Water-Holding Characteristics of Forestry Residues for Urban Bare Soil Mulching

Objective: Forestry management produces abundant residues including wood chips, fallen leaves and bark. Reusing them as urban organic mulches improves soil quality, mitigates soil erosion and optimizes urban green space ecology. This study analyzed the water-holding characteristics of four typical forestry residues to guide urban mulch selection. Methods: Soaking lab tests were conducted on pine bark (PB), oak leaves (OLs), pine needles (PNs), and fir wood chips (FWCs) to monitor dynamic variations in water-holding capacity and absorption rate over soaking time, with data fitted by mathematical models. Results: All forestry residues exhibited considerable water-holding capacity, with OLs showing the highest water-retention performance (175.67 t/ha, 145.42%), effective interception capacity (119.83 t/ha) and interception rate (99.19%) among all tested materials, followed by FWCs. The water-holding capacity increased rapidly and then leveled off with prolonged soaking time, and this trend conformed to a logarithmic equation, expressed as Q = a·ln(t) + b. Water absorption peaked at 15 min before declining slowly until equilibrium, and this dynamic process was well fitted by a power function, expressed as V = k·tn. Conclusions: Given their superior water-holding characteristics, OLs and FWCs are highly recommended as preferred organic mulches for urban soil applications.