Relationship between resin flow on the surface of tree trunks and thinning rate and site conditoins in planted Chamaecyparis obtusa Endl. forests with heavy thinning

Abstract

In order to elucidate the causal relationship between heavy thinning and resin flow on the trunks of remaining Hinoki cypress (Chamaecyparis obtusa) trees without any external signs of physical or insect damage and fungal infection, relation between the resin flow and thinning rate and site conditions was studied in 35 Hinoki cypress stands from 11 districts of Kochi Prefecture. In addition, traumatic resin canal formed in secondary phloem under the starting point of resin flow was observed microscopically with 5 sample trees from two studied stands. Larval tunnels and/or feces of insects were also checked with the same samples. One or two tangential lines of traumatic resin canals were found in all the samples which differed from the many lines of traumatic resin canals characteristic of the "Rooshi resinous canker". Traces of insects were not found in inside as well as outside of the bark. Thus, the cause of the resin flow observed in the suited stands was considered not to be fungal infection and insect damage. The resin flow was not found in most of the control stands without thinning. Ratio of number of trees with resin flow to the total number of trees (RRF) increased with increasing rate of thinning. Number of the spots of the resin flow on individual trees also increased as thinning rate increased. RRF was lower in those stands on north-facing slopes and/or at altitudes of more than 1,000m than elsewhere. Number of the spots of the resin flow was fewer on the northern hemicycle than on the southern one of tree trunks. Based on these findings, it was concluded that the resin flow is a response of Hinoki cypress trees to some kind of environmental stress caused by heavy thinning and the level of the resin flow rises with the increase in the stress and varies with site conditions.