Primary and Secondary Succession

Primary succession is the kind of ecological succession that begins on a substrate which has never previously supported any biological community at all -- a completely bare site with no pre-existing soil, no buried seeds or spores, and no surviving organisms of any kind to help the process along. Typical starting points for primary succession include freshly exposed bare rock surfaces, newly cooled and solidified volcanic lava flows, freshly deposited sand dunes, and a newly formed pond or lake basin that has never previously held water or supported aquatic life. Because there is no soil present at all when primary succession begins, and because fertile soil must first be built up gradually from the physical weathering of the parent rock together with the slow accumulation of organic matter contributed by the earliest colonising organisms, primary succession is generally an extremely slow process, often taking many hundreds or even thousands of years to progress from the very first pioneer colonisers through to a mature climax community.

Secondary succession, by contrast, is the kind of ecological succession that begins on a site where a biological community previously existed and has since been partly or wholly destroyed or removed, but where the soil (and frequently a bank of dormant seeds, roots, or other propagules left over from the earlier community) has NOT been destroyed along with it, and remains available to support renewed plant growth. Common starting points for secondary succession include agricultural land that has been abandoned and left uncultivated, a forest that has been cleared by logging or destroyed by a severe fire, and a shallow pond or wetland that has been partially drained. Because fertile soil and often a ready source of propagules are both already present at the very start of secondary succession -- the single slowest and most time-consuming requirement of primary succession having already been met -- secondary succession proceeds considerably faster than primary succession, and can, in favourable conditions, progress from a disturbed, largely bare site back to a reasonably mature community within a matter of decades rather than centuries. …