... will have to begin growing there again. The first species to colonise bare ground like this are called pioneer plants. They are able to survive in very difficult conditions. Some plants are able to fix nitrogen, which helps them to grow even where there is almost no nitrate in the soil. The presence of the pioneer plants gradually changes the environmental conditions: they provide shelter for other seeds to germinate, or for insects to hide. Dead leaves that fall from them provide humus that becomes part of the soil, improving its water-holding capacities and nutrient content. So, over many years, the environmental conditions become suitable for a wider range of plants to live. The number of species increases, and some of the pioneer plants will disappear because they are not good at competing with the newcomers. This gradual, directional change in a community over time is called succession. In this ...

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