Effect of canopy thickness and canopy saturation on the amount and kinetic energy of throughfall: An experimental approach

Abstract

[1] To investigate how canopy thickness and canopy saturation affect the amount and kinetic energy of throughfall, we conducted indoor experiments using a 9.8-m-tall transplanted Japanese cypress (Chamaecyparis obtusa) and a large-scale rainfall simulator with spray nozzles at a height of 16 m. The amount of throughfall and raindrop sizes and velocities were measured at twenty-four points under four canopy structures generated by staged branch pruning. Decreasing the canopy thickness resulted in increases of the initial throughfall amount, volume proportion of large throughfall drops, the number of drops with high velocities, and throughfall kinetic energy. Compared to a saturated canopy, a canopy undergoing wetting had lower throughfall amounts and volume proportion of large drops, but higher mean drop velocity. Canopy thickness affected throughfall generation by affecting the processes of canopy saturation and drop generation within the canopy. Citation: Nanko, K., Y. Onda, A. Ito, and H. Moriwaki (2008), Effect of canopy thickness and canopy saturation on the amount and kinetic energy of throughfall: An experimental approach, Geophys. Res. Lett., 35, L05401,

Throughfall kinetic energy in young subtropical forests: Investigation on tree species richness effects and spatial variability

“…These findings strengthen the assumption that different mechanisms in forests cause this high spatial variability of TKE. Furthermore, we observed a trend toward a positive distance to stem effect (Bochet et al, 2002Nanko et al, 2008, which appears at all rainfall events with rainfall amounts >20 mm. This increase of TKE toward the crown perimeter is caused by concentrated dripping like that from a peaked roof (Clements, 1971).…”

“…In addition, few branches prevent drops from confluence resulting in lower TKE due to lighter drop mass. Despite these tree characteristics, the first branch is the last barrier for drops before reaching the soil surface (Nanko et al, 2008). Hence, low rain drop velocities occur more often resulting in low TKE.…”

“…As a result, stratified canopies with a high degree of crown overlap and, thus an increased mean vegetation cover and greater biomass density can be found in mixtures compared to monocultures (Lang et al, 2010(Lang et al, , 2012Menalled et al, 1998;Pretzsch, 2014). Concerning soil erosion, TKE in particular reacts strongly to these tree characteristics (Geißler et al, 2013;Nanko et al, 2006Nanko et al, , 2008. As a consequence, tree species richness might affect soil erosion processes.…”

“…Soil erosion threatens ecosystem functioning by reducing soil organic carbon stocks, relocating nutrients and reducing the species diversity of plants, animals and microbes (Pimentel, 2006;Pimentel TKE in forests are abiotic factors, such as rainfall amount, drop size distribution and drop fall velocity as well as biotic factors, such as tree height and density of the canopy, crown cover, leaf traits, leaf area index and branch architecture (Cao et al, 2008;Geißler et al, 2012b;Gómez et al, 2001;Hall and Calder, 1993;Herwitz, 1987;Nanko et al, 2008;Staelens et al, 2008;Tsukamoto, 1966). For instance, higher crown cover and density can alter TKE by creating slower, but larger rain drops and additionally change throughfall amount.…”

“…Nanko et al (2011) showed a distance to stem effect, where TKE increased below a single Japanese cypress Chamaecyparis obtusa with increasing distance to the stem. In addition, TKE under this tree species was negatively affected by canopy thickness (Nanko et al, 2008).…”