Perennial pasture grass invasion changes fire behaviour and recruitment potential of a native forb in a temperate Australian grassland

Abstract

Invasive grasses can modify fire regimes of native ecosystems leading to changed ecosystem structure, composition, and functioning. Temperate grasslands in Australia are currently being invaded by a suite of exotic perennial pasture grasses, but their effects on ecosystems remain largely unknown. We aimed to determine the effect of invasion by the exotic perennial grass Phalaris aquatica on fire behaviour, as well as the regeneration potential of an endangered forb in temperate native grasslands in south-eastern Australia. Frequently burnt native grasslands invaded by exotic grasses were found to have two times more fuel than grasslands dominated by native grasses; in less-frequently burned native grasslands, exotic grasses contributed to fuel loads that were five times higher than native grasslands. Exotic-dominated grasslands burned differently than native grasslands; fire intensities were three times higher in exotic-dominated grasslands and had a wide variability in fire residence times. Soil heating was positively related to fire residence time but had no clear relationship with fire intensity. Seed germinability of Leucochrysum albicans var. tricolor (Hoary Sunray, Asteraceae) was reduced by exotic grass-fueled fire and increasing fire residence times. The observed changes in fire behaviour represent an invasion-driven shift in the ecosystem’s fire regime. By increasing fuel mass, fire residence time increased, and this influenced seed survival and subsequent germinability. Increased fire intensity following invasion highlights that invasive grasses can increase the fire-risk of grasslands. Maintaining native grasslands free of invasive pasture grasses therefore has environmental and fire-risk benefits.

Restored roadside grasslands provide an exciting template for road network conservation

“…Biomass reduction is an important part of general roadside maintenance, and studies show that high fuel loads on Phalaris dominated road verges dramatically increase fire risk (Walker & Morgan 2022). In this light, an important feature of these species rich restorations was the low level of biomass they produced – equivalent to ~1.3 t per hectare, in stark contrast to that from the nearby section of Phalaris dominated roadside showing biomass at equivalent to 13 t per hectare.…”

“…In arid and semi-arid regions, native vegetation is common on verges. Conversely, in arable landscapes while some roadsides are reservoirs for rare native vegetation (Ries et al 2001;Spooner 2007Spooner , 2015Barton & Garcia 2015), most are dominated by exotic species (Walker & Morgan 2022). This presents complex and costly management issues for road agencies (Navie et al 2010;Cooke 2012).…”

Global Patterns and Dynamics of Burned Area and Burn Severity

“…Our results revealed that most biomes burned more in Africa and Australia than on the other continents. In Africa, extensive burning is facilitated by the low population density and decreases in grazing by bulk-feeding herbivores [12], whereas the proneness of Australian biomes to fire is fostered by the extreme climate seasonality, the high number of dry lightning events, aboriginal fire management practices, the physiognomy of eucalypts vegetation [31,42,44], and even by the colonization of exotic grasses [45].…”