Our Nature Reserves are FRAGMENTED
Take a look at the aerial map of Singapore taken from Google earth. The Bukit Timah Nature Reserve (BTNR) and the Central Catchment Nature Reserve (CCNR) covers 30.43km2, which is about 4.3% of the total surface area of Singapore. [Source of area taken from NPark’s website]
It looks green, lush and continuous but take a closer look at the green patch.
Can you identify the areas that are not green? What are these areas?
BTNR is separated from CCNR by the Bukit Timah Expressway (BKE) since the 1980s. If we examine the aerial map carefully, we will find that there are many structures, roads and features that breakup our continuous forests into patches. Our forest is fragmented.
Forest Fragmentation occurs when large intact and continuous forests are divided into smaller pieces, by roads cutting through, clearing for agriculture, housing and other urban development.
Our central forest in Singapore has been fragmented since pre-independence days by the creation of golf courses, expressway, sealed roads, pipelines, Nee Soon Firing Range, Zoo, Night Safari, reservoirs, military facilities and security fences. The forest in the Central Catchment Nature Reserve is no longer a continuous and integrated forest but broken into 24 fragments forming habitat islands.
What are the consequences of Forest Fragmentation?
Forest fragmentation can have negative and often irreversible effects on local environments, especially when associated with human development.
Habitat reduction in size and diversity
When habitat is reduced to smaller and smaller patches, not only there is a decrease in the overall habitat area, there is also less diversity in habitat types.
Smaller population and decrease in biodiversity
A reduced amount of habitat supports correspondingly smaller populations of wildlife, as well as fewer species. Some species may find it more difficult to breed, hide from predators, find food or shelter. Species richness and abundance or density of forest-dependent species generally declined in disturbed compared to mature forests
Edge habitat increases
When a habitat is fragmented, the amount of edge habitat increases at the expense of interior habitat. There is a decrease in humidity and an increase in temperature as the forest becomes drier at the edges. Species dependent on interior habitat suffer, while edge-dependent species, including invasive species and predators, thrive. Invasion and predation by alien and non-forest species, introduction of diseases from urban zones to the forest wildlife, which have no immunity or resistance to them and increase conflict between human and wildlife at the forest edges may result. Edge effects can extend from 100 to 300 metres into the forest.
Illustrations by Clive Dobson
The widths of many patches of the forest in the Nature Reserve are extremely thin and some lacking interior habitat. This is similar to the first illustration shown above. The small forest patches have a proportionately high amount of edge habitat. Ecologists often equate the edge habitat to an ecological buffer that is typically 100 m in width. Therefore, forest habitat must be at least 100 m from the edge before it can be considered “interior”. Our forests have little of “interiors”. More buffers should be created to prevent the edge effects. Housing development should not allowed in areas where the fragmented patch is narrow.
Vulnerability during movement among patches.
Wildlife attempting to cross between patches becomes temporarily vulnerable to predators, harsh environmental conditions, or simply to starvation. When the BKE was build in the 1980s, many roadkills have been reported along the expressway where Bukit Timah Nature Reserve was separated from the Central Catchment Nature Reserve. Even today, roadkills are still being reported along our expressways or roads. Raffles Museum of Biodiodiversity Research has been collecting data on roadkills in Singapore.
Juvenile Female Scaly Anteater or Sunda Pangolin (Manis javanica) found off Petir Road
on 11 Jan 2013. Photo by Marcus Chua
For more stories on roadkill check out Lazy Lizard tales (http://lazy-lizard-tales.blogspot.sg/2009/04/no-jaywalking-monkeys-more-law-abiding.html). Warning: The photographs may be upsetting.
Isolation of a population
Both plant and animal populations can become isolated within a patch when surrounding patches of habitat are destroyed. Migration or movement becomes difficult and hazardous. Isolated populations are prone to decline due to inbreeding, swings in numbers due to over-exploitation of habitat.
Banded leaf monkey (Presbytis femoralis femoralis) was common in Singapore in the 1920s. As the habitats were destroyed with the development of Singapore, their population was confined mainly to the BTNR and CCNR. With the construction of BKE, the two reserves were separated and did the population of the Banded leaf monkey. In the Raffles Museum of Biodiversity and Research (RMBR), a preserved elderly female monkey can be seen. The sad story has been told to many visitors as to how the last lonely survivor of the troop left behind alone in the forest of BTNR, descended to the forest ground in October 1987 and was mauled to death by a pack of wild dogs.
In a recent 2-year study by Ang et al. (2010), they found 5 to 6 groups of about 40 Banded leaf monkey inhabiting in 455 ha of secondary and swamp forests in CCNR. This is our critically endangered species of mammals in Singapore.
[Ang et al., 2012. Low Genetic Variability in the Recovering Urban Banded Leaf Monkey Population of Singapore, THE RAFFLES BULLETIN OF ZOOLOGY 2012 60(2): 589–594]
Wildlife should be able to move freely from one forest patch to another. This movement allows for interbreeding, creating genetically stronger populations and ensuring that suitable habitats can be filled.
On 30 July 2011, NParks and LTA started the construction of Ec-Link@BKE to connect back BTNR and CCNR after they have been separated for more than 3 decades.
“Linking two high points on opposite slopes of the nature reserves and measuring 50 metres at its narrowest point, Eco-Link will be a forest habitat in itself. When ready in 2013, populations of native animals such as flying squirrels, monitor lizards, palm civets, pangolins, porcupines, birds, insects and snakes, will be able to travel between the nature reserves to find other food sources, homes and mates. This will also help plant species to propagate by way of pollination and dispersal by the animals.”
Decrease Water Catchment
Our closed Catchment forests filter rainwater as it flows across land into streams, rivers and reservoirs. Forests act as filters, and removing forest near streams may adversely affect water quality and human drinking water supplies. Less rainwater percolates into the ground, changing surface and subsurface water flow patterns. Less moisture is available to plants and animals, but it can also decrease the amount of water in underground aquifers and increase the risk of flash floods downstream.
Source: Helena Rusak, Federation of Ontario Naturalists, “Forest Fragmentation”
Some Academic Papers published on Forest Fragmentation
1. Hill, J.K. et al, 2011. Ecological impacts of tropical forest fragmentation: how consistent are patterns in species richness and nestedness?. Phil. Trans. R. Soc. B (2011) 366, 3265–3276
2. Sodhi, N. S. et al. 2010. Conserving South East Asian forest biodiversity in human-modiﬁed landscapes. Biol. Conserv. 143, 2375–2384. (doi:10.1016/j.biocon.2009.12.029)