4.2.3 Forests and Fire Regimes of the United States

Prior to British colonization of the Americas [63], forests covered an estimated 420 million ha [approx. 46%] of the United States, of which 104 million ha has subsequently been subject to land-conversion, leaving an estimated 310 million ha of forested land [approx. 33.8%] (Oswalt, 2012) [Fig. 23]. Together with the forests of Central America, this constitutes 17% of forests worldwide (Pan et al, 2013). 56% of U.S. forests are under private ownership, of which 75% is divided between several million individuals and families, with the remaining 25% owned by corporations, partnerships, and tribes (Oswalt, 2012). 75% of forests under public ownership are in the western United States, of which the majority have protected status (Ibidem), whereas the contrary is true of forests under private ownership.

Omitting agricultural, urban/developed, and barren lands, 48% [240 million ha] of Federal and non-Federal territory in the conterminous United States falls within the historical range for biomass composition, structure, and fuel loadings. Whereas, 38% [190 million ha] lies moderately outside thereof, with 15% [73.6 million ha] of lands classified as significantly outside of their historical range (USDA, 2015). Given biotic assemblages are coupled to their fire regimes, the above statistics essentially indicate that, whereupon wildland fire takes hold in these lands, currently, roughly 50% are likely to manifest levels of fire severity on a par with that which the historical record suggests to be probable. However, the biomass composition, structure and fuel loadings of the other 50% or so of lands suggests that, to a lesser or greater extent, whereupon wildfire manifests there is an increased probability that the level of fire severity may vary from the historical record.

63% of the vegetated lands of the conterminous United States [640 million ha] historically experience frequent fires [0-35-year occurrence] (Hardy et al, 1998a, 1998b, 2000), and it is at these sites that the fire regimes, therein fire behaviour and severity, are changing most (Morgan et al, 1996, 2001). Distinct patterns are starting to emerge in the spatiotemporal shifts underway (Parisien et al, 2012), and these are born of the tight coupling between the variables within the regional bio-chemical complexes. The data evidences that some biome types are currently experiencing a greater degree of change than others, and in particular dry forests, woodlands, and grasslands, each of which are native to the western United States. Given that 1% of all fires in the conterminous United States currently account for 98% of the area burned (Strauss et al, 1989; Morgan et al, 2001), the recent data suggests we might reasonably assume this ratio will alter in the years and decades to come, and that the biome-types indigenous to the study region are more, not less likely to manifest change, and despite the fact that, historically, fire has been the foremost natural disturbance in the region (Spurr and Barnes, 1980).

Mediterranean Forests, Woodlands, and Scrubs

Globally, this ecoregion type sustains some 10% of flora species (WWF, 2012b). Comprised an assemblage of woody, herbaceous, and graminoid [64] plants, Mediterranean forests, woodlands, and scrubs are amongst the foremost fire-prone ecosystems on Earth (Keeley et al, 2012). Climatically, long, hot, and dry summers are juxtaposed against mild and relatively wet winters, the latter enabling the accumulation of biomass, the former converting the sum thereof to tinder-dry fire- ready fuel. Manifold functional traits [65] that enable flora to flourish within ecosystems classified under this ecoregion type, and in particular those that enable coexistence with fire, pre-date the onset of the Mediterranean climate, and, within the case study region, by a period of at least 50 million years (Lamont and He, 2017; He, Lamont, and Manning, 2016). Covering an area of 4.7 million ha, California Chaparral and Woodlands is one of five variants of the Mediterranean shrublands ecoregion worldwide (WWF, 2016b). Ascribed critical/endangered status, anthropogenic threats to the region include overgrazing by cattle; logging; introduction of exotic species; dams and hydrological disruptions of various kinds; urbanisation; and myriad actions that affect the historical fire regime.

Temperate Coniferous Forest

Populated by members of the genus Pinus, the fossil record and phylogenetic [66] analysis pinpoint the emergence of the taxonomic family that populate this ecoregion to the Middle Carboniferous [340-310 mya] (He et al, 2016; Wang and Ran, 2014). A fire-preserved Pinus fossil dated to the Early Cretaceous [140 – 130 mya] evidences fire as the evolutionary driver of functional traits in coniferous forests since at least that date (Falcon-Lang, Mages, and Collinson, 2016). Generally, the climatological realm in which this highly flammable evergreen ecoregion persists is temperate, known for warm summers and cool winters, the latter endowed with suffice levels of precipitation to sustain the highest levels of biomass to be found in a terrestrial biome (WWF, 2016a). Compared to some other forest ecoregions, such as tropical rainforests, Temperate Coniferous Forests are structurally simple, generally comprised just two layers: understory and overstory. Covering an area of 29.5 million ha, the Pacific Temperate Rainforests are one of seven variants of the Temperate Coniferous Forest ecoregion worldwide (WWF, 2016a). Orientated North to South, The Rocky Mountains stretch from New Mexico to Canada, which at a distance of some 3,000 miles makes them the second-longest mountain range in the world. Centred on the Yellowstone Plateau, the forests of the South Central Rockies span nearly 16 million ha, and are home to world’s oldest and most renowned national park. Climatically, these forests experience the strongest seasonality of any in this ecoregion type, juxtaposing relatively brief but dry, continental-style summers against, at times, bitterly cold, and in higher elevations, snowy winters, though the impact thereof varies sizeably with the topology of the landscape. 83% protected (Hoekstra et al, 2010), the South Central Rockies forests are classified as vulnerable, with logging, hard-rock mining, oil and gas development, WUI development, livestock grazing, and the introduction of exotic species listed as the primary threats to the integrity of its biotic assemblages (WWF, 2016c).

>Continue to Chapter 4.2.4 here.

Footnotes

[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).

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.