The contribution of litter and soil to water conservation capacity as affected by land use change and stand age in Carya cathayensis plantations

The conversion of natural forests to plantations often degrades hydrological functions, yet the recovery trajectory and the relative roles of litter and soil remain poorly quantified. Using a chronosequence of Carya cathayensis plantations (6-, 20-, 50-year-old) and a natural forest (NF) control, we quantified how land use change and stand age affect water conservation capacity through litter and soil pathways. Conversion significantly reduced ( p < 0.05) litter accumulation (LA) and soil porosity, impairing water storage and infiltration. Recovery was nonlinear: the 20-year-old plantation (CP 20 ) exhibited the peak comprehensive water conservation capacity, driven predominantly by its well-developed litter layer. In the 50-year-old stand (CP 50 ) showed a shift in functional balance, with the soil layer playing a co-dominant regulatory role alongside the litter layer. Structural equation modeling (SEM) highlighted that: (1) Conversion to plantations reduced litter storage capacity ( W eff and R m ) and soil clay content, collectively impairing soil porosity and water conservation capacity; (2) Increasing stand age enhanced LA, clay, and soil organic matter, fostering soil total porosity, IIR , and saturated water-holding capacity. Our results underscore that boosting LA is critical for improving water conservation, with 20-year-old stands offering optimal ecological benefits. Management practices should prioritize retaining understory vegetation to support the litter layer throughout stand development. • Converting natural forests to Carya cathayensis plantations reduces water conservation capacity. • The 20-year-old stands exhibit the highest water conservation capacity among all ages. • Litter accumulation is the primary driver of water conservation capacity in Carya cathayensis plantations. • Soil water infiltration curves shift from flattened to S-shaped patterns as stand age increase. • Increasing stand age enhances litter accumulation, clay, and soil organic matter, boosting water conservation.