A 30-year chronosequence of burned areas in Arizona: effects of wildfires on vegetation in Sonoran Desert Tortoise ( Gopherus morafkai ) habitats

Abstract

Fire is widely regarded as a key evolutionary force in fire-prone ecosystems, with effects spanning multiple levels of organization, from species and functional group composition through landscape-scale vegetation structure, biomass, and diversity (Pausas and others, 2004; Bond and Keeley 2005; Pausas and Verdu, 2008). Ecosystems subjected to novel fire regimes may experience profound changes that are difficult to predict, including persistent losses of vegetation cover and diversity (McLaughlin and Bowers, 1982; Brown and Minnich, 1986; Brooks, 2012), losses to seed banks (Esque and others, 2010a), changes in demographic processes (Esque and others, 2004; DeFalco and others, 2010), increased erosion (Soulard and others, 2013), changes in nutrient availability (Esque and others, 2010b), increased dominance of invasive species (Esque and others, 2002; Brooks and others, 2004), and transitions to alternative community states (Davies and others, 2012). In the deserts of the Southwestern United States, fire size and frequency have increased substantially over the last several decades because of an invasive grass/fire feedback cycle (Schmid and Rogers, 1988; D’Antonio and Vitousek, 1992; Swantek and others, 1999; Brooks and Matchett, 2006; Esque and others, 2010a), in which invasive annual species are able to establish fuel loads capable of sustaining large-scale wildfires following years of high rainfall (Esque and Schwalbe, 2002). Native perennial vegetation is not well-adapted to fire in these environments, and widespread, physiognomically dominant species such as creosote bush ( Larrea tridentata ), Joshua tree ( Yucca brevifolia ), giant saguaro cactus ( Carnegiea gigantea ), and paloverde ( Parkinsonia spp.) may be reduced or eliminated (Brown and Minnich, 1986; Esque and others, 2006; DeFalco and others, 2010), potentially affecting wildlife populations including the Sonoran and federally threatened Mojave Desert Tortoises ( Gopherus morafkai and Gopherus agassizii , respectively; Brooks and Esque, 2002; Esque and others, 2003; Drake and others, in press).