(a) Name the pioneer species organisms on a bare rock.
(b) How do pioneer species help in establishing the next type of vegetation

Explanation

(a) Pioneer community in lithosere ( succession on a bare rock ) is formed of crustose lichens like Graphis , Rhizocarpon and Rinodina.
(b) These produce organic acids which cause weathering of rocks to liberate the minerals and hold the fine particles of the rock and sand to initiate soil formation which invites the foliose type of lichens.