Bull. Kitakyushu Mas. Nat. Hist., 16: 113-135. March 28, 1997 Vegetation Structure of a Secondary Grassland at a Line Corridor in Fukuchi Mountain System, Northern Kyushu Tohru Manabe1, Kazuaki Naito2 and Nobukazu Nakagoshi3 'Kitakyushu Museum and Institute of Natural History, Nishihonmachi 3, Yahatahigashiku, Kitakyushu 805, Japan 2Department ofAnimal Production, Chugoku National Agricultural Experiment Station, Kawai-Cho, Oda, Shimane 694, Japan 3Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739, Japan (Received December 5, 1996) Abstract Vegetation structure was studied at a line corridor which has been formed and maintained as fire prevention belt by periodic mowing at the ridge of a mountain system, northern Kyushu. Grassland herbs were dominant, although forest herbs which usually grow on forest floor occurred at the corridor. The grassland at the corridor was identified phytosociologically as Bupleuro-Miscanthetum sinensis belonging to Arundinello-Miscanthion sinensis alliance. The corridor was classified as trough corridor, because its vegetation height was lower than that of the adjacent matrix. The corridor was composed of various kind of tessera which were brought by many types of landscape element at the adjacent matrix, microtopography and surface geology at the corridor. Those tessera were distributed heterogeniously over the corridor. Distribu tion patterns of the plant species within the corridor were also affected by those of the tessera. Thus, this narrow line corridor had the function of habitat for many grassland herbs which are becoming rare. And variety of the tessera brought about variety of landscape structure generated high composition diversity of the plant species at the corridor. Introduction Secondary grasslands, which were one of the main landscape element types (Forman and Godron, 1986), had been maintained by mowing and pasturage under the traditional sustainable land use systems inJapan (Naito and Nakagoshi, 1994). Popularization of petroleum fuels and chemical fertilizer in the 1960's, which is called the fuel revolution, led to abandonment of the traditional land use, and brought about rapid and drastic changes in distribution patterns of landscape elements (e.g. Kamada and Nakagoshi, 1996). Secondary grasslands are one of the typical landscape elements which have rapidly decreased in area since the fuel revolution (Someya et aL, 1989; Naito and Nakagoshi, 1994; Shoji et aL, 1995). The collapse of traditional land use systems also made some grassland species become rare, since 114 Tohru Manabe, Kazuaki Naito and Nobukazu Nakagoshi secondary grasslands were favorable habitats for them (The Investigation Commit tee for Important Plant Species and Communities for Conservation in Japan, 1989). In northern Kyushu, secondary grasslands are distributed on limestone plateaus showing patch shape in suburb landscape. These grasslands function as habitat for some grassland species (The Kitakyushu Municipal Education Board, 1973; Naito et aL, 1995). Secondary grasslands also distribute on the ridge of the moun tains located at the suburb. These grasslands, which have been formed and maintained as fire prevention belt by periodic mowing, take the form of line corridors. The line corridors with secondary grasslands are surrounded with various kinds of matrix such as coppices and conifer plantations, and are on the mountain ridges with various microtopography. These line corridors might contain many kind of tessera (Forman and Godron, 1986) which were brought by the various matrix, microto pography and so on. Thus, these secondary grasslands established at the line corridors might be also complex of microsites with various microenvironmental conditions for plant species. But, flora of these line corridors has not been reported because of its strip figure with nallow width. Further, there are few evaluation of these line corridors as habitat for grassland species. Corridors, which are defined as "narrow strips of land that differ from the matrix on either side" (Forman and Godron, 1986), perform well known functions in landscape such as habitat, conduit and filter (or barrier) as well as functions known empirically or conceptually such as source and sink (Forman and Godron, 1986; Saunders and Hobbs, 1991; Smith and Hellmund, 1993; Forman, 1995). Those five major functions of corridors in landscape are affected not only by biological attributes such as kind, number and /or biomass of living things growing within the corridors and at the matrix adjacent the corridors, but also by pattern and process of landscape structure such as width, length, connectivity and curvinearity of corridors, relationships to the matrix, origin of corridors and so on (Forman and Godron, 1986; Crome and Richards, 1988; Saunders and Hobbs, 1991; Smith and Hellmund, 1993; Forman 1995). Habitat and conduit functions of corridors are also important on the view pointof biological conservation, because these functions might havea roll to promote interchange among individuals in isolated sub-populations within fragmented landscape (Saunders and Hobbs, 1991; Forman, 1995). Although habitat and conduit functions of corridors have been analyzed for birds, mammals and insects growing within corridors (e.g. Adams, 1984;Opdam et aL, 1984, 1985; Kealv and Majer, 1991; Lynch and Saunders, 1991; Andreassen etaL, 1996), only a few works have done those for plants (McDowell et aL, 1991; Johansson et aL, 1996; Riffell and Gutzwiller, 1996). Structural and functional features of corridors have discussed mainly on wooded strip corridors at flat plain suchas hedgerows and on stream and river corridors such as riparian forests, but few on corridors with complex three-dimensional form such as those located at the ridge Secondary Grassland at a Line Corridor 115 of mountains in northern Kyushu. In this paper, we describe the vegetation structure of a secondary grassland at a line corridor which might contain many kinds of tessera and the matrix surrounding a corridor. And we discuss the feature of habitat and conduit function of the line corridor, especially those for grassland plant species. Nomenclatures are followed by Ohwi and Kitagtawa (1992) for Sperma- tophytes and by Iwatsuki (1991) for Pteridophytes. Study Site The line corridor locates at the ridge of Fukuchi mountain system (33°43'N- 33°40'N, 130°48'E-130°49'E) ranging north to southeast across Kitakyushu City, Akaike-cho, Houjo-cho and Kawara-cho in Fukuoka Prefecture. This corridor has been formed and maintained as fire prevention belt by periodic mowing. Then, the corridor have secondary grassland owing to periodic human impacts, and it has been also using as the path along the ridges for mountain climbers. The corridor has about 10 m width, while it has more than 6,000 m length. That is, this corridor is classified as a line corridor (Forman and Godron, 1986). Many peaks within the corridor such as Mt. Fukuchi (900 m), Mt. Akamutanotsuji (791 m) and Mt. Yakitate (759 m) generate complex three-dimensional structure having ca. 250 m disparity in a.s.l. (Fig. 1). Various types of vegetation such as deciduous broad- leaved forests and evergreen broad-leaved forests occur over the mountains, although Japanese seder {Cryptomeria japonica (Linn, fil.) D. Don) plantations are most dominant. The surface geology of the corridor is classified as three types: northern part and southern part of the corridor are dominated by metagabbro and quartz- porphyry, respectively, the middle site formed by shale, sandstone or conglomerate is a little (Fukuoka Prefecture, 1970). Methods An actual vegetation map of the rectangle area, which contains line corridor, with 1 km width and 6 km length was drawn at a scale of 1: 25,000. The boundary of each landscape elements, which are recognized by homogeneous physiognomy, was determined by using air photographs taken in 1994 at a scale of 1 :20,000 by the Geographical Survey Institute, the Ministry of Construction. Phytosociological survey of vegetation (Braun-Blanquet, 1964) was conducted at thirty two of 2 mX2 m quadrats established at a central part of the corridor in the middle of May, 1996 (Fig. 1). Vegetation and microtopographical structure of the corridor and adjacent matrix were analyzed at 10sites in the middle of September, 1996. The inclination of each 1m was measured on a 10m line which was parallel to the corridor at each site. Another line was established at each site so as to cross Mt. Fukuchi 1,0001— Mt. Akamutanotsuji (901 m) (791 m) Mt. Yakitate (759 m)13^3*4 *1 21 90 B1 A H > S 500 31 29 27 > O 3 oL 500 m Fig. 1. Maps showing the study area. Dots; quadrats investigated composition of vegetation, asterisks; sites investigated vertical structure of vegetation. Secondary Grassland at a Line Corridor 117 the corridor and both side of the matrix, that is, this line and the 10 m line were at right angles. Vegetation structure such as names and diameter at breast height (d.b.h.) of dominant species and vegetation height were recorded within both 1 m sides of the line. Microtopographic locations of the quadrats and the sites were also recorded according to Tamura (1980). Results Landscape structure The curvilinearity of the corridor on the horizontal projection was low, although the corridor branched complexity at the southern end of it (Fig. 2). The main part of the corridor ranging north to southeast connected five branch corridors from west side and one branch corridor from east, indicating that the corriodor formed relatively simple network. The twelve types of landscape element were identified such as evergreen broad- leaved forests dominated by Quercus acuta Thunb. and Neolitsea sericea (Blume) Koidz., evergreen broad-leaved and deciduous broad-leaved mixed forests (hereafter mixed forest) composed of above evergreen trees and Q. serrata Thunb. and Carpinus tschonoskii Maxim., pine forests dominated by Pinus densifiora Sieb. et Zucc or P. thunbergii Parlet., plantations of Cryptomeria japonica or Chamaecyparis obtusa (Sieb. et Zucc.) Sieb. et Zucc, apud Endl., dwarf bamboo communities dominated by Sasa senanensis (Franch. et Savat.) Rehder, grasslands dominated by Miscanthus sinensis Anderss., and so on.