Weak or Strong Porter Effect? County-Level Evidence from China’s Prohibited Breeding Zone Policy in the Yangtze River Basin

Abstract

The extent to which environmental regulation yields a “weak” or “strong” Porter effect is fundamentally shaped by the trade-off between industrial output and productivity improvements, a complex dynamic that requires granular, sub-national empirical evidence. This study employs a continuous multi-period DID approach to evaluate the impact of China’s prohibited breeding zone policy (PBZP) on sustainability indicators—specifically, pig green total factor productivity (PGTFP) and its components, green technology efficiency (GEC) and green technology progress (GTC)—across 371 counties in the Yangtze River Basin from 2013 to 2021. The results indicate that PBZP significantly boosts county-level PGTFP and GTC in the basin, with an effect size of 0.206 for PGTFP and GTC identified as its primary driver, thereby supporting the “strong Porter hypothesis”, as confirmed by robustness and endogeneity tests. Channel exploration shows that PBZP has enhanced PGTFP through capital factor optimization and spatial restructuring. Heterogeneity analysis identifies significant regional differences across the upper, middle, and lower reaches of the Yangtze River. Further analysis reveals a trade-off between the impact of PBZP on PGTFP and the production capacity of pigs. Finally, this study outlines several policy recommendations for fostering new quality productive forces in pig farming by improving PGTFP while safeguarding effective pig production capacity.