Multivariate drivers of diversity in temperate Australian native grasslands

Abstract

Disturbance has been considered essential for maintaining biodiversity in temperate grassy ecosystems in Australia. This has been particularly well demonstrated for inter-tussock plant species in C4 Themeda-dominated grasslands in mesic environments. Disturbance is also thought crucial to maintain the structure of preferred habitat for some animals. Relationships between disturbance and diversity may be contingent on ecosystem productivity, but little is known about the generality of the disturbance-promoting-diversity paradigm across the range of temperate grasslands. To date, the disturbance-promoting-diversity paradigm has taken a univariate approach to the drivers of biodiversity; rainfall is seen as a key driver of productivity, which then drives diversity, mediated by disturbance. We argue that this framework is too simplistic as biodiversity drivers are multivariate. We suggest that the accumulation of phytomass (live and dead plant material) is an important determinant of diversity in grassy ecosystems and that phytomass accumulation is governed by multiple drivers (of which disturbance is just one). For fauna, it is structure – not biomass – that determines habitat suitability, and this can be moderated by both abiotic and biotic drivers. The assumption that there is a consistent effect of disturbance on diversity through the range of temperate grassland settings in southern Australia ignores the likelihood that biodiversity also responds to other factors such as spatial heterogeneity in the environment, resource availability and climatic variation. We developed a conceptual model of the multivariate drivers of grassland diversity that explores mechanisms underpinning patterns of species richness. Despite four decades of research, it is clear that our understanding of the multivariate drivers of diversity across the range of temperate grasslands in Australia is still incomplete. Further research into the conditions under which disturbance is required to maintain biodiversity in grasslands is integral to conservation planning in these endangered systems.

Social and Ecological Dimensions of Urban Conservation Grasslands and Their Management through Prescribed Burning and Woody Vegetation Removal

“…In urbanised grasslands, natural processes have also been replaced with alternative management regimes such as livestock grazing or slashing, further changing grassland community structure and composition [12]. This decline in fire frequency has, in part, resulted in significant changes in grassland community structure and composition [13].…”

Land‐use legacies limit the effectiveness of switches in disturbance type to restore endangered grasslands

“…Much of the focus in grassland conservation management and restoration has therefore centered on identifying appropriate disturbance regimes to maintain and recover diversity (e.g. Olff & Ritchie 1998; Morgan & Lunt 1999; Price et al 2019). However, different disturbance types (e.g.…”

“…However, different disturbance types (e.g. fire vs. grazing) can have fundamentally different impacts on native biodiversity, and hence they are not necessarily interchangeable (Price et al 2019). Exposure to an endogenous (historic) disturbance regime likely fosters ecosystem resilience, whereas exogenous disturbances can have substantial (negative) impacts on plant communities (Hobbs & Huenneke 1992; Yates et al 2000).…”

“…Bioturbation by digging mammals (such as bettongs and bandicoots), now largely extinct in much of their previous range, also provided regular, small disturbances (Fleming et al 2014; Valentine et al 2017). While temperate grassland distributions in Australia are mostly driven by “bottom up” processes (Morgan et al 2017), it is likely that regular disturbance maintained alpha diversity, particularly in high productivity grasslands (Price et al 2019).…”

“…If there is a legacy of the past management, grazing may have eliminated grazing‐sensitive native species and there may be very few native species that can then take advantage of a new regime; they have been lost from the species pool. Further, it is unclear if grassland species rely on fire to maximize germination through effects of heat and smoke, or if fire promotes recruitment by reducing light limitation, and hence whether fire is substitutable (Hodges et al 2019; Price et al 2019). It remains unclear if changes in disturbance type can enhance conservation outcomes, by promoting native species that are currently suppressed or disadvantaged, while simultaneously reducing exotic plant cover and richness.…”