Enhancement of palatable perennial grasses by disturbance and seed addition in degraded native grasslands of the dry pampas in Central Argentina

Abstract

Land use has changed the original composition of the natural grasslands in the dry pampas of central Argentina, to the detriment of palatable perennial grasses (PPG). Long-term elimination of anthropogenic disturbances has not been enough to effectively recover the PPG, which suggests that availability of seeds and/or habitats may be limiting their recruitment. Therefore, our objectives in a degraded grassland site were to assess: (1) the germinable soil seed bank and (2) changes in botanical composition after addition of PPG seed following canopy disturbance. In autumn 2015, we randomly selected 10-paired plots, measured the aboveground biomass and took soil samples to assess the germinable soil seed bank. Afterwards, we disturbed the resident vegetation in each paired plot and either added PPG seeds or left the plot without any seed addition as a control. We quantified the seedling density of seeded and spontaneous species in the spring of 2015 and 2016, and the aboveground biomass at the end of 2017. Annual grasses and forbs (AGFS) dominated the soil seed bank, while PPG and unpalatable perennial grasses (UPG) occurred at low seed density and richness. Addition of PPG seeds resulted in the successful establishment of one key seeded PPG (Poa ligularis). In the spring 2017, the aerial biomass of PPG was highest in the seeded plots, where P. ligularis accounted for 94%. Our results showed that PPG were poorly represented in the soil seed bank of the degraded grassland and that disturbance of the resident vegetation combined with PPG seed addition enabled successful recruitment of a key PPG. So, enhancement of the pastoral value of degraded dry pampas grasslands would be possible through disturbance of the resident vegetation and addition of PPG seed.