Water consumption turning point for Robinia pseudoacacia occurs at its middle stand age

Aims: Over recent decades, the Chinese government has instigated large-scale vegetation restoration projects across the Loess Plateau to control soil erosion. Yet, this project coupling effect with associative interannual variations and magnitudinous decreases during vegetation species’ developmental stages have rarely been explored. Therefore, we conducted experiments to explore the water budget characteristics under different stand ages of Robinia pseudoacacia. Methods: We selected five R. pseudoacacia stand ages (i.e., 6 yr, 16 yr, 20 yr, 35 yr, and 45 yr) to investigate their individual interannual water budgets over four consecutive years (2019–2022). Results: Compared with grassland, the significant soil water amounts were consumed within the deep soil layers (> 200 cm) of all R. pseudoacacia stand ages. The soil water storage (SWS) deficit gradually worsened between 6–20 yr but then improved between 35–45 yr. Also, SWS values of all five R. pseudoacacia stands significantly differed (p < 0.05). Interestingly, as the stands aged, the increasing rate of actual evapotranspiration (AET) largely decreased from 125 mm yr⁻¹ to 29 mm yr⁻¹. The relationship between cumulative precipitation and AET further revealed that the water equilibrium input–output state reached at the stand’s middle age (~ 20 yr), after which the positive water input feedback occurred. Conclusions: These findings highlight that the water consumption process turning point for R. pseudoacacia occurs at the stand’s middle stage, indicating its role in SWS recovery. Our experimental evidence will benefit both researchers and policymakers, helping them to better regulate water resources and to optimize forest management alternatives.