SEASONAL CHANGES IN CANOPY WATER BALANCE OF JAPANESE PLANTATION FOREST

Abstract:

Stemflow, throughfall and canopy interception are some of the most critical parameters for hydrologic behavior and watershed management. When rainfall occur within forest ecosystem, small amounts of rainfall will be trapped by the tree canopy (Canopy interception – Ic) until it becomes saturated and canopy storage is exceeded, throughfall (TF) – precipitation which reaches the forest floor by passing through or dripping from the canopy, will occur. When the trunk storage capacity is exceeded, water will flow down the tree trunk and reach the ground as stem flow (SF).Among the factors that can affect to canopy water balance, seasonal change is one that requires further investigation (because of the differences in meteorological parameters). There have been some study focus on the changing of seasonal within forest ecosystem in different aspects such as soil respiration (Ivan Jessen, 2003), canopy structure (Deguchi et al, 2006) in different kind of forests including Mixed Temperate Forest (Christophe et al, 2000), tropical forest (Sawada et al), deciduous forest (Stalens, 2011). However, the effects of seasonal changes in evergreen forest can be underestimated because canopy structure undergoes very little change during seasons. Since the canopy remain unchanged, the meteorological factors have more effect on the canopy and which indirectly affects the interaction between soil, vegetation and atmosphere (Stalens, 2014). It is important to study the seasonal change in evergreen forest because it can affect the water regulation of the forest especially during dry seasons. The change in the transmission of the water can further affect the other meteorological factors, as they have an interdependent relationship. The goals of this study will be to examine the seasonal change and its effect on canopy water balance processes in Japanese plantation forests. Main findings of this study including: There are changes in the canopy water balance before and after thinning, and some differences between seasons. Within the partitioning of Pg, TF has the largest proportion (64.2%), followed by Ic (25.2%) and SF (10.6%). After thinning, TF rate increased to 12%, SF rate decreased to 4%, and Ic rate decreased to 8%. TF, SF, and Ic amount tend to be higher in summer and autumn but lower in winter and spring. TF and SF also tended to be higher during summer and autumn, but Ic rate is higher during winter and spring. TF, SF and Ic amount showed positive relationship with amount of Pg in all seasons. The TF and SF rate revealed strong relationship with gross rainfall in spring, summer and autumn but only mild relationship in winter. TF and Ic rate affected by wind speed in winter. Canopy saturation is different during season, it needed less water in spring to start stemflow and more water in summer to start SF.

Keywords: seasonal changes, throughfall, stemflow, interception, wind speed, gross rainfall.