(1) Pioneer Stage: Starts on bare rock surface, first signs of life on are lichens (pioneer species). Lichens (stable symbiotic association between a fungus and algae/or cyanobacteria) secrete acids into the rock to grow into it for anchorage. Causes crevices in the rock. (2) The Moss Stage: When lichens die, they fall into the crevices, along with rock particles, filling the crevices with soil. Mosses will begin to grow in these crevices and take advantage of the little soil which contains nutrients allowing it to grow. Mosses can survive as they create a thick cover on the rock. When rain falls the layer of moss traps some water underneath the blanket. When the mosses die, they add to the organic material. (3) Herb Stage: The herb stage happens when the mosses have created a thin layer of more stable soil. Little plants with shallow roots begin to grow. They can survive because there is enough nutrient and water in the soil. Many of the herbs are leguminous, and have root nodules, with the capacity to supply nitrates by nitrogen fixation. Plant roots further stabilise the soil and allow it to deepen. (4) Shrub Stage: Soil is deep enough for larger, deep rooted plants to grow. Larger, faster growing plants produce more leaf litter, and have deeper, more extensive roots. The soil becomes even thicker and withholds more moisture. Greater diversity of plants can now grow here, with a greater diversity of animals. The BIOTIC environment has a much stronger influence than it did in earlier seral stages. (5) The forest stage: Bigger, stronger deep-rooted trees colonize the area. These make up a climax community. There is usually a slight decline in biodiversity, as the trees are specialised to grow tall, and effectively out-compete many plants for light. Only human influence, by clearing small sections of woodland, can keep biodiversity growing.