After Māori started to burn vegetation on the drier eastern side of the South Island (from around 1300 CE), grasslands expanded. For 500 years they retained much of their native biodiversity. This changed soon after Europeans settled in New Zealand from the 1840s. A wide range of animals and plants were introduced, and farming began on the grasslands.
Canterbury runholder Mary Anne Barker wrote in December 1867 of one of her great pleasures – burning tussock. ‘I am obliged to be careful not to have on any inflammable petticoats, even if it is quite a warm day, as they are very dangerous; the wind will shift suddenly perhaps as I am in the very act of setting a tussock a-blaze, and for half a second I find myself in the middle of the flames.’ 1
Burning and grazing
Europeans used fire to clear land for farming. Good wool prices in Britain encouraged high stock numbers on the tussocklands of the South Island high country.
Adverse effects were soon obvious. Concern was raised about the combined effects of burning, grazing by introduced mammals, and the spread of aggressive weeds. Comments by botanist-artist John Buchanan in the 1860s, agricultural scientist Alfred Cockayne in 1910 and ecologist-botanist Leonard Cockayne in 1919 showed a disquiet that has continued until today.
For decades, research and conservation efforts focused on native forests, rather than tussock grasslands. Detailed ecological studies of the high-country snow tussocks only really began in the late 1950s. This research confirmed their slow growth and long life. Mature snow tussocks have hundreds of stems, with a range of ages. Each stem takes 10–15 years to mature, after which it may flower and die, and is then usually replaced by one or more new stems. This pattern of rejuvenation means the tussock may potentially live forever, but it also means that scientists cannot tell the age of individual plants.
Tussocks were found to tolerate fire but not grazing mammals, particularly after fire when the new leaves are highly palatable. Concentrated grazing on small burnt patches can kill snow tussocks in just one season, and probably explains their absence in some areas where they would be expected to grow.
Some farmers were slow to apply these findings to farm management, and the destructive effects of farming have continued in many areas. Grazing and burning opens up the plant cover, exposing the soil to weeds and rabbits. Grazing animals eat the more palatable species first, leading to a concentration of unpalatable species. This may encourage more burning by farmers.
Exposed areas of soil are also prone to erosion.
Recent studies have highlighted the ability of snow tussock grasslands in good condition to produce high water yields from their upland catchments.
Studies showed water yields of up to 80% of measured annual rainfall, and 86% for the snow-free six months, on unburnt snow tussockland on the southern Lammerlaw Range. This unburnt grassland was compared with areas with shorter cover – recently burnt tussocks, pasture grassland, blue tussock short grassland and bare soil. These produced much less water, as did exotic pine forest.
Snow tussock areas also have very low water losses through evaporation or transpiration. In some places, fog deposits water directly onto tussock leaves, adding to the water yield. Tussock grassland retains water and releases it gradually, reducing the chance of flash floods downstream.