Regeneration of native plant species in restored forests on degraded lands in Singapore

The pattern of natural regeneration was studied in three 1-year old and three 4-year old native species reforestation sites on degraded lands in Singapore. On each site, twenty 25 m2 plots were set up and plant regeneration was surveyed. For each woody species regeneration, life form, mature height, dispersal mode and successional status were accessed. We also investigated how the successional status and condition of the surrounding forest influence the course of early succession on these sites. A predictable suite of typical early pioneer species of degraded lands dominated all 1-year old reforestation sites. Natural regeneration on a site surrounded by primary forest was not any more diverse nor was the rate of succession accelerated compared to other sites surrounded by mature and degraded secondary forest. Principle components analysis (PCA) showed that the type of landscape matrix and seed dispersal become increasingly important in determining succession as the planted saplings grow and canopy cover is restored. The regenerating woody community on the 4-year old reforestation sites was fairly species rich with 73 species observed. However, the community was dominated by a subset of small-seeded secondary forest species of medium stature, while some of the prominent primary forest families such as Dipterocarpaceae were completely missing from the regeneration. The results showed that reforestation has been successful in promoting native forest development, but it also illustrated the need for management intervention in restoring the floristic diversity and structural complexity of a primary forest especially where the natural successional processes are hampered by soil degradation, habitat fragmentation and the loss of native fauna.