Severe fire reduces flowering in Corymbia maculata: implications for Avian flower-visitors

In the Austral summer of 2019/2020, south-east Australia experienced an unprecedented wildfire season. Although much of the Australian flora is adapted to fire, little is known about how fire affects flowering and flower-visiting fauna. Our aim was to investigate the relationship between fire severity and abundance of flowers produced by Corymbia maculata, a dominant canopy tree in forests along the south-east coast of Australia. We also examined whether fire severity and flowering effort impact the abundance and diversity of avian flower-visitors. Three study sites were established in each of three fire severity classes, in three locations (Nowra State Forest, Meroo National Park and Murramarang National Park). Fire severity classes were canopy burn (> 90% canopy scorched or consumed), understory burn (> 10% burnt understory, < 90% canopy scorch) and unburnt. Surveys were conducted every 4 weeks over the flowering season from May to September 2022 and 2023, with no flowering observed in 2023. At each site, a 50 m transect was established and all trees within 1 m of the transect measured (diameter at breast height) and the percentage of the canopy covered in flowers assessed. Avian flower-visitors were recorded during each site visit on five trees for 15 min per tree. We observed that significantly fewer trees flowered at sites with a canopy burn (8% ± SE 5.1, n = 16), compared to understory burn (26.9% ± SE 5.2, n = 63), or unburnt (31.3% ± SE 8.1, n = 78). We also observed that larger trees had a greater probability of producing flowers. While there were differences in abundances of Trichoglossus moluccanus and Caligavis chryops, overall bird diversity did not differ among fire severities. By studying the impact of fire on post-burn flowering success, we can better understand the potential impacts on plant reproduction and the availability of food resources for nectarivores and pollinivorous organisms.