Subtropical native grasslands may not require fire, mowing or grazing to maintain native-plant diversity

Abstract

The rarity of native grasslands in agricultural districts heightens the requirement for optimal management to maintain diversity. Previous studies have suggested that disturbance is required to maintain species diversity in temperate Australian grasslands, but grasslands in semiarid environments do not have the same disturbance requirement. The current study examines the short-term responses to disturbance of subtropical grassland of the Darling Downs, south-eastern Queensland. We also compare temperate and subtropical grasslands in terms of biomass and rainfall. A field experiment was established with treatments, including burning in 2013, burning in 2014, burning in both years, mowing in both years, mowing and raking in both years, and an undisturbed control. Treatments were replicated at each of seven sampling stations in similar environments. The initial sampling after 2013 followed a wet summer and the final sampling was in 2015 after a dry summer. Non-metric multi-dimensional scaling showed that environmental differences, including silt content, soil pH, waterlogging and rainfall history, had more effect on the variation in species composition than did the treatments. The treatments engendered no significant response in species diversity. Of 51 widespread species, only four had a significant change in abundance in response to treatment. Herbaceous biomass was higher in temperate than subtropical grassland after a dry period. The grassland sward may be more open in the subtropics than in temperate grassland because of higher decomposition rates. A comparison of rainfall distribution between subtropical grassland and temperate grassland indicated that droughts are much more frequent in the former environments. These occasional droughts may provide a stress that reduces perennial grass cover, supplanting the requirement for grazing or fire to maintain plant diversity in grasslands. The management of grassland remnants in the subtropics, therefore, seems straightforward because there is little response in species richness or composition to disturbance. However, soil disturbance should be avoided to ensure that exotic species do not proliferate.

Annual mowing maintains plant diversity in threatened temperate grasslands

“…Declines in mowing and haymaking over the past century have reduced biodiversity in regions where mowing has been integral to the historical management of semi‐natural grasslands (e.g., several hundred years in Asia and over a thousand years in Europe; Baoyin et al., ; Feurdean et al., ; Koyama, Koyanagi, Akasaka, Takada, & Okabe, ; Pärtel, Helm, Reitalu, Liira, & Zobel, ). Few studies have quantified the effect of mowing on biodiversity in Australian grasslands (Fensham et al., ; Lewis et al., ; Morgan, ; Verrier & Kirkpatrick, ). The distribution of temperate grasslands in Australia is controlled predominantly by soil and climate (Lunt, Prober, & Morgan, ) but, prior to European colonization, their composition was maintained by native herbivore grazing and burning (ignited by lightning or Aboriginal people; Lunt & Morgan, ).…”

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

“…Hence, the disturbance requirement for maintaining alpha diversity might not be ubiquitous across the range of grasslands. Indeed, in subtropical grasslands, no change in native richness was found when mowing and fire were introduced in previously undisturbed sites, likely due to lower rates of biomass accumulation compared to temperate grasslands (Fensham et al 2017). Introducing disturbance into undisturbed sites also increased exotic richness (Kirkpatrick 1986; Smith et al 2018), but most studies did not explore this (Table 1).…”

Multivariate drivers of diversity in temperate Australian native grasslands

“…Importantly, phytomass accumulation does not follow a linear function of time-sincedisturbance, i.e. it is decoupled from disturbance (Fensham et al 2017). Lewis et al (2008Lewis et al ( , 2010 found in arid (Astrebla) grasslands, with a highly variable climate, that recent rainfall events were far more important for sward density than disturbance.…”

“…In subtropical and semiarid ecosystems, low biomass accumulation might reflect high decomposition rates (Fensham et al 2017) or erratic production (e.g. tied to above-average rainfall; Austin and Williams 1989).…”