(a) Pioneer community is the first biotic community on a bare area. Plants that are first to invade the bare area are called pioneer species. Lichens are the pioneers in lithosere and phytoplanktons are the pioneers in hydrosere. (b) The lichens are the organisms which produce the acids like the oxalic acids. These acids cause crevices in the rock where the organic matter gets collected and the rocks break and the soil particles are formed. This results in the succession process to start.