within a plant, otherwise described as “undifferentiated cells” (Steadham, 2017, online).

[90] Latin motto ‘Vitai Lampada Tradunt’ translates to ‘They hand on the torch of life’. 91 Pioneer species are usually the first species to populate a disturbed site.

[92] Ramet refers to an individual member within a clonal community.

[93] Cambium refers to the layer of cells at the interface of the xylem and phloem, which in woody plants continue to divide throughout the plant’s life, thus creating secondary xylem and phloem, of which the consequence is a thickening of bark.

[94] Monoecious refers to a species that bears both male and female reproductive organ.

[95] P. ponderosa subspecies west of the Sierra Nevada, CA, average medium seed crops every 2-3 years and heavy crops every 8 years. Whereas, subspecies in Montana have been recorded to have just one good seed crop in 23 years (Oliver and Ryker, n.d).

[96] Whereupon, having re-evaluated the premise of a scientific theory, the research community concludes there potential for a more viable alternative, thereon displaces prior fundamental assumptions, and its “imagination” is stimulated suffice to transform a discipline, or collective thereof, a new paradigm will emerge. In ‘The Structure of Scientific Revolutions’ Thomas Khun described the processes thereof through a series of historical precedents, including the events that led to Lavoisier’s oxygen theory of combustion.

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

Note that figures have been removed from the digital version hosted on this site, but are included in the PDFs available at the links above.

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.