Answer:
PRIMARY SUCCESSION -SEQUENCE OF SPECIES ON NEWLY EXPOSED LANDFORMS THAT HAVE NOT PREVIOUS BEEN INFLUENCED BY A COMMUNITY e.g. AREAS EXPOSED BY GLACIAL RETREAT.
SECONDARY SUCCESSION- SUCCESSION IN WHICH VEGETATION OF AN AREA HAS BEEN PARTIALLY OR COMPLETELY REMOVED BUT WHERE WELL DEVELOPED SOIL ,SEED SPORES REMAIN SO THAT THE RESULTING SEQUENCE OF SPECIES IS DRIVEN PRINCIPALLY BY INTERACTIONS SUCH AS COMPETITION AND HERBIVORE'S e.g. FAMILIAR OLD FIELDS