1 ) 

Following a drought, there is almost always significant die-back for most plant species. In these conditions, xerophytic pioneers colonise the area with limited competition.

2 ) 

Pyrophytes are adapted to cope with conditions associated with wildfire. Root systems can cope with loss of vegetation above ground. This vegetation quickly returns after fire.

3 ) 

Plant species which require very few nutrients to survive and will colonise bare rock. These species are the first to colonise following a volcanic eruption and succession follows.

4 ) 

Once human activity has altered the climatic climax vegetation, the species are quick to adapt to the niche which is created. Pioneers readily exploit the available environment.