Abstract:The effects of rainfall conditions and the morphological characteristics of leaves on the moisture dynamics of litter layers were investigated. Maximum water storage capacity and interception storage capacity under various rainfall conditions were evaluated for two contrasting litter types: a needle-leaf type, represented by Cryptomeria japonica leaves; and a broad-leaf type, represented by Lithocarpus edulis leaves. An artificial rainfall simulator was applied to measure each litter type's interception storage capacity under various rainfall intensities. Our results indicated that (1) the maximum water storage capacity of each litter layer was proportional to the litter mass (kg/m 2 ) regardless of layer thickness; (2) the litter interception storage capacity increased with rainfall intensity in the range of realistic rainfall conditions (under 50 mm/h); (3) the broad-leaf litter of L. edulis intercepted more rainwater than the needle-leaf litter of C. japonica; and (4) the rainwater moved laterally in the litter layer of L. edulis whereas it moved directly down in the litter layer of C. japonica. These results show that not only the litter mass but also the rainfall conditions and leaf shapes are important in evaluating the moisture dynamics of litter layers.

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[1] Although coarse woody debris (CWD) is an important component of stream ecosystems in forested areas, the processes of CWD distribution, transport, and retention have not been clarified. In this study the distribution process of CWD pieces shorter than the bankfull width (S-CWD) is discussed using an in situ field experiment of log transport and a field survey of CWD distribution in mountain streams. The transport experiment showed that transport distance has a close relation to flow depth and also implied that the magnitude and sequence of a series of flows were important factors for S-CWD transport and retention in streams. The survey of CWD distribution indicated that in-stream obstructions played an important role in the S-CWD retention in deeper channels where S-CWD pieces were potentially transported distances more than spacing between trapping sites of CWD. Overall, the in situ field experiment and the segment-to reach-scaled analysis using h* (=depth/diameter) helped us understand the actual movement and distribution of CWD.

Modern ecohydrologic science will be critical for providing the best information to policy makers and society to address water resource challenges in the 21st century. Implicitly, ecohydrology involves understanding both the functional interactions among vegetation, soils, and hydrologic processes at multiple scales and the linkages among upland, riparian, and aquatic components. In this paper, we review historical and contemporary ecohydrologic science, focusing on watershed structure and function and the threats to watershed structure and function. Climate change, land use change, and invasive species are among the most critical contemporary issues that affect water quantity and quality, and a mechanistic understanding of watershed ecosystem structure and function is required to understand their impacts on water quantity and quality. Economic and social values of ecosystem services such as water supply from forested watersheds must be quantified in future research, as land use decisions that impact ecohydrologic function are driven by the interplay among economic, social, political, and biological constraints. Future forest ecohydrological research should focus on: (1) understanding watershed responses to climate change and variability, (2) understanding watershed responses to losses of native species or additions of non-native species, (3) developing integrated models that capitalize on long-term data, (4) linking ecohydrologic processes across scales, and (5) managing forested watersheds to adapt to climate change. We stress that this new ecohydrology research must also be integrated with socio-economic disciplines. Published in 2011. This article is a US Government work and is in the public domain in the USA.