Interactions between rainfall, fire and herbivory drive resprouter vital rates in a semi‐arid ecosystem

Abstract

Summary Global change is threatening ecosystems and biodiversity world‐wide, creating a pressing need to understand how climate and disturbance regimes interact and influence the persistence of species. We quantify how three ecosystem drivers – rainfall, fire and herbivory – influence vital rates in the perennial resprouting graminoid, Triodia scariosa, a foundation species of semi‐arid Australia. We used an 11‐year dataset from a fire and herbivore exclosure experiment, to model flowering, post‐fire recruitment and the post‐fire survival of seedlings and resprouting plants. Regression modelling quantified the effect of rainfall, inter‐fire interval, fire type (wildfire or prescribed fire), grazing by herbivores (native and feral) and an interaction between fire type and herbivory on T. scariosa populations. Rainfall, fire and herbivory had significant effects on post‐fire recruitment and the survival of seedlings and resprouting plants, including strong interactions between these drivers. Herbivory following wildfire had a minor effect, but in years of below‐average rainfall herbivory following prescribed fire had a large effect, reducing the survival of seedlings and resprouting plants by 20% and over 50% respectively, relative to post‐fire survival under average rainfall conditions. Variation in rainfall underpinned significant variation in post‐fire resprouting and seedling survival, thus we postulate rainfall primarily drives the dynamics of T. scariosa populations. Synthesis. This study highlights the importance of modelling interactions between key ecosystem drivers when predicting how changes in global climate and disturbance regimes influence plant vital rates. Relatively small changes to disturbance regimes can substantially alter population processes, even in perennial resprouting species. This work suggests that conservation of foundation species, such as T. scariosa, will benefit if fire management decisions are better integrated with inter‐annual weather forecasts and herbivore management.

Fire, leaf harvest, and abiotic factors drive demography of an ecologically and culturally important understory plant

“…, Giljohann et al. ). In our study, high‐severity fire plots had the lowest soil moisture and almost no seedling recruitment, while low‐severity fire plots had the highest soil moisture (Appendix ), and the greatest seedling recruitment.…”

“…, Giljohann et al. ). Further, despite the ecological significance of the understory (Gilliam ), modeling of temperate forest dynamics rarely incorporates this stratum (Landuyt et al.…”

Recovery of food webs following natural physical disturbances

“…Studies in Amazon forests by Massad et al . and semiarid sand dunes in Australia by Giljohann et al . showed that overall herbivory was higher following fires for a variety of plant species.…”

“…found that adding nutrients to burned plots increased herbivory. Giljohann et al . found that fire increased herbivory in dry years but not wet years.…”

“…Herbivore populations increase but their growth rate is reduced by growing populations of the surviving predators, so the increase in herbivory is not dramatic and the effect of herbivory on plant abundance is less noticeable. This diagram may fit studies of terrestrial plants severely damaged by a river flood surrounded by plants with less damage and studies of fires which do not burn all plants in the study area …”