and erosion protection (A. Dobson et al. 2006; Song, Huang, and Townshend 2014). (See Appendix 3: _Environmental Indicator: Ecosystem Effects as Measured by Forest Cover Change in CICPEC_ .) Roads are considered one of the leading proximate causes of habitat destruction, especially tropical deforestation.<sup>4</sup> For example, a meta‐analysis by Geist and Lambin (2001) of the existing literature on the causal factors for tropical deforestation found that the extension of road infrastructure was a proximate cause of deforestation in 61% of the cases studied (93 of 152) while rail expansion was a proximate cause in 11% (17 or 152). Such evidence has led to the development of a relatively new discipline, “road ecology,” which addresses solely the impacts of road construction and operations and their mitigation (Coffin 2007; Forman 1998; Forman et al. 2003; van der Ree, Smith, and Grilo 2015). More recently, “railway ecology” has also been proposed (Popp and Boyle 2017; Wingard et al. 2014), although the general assumption has been that the environmental impacts from rail, while similar in nature, are less severe in intensity to those from roads. Perhaps for this reason, the great majority of the research on environmental impacts has focused on roads rather than railways. For example, a survey of transport‐ related impacts on wildlife found that 94% of peer‐reviewed articles were about impacts of roads, with only 6% on rail impacts (Popp and Boyle 2017).

# ii. Edge Effects

The "road effect" (also known as the “edge effect”) is the area over which the ecological effects of a road and traffic extend into the adjacent landscape due to habitat disturbance effects (van der Ree, Smith, and Grilo 2015). This is a more subtle but pervasive ecosystem effect of a road that extends well beyond the initial loss in habitat from the transportation corridor. The newly created edges along a roadside allow penetration of light, wind, and chemical pollution and modify microclimatic conditions. Such alterations affect the distribution and abundance of plant and animal species. Specialized “habitat‐ interior” species of plants and animals are often outcompeted by “edge‐adapted” generalist or weedy species (Bruschi et al. 2015). The edge effect can also lead to cascading abiotic effects. For example, because the edges are desiccated from light and wind exposure, they are especially prone to forest fires. In the Amazon, edges are particularly vulnerable to fires initiated in adjacent burned pastures and/or selective logged forests with their built‐up fuel load. Once the forest fire enters along the roadside, forest fires can burn deep into the interior of the forest (Cochrane and Laurance 2002).

The penetration of the road‐effect zone into the adjacent landscape is determined by the characteristics of the (i) road (divided versus undivided, paved versus unpaved, elevation relative to adjacent landscape); (ii) traffic (vehicle type, volume, speed); (iii) adjacent landscape (topography, hydrography, vegetation type, habitat quality); (iv) prevailing wind speed and direction; and (v) species traits and their sensitivity to the impact (R. van der Ree, Smith, and Grilo 2015). The road effect zone can be felt as far as 1500 m from a highway (Bruschi et al. 2015). It is estimated that 15‐20% of the earth’s landcover is influenced by this road effect (Forman 1998). Given that most BRI road projects are relatively large, we can estimate that the “road effect” will extend on average at least a kilometer into the adjacent roadside habitat (Benítez‐López, Alkemade, and Verweij 2010; Ibisch et al. 2016). The China‐Indochina Peninsula Economic Corridor in tropical Southeast Asia is especially vulnerable to edge effects because research has shown that this effect is especially pronounced in tropical ecosystems (Goosem 2015).

> 4 It should be noted that much of the research focused on roads and deforestation in Latin America, especially the Amazon, and that more recent rigorous research in Asia also very strongly supports that the contexts are critical.

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