Stages of Invasion

The pattern of Hieracium invasion conforms to the three stages of invasion shown in Figure 1.

1. During stage 1 the Hieracium enters the new habitat and is present at low levels.

2. The second stage is characterised by a rapid increase in invader abundance, and is triggered in the tussock grasslands by an opening up of the plant community or an increased instability in the system (e.g. development of short tussock communities).
   
3. The third stage is reached when the abundance of the invader no longer increases, but exerts dominance on the plant community.

Although figure 1 indicates a complete dominance of Hieracium in the third stage, site-specific environmental factors (soil type, rainfall zone, etc.) will affect the dynamics of the vegetation, and therefore the relative abundance at which stability occurs.