Characteristics of throughfall kinetic energy in an unmanaged Japanese cypress plantation laden with dead branches

• Published in: Catena (Giessen) Vol. 243; p. 108181
• Main Authors: Jeong, Seonghun, Nanko, Kazuki, Katayama, Ayumi, Kume, Tomonori, Koga, Shinya, Otsuki, Kyoichi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.08.2024
• Subjects: Dead branches; Japanese cypress; Monte Carlo; Sand-filled splash cup; Splash soil erosion; Throughfall kinetic energy; Dead branches; Splash soil erosion; Monte Carlo; Sand-filled splash cup; Japanese cypress; Throughfall kinetic energy
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/j.catena.2024.108181

•Throughfall kinetic energy (TKE) can be affected by under-canopy dead branches.•The present unit TKE was much lower than that reported, with fewer/no dead branches.•Empirical unit TKE model only considering upper-canopy structures overestimates.•6–15 sand-filled splash cups are appropriate for stand-scale TKE measurements.•Branch pruning may be unnecessary for soil erosion control. Among soil erosion processes, the initial stage of splash soil erosion caused by throughfall kinetic energy (TKE) plays a crucial role in soil conservation within forest ecosystems. Throughfall (TF) through the upper canopy structure considerably influences TKE in coniferous plantations. Recent studies have revealed that the under-canopy structure laden with dead branches in unmanaged coniferous plantations reduces the TF; however, its specific impacts on TKE and appropriate sampling strategies remain unexplored. This study used 40 splash cups (4 for free kinetic energy and 36 for TKE) for one event (total: 600 splash cups for 15 events) in an unmanaged 36-year-old Japanese cypress plantation laden with dead branches. Additionally, unstratified and stratified Monte Carlo simulations were used to determine optimal sample sizes for stand-scale TKE estimation. Results demonstrated a strong correlation between TKE (J m−2) and TF (mm) (R2 = 0.98) across all events. The stand-scale unit TKE of 12.5 J m−2 mm−1 was much lower than those in seven previous studies with fewer or no dead branches (range: 16.4 to 28.2, median: 18.8 J m−2 mm−1). The previously developed empirical stand-scale unit TKE model considering under-canopy structure solely exhibited a 1.7-fold overestimation. Among the stand structures, a positive relationship of TKE with the distance between a sampling point and its nearest trunk (Dmin) was observed, which was positively correlated with the lowest dead branch height. This indicated that under-canopy dead branches weakened the TKE, likely by reducing TF and raindrop fall velocity. Stratified Monte-Carlo simulation considering the Dmin related spatial patterns of TKE provided a more efficient approach for capturing variability. To achieve high precision with potential errors of ≤5–10 %, a total sample size of 6–15 was appropriate. Our findings implied that the presence of under-canopy dead branches mitigates the soil erosion risk in unmanaged Japanese cypress plantations.