Fire interval effects on persistence of woody plants in Mediterranean shrublands of Western Australia

Background/Question/Methods

Disturbance frequency, such as the interval of time between successive fires, is widely recognised as an important driver of vegetation structure and composition. Of particular interest is the effect of shortened fire intervals and their interactive effects with changing climate to fundamentally change the plant communities and the relative abundance of differing life history strategies.  Concern regarding short-interval fires (also known as reburns) is widespread but studies are often limited to a single example, especially in fire-prone systems with longer intervals. 

 Using a series of experimental fires (N=33) over four years, we studied the effects of shortened fire intervals ranging in time from 3-24 years in high diversity Mediterranean shrublands of Western Australia.  These shrublands possess fire intervals variously estimated at 13-17 years.  Plots were measured before fire using eight 4x4 m plots per fire where all species were identified and counted.  Species were classified into two plant functional types based on fire-related traits of post-fire regeneration (sprouting vs. non-sprouting) and seed storage (canopy, soil with smoke cued germination, or soil with heat-cued germination).  Pre to post changes in abundance for each plant functional type were analysed with respect to fire interval, winter rainfall, and geology (acid sands vs. calcareous sands). 

Results/Conclusions

Fire interval was a strong predictor of post-fire changes in abundance with non-sprouting, canopy-stored seed species being the most sensitive to short-interval fires and resprouting, soil-smoke stored species being the least sensitive.  Winter rainfall also influenced post-fire persistence with a strong interaction with fire interval.  Neutral responses of most plant functional types (i.e. persistence through fire of species) were achieved by approximately 9-11 years following fire, depending on plant functional type and winter rainfall.  Application of prescribed fire at shorter intervals is likely to result in reduction of certain plant functional types on the landscape.