Establishing an understanding of Hieracium invasion first requires establishing an understanding of the broad dynamics of tussock grassland vegetation. To communicate this widely, we developed a simplified series of easily comprehended "pictures". Combining these with the stage of invasion integrates our understanding of vegetation dynamics (Figure 2).
Figure 2:
Pictorial model of vegetation change in undeveloped tussock grasslands indicating the stage of H. Pilosella invasion in different vegetation states (Gibson 1996)From left to right, the top line represents the composition of tussock grasslands as it would have changed under the impact of historical pastoral practices. This can be summarised as steps from tall tussock grasslands (vegetation state A) through mixed (B) and short tussock grasslands to weed communities (C). Note the simplified model is only for unimproved tussock grassland and does not attempt to include the soil fertility effects.
Hieracium invasion can be examined within this framework. While low incidences of H. pilosella (the first stage of invasion) can occur in all of these states, the second and third stages are more likely to develop in the more modified communities characterised by a high proportion of short tussocks and/or exotic grasses.
