Resistance and resilience to changing climate and fire regime depend on plant functional traits

Abstract

Changing disturbance-climate interactions will drive shifts in plant communities: these effects are not adequately quantified by environmental niche models used to predict future species distributions. We quantified the effects of more frequent fire and lower rainfall - as projected to occur under a warming and drying climate - on population responses of shrub species in biodiverse Mediterranean-climate type shrublands near Eneabba, southwestern Australia. Using experimental fires, we measured the density of all shrub species for four dominant plant functional groups (resprouter/non-sprouter × serotinous/soil seed bank) before and after fire in 33 shrubland sites, covering four post-fire rainfall years and fire intervals from 3-24 years. Generalized linear mixed effects models were used to test our a priori hypotheses of rainfall, fire interval and plant functional type effects on post-fire survival and recruitment. At shortened fire intervals, species solely dependent on seedling recruitment for persistence were more vulnerable to local extinction than were species with both seedling recruitment and vegetative regrowth. Nevertheless, seedling recruitment was essential for population maintenance of resprouting species. Serotinous species were less resilient than soil seed storage species regardless of regeneration mode. Critically, in relation to changing climate, a 20% reduction in post-fire winter rainfall (essential for seedling recruitment) is predicted to increase the minimum inter-fire interval required for self-replacement by 50%, placing many species at risk of decline.Synthesis. Our results highlight the potentially deleterious biodiversity impacts of climate and fire regime change, and underscore weaknesses inherent in studies considering single impact factors in isolation. In fire-prone ecosystems characterized by a projected warming and drying climate, and increasing fire hazard, adaptive approaches to fire management may need to include heightened wildfire suppression and lengthened intervals for prescribed fire to best support the in situ persistence of perennial plant species and of plant biodiversity. This conclusion is at odds with the view that more managed fire may be needed to mitigate wildfire risk as climate warms.