Deep soil depletion and edge compensation: Insights into optimized strategies for addressing water imbalance in arid-region plantations

In recent years, the contradiction between vegetation restoration and the sustainability of soil water resources in arid regions has become increasingly prominent. Numerous studies have provided evidence that changes in land use significantly impact soil moisture; however, they often overlook the interconnections between different ecological landscape units. This study focuses on the Pinus sylvestris. artificial forest in the Mu Us Sandy Land, analyzing the spatial distribution characteristics of soil moisture profiles from 0 to 500 cm, and revealing the moisture dynamics and driving mechanisms within the forest and at the forest edge. The results indicate that the planting of P. sylvestris leads to a significant reduction in soil water storage (P < 0.05), with notable depletion of soil moisture observed in 25-year-old P. sylvestris stands. Although soil moisture partially recovers as the trees mature, deep soil moisture remains continuously deficient, reflecting a long-term imbalance between vegetation water consumption and replenishment. Additionally, internal water competition is induced within 25- to 35-year-old stands, manifested by the absorption of moisture from the 100–300 cm soil layer of grassland at the forest edge by lateral roots of P. sylvestris, with an extent reaching up to 11 m. In the soil moisture profile from within the forest to the edge (19 m distance), a significant positive correlation is observed between root biomass and soil moisture (P < 0.05), although this correlation gradually weakens with increasing distance from the forest edge. These findings suggest that the depletion of soil moisture within the forest encourages trees at the edge to extend their lateral roots to access additional water resources. Therefore, it is recommended that future forest management incorporate ecological nurturing measures centered on density regulation and spatial optimization. This study provides a scientific basis for promoting sustainable water resource management in P. sylvestris forests through thinning, and holds significant practical implications for vegetation restoration in arid regions.