Nasella tussock

Nasella tussock in North Canterbury

Nassella tussock
(Nassella trichotoma) invaded indigenous tussock-grasslands in the eastern parts of the Marlborough and Canterbury regions of New Zealand following their modification for
pastoral farming by the early colonists in ca. 1860.

Since the wide-scale renovation of
these infested grasslands (by improving soil fertility and sowing pasture grasses and legumes) in the mid 20th century, re-invading plants have been removed annually by manually digging them
out (a process known as grubbing) in regionally-coordinated management programmes. This effort, sustained until the present day, has resulted in the weed falling to densities that no longer reduce live-weight gains of sheep and other grazing animals.

The extent to which ongoing management of this weed is economically worthwhile remains a topic of intense debate within the scientific and farming communities. To help inform this debate, the potential range of nassella tussock in New Zealand was estimated using a climate model developed from global
distribution data. The map generated from the model reveals vast tracts of land, particularly in eastern Canterbury and Otago, which are currently climatically suitable yet unoccupied by the weed. This information enables regional authorities to recognise sites most at risk of invasion (those with high climatic suitability that are nearby current or historical infestations), and to factor this into their management programmes.