Fate, Luck or Destiny? Regeneration of Tropical Rainforest in Singapore
- Author(s): Chua, Siew Chin
- Advisor(s): Potts, Matthew D
- et al.
To date, our understanding of the long-term recovery of secondary forests in the tropics is based on surprisingly little empirical data. In my dissertation, I examined some of the stochastic (dispersal events) as well as deterministic factors (environmental filtering) that are important to community dynamics and thus the on-going regeneration of older tropical secondary forests in Singapore. These secondary forests underwent intensive agricultural activities from the late 1800 to early 1900, and have today, recovered differently after at least 56 years of regeneration. Chapter 1 provided a synopsis of how my research is situated within the larger theoretical framework of tropical forest succession, along with rationale for the focus on older secondary forests in Southeast Asia. In Chapter 2, I compared the floristic composition and structure of a two hectare secondary forest to an adjacent two hectare primary forest in Bukit Timah Nature Reserve, and also examined the extent to which dispersal limitations was limiting forest recovery. In Chapter 3, using nine secondary and three primary forest plots in the Central Catchment Nature Reserve, I determined the effect that changing environmental variables and distance to the nearest mature forest had on seedlings' abundance, diversity as well as the distribution of four broad functional groups. In Chapter 4, using the same twelve research plots, I investigated the linkages between the regenerating environment and functional traits of seedlings and adult trees, as well as analyzed their relative influence on forest recovery. Results from Chapter 2 and 3 demonstrate that forest recovery in Singapore, in terms of species composition, species richness and stand structure, is very slow compared to other old secondary forests elsewhere in the tropics. I found that local Ultisol soils have inherently low nutrients, even when compared to other Dipterocarp forests, and decades of intensive agricultural activities has further resulted in soils whose high aluminum saturation, soil C:N ratio and low available phosphorus inhibit forest regeneration. Overall, forest succession in Singapore is characterized by plant species whose nutrient conserving traits allowed them to specialize on degraded soil, along with the changing light environment, as the forest regrow. The longevity of these plants on degraded land, their ability to slow nutrient returns as well as the strong dispersal limitation in these fragmented forest reserves are important factors that explain the overall slow recovery.