Xeroseres旱生演替系列 (1)Invasion by lichens and mosses 地衣、苔藓植物阶段 The first organisms to arrive are usually lichens or mosses,which are called pioneer species They secrete acids that can break down rock 。 Their dead,decaying organic materials,along with bits of sediment from the rock make up soil. .It occurs very slowly at first 11 11 (1) Invasion by lichens and mosses 地衣、苔藓植物阶段 地衣、苔藓植物阶段 The first organisms to arrive are usually lichens or mosses, which are called pioneer species. • They secrete acids that can break down rock • Their dead, decaying organic materials, along with bits of sediment from the rock make up soil. Xeroseres 旱生演替系列 •It occurs very slowly at first