Response of grass species to different fire frequencies in semi-arid rangelands of central Argentina

Abstract

The study was undertaken to quantify the effect of different controlled fire frequencies on foliar cover, density, individual basal area, and mortality of the most common perennial grass species in the semi-arid rangelands of the southern Caldenal in central Argentina over a 20-year period. Cover of bare soil was also assessed. The study comprised three fire treatments: (i) high fire frequency (controlled burns every 3–5 years; HFF); (ii) low fire frequency (controlled burns every 8 years; LFF); and (iii) unburned control (C). Fire treatments, regardless of frequency, induced an increase in foliar cover and density in desirable grasses, no changes in intermediate grasses, and a decrease in undesirable grasses. Individual basal area tended to be higher for desirable grasses and lower for intermediate and undesirable grasses when subject to fire. Most of the species under study exhibited higher mortality rates in the HFF treatment than in the LFF and C treatments. The results of the study suggest that recurrent controlled burns of moderate intensity may favour the herbage production of desirable perennial grasses. This, in turn, assuming appropriate grazing management, may have a beneficial impact on livestock production. Nevertheless, given the effects of fire on the cover of bare soil and mortality of grasses, further research is needed in order to determine the appropriate fire frequency in terms of rangeland sustainability.

Fire ecology of C3and C4grasses depends on evolutionary history and frequency of burning but not photosynthetic type

“…Corresponding Editor: J. Cavender-Bares. 6 E-mail: b.ripley@ru.ac.za intensity, has a significant effect on the regrowth and survival of grasses (Trollope and Tainton 1986, Trollope et al 2002, Uys et al 2004, Pela´ez et al 2013 and is likely to be the stronger selective force in determining fire-associated traits. As grasses are the fuels in these systems, fire tolerance and flammability traits are likely to be somewhat related, with fast regrowth rapidly producing fuel and allowing for frequent fires.…”

Burn hot or tolerate trees: flammability decreases with shade tolerance in grasses

“…Some species (e.g. B. gracilis , N. tenuissima , N. viridula , C. latifolium and A. purpurea ) under 0% shade did not reach the same size as mature plants we observed in the field (Sorensen et al 2012, Peláez et al 2013, Gao and Schwilk 2018). Variation in aboveground biomass can contribute to flammability variation that may not be observed in mature perennial grasses.…”

Resprouting grasses are associated with less frequent fire than seeders

“…Likewise, grass seeds can survive grassland fire temperatures (Gashaw & Michelsen, 2002), or disperse into recently burnt areas using anemochory, epizoochory or autochory (Ernst et al ., 1992). Indeed, evidence relating to other grass traits suggests that fire intensity is not an especially strong selection pressure on grasses (Trollope et al ., 2002; Uys et al ., 2004; Peláez et al ., 2013). The association between resprouting and high‐intensity fire may result from the ability of resprouters to accumulate more biomass than seeders between fires (e.g.…”

“…dominated) grasslands of Australia experience very hot fires; Archibald et al, 2013). Therefore, intensity may not be a relevant fire characteristic in determining the distributions of grass seeders and resprouters, as has been found for other grass traits (Trollope et al, 2002;Uys et al, 2004;Peláez et al, 2013) because it does not represent a strong selection pressure. High fire intensities may cause mortality, particularly in resprouters.…”