Research on two Otago sites by scientists from Landcare Research and Scion, showed however, that late-season fires in dry conditions, resulted in greater loss of biomass, carbon and nutrients and the short to medium term loss of tussock dominance.
High country farmers intermittently burn tussock in late winter or early spring, to open up access for stock, promote the growth of vegetation for stock feed and to remove woody weeds.
But environmentalists claim the practice destroys native flora and fauna, increases the opportunity for weed infestation and causes soil erosion.
Researchers lit controlled fires on a lowland tussock grassland site at Deep Stream, inland from Dunedin, to replicate spring conditions in October 2001 and summer conditions in March 2001.
At the higher altitude Mt Benger site near Roxburgh, a spring fire was lit in November 2000 but the summer burn was delayed until March 2006 by fire restrictions and weather.
Among the questions the researchers sought to answer, was whether fire caused long-term damage to tussock grassland communities and if accidental summer-autumn burns caused more damage than late-winter early-spring fires.
Fire temperatures reached more than 1000degC and they lasted between four and eight minutes, having little heating affect on the soil, according to the researcher's findings.
"Biomass, carbon and nutrient losses were lowest when the grasslands were burned under damp conditions and increased as soil and plant moisture levels declined."
Six months after the spring fire at Mt Benger, plots showed vigorous tussock and other plant regrowth and five years later "there was an intact tall tussock grassland."
The summer fire at the plot resulted in high tiller mortality and tussocks were unlikely to fully recover soon.
At Deep Stream, both spring and summer fires resulted in a large percentage of tussock death and removal of ground cover.
Within 12 months browntop, which was already present, dominated the burned areas, but five years later the surviving tussocks were competing much more vigourously.
The researchers concluded that fires in late winter or early spring when conditions were damp, posed little threat to the long-term survival of tussock.
But they also recommend minimising grazing pressure for one to two years after the fire.
Fire late in the season or when soil conditions were dry, had the potential to "cause significant damage to tall tussock grassland communities."
The scientists said the next stage for the research would be to look at the consequences of continued grazing, with or without fire, on the long term sustainability of tall tussock grasslands.