Flowering Phenology of Native and Exotic Plants in Species‐Rich Themeda triandra Grasslands, Western Victoria: Implications for Fire Management

Frequent fire in temperate native grasslands in south‐east Australia has maintained high plant diversity. The timing of fire implemented by fire agencies over the last several decades has been in summer and autumn. This coincides with the dormant season for many grassland plants. Recent trends in agency burning, partly driven by earlier curing and the need to protect high‐asset crops in the wider landscape, have seen a shift to earlier season burning, often coinciding with when grassland plants may be growing or flowering. The potential implications of this shift in burning season have not been documented. We sought to understand how earlier fires may impact grassland species by studying their phenology (i.e., the timing of flowering). We demonstrate that flowering was strongly seasonal; native species flowered predominately in spring, while exotics peaked in early spring and declined thereafter. Four types of species‐level phenology were identified. For native species, phenological patterns included (i) early‐season (strictly spring‐flowering only), (ii) late‐season (strictly summer‐flowering only), (iii) long‐flowering, and (iv) spring–summer overlap flowering. Exotic species were predominantly early‐season flowering, or spring–summer overlapping. Differences in phenology can be explained by life form. Exotic species were predominantly C3 therophytes (annuals), whereas native species include a mix of C3 geophytes and hemicryptophytes. Hence, the greatest proportion of native and exotic species are reproductive at the time of spring burning, with consequent effects likely for their flowering and seed set. Strategic use of spring burns may suppress annual exotic species populations by preventing seed set, a potentially useful management tool; efforts to control exotics must be carefully balanced against risks to native flora that also flower in spring. Understanding species phenology can help frame hypotheses about how fire season may affect grassland communities, but direct studies of fire impacts are needed to guide management.