The commodity trap in specialty agriculture: temporal asymmetry and the limits of black fungus specialization in China

This study examines whether variety-specific agricultural specialization is associated with both horizontal industrial scale expansion and vertical unit-value upgrading. Using a balanced panel of 26 Chinese provinces from 2014 to 2024, we analyze black fungus ( Auricularia auricula-judae ) specialization through a between-within random-effects decomposition that separates long-term between-province structural specialization from short-term within-province fluctuations. The results reveal a clear temporal asymmetry. Persistent structural specialization is significantly and positively associated with horizontal industrial scale expansion, whereas short-term specialization changes show no statistically significant association. However, neither structural nor transitory specialization is significantly associated with aggregate edible mushroom unit-value upgrading. This divergence suggests a potential commodity-trap pattern in which horizontal production expansion coexists with limited improvement in value capture, although the empirical model does not directly identify the underlying market-level supply–price mechanism. Heterogeneity analysis provides suggestive evidence that the specialization–scale association may be stronger in provinces with lower structural road accessibility. While the continuous interaction term is negative but statistically insignificant, the supplementary subgroup results point in the expected direction. This pattern is consistent with the possibility that the storability of dried agricultural products may reduce the dependence on high-quality transport infrastructure, but this evidence should be interpreted as exploratory. The findings suggest that black fungus specialization is associated with sectoral scale formation, especially in infrastructure-constrained regions, but that sustainable upgrading requires value-chain integration through processing, certification, grading, branding, and coordinated marketing.