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Summary Fire is a major determinant of vegetation structure worldwide, and structural vegetation change following fire exclusion is well documented throughout Australia. Such changes include the displacement of treeless ecosystems by forest and the transition of open forest to rainforest. These changes displace essential habitat for myriad plant and animal species and are likely drivers of localised species extinctions. Despite these potential consequences, research identifying the spatial extent of fire‐excluded ecosystems is largely absent from the ecological literature. This study identifies the spatial and temporal extent of fire exclusion in Byron Shire in north‐east New South Wales. GIS analysis compared modern fire history with recommended fire intervals for the maintenance of fire‐dependent vegetation types. Fire exclusion (low‐frequency fire) vastly exceeded high‐frequency fire, comprising 99.1% of areas affected by inappropriate fire frequency. Most fire‐dependent vegetation was fire‐excluded, with less than 10% within recommended fire interval thresholds. Most affected areas were fire‐excluded for multiple recommended fire‐return cycles, increasing the likelihood of vegetation change and localised extinctions. These findings demonstrate the operation of a major threatening process affecting Byron Shire's biodiversity that has previously been little recognised. A growing body of ecological literature suggests that irreversible change to fire‐excluded vegetation is likely wherever plant growth resources are sufficient to enable transition. Irreversible vegetation change and rapid species declines have been reported for several communities in Byron Shire, and there is compelling evidence that further change may be widespread. With increasing time since fire, efforts to restore these sites may be complicated by encroaching trees resistant to removal by fire alone and the difficulties of reintroducing low‐intensity understorey fires where the flammable understorey has been lost through shading. Further research into the impacts of fire exclusion is urgently required, as is the reinstatement of fire to fire‐excluded vegetation to prevent ongoing displacement of fire‐dependent biodiversity values.

The conservation implications of large-scale rainforest clearing and fragmentation on the persistence of functional and taxonomic diversity remain poorly understood. If traits represent adaptive strategies of plant species to particular circumstances, the expectation is that the effect of forest clearing and fragmentation will be affected by species functional traits, particularly those related to dispersal. We used species occurrence data for woody plants in 46 rainforest patches across 75,000 ha largely cleared of forest by the early 1900s to determine the combined effects of area reduction, fragmentation, and patch size on the taxonomic structure and functional diversity of subtropical rainforest. We compiled species trait values for leaf area, seed dry mass, wood density, and maximum height and calculated species niche breadths. Taxonomic structure, trait values (means, ranges), and the functional diversity of assemblages of climbing and free-standing plants in remnant patches were quantified. Larger rainforest patches had higher species richness. Species in smaller patches were taxonomically less related than species in larger patches. Free-standing plants had a high percentage of frugivore dispersed seeds; climbers had a high proportion of small wind-dispersed seeds. Connections between the patchy spatial distribution of free-standing species, larger seed sizes, and dispersal syndrome were weak. Assemblages of free-standing plants in patches showed more taxonomic and spatial structuring than climbing plants. Smaller isolated patches retained relatively high functional diversity and similar taxonomic structure to larger tracts of forest despite lower species richness. The response of woody plants to clearing and fragmentation of subtropical rainforest differed between climbers and slow-growing mature-phase forest trees but not between climbers and pioneer trees. Quantifying taxonomic structure and functional diversity provides an improved basis for conservation planning and management by elucidating the effects of forest-area reduction and fragmentation. Efectos de la Forma de Crecimiento y Atributos Funcionales en la Respuesta de Plantas Leñosas al Desmonte y Fragmentación de Bosque Lluvioso Subtropical.

Interactions between rainforest plants and fire occur when fires encroach into rainforest and when rainforest pioneers colonise fire-prone open forests. Although numerous studies show that many rainforest plants survive fire by resprouting and postfire seedling recruitment, data is lacking for several major Australian rainforest types. In this study, we examine fire-resilience traits among 228 taxa of woody rainforest plants in four rainforest classes (subtropical, warm temperate, dry and littoral rainforest) less than 1 year after being burnt in the extensive wildfires of 2019–2020. Among taxa with ≥ 5 records of complete crown scorch (126), resprouting occurred in 63% of taxa overall and 61% of late-successional taxa. Fire-cued seedling recruitment occurred in 62% of taxa overall and 48% of late-successional taxa. Surprisingly, species richness of woody plants increased 22% postfire due to high rates of persistence and emergence of new taxa into standing plant populations as seedlings. Stem density increased ∼400% postfire due to high rates of resprouting and reproduction through suckering and seedling recruitment, although there was a significant redistribution from medium to smaller stem size classes. Larger stems (>10 cm diameter at breast height) were not significantly reduced in rainforest stands. High resprouting rates in small rainforest plants (1 cm diameter at breast height, 1 m tall) suggests rapid attainment of resprouting capacity. Our findings demonstrate that most subtropical, dry, warm temperate and littoral rainforest plant taxa are resilient to rare fires, and suggest that rainforest plants that invade rarely-burnt open forests may quickly become resistant to removal by infrequent fires, with potential for increased populations through fire-enhanced seedling germination.

Question Suppression of Aboriginal burning and wildfire from forests in which fires were historically frequent may trigger environmental changes that further suppress fire frequency and intensity. In high‐rainfall regions of eastern Australia, long‐unburnt open forests are frequently invaded by rain forest pioneer trees, which in turn modify open‐forest understorey structure and composition. We examine altered understorey fuel properties as potential fire suppression feedback mechanisms reinforcing switches from fire‐dependent eucalypt open forest to fire‐resistant closed forest. Location Northeastern New South Wales, Australia. Methods We characterized forest understorey leaf traits, plant crown architecture and vegetation structure to test for differences in flammability across a mosaic of contrasting times since fire (recently burnt — 4 years; long unburnt — 16 years) and midstorey composition (open, sclerophyll, rain forest) in subtropical shrubby dry sclerophyll eucalypt forest. Results Drivers of flammability were lower in long‐unburnt open forest with a rain forest pioneer midstorey at multiple scales (leaf, foliage clump, crown and stratum) than either long‐unburnt open forests with a sclerophyll midstorey or recently burnt open forest with an open midstorey. Grassy (graminoid) and sclerophyllous shrub fuels declined sharply beneath a rain forest pioneer midstorey, consistent with the fire suppression feedbacks regulating tropical savanna to closed forest transitions. Rain forest pioneers also reduced understorey flammability drivers through floristic compositional changes that increased leaf and foliage clump separation in shrub and midstorey fuel strata, and increased leaf moisture in the shrub stratum. Conclusion Our results suggest that rain forest pioneers are ecosystem engineers that modify open‐forest fuel properties, initiating a positive fire suppression feedback that facilitates their persistence and continued transition to a fire‐resistant closed forest. The fire suppression feedbacks we identify may help explain paleoecological and modern observations of rain forest expansion under high CO2 atmospheres, despite increased temperatures and seasonal drought severity.