Resilience of a forest fragment exposed to long-term isolation in Singapore

Abstract

Background: Fragmentation can fundamentally alter the structure of tropical forests. However, the impacts of fragmentation may vary significantly among regions and lead to different outcomes.

Aims: We examined the structure, composition and dynamics of a forest fragment in Singapore to investigate reasons for the apparent resilience of this forest to long-term isolation.

Methods: We conducted 5 censuses of 12,688 trees ≥1-cm dbh in a 2-ha plot on the edge of the fragment between 1993 and 2012.

Results: Stem density and basal area were not significantly different between 1993 and 2012 and were typical of other south-east Asian forests. However, there were short-term decreases in both variables after droughts in 1997 and 2009, both followed by recovery. Total mortality rate over the 19 years was 3.3% year⁻¹, considerably higher than other tropical forests in Asia, but it was balanced by high recruitment. The 10 most abundant species were primary forest species, pioneer species comprised <5% of all stems, and none of the 338 species in the plot was exotic. However, species abundances changed more than expected by chance for 86 species, and the rank order of the commonest species changed significantly. Species abundance changes were not related to known species traits.

Conclusions: Despite the long period of isolation, we found a surprising level of resilience of the Bukit Timah forest. While the forest may be more sensitive to the effects of climatic fluctuations at decadal time scales, there were very few signs of forest degradation in this diverse fragment of tropical forest.

Keywords:

• Bukit Timah Nature Reserve
• forest dynamics
• forest fragmentation
• growth rates
• south-east Asia
• species composition
• tropical forest
• turnover

Acknowledgements

The Bukit Timah plot is a collaborative project between the Center for Tropical Forest Science-Forest Global Earth Observatory (CTFS-ForestGEO) of the Smithsonian Tropical Research Institute, and the National Institute of Education (NIE), Singapore. The project has been supported by the National Parks Board and the Arnold Arboretum of Harvard University. We thank S. K. Lee for his support towards the permanent plot and S. Chan, S. Teo and Y. K. Chua for providing research access to the permanent plot. We also thank J. V. LaFrankie, A. Ercelawn, I-F. Sun and L. K. Wang for their early work in the plot, M. S. Khoo, S. C. Chua, M. F. Mohamed and the numerous field workers who helped in the surveys, R. Chisholm for help with data analysis and A. Itoh, T. Hosaka, S. Numata and two reviewers for helpful comments on earlier drafts of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The project has been supported by the National Parks Board - Singapore and the Arnold Arboretum of Harvard University.

Notes on contributors

Kang Min Ngo

Kang Min Ngo was a research assistant at the Center of Tropical Forest Science in Singapore and is now a Ph.D. student.

Stuart Davies

Stuart Davies, director of CTFS-ForestGeo., has interests in tropical forest ecology, particularly in south-east Asia.

Nik Faizu Nik Hassan

Nik Faizu Nik Hassan was a botanist and was a field manager for the plot censuses.

Shawn Lum

Shawn Lum has interests in forest ecology, evolutionary biology and education. He is the principal investigator of the Bukit Timah permanent plot.