Over the past four decades a number of Hieracium species have spread significantly throughout much of the high country, and appear likely to continue to increase at the expense of both native biota and introduced forage species (Scott, 1984). They are most common on pastoral lands, and have a detrimental impact on farming enterprises through an associated decrease in productive capacity (Martin et al., 1994).
Conservation values are threatened in a similar manner. A recent survey classified their abundance through 1,500,000 ha of this area (around 10% of the South Island) as sufficient "to characterise the appearance of the vegetative cover and to be among the main species present" (Hunter, 1991). Over a third of this area Hieracium species were recorded as being dominant, in some cases even being pure stands.Unfortunately, there were no clear explanations which accounted for the dramatic increase in Hieracium species over recent years. In relation to H. pilosella, the most widespread species, the two major explanations offered by scientific opinion appear to be in conflict.
On the one hand explanations focus on its aggressiveness as an invader, while on the other it is seen as directly related to the degree of degradation caused by pastoral impacts such as grazing or fire (Rose et al 1992 & 1996; Treskonova, 199?). The farming community was also divided and disturbed about the causes of invasion, the former explanation offering little hope and the latter seeming to point the blame at current pastoral practices. These conflicting viewpoints also made it difficult to identify possible solutions to the problem.