line with Carr`ere and Strauss-Kahn (2017) who show that experience raises the survival of developing countries’ exports to the OECD; and Albornoz, Calvo Pardo, Corcos, and Ornelas (2012) who underscore the importance of learning by exporting for survival. Sectors with larger and more productive firms are more likely to enjoy higher rates of export survival and lower exit rates.<sup>24</sup> TFP is also positively associated with firm entry rates, consistent with Melitz (2003) and Bernard, Eaton, Jensen, and Kortum (2003). Standard proxies of bilateral trade costs including tariffs, distance and limited participation in economic integration agreements lower export survival and increase exit rates. High costs of starting a business in the exporting country, which reflect the extent to which the business environment is conducive to firms’ activities, also deter the survival of entrants but reduce the exit rate.<sup>25</sup> Beyond these baseline estimates, we also investigate possible heterogeneity in the impact of unpredictable border clearance times for imports on export dynamics. First, we examine whether the adverse effect of import uncertainty on firm survival rates is more pronounced for exports to high-income countries. The rationale behind this assumption lies in the growing share of trade flows that belong to global value chains (GVCs). Multinational firms based in high-income countries outsource part of their manufacturing process, typically labor-intensive tasks, to suppliers in developing countries. Combined with the observation that importer-exporter relationships involving developed countries tend to rely more heavily on lean supply chain strategies (Volpe Martincus, 2016), this makes buyers in high-income countries particularly sensitive to delivery schedules, and hence more prone to terminate trade relationships with unreliable suppliers in developed countries. We argue that by raising importing firms’ probability of missing delivery deadlines, uncertainty in the time required to clear foreign inputs through Customs exerts a stronger effect on firm survival in high-income export markets. To test this prediction, we estimate the baseline regressions in two sub-samples distinguishing between high-income (South-North trade) and non-high-income (South-South trade) destinations. Tables 4 and 5 present the results. The impact of uncertainty in import clearance times on export survival is mainly driven by South-North trade (Table 4), as coefficients on the dependent variable of interest lose statistical significance in the sub-sample of South-South trade (Table 5).<sup>26</sup> In a context of global supply chains where time management is critical, this confirms the distinctive sensitivity of buyers in high-income countries to timeliness.

In the same vein, one would expect exports from time-sensitive industries to be more affected by unpredictable delays to clear imported inputs at the border. (Hummels, 2001, 2007) and Hummels and Schaur (2013) provide a classification of goods according to their time-sensitivity, based on trading firms’ choice between using expensive but fast air transportation versus inexpensive and slow sea shipping for their products. Time-sensitive goods include for instance perishable products likely to be spoiled in the

> 24Bilateral distance and the dummy for participation in economic integration agreements enter with a positive and negative sign, respectively in Column 1. This seems to relate to the importance of South-North trade and relatively limited intra-regional trade, hence leading firms from developing countries to enter mostly rich markets. It is also worth noting that Fernandes, Freund, and Pierola (2016) find a positive association between bilateral distance and firm export entry rate.

> 25Since the pool of firms exiting the export market in _t_ comprises firms that were identified as entrants or incumbents in _t −_ 1, business start-up costs seem to act as a sunk cost of entry into foreign markets that only the most productive firms - presumably the incumbents - can cover. The role of sunk costs in mediating the relationship between import uncertainty and export dynamics is also explored in this paper.

> 26To rule out the concern that results may be driven by sample size, we also carry out alternative regressions by augmenting the baseline model with a dummy equal to 1 if the destination is a high-income country and its interaction term with import uncertainty (results are available upon request). The message remains similar.

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