ABSTRACT
Aim : Drastic changes in fire regimes are altering plant
communities, inspiring ecologists to better understand the relationship
between fire and plant species diversity. We examined the impact of a
2011 megafire on woody plant species diversity in an arid mountain range
in southern Arizona, USA. We tested recent fire-diversity hypotheses by
addressing the impact of the fire severity, fire variability, historic
fire regimes, and topography on diversity.
Location : Chiricahua National Monument, Chiricahua Mountains,
Arizona. USA., part of the Sky Islands of the US-Mexico borderlands.
Taxon : Woody plant species.
Methods : We sampled woody plant diversity in 138 plots before
(2002-2003) and after (2017-2018) the 2011 Horseshoe Two Megafire in
three vegetation types and across fire severity and topographic
gradients. We calculated gamma, beta, and alpha diversity and examined
changes over time in burned vs. unburned plots and the shapes of the
relationships of diversity with fire severity and topography.
Results : Alpha species richness declined and beta and gamma
diversity increased in burned but not unburned plots. Fire-induced
enhancement of gamma diversity was confined to low fire severity plots.
Alpha diversity did not exhibit a clear continuous relationship with
fire severity. Beta diversity was enhanced by fire severity variation
among plots and increased with fire severity up to very high diversity,
where it declined slightly.
Main Conclusions : The results reject the intermediate
disturbance hypothesis for alpha diversity but weakly support it for
gamma diversity. Spatial variation in fire severity promoted variation
among plant assemblages, supporting the pyrodiversity hypothesis.
Long-term drought probably amplified fire-driven diversity changes.
Despite the apparent benign impact of the fire on diversity, the
replacement of two large conifer species with shrubs signals the
potential loss of functional diversity, emphasizing the importance of
intervention to direct the transition to a novel vegetation mosaic.