Throughfall (TF)—as a diffusive hydrological water flux—significantly affects ecohydrological and biogeochemical processes within forest ecosystems. Recent investigations have revealed the impact on TF generation processes within unmanaged coniferous plantations of under-canopy structures, particularly those laden with dead branches, as well as upper-canopy structures. However, spatiotemporal variations in TF in such plantations remain unexplored. We investigated these variations in TF in a 33-year-old unmanaged Japanese cypress (Chamaecyparis obtusa Endl.) plantation, laden with dead branches, with a high stand density (SD) of 2,500 stems ha−1. Over a two-year period (May 2017 to May 2019), we conducted weekly TF measurements using 28 manual-type TF collectors. We compared the present TF ratio and canopy water storage capacity (S) with those of previous investigations conducted on Japanese cypress plantations. Moreover, we assessed key indices contributing to spatiotemporal TF variations (canopy cover: CC and distance to the nearest stem: TFd) and potentially influential dead branch indices (number of dead branches: TFdb and vertical spacing length on a stem: TFs) to elucidate TF spatial patterns. The results showed that the TF ratio was notably lower than that in previous studies (n = 13), with SD (r = –0.92, p < 0.001) and S (r = –0.87, p < 0.001) emerging as key influential factors among other stand-structure parameters. Spatial TF patterns exhibited a decreasing trend as the gross rainfall (GR) increased. Temporal stability was not significantly associated with CC (r = 0.120, p = 0.544), TFd (r = 0.068, p = 0.731), TFdb (r = 0.211, p = 0.281), or TFs (r = 0.206, p = 0.292) for any of the TF collectors. These findings underscore the important role of GR in determining the spatial variation of TF. Collectively, our results contribute to an enhanced understanding of TF spatiotemporal heterogeneity in unmanaged Japanese cypress plantations with dead branches.

Introduction
Materials and Methods
    1. Study site description
    2. Measurements
    3. Canopy interception parameters
    4. Throughfall spatial variability
    5. Time stability of throughfall spatial patterns
    6. Spatial and temporal throughfall indices
Results and Discussion
    1. Gross rainfall and throughfall
    2. Throughfall and forest structure relationships
    3. Throughfall spatial variability
    4. Throughfall temporal stability
    5. Relationship between temporal stability andindices of throughfall
Acknowledgements
References

• Seong Hun Jeong(Professor, Department of Forest Environmental Resources, Gyeongsang National University, Jinju 52828, Republic of Korea, Professor, Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea)
• Hyun Shik Moon(Professor, Department of Forest Environmental Resources, Gyeongsang National University, Jinju 52828, Republic of Korea, Professor, Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea)
• Hyung Ho Kim(Professor, Department of Forest Environmental Resources, Gyeongsang National University, Jinju 52828, Republic of Korea, Professor, Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea) Corresponding author