4.2.8 Vitai Lampada Tradunt [90]: Six Fire-Resilient Specimens

“At the festival of Attis, a sacred pine tree was cut down and carried in a procession, its branches hung with violets, signifying nature’s endless cycles of death and renewal”. Ronnberg and Martin, 2010.

A selection of species that exhibit the traits of endurer, evader, and resister are described below:

Endurers

Quaking aspen

A shade intolerant pioneer species [91], Quaking aspen (Populus tremuloides) is the most widely distributed tree in the northern United States (Little, 1971). Enduring fires at frequencies of 3> years, the species flourishes in myriad alluvial variants, including the mineral soils that fires create (Perala, n.d). Within a year, Quaking aspen seedlings have capacity for reproduction by resprouting, this being a trait that is expressed copiously in mature stands (Jones, 1974), and that is stimulated by fire. Prolific seeders, once established, stands usually yield a heavy seed crop every 4-5 years, with lighter crops in the interim (Perala, n.d). While individual trees and ramets [92] ‘live fast, die young’, usually surviving no more than two centuries at most (Hunt, 1986; DeByle and Winokur, 1985), the clone colony from which they sprout may be millennia old (Kemperman and Barnes, 1976).

Canyon live oak

A native of the western United States, the Canyon live oak (Quercus chrysolepis) endures wide-ranging terrains and soil types. But, as its name implies, it is particularly well adapted to sheltered canyons. Found in several MTC ecoregions, including chaparral and mixed conifer forests, the species flowers from 15-20 years of age, in some instances yielding acorns each year, but with good seed crops averaging every 2-4 years (Thornburgh, n.d). Seeds mature and fall within one season, generally dispersing within the immediate vicinity, though sometimes dispersed further by fauna or by falling down a steep slope (Ibidem). While its seeds germinate in a variety of seedbed types, their survival rate is higher when soil is moist, covered by leaf litter, and an overstory is present (Ibidem). However, while a fire can eradicate these conditions, thus, seedlings rarely germinate post-fire (SDSUF, 2004), Canyon live oak is a resprouter adept at repopulating disturbed sites (Talley and Griffin, 1980). A process stimulated by injury, resprouting is more vigorous in healthy parent specimens (Thornburgh, n.d). Other genus members that exhibit this rapid post-fire repopulation trait include the Gambel oak (Quercus gambelli) and the California black oak (Quercus kelloggii).

Evaders

Lodgepole pine

A ubiquitous species of which the name originates from its use as a structural component of Native American tipi shelters, Lodgepole pine (Pinus contorta) has several morphologically and ecologically distinct subspecies, of which the Rocky Mountain-Intermountain Race (P.contorta var. latifolia) is the variant of particular interest in this study. Producing plentiful seeds from the age of 5-10 years, with good crops averaging as often as 1-3 years, the species protects its faunal offspring in both serotinous and non-serotinous cones (Lotan and Critchfield, n.d), the selection therefrom shaped by the regional historical fire regime [HFR]. In the former instance, cones may remain closed for decades, which given annual seed production can run as high as 790,000 seeds per ha (Ibidem), provides P.contorta with a robust insurance policy against extinction, so long as the HFR remains in situ. Favouring germination in bare mineral soils or distributed duff in landscapes devoid of shade and competing flora, this evader species can repopulate disturbed sites in great abundance, hence commonly found in monotypic stands at sites including Yellowstone National Park (Ibidem).

Knobcone Pine

A fast-growing West Coast indigene, Knobcone pine (Pinus attenuata) is the region’s most widely dispersed closed-cone species (Howard, 1992). Residing at the interface of MTC chaparral and woodland, P.attenuata is shade intolerant and short-lived, surviving <100 years (Horton, 1960). A pioneer species that prefers higher elevations, its cones are sealed by resin that requires temperatures of 203°C> to melt, thus pyrogermination is its sole means of reproduction (Ibidem). Remaining attached to the tree for its life-term (Zedler, 1986; Vogl, 1967) the cone begins to disperse its contents within 1-12 hours of a fire’s passing, continuing the process thereof for 4> years (Vogl, 1973). Hence, the Knobcone pine is dependent on stand replacing crown fires for its survival. The species open and multi-trunked form helps propagate its affiliated fire regime (Ibidem), and vice versa: fire both enables the mechanisms of distribution of its seeds and the rapid germination thereof; studies suggest that germination of Knobcone pine seedlings may require the elevated soil pH that fire creates (Ibidem). Their length the longest of the Californian closed-cone pines, morphologically, P.attenuata’s seeds, which form when the parent plant reaches 10- 12 years old, are designed for dispersal (Howard, 1992). Tolerant of nutrient-poor soils, post-fire, this thin-barked evader species commonly forms even-aged stands of which the density widens as the elevation level increases (Ibidem).

Resisters

Coulter pine

A shade intolerant inhabitant of mixed conifer and mixed chaparral MTC ecoregions (Cope, 1993), the Coulter pine (Pinus coulteri) produces the largest cones of any conifer species [Fig. 29]. Typically found on south-facing slopes and ridges at elevations of 300 – 2,100 meters (Kral, 1993), the species thrives in mineral soils and open canopy. A resistor species, mature P. coulteri have pyro-armoury in the form of thick, furrowed bark of sufficient depth to protect against relatively frequent, low to moderate intensity surface fires (Cope, 1993). Fast-growing and living to <100 years (Ibidem), the species produces both serotinous and non-serotinous cones from the age of 10-15 years onwards, bearing good seed crops every 3-6 years (Krugman and Jenkinson, 1974). Pyriscence is markedly more frequent in P. coulteri cohabiting with chaparral, Canyon live oak, and Sargent Cypress [Cupressus sargentii) communities (Cope, 1993). Whereupon the trait is present, copious seedlings may germinate, such that, in the immediate years after a fire’s passing, stands tend be even-aged and dense, that latter in part due to seedlings’ dispersal being limited due to the great size of the cones (Ibidem). Listed near-threatened (IUCN, 2013), the species distribution has been in decline for some decades, with changes to regional fire regimes posited as the primary causation (Ibidem).

Ponderosa pine

An autochthonous species of western North America, Ponderosa pine (Pinus ponderosa) has evolved into five morphologically distinct subspecies (Callaham, 2013), the matter thereof reflecting the wide expanse and relative diversity of its territory. Inhabiting elevations from sea level [California, 150 – 1070m] to <3050m [southern Rockies], P.ponderosa forests shift to progressively higher altitudes along a north to south axis (Oliver and Ryker, n.d). Shade intolerant, this resistor species commonly lives to between 300 – 600 years old (Ibidem). Studies of the basal scars in old growth forests evidence that prior to European colonisation P.ponderosa stands commonly burned at intervals of 5-20 years (James, 1979). Endowed with some of the most formidable pyro-armoury of any fire-adapted flora species, mature P.ponderosa usually withstand multiple surface fires thanks to defences including thick bark, which forming from 3>5 years, becomes fissured and furrowed, morphing into a plated pattern over time (Callaham, 2013), the configuration thereof dissipating heat, hence helping to protect the cambium [93] (Jensen and McPherson, 2008). Ponderosa pine trees have been known to outlive fires of such severity as to scorch <50% of their crown (Oliver and Ryker, n.d). A contributing factor to their survival is the comparatively open canopy structure that the species’ stands form, this trait further enabling the dissipation of heat (Jensen and McPherson, 2008). Often growing in even-aged stands, its seeds are relatively large for members of the genus Pinus, thus tend not be carried far by the wind (Jensen and McPherson, 2008). P. Ponderosa can populate sites of which the general conditions, including soil quality and depth, is too poor for most plant biota, and particularly other perennials, to become established. Thus, the species frequently cohabits with graminoids, forbs, and shrubs (National Park Service, n.d). One of the functional traits that both helps this species to withstand fires (Jensen and McPherson, 2008), and to persist in relatively inhospitable terrain is its seedlings’ capacity to sink roots to depths to 50cm in moist porous soil (Larson, 1963), thereon to 2m in maturity (Oliver and Ryker, n.d). Monoecious [94], Ponderosa pine produces cones from 7 years and upwards to 350 years or more, with stands aged 60 – 160 years bearing the most viable seeds (Ibidem). However, both in volume and frequency, seed crops vary across the subspecies (Ibidem): the seed distributions seemingly coupled to the historical fire regime within which the P.ponderosa variants reside. As with elevation, a north to south alignment [95] in the trait’s geographical arrangement is evident. These are but a few of the factors that make Ponderosa pine one of, if not the most, die-hardy of fire-adapted species.

“the pinecone often crowned the mythic Tree of Life, abode of the Great Mother, fecund source and vessel of nurturance, healing and transformation”. Ronnberg and Martin, 2010.

The distribution of these and other endurer, evader, and resister species reveals a landscape’s historical fire regime. Whereupon combinations of the three fire-adapted types are found at one site it speaks to the mixed-severity regime, this being commonplace due to the highly diversified topographic, alluvial, and other environmental characteristics of many ecoregions of the western United States.

>Continue to Chapter 4.2.9 here.

Footnotes

[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).

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.