Abiotic and biotic interactions as drivers of plant reproduction in response to fire frequency

Abstract

Plant reproduction is influenced by abiotic resources and biotic mutualistic and antagonistic interactions, which in turn can be affected by anthropogenic disturbances such as increased fire frequency. Because frequent fires deplete soil fertility and thus decrease resource availability for plants, we hypothesize that increased fire frequency decreases specific leaf area (SLA) and reproductive success. In addition, lower SLA levels in frequently burned sites should decrease herbivore damage because of reduced leaf palatability. Finally, increased fire frequency will have stronger negative effects on specialist insects (seed predators) as compared to generalist feeding insects such as herbivores and pollinators, which can have direct consequences on plant reproduction. Through an integrative path analytical approach, we assess fire frequency effects on the reproductive success of two resprouting legumes from the Chaco Serrano (Desmodium uncinatum and Rhynchosia edulis), estimating the relative importance of SLA along with pollination, insect herbivory and seed predation interactions. Increased fire frequency decreased SLA but it did not affect biotic interactions in both plant species, with the exception of increased leaf herbivory in R. edulis. Sexual reproduction of D. uncinatum was reduced in burned sites but it remained similar across burned and unburned sites in R. edulis. Within burned areas, both species efficiently maximized the allocation to reproduction, showing a conservative strategy in the use of resources when SLA levels are extremely low. Decreased plant fecundity, especially in D. uncinatum, is likely to impact on the density and long-term viability of populations growing in anthropogenic high fire frequency areas.