Abstract
The Mojave Desert of North America has become fire-prone in recent decades due to invasive annual grasses that fuel wildfires following years of high rainfall. Perennial species are poorly adapted to fire in this system, and post-fire shifts in species composition have been substantial but variable across community types. To generalize across a range of conditions, we investigated whether simple life-history traits could predict how species responded to fire. Further, we classified species into plant functional types (PFTs) based on combinations of life-history traits and evaluated whether these groups exhibited a consistent fire-response. Six life-history traits varied significantly between burned and unburned areas in short (up to 4 years) or long-term (up to 52 years) post-fire datasets, including growth form, lifespan, seed size, seed dispersal, height, and leaf longevity. Forbs and grasses consistently increased in abundance after fire, while cacti were reduced and woody species exhibited a variable response. Woody species were classified into three PFTs based on combinations of life-history traits. Species in Group 1 increased in abundance after fire and were characterized by short lifespans, small, wind-dispersed seeds, low height, and deciduous leaves. Species in Group 2 were reduced by fire and distinguished from Group 1 by longer lifespans and evergreen leaves. Group 3 species, which also decreased after fire, were characterized by long lifespans, large non-wind dispersed seeds, and taller heights. Our results show that PFTs based on life-history traits can reliably predict the responses of most species to fire in the Mojave Desert. Dominant, long-lived species of this region possess a combination of traits limiting their ability to recover, presenting a clear example of how a novel disturbance regime may shift selective environmental pressures to favor alternative life-history strategies.
Highlights
Fire acts as an evolutionary filter in vegetation communities, favoring species with traits that allow them to survive burn injury or to successfully reproduce in postfire environments (Bond and Keeley 2005; Pausas et al 2006)
Greater than 90% of the constrained variability could be attributed to the outlying mean index (OMI) X-axis, which corresponded to fire treatment based on the biplot (Fig. 1)
The small amount of constrained variability attributed to the OMI Y-axis (
Summary
Fire acts as an evolutionary filter in vegetation communities, favoring species with traits that allow them to survive burn injury or to successfully reproduce in postfire environments (Bond and Keeley 2005; Pausas et al 2006). Species composition of burned communities may simultaneously diverge due to variation in initial community composition and postfire environmental conditions (Fukami et al 2005; Smart et al 2006), complicating efforts to predict species-level changes through time. Under these circumstances, a plant functional type (PFT) approach may be well suited for modeling community dynamics, where PFT is defined as a group of species with a similar response to disturbance based on a shared combination of functional traits
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