Ecological Impacts of Roads: The Pan Borneo Highway

Considering the contribution good roads can make to economic growth and rural connectivity, it is justifiable to expand a country’s network of roads. However, significant problems arise when road proponents do not consider the full costs and risks that roads may pose to the economy, society, and environment.

Road building comes hand in hand with increased forest conversion, illegal hunting, and illegal wildlife trade. The tropical climate, sporadically distributed communities, and exceptionally biodiverse and sensitive forest landscapes in Malaysian Borneo mean that building good roads is especially challenging. Furthermore, inadequate environmental impact assessments (EIAs) fail to expose the true risks, and thus do not enable policy makers and approving bodies to adequately respond to minimize potential risks.

Roads penetrating into Earth’s remaining wildernesses are a major driver of habitat loss and fragmentation, wildfires, overhunting, and other environmental degradation. The Pan Borneo Highway poses a particular challenge, as it will dissect some of the last remaining habitat for critical species, such as elephants, clouded leopards, sun bears, orangutans, and gibbons. Road penetration will increase risks of poaching, deforestation, and degradation, which will push many threatened species to the edge of extinction. Furthermore, because major roads in tropical areas often fail to deliver economic and social expectations due to the difficult terrain, intense seasonal rainfall, and high maintenance requirements, they rapidly become an economic liability.

Impacts of Roads on Wildlife

Tropical species of animals and birds are particularly vulnerable to road infrastructure. The unique and complex architecture of rainforests sustain many species that are specialized for forest-interior and understory conditions, including some species that are unable to traverse even narrow forest clearings. Other tropical species are susceptible to hunting, road kill, elevated predation and species invasions near roads. (Laurance, Goosem, and Laurance, 2009).

Roads also fragment habitats and prevent migration, resulting in inability to access key areas for food and reproduction, and in populations of key species being isolated from one another. This leads to unstable populations in certain species and can lead to extinction. Preserving or creating landscape connectivity has become increasingly recognized as a key strategy to protect biodiversity, maintain viable ecosystems and wildlife populations, and facilitate the movement and adaptation of wildlife populations in the face of climate change. Species that are rare, such as apex predators and large-bodied mammals and birds, and that require large home ranges or have low reproductive rates, are generally most vulnerable to elevated mortality from roads built in key habitat (Laurance, Goosem, and Laurance, 2009).

Narrow forest roads facilitate road-crossing movements by animals, however they also lead to greater road kill. Hunting by humans near roads can create zones of elevated mortality and animal avoidance within 5–10 km of roads, and possibly much further for wide-ranging species, such as forest elephants and some primates.

In tropical areas roads significantly change the climates of the surrounding forest. Forests within 50–100m of road edges experience greater diurnal fluctuations in light, temperature and humidity, being typically drier and hotter than forest interiors, with elevated tree mortality, numerous canopy gaps, and a proliferation of disturbance-adapted vines, weeds and pioneer species. (Laurance, Goosem, and Laurance, 2009).

The intensity of road impacts is influenced by road design. Clearing width is important, with narrow (<20-m width) clearings resulting in less disturbance and desiccation stress than wider clearings (Laurance, Goosem, and Laurance, 2009). The orientation of linear clearings with respect to solar angles can also influence edge-effect intensity; clearings parallel to the solar track are exposed to sunlight throughout the day and, thus, are likely to suffer greater heat and desiccation at ground level than are those that are perpendicular to the path of the sun, which are fully insulated only at midday. Furthermore, the maintenance of roads with herbicides, fires, or cutting of foliage repeatedly disturbs the adjoining forest vegetation and, by preventing natural edge closure, can cause edge effects to be elevated in intensity (Laurance, Goosem, and Laurance, 2009).

Roads are facilitating widespread species invasions in the tropics, for taxa ranging from little fire ants (Wasmannia auropunctuta) and exotic earthworms and to fungal die-back, caused by Phytophthora spp., and a myriad of weed species (Laurance, Goosem, and Laurance, 2009).
Increase in Deforestation, Forest Conversion, and Wildlife Trafficking Deforestation behaves much like a cancer. Across the world, forest clearing is highly “contagious” spatially, as new clearings tend to spread out from existing clearings. When someone cuts the first road into a pristine forest, deforestation begins to grow along the road. The road then spawns secondary and tertiary roads, and deforestation spreads (Campbell, Alamgir, and Laurance, 2017).

In the tropics, roads and highways often facilitate invasions of hunters, miners, colonists and land speculators , a phenomenon dubbed the ‘Pandora’s Box Effect’. Roads can also increase trade in illegal wildlife products; for example, on average, eight killed mammals were transported per hour along a single highway in Sulawesi, Indonesia (Laurance, Goosem, and Laurance, 2009).

Deficiencies in the EIA Process

Compared to other similar countries, Malaysia’s mandatory EIA process for prescribed infrastructure projects is more robust and has resulted in reduced environmental impacts. However, many relevant road risks are not adequately identified during the EIA process, resulting in inadequate mitigation measures. Inadequacies in the EIA process include spatial and temporal ignorance, conflict of interests, and the flexibility of legislative requirements . EIAs in road infrastructure projects often assess a narrow spatial and temporal scale that is inadequate to identify the impact on wildlife, such as tigers and elephants. Assessments also fail to adequately assess the impact of development on the whole landscape.

Flooding, Erosion, and Pollution

In wet tropical regions, rapid erosion from roads and the resulting heavy pulses of sediment into streams and rivers elevate water turbidity and temperature, reduce dissolved oxygen content, and alter natural flow regimes. Road-induced erosion is much greater in steep or dissected terrain, in part because heavier roadworks (more cut-and-fill activities to level the road surface) are needed. Silt and nutrient inputs into freshwater ecosystems can also promote eutrophication, which can kill sensitive fish and freshwater invertebrates and reduce water quality for humans and livestock (Alamgir et al 2017) .

Rapid surface flows from roads increase both local and downstream flooding. Few roads in high- rainfall zones have sufficient culverts, bridges or other drainage structures to divert water through or around the roads. The recurring impediment of water causes localized flooding and vegetation mortality, peaking during periods of intense rainfall. Road construction in mountainous areas also increases the risk of landslides.

Suggestions and Solutions

Limit Road Expansion

Avoid the first cut in intact habitats. Experts recommend that roads penetrating into remote frontier regions be avoided wherever possible. (Laurance, Goosem, and Laurance, 2009). Wilderness regions, parks and protected areas, remnants of rare ecosystems, surviving fragments of intact habitat within biodiversity hotspots and regions with many locally endemic species, such as islands and isolated mountaintops, are examples of environments where roads and other infrastructure should be stringently limited or avoided altogether (Laurance et al, 2015).

Create Protected Areas along Roads

When roads in frontier areas cannot be avoided, uncontrolled forest loss and invasions can be reduced by creating protected areas (PAs) along the road route in advance of road expansion. In the Brazilian Amazon, for example, forest destruction has been more severe along highway that did not have PAs in place prior to road construction (Laurance, Goosem, and Laurance, 2009). Furthermore, fires along roads were less common in areas close to PAs.

When Possible Establish Railroads and Ferries

Establish railroads rather than roads in frontier areas. Through rail transportation, incursions into forests can be partially controlled because trains stop only at designated locations, and these can be situated strategically to limit invasions of environmentally sensitive areas. When coastal access is available, smaller roads and ferries can connect two remote locations with less negative impact than a major highway.

Road Design Strategies

Properly constructed large culverts for streams under roads can minimize destructive flooding and maintain stream flows. These should be designed so that increased stream velocity within them does not create a barrier to aquatic fauna. Soil erosion and stream sedimentation can be reduced by confining the use of heavy equipment to drier months and by seeding fast-growing native plants over road cuts and disused quarry sites (Laurance, Goosem, and Laurance, 2009).

Edge effects along road clearings can be reduced by allowing secondary growth and vines to proliferate along forest margins, road cuts, and embankments, thereby providing a physical buffer that lessens forest desiccation. Mowing and brush cutting are generally better than broad-scale herbicides and fire for controlling regrowth along clearing verges because they are less likely to damage regenerating forest-edge vegetation (Laurance, Goosem, and Laurance, 2009).

Barrier effects on wildlife can also be minimized by limiting road widths and maintaining a nearly- continuous canopy overhead, although such measures can increase road kill because road- crossing movements are more frequent. Regrowth forest along road margins can further reduce the isolating effects of roads. Bridges over watercourses that include a corridor of unflooded vegetation and natural streambed are especially effective for maintaining connectivity, both for terrestrial and aquatic fauna (Laurance, Goosem, and Laurance, 2009).

Within roadside forests that are being selectively logged, sustainable forest management regimes should be improved to minimise threats from logging roads. Wherever possible, close existing roads in high-risk places such as prime wilderness.

Speed Control, Driving Hours, and Enforcement

Road user management should be implemented, involving measures such as speed cameras, speed bumps, speed-reducing strips, warning lights, wildlife signs, and if feasible, road closures during the night (Clements 2013). Road-kill mortality can be reduced by limiting vehicle speeds, measures such as low legal speed limits, road-painting, warning strips and speed-bumps), posting warning signs, establishing wildlife fences along busy highways that help steer animals toward culverts, and in high-priority areas, by restricted nighttime driving. Most road kills occur at night and near dawn and dusk, when animal activity is highest. In tropical Africa, restrictions on night-time driving within a PA have proven effective at reducing illegal hunting activity (Laurance, Goosem, and Laurance, 2009).

Avoid Critical Habitats for Endemic and Endangered Species

In areas of high conservation significance various measures can be used to reduce road impacts. For nature reserves, roadworks and road density should generally be minimized, and roadless core- areas maximized, to sustain hunting-sensitive wildlife and reduce exotic-species invasions.
A method has recently been developed to evaluate certain mammal species whose populations are at ‘tipping points’ (see Clements 2013 and 2014). It is a combined approach that uses IUCN threat categories together with a “S.A.F.E. index” – “Species Ability to Forestall Extinction” , which provides a good proxy for gauging the relative “safety” of a species from extinction. The S.A.F.E. index can be used to prioritise roads that warrant urgent conservation attention based on their passage through habitats with the most number of mammal species whose populations are at ‘tipping points’ (Clements, 2013).

Strengthen the EIA Process

Inadequacies in EIAs can be minimized by incorporating proactive planning and greater community engagement, increasing financial resources provision for assessments, and ensuring highly skilled field personnel. This would enable more effective EIA delivery through all stages, including the revision of current EIA requirements and processes, the effective monitoring practices of road developments, and the strict enforcement of legislation. With such improvements, the producers of EIAs will be required to reach minimum satisfactory standards (Alamgir et al 2018).

Another needed change is better transparency and accountability of results from environmental and social impact assessments of proposed roads, which have had limited success in mitigating the impacts of these proposed roads. Wherever possible, projections of economic and biodiversity loss prior to road development should be conducted to guide decision-making involving the construction of new roads. Smaller roads at local scales should not be spared from assessments even if funds are constrained (Alamgir et al 2018).

Increase Enforcement Efforts

At existing roads where the probabilities of illegal forest conversion and hunting pressure are high, increased law enforcement is essential. Law enforcement efforts should be strengthened to prevent wildlife poaching and trafficking along roads, particularly those leading to border checkpoints.

The need to increase enforcement efforts along roads to deter illegal hunting has already been recognized in some countries. Along Federal Route 4 in Peninsular Malaysia, government enforcement agencies stepped up enforcement efforts after World Wide Fund for Nature (WWF)- Malaysia patrols detected large number of snares along roadside forests (Laurance, Goosem, and Laurance, 2009). Law enforcement strategy also identified closing illegal roads as a required action for reducing forest encroachment and illegal timber extraction.

Resolve Land Rights Issues

To minimise the impacts of roads on people’s livelihoods, land rights and tenure should be resolved prior to road construction. One of the key drivers of habitat loss is the absence of land and resource tenure along roads. This has resulted in an uncontrolled influx of people seeking to clear and claim land along roads (Clements et al 2014). To minimise illegal settlements along roads bordering important biodiversity areas, relevant government agencies should complete the allocation of lands for villages and protected areas prior to road construction. (Laurance, Goosem, and Laurance, 2009)

Minimize threats from logging roads via sustainable forest management regimes

Closing logging roads after cessation of logging can help restrict access to poachers and illegal loggers (Clements et al 2014). Forestry departments should prioritise the closure of logging roads that contribute to the transport of illegally harvested timber. This is especially important at the Malaysian-Indonesian boundary on Borneo where, on satellite images, 137 cross-border logging road intrusions have been detected (Clements et al 2014). When new logging roads are constructed through previously undisturbed mammal habitats, greater law enforcement must be afforded together with publicised policies and measures that deter poaching (Laurance, Goosem, and Laurance, 2009).

Increase engagement with road development agencies in conservation planning

Agencies responsible for road development are rarely included as main project partners in species conservation plans. Because roads can be the precursor of forest conversion and hunting, road- relevant stakeholders should be included in the early stages of conservation planning. Plans should include scientifically-sound guidelines of where roads can be constructed or upgraded to maximize agricultural benefits and minimize biodiversity loss. Ad hoc planning with little or no cross-sectoral communication between government departments is often the root of environmental problems associated with roads. In Malaysia, the Department of Wildlife and National Parks laudably worked together with the Public Works Department to incorporate underpasses along a new highway to facilitate mammal migration in important wildlife corridors (Laurance, Goosem, and Laurance, 2009).

Wildlife Bridges and Underpasses

The integration of green infrastructure options (e.g., underpasses, overpasses, “eco-viaducts”, road signs and culverts) into proposed road designs, along with incorporating measures to evaluate their efficiency of use, may be beneficial for the movement of mammals through fragmented habitats. However, recent research has found that wildlife underpasses in Malaysia are inadequate and can even lead to increased wildlife poaching. The following information comes from Clements, 2013 and personal communications with William Laurance.

  1. Most roads bring with them substantial wildlife poaching and deforestation along the road route. Therefore, the most sensitive and vulnerable species generally tend to avoid roads, along with overpasses and underpasses, unless law-enforcement is extremely strict and rigorous to stop the threatening activities.
  2. Highway bridges are generally like treating cancer with a band-aid: they do not mitigate the illegal encroachment and deforestation activities that bring such a peril to wildlife.
  3. Available studies suggest that the most vulnerable and extinction-prone species do not use road-bridges. These species either avoid the general vicinity of roads altogether or they simply cross the road wherever they want (elephants are famous for doing this, even when one tries to put up electric fences to ‘steer’ them to the underpass).
  4. Some species will use underpasses, but these are typically more generalized and less vulnerable species that are not of high conservation concern.
  5. A bridge is better than nothing, but it is about 10% as effective as having intact forest in place. Wildlife bridges are generally inadequate compared to the many threats that roads bring to a forested area.
  6. There is a serious need for more research on underpasses; while their effectiveness may be limited in most circumstances, there are likely many local contextual factors that will impact their success.
  7. Proponents of wildlife underpasses and overpasses often grossly overstate their effectiveness, with very little data. Such structures make us feel we can have our cake and eat it too, but there are simply too many serious changes wrought by roads for this to realistically happen.
  8. Research has shown that wildlife crossings in Malaysia can become shooting galleries for poachers, who will camp out in areas where law enforcement is lax (Clements, 2013). Unfortunately, roads and viaducts can also provide encroachers with greater access to adjoining forests. This means that viaducts without effective monitoring or enforcement against poaching and encroachment can in fact help create an increased threat to wildlife.

Better Underpasses:

Key management interventions to improve efficiency of underpass use include regulating the negative effects from the road (e.g. high vehicle traffic) and reforestation of open areas between forest edges and underpasses. Further, because human activity near underpasses can deter the use of these underpasses by large mammals, measures such as regular law enforcement patrols and warning signs beneath underpasses might be useful to deter human presence. Such management interventions should be accompanied by long-term monitoring to assess the effectiveness of such interventions. In addition, extensive studies to determine animal migration patterns over large areas need to be conducted in order to insure the underpass is built in the correct location that will be useful to animal patterns. Underpasses and overpass that do not specifically research consider animal migration patterns result in little to no use by key species.


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