A project undertaken at the Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University, and supervised by Dr Tim Doherty
Biodiversity is under threat largely through the actions of people. The conversion and intensification of land used for agriculture is a key component of this crisis. Given limited land and increasing pressure for greater agricultural production, it is critical to maximise the quality of remnant vegetation embedded within agricultural land. A potentially efficient way to do this is to focus on key species that are fundamental to the structure, function and resilience of ecosystems. Foundation species fulfil this role by creating habitat and strongly influencing other organisms.
We studied spinifex grass (Triodia scariosa) in remnant mallee woodlands to assess what influences the distribution, abundance and persistence of this foundation species in agricultural landscapes. We also explored methods for improving recruitment and abundance. Our study region was in south-central New South Wales.
A key driver of spinifex occurrence in remnant vegetation was proximity to reserves, and we found evidence this was due to past land clearing patterns, with spinifex possibly undergoing the payment of an extinction debt. The distribution of spinifex was negatively associated with compact soils and high nutrients (nitrogen and phosphorus), though the relationship with nutrients exhibited complex interactions with other grasses, potentially as competitors to spinifex. Further, we found differences in a range of variables unfavourable to spinifex persistence within linear remnants compared to nature reserves. Linear remnants had more non-spinifex grass, higher soil nutrients, more compact soils and less bare ground. Our attempts to promote recruitment of spinifex in situ produced mixed results. While net spinifex abundance decreased overall, the best recruitment occurred where fire and grass removal treatments were combined. Spinifex abundance also rebounded best within reserves and where large herbivores were excluded.
Overall, our findings paint a bleak picture for this foundation species, with evidence of ongoing population declines, continuing inappropriate biotic and abiotic conditions, particularly in linear remnants, and the limited effectiveness of two management practices to increase spinifex abundance. We recommend future efforts focus on how to address these stressors to improve long-term spinifex persistence in agricultural landscapes. More broadly, despite their importance to ecosystem function, foundation species are poorly recognised and underrepresented in comparison to other ecological concepts such as keystone species. We recommend similar research into the processes that threaten foundation species worldwide as a key tool to achieve conservation goals in the Anthropocene.
Figure 1. Habitat condition photos: top: healthy spinifex; middle: over-abundant native Austrostipa grass engulfing spinifex clumps; bottom: exotic weeds and dead spinifex clumps.
Our study will address these important questions using a model landscape in central New South Wales. The study area is dominated by cropping land, but also contains remnant mallee woodlands with a spinifex understorey, which is a keystone habitat for many reptile species. Weeds and native grasses dominate the understorey of much remnant mallee in the region, particularly along roadsides, and this may be to the detriment of spinifex and hence reptile populations. Our overall objective is to understand the condition and trajectory of a keystone habitat feature (spinifex, Triodia scariosa) across a large (5,000 km2) study area dominated by cropping land, but containing remnant mallee vegetation.