Restoration of a declining foundation plant species: Testing the roles of competitor suppression, fire reintroduction and herbivore exclusion

Maintaining ecosystem processes within patches of remnant vegetation is critical to minimising biodiversity loss in agricultural landscapes. Foundation species—habitat-forming organisms that interact with many other species—are therefore a priority for conservation and restoration in farming areas. Triodia spp. grasses are foundation species of arid and semi-arid Australia that largely depend on fire for recruitment, but fire is suppressed or excluded in many agricultural areas. We tested the effectiveness of controlled burns and competitor removal (exotic and native grasses), both in isolation and combined, on recruitment rates of Triodia scariosa in remnant vegetation using a before-after, control-impact study across 126 plots. A subset of plots were located in an herbivore exclusion area inside a reserve. There was no recruitment of T. scariosa 1 year after burning, regardless of treatment or control, and the burns killed all existing plants. However, T. scariosa germinated by 2 years post-burn, with the greatest recruitment in sites where both burning and grass removal were applied. Two years after burning, T. scariosa abundance (adults and recruits) remained low outside reserves, but returned to original levels in reserves and in areas where large herbivores were excluded. Synthesis and applications. Despite failing to increase overall abundance, we show that restoration of a foundation plant species in degraded, agricultural landscapes can be achieved through a combination of fire reintroduction and competitor suppression. Germination trials from soil samples suggest a depleted seed bank limited recruitment rates, and therefore emphasise the importance of carefully timing restoration actions to overcome recruitment bottlenecks

Acclimation to water stress improves tolerance to heat and freezing in a common alpine grass

Alpine plants in Australia are increasingly exposed to more frequent drought and heatwaves, with significant consequences for physiological stress responses. Acclimation is a critical feature that allows plants to improve tolerance to environmental extremes by directly altering their physiology or morphology. Yet it is unclear how plant performance, tolerance, and recovery are affected when heat and water stress co-occur, and whether prior exposure affects responses to subsequent climate extremes. We grew a common alpine grass species under high or low watering treatments for three weeks before exposure to either none, one, or two heat stress events. We determined photosynthetic heat and freezing tolerance (LT50, mean temperature causing 50% irreversible damage to photosystem II) and growth. Physiological adjustments to low watering, including more negative water potentials and reduced growth, were also characterised by improved tolerance to high and low-temperature extremes. Shifts to higher heat tolerance were also evident with increasing exposure to heat stress events, though freezing tolerance was not affected. Acclimation effects were mostly short-term, however; prior exposure to heat and/or water stress had little to no effect on growth and thermal tolerance following the six-week recovery period. We conclude that rapid acclimation to water and heat stress that co-occur during summer enhances the capacity of alpine plants to tolerate increasingly frequent temperature extremes