Post-fire plant reproductive success of generalist vs. specialist pollinated native perennials in the Mojave Desert, USA

Background/Question/Methods

The occurrence and size of fire events in warm desert regions of the Southwestern United States has rapidly increased in recent years. This coupled with the historical infrequency of fire disturbance in these areas, has resulted in poor resiliency of native desert plant communities to fire. Native perennial species generally experience high mortality rates and few species resprout in response to fire, which can also compromise seed banks. Unfortunately, restoration efforts in these landscapes frequently fail, making recovery exclusively dependent on the reproductive success of surviving vegetation from nearby areas that can serve as seed sources. Currently fire impacts on the reproduction of desert plant communities are unknown. Our objective was to elucidate the effects of fire on the pollination success of surviving native plants situated within burned areas of the Mojave Desert region of Southern Utah, USA.  We expected reproductive success of surviving vegetation to vary depending on pollination strategies among species, and by the extent that animal pollinated plants depend on specific pollen vectors. We counted the number of flowers and fruits set on several common plant species that utilize various reproductive strategies in adjacent burned and unburned areas throughout the spring blooming period of 2012 and 2013. 

Results/Conclusions

Plants pollinated by a broad array of insects, or who are not dependent on animal mediated pollen, showed significantly high flower and fruit set in burned areas when compared to unburned areas. Plant species heavily dependent on a narrow pool of pollinating organisms expressed reduced fruit set in burned areas even though flower set did not differ between burned and unburned areas for these species. Commensurate flower production within burned and unburned areas suggests that observed discrepancies in fruit set for pollinator specialist plants is not the result of resource limitations to these plants, but that some other factor(s) may be responsible for low fruit set in burned areas. Our data suggests that highly specialized plant-pollinator relationships are highly sensitive to fire fragmentation and isolation.   The sensitivity of highly specialized plant pollinator relationships compared to generalized pollinator systems could explain the strong divergent reproductive success patterns observed among desert species. Failure for species to adapt to current disturbance patterns may be detrimental to the survival of native species, and could result in their extirpation from these regions and have ecosystem-wide effects.