Changes in plant species and functional composition with time since fire in two mediterranean climate plant communities




Do floristic composition and plant functional type (PFT) richness and dominance change with time since fire, in the directions predicted through consideration of their fire response traits?


Two vegetation communities in the globally significant biodiversity hotspot of south-western Australia: mallee, dominated by resprouters, and mallee-heath, dominated by non-resprouters.


Species richness and cover were sampled in replicated plots across a time since fire gradient ranging from 2 to >55 yr post-fire, using a space-for-time approach. Species were allocated to PFTs according to traits relevant to the processes of vegetation change underpinning the initial floristic composition model of vegetation assembly: their capacity to resprout, the location and persistence of the seed bank, competitive stratum and longevity. Ordination and ANOVA were used to test for differences in floristic and PFT composition between young (<10 yr post-fire), mature (18–35 yr) and old (>40 yr) vegetation in each community.


Plant functional type and floristic analyses were similar, showing substantial changes in the composition of mallee-heath vegetation with time since fire, but not in mallee. The direction of change in PFT composition in mallee-heath was consistent with predictions, with increasing cover of non-resprouting, serotinous PFTs, an intermediate peak in cover of PFTs with persistent soil-stored seed banks, and decreasing cover of post-fire ephemerals and non-resprouting, non-serotinous dwarf shrubs, herbs and graminoids with increasing time since fire. Success in predicting changes in PFT dominance in mallee was lower.


The similarity of floristic and PFT analyses suggest that these approaches are interchangeable for characterizing vegetation change with increasing time since fire. PFTs were more effective for predicting fire response trajectories in the vegetation community dominated by non-resprouting, serotinous shrubs (mallee-heath) than that dominated by resprouting, serotinous trees (mallee). The underlying vegetation assembly model and PFTs used appear suitable for broader application in fire-prone communities with competitive dominance by non-resprouting, serotinous shrubs, but less so in communities dominated by other PFTs.