Quantitative description of site characteristics of 'Urajiro (Gleichenia japonica Spr.)-Koshida (Dicranopteris linearis Burm. f.) type' as an undergrowth type of Hinoki cypress (Chamaecyparis obtusa Endl.) plantations
2007
Watanabe, N.(Kochi-ken. Forestry Technology Research Center, Kami (Japan)) | Kajihara, N. | Tsukamoto, J.
Two species of fern, Urajiro (Gleichenia japonica Spr.) and Koshida (Dicranopteris linearis Burm. f.), often grow to form an extremely dense undergrowth in coniferous plantations, especially in Hinoki cypress (Chamaecyparis obtusa Endl.) plantations on more or less poor soil. They are considered to be a serious obstacle to the forest management aiming at laborsaving and improvement of public functions of forests in which coniferous plantations are left untouched after heavy thinning and shifted naturally to mixed forests of coniferous and broad-leaf trees. In this context, characteristics of the sites dominated by the two ferns was described quantitatively in order to demarcate those sites unsuitable for the management mentioned above. Undergrowth vegetation of Hinoki cypress plantations was divided into two types, 'Urajiro-Koshida type' and 'Others', based on the combined coverage of the two ferns. Site index, chemistry of the surface soil, and topography of the stands were contrasted between the two types. Relative frequency of the Urajiro-Koshida type was clearly higher among the stands of lower site index ( 14.0), although separation of the two types in terms of site index was not complete. Higher acidity (pH (H2O) 5.0), lower contents of exchangeable Ca Mg and K, higher content of exchangeable Al and higher C/N were characteristic of the Urajiro-Koshida type. Clear-cut ridge-shaped slope was the typical topography of the Urajiro-Koshida type. Based on these findings, we proposed the following site conditions as unsuitable for the forest management mentioned above: site index of Hinoki cypress lower than 14.0, pH (H2O) of the surface soil lower than 5.0, and topography of clear-cut ridge-shaped slope.
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