|Green and grey lichens growing on rock.|
Organisms that can colonize bare rock are called pioneer species. Lichens are usually the first pioneer species, and they look like color splotches on the surface of rocks - white, green, grey, yellow or even orange. Lichens are actually two organisms for the price of one: a fungus and an alga living together. The fungus and alga form a mutualism - an interaction where both organisms benefit. If you remember from the beginning of the year, algae grow in our pond - algae can only live where they don't dry out. In lichens, they live surrounded by cells of fungus so they can live outside of a pond. In return for this good protection, the algae provide the fungus with food from doing photosynthesis. Together, the organisms that form lichens make acids that slowly dissolve the rock on which they grow, which makes tiny crevices in the rocks.
|White, green and grey lichens plus dark green mosses growing on a rock.|
Just as mosses build habitat for small flowering plants, the flowering plants provide habitat and food for more creatures. Flowering plants have roots that hold the soil in place, and they also add to the soil as they die back each winter and decompose. Mosses and plants can host tiny insects, adding to the variety of life growing on a formerly bare rock. As the years go on, the soil builds and builds and larger plants, shrubs and eventually trees can grow on what was once bare ground. Eventually a mature forest might be found where once there was bare rock, and succession has been a success.
|A rather large moss behind the waterfall.|