They have special adaptations that enble them to survive on dry and nutrient poor soil.Pioneer species are hardly plants which usually have dense root systems to bind the sand particles and hold water and humus.they have  a short life cycle.When they die,their remains add to the hummus content of the soil.Hence,the pioneer species modify the environment,eventually creating conditions which are less favourable to themselves.Instead they establesh conditions that are more condusive to other species which are called successor  spesies.