Dripping Rainfall from Detached Stemflow Influences Throughfall Near Boles in a Japanese Cedar Forest

Abstract

Throughfall near the trunk was measured for three Japanese cedar (Cryptomeria japonica) trees by installing water pools around tree boles in a Japanese cedar plantation forest. These amounts were compared with throughfall index measured using 10 storage-type rain gauges, which generally measure throughfall in the forest. Observations of rainfall, throughfall, and stemflow during rainfall of three targeted trees clarified that processes of rainwater collection at the tree canopy and stemflow generation differed among trees, as did the probability of departure from the trunk. The total annual throughfall near the trunks was approximately equal to the average throughfall index observed using 10 storage-type rain gauges, but less than the throughfall index during a low rainfall event and greater at times of heavy rainfall, which sometimes recorded twice the throughfall index. Results demonstrated the possibility of underestimating throughfall amounts when near-trunk throughfall is ignored during heavy rainfall.