The beginning of the long process of succession commences with bare soil, as a result of landslip, fire, storm damage or tree fall.
As the forest regenerates the bare soil is quickly covered with young plants, then the process of succession begins as one stage in the vegetation gives way to another. Together, these stages form a succession.
PIONEERS – THE FIRST COLONISERS
On bare soil and in hot bright sunshine, the seeds which will germinate belong to species of the first stage of succession, the pioneers. In the shade of the surrounding forest, these species do not survive, and their nearest location may be kilometres away. Yet the seeds are there. Either they were already present in the soil, or they have travelled far. A full-grown pioneer plant produces large quantities of small seeds readily dispersed mainly by birds in our local area.
Their small hard-shelled, long-lived seeds wait for the opportunity of a break in the canopy and exposed soil to grow and in turn set seed again. Wherever there is open soil, pioneers grasp their opportunity. They quickly produce a mass of foliage on weak stems, cast shade and leave litter on the soil (thus enriching it), and may just as quickly die. Other species, ones that do not need light quite so much when they are young, take their place.
Typical species are: Omolanthus nutans, Macaranga tanarius, Pipturus argenteus.
SECONDARY SPECIES – THE NEXT STAGE
We call this vegetation “secondary” because it grows where the original, primary forest has disappeared. At first, secondary forest does not have structure. It is thick, but its vegetation is not strong or long-lived. Other types of vegetation can easily replace it i.e. environmental weeds. Secondary species often require the protection of the pioneers to germinate and grow and create the increased shade and humidity suitable for the germination of climax species
Typical species are: Polyscias elegans, Melicope micrococca, Guioa semiglauca
MATURE OR CLIMAX FOREST – THE CYCLE COMPLETED
Seed from the mature phase species is short lived and does not persist in the soil seed-bank. Therefore, seed of these species must come from a seed source forest that exists close by the regenerating gap otherwise the regeneration will at best stagnate at the pioneer or secondary stage, but most likely become dominated by exotic species i.e. Lantana and/or Privet. In the ideal situation, the forest will progress through the various stages of regeneration until a mature stage rainforest ecosystem is re-established. This process may take several hundred years to complete. The regenerative process will however only continue to progress from the initial pioneer and secondary species mix if there is a ready seed source of mature phase species close by. Mature forest is made up of ancient trees that will last as individuals in excess of 800 years.
Typical species are: Argyrodendron trifoliatum, Sloanea woolsii, Ficus macrophylla.
References: Growing Rainforest – Rainforest Restoration and Regeneration. R. Kooyman.
Living Earth, livearth@gn.apc.org
Natural regeneration of the rainforests of Brisbane – Kenneth McClymont
by Spencer Shaw