Resources plant studies on the natural forest in subtropical Okinawa VH. About plant distribution on the main islands of the Ryukyus

摘要

Within the frame work of a series of plant resource studies on the natural forests in the subtropical Okinawa, the present study was undertaken to clarify the distribution of forest plant for both indigenous and exotic species on the Ryukyu Islands, especially for the 4 main Islands, i.e. Okinawa, Miyako, Ishigaki and Iriomote Islands in the Ryukyus based on the database of the five reference books. The considerable difference was found for the total number of species among the references. The plants distributed in the entire Ryukyu Islands were 238 families, 1,688 genera and 5,473 species based on Flora of the Ryukyus, Southern of Amami Island (FRSAI), which had the highest number of species, while Flora of Okinawa and Southern Ryukyu Island (FOSRI, 1976) recorded 239 families, 1,061 genera and 2,560 species. According to Check List Vascular Flora of the Ryukyu Islands (CLVFR), 200 families, 949 genera and 2,275 species were present. Flora of the Ryukyus (FR) recorded the least species with a total of 182 families, 863 genera and 2,142 species. The methods of the handling of plant distribution to the exotic species may be responsible for the obvious differences in the main factor on the total number of species among these references. For the composition of the indigenous species, in Okinawa Island, 1,451 (FR), 1,445 (FRSAI) and 1,404 (CLVFR) species were recorded; l,099(FR), 1,132 (FRSAI) and 1,119(CLVFR) species in Ishigaki Island; 1,151(FR), 1,139 (FRSAI) and 1,142(CLVFR) species in Iriomote Island. No obvious differences were found among the 3 references. Moreover, for the abovementioned indigenous species, the order of species number were Okinawa > Iriomote > Ishigaki > Miyako. As for the least value of indigenous species in Miyako Island, it is thought that the greater part of the Island is covered with the limestone of the upheaval coral reef, and the mountainous forest plant is less than other Islands because of its smooth landform on the Island. Each reference recorded a lot of endemic plants in the Okinawa Island, with 16 species recorded in VJOO, 15 species in FR, and 33 species in CLVFR, while Iriomote Island had the second highest value for endemic plants with 13 species recorded in VJOO, 10 species in FR and 9 species in CLVFR. In Miyako or Ishigaki Islands, few endemic plants were present with a range of 1-3 only.%本研究は、亜熱帯沖縄における天然林の資源植物学的研究の一環として、亜熱帯・沖縄県の主要島嶼の沖縄島、宮古島、石垣島、西表島を対象に既応の著書・文献を用いて分布植物のデータベース化をはかるために森林植物を中心とした全ての在来植物の分布種及び外来種を明らかにするために行ったものである。琉球列島全体の分布植物は、琉球植物目録（FRSAI、1994）で238科、1688属、5，473種で最も多く、Flora of Okinawa and Southern Ryukyu Island（FOSRI、1976）で239科、1，061属、2，560種、琉球列島維管束植物集覧（FRSAI、1997）、200科、949属、2，275種、琉球植物誌（FR、1975）182科、863属、2，142種の順であった。全体的に総分布種は文献間に差異があり、その主な要因は外来種の分布の取り扱いによるものと思料される。在来植物の種の構成は沖縄島FR1，451、FRSA1 1，445、CLVFR1，404、宮古島FR 640、FRSAI 656、CLVFR 633、石垣島 FRl，099、FRSAI 1，132、CLVFR 1，119、西表島FR 1，151、FRSAI 1，139、CLVFR1，142で各島嶼とも分布種に大きな差異はなかった。また、島嶼別の在来種は沖縄島＞西表島＞石垣島＞宮古島の順であった。宮古島が最も少ないのは、同島の大部分が隆起サンゴ礁の石灰岩でおおわれ、平坦な島であるため、分布植物において山地性植物の森林植物が他島に比べて少ないものと思料される。島嶼別固有植物はいずれの文献も沖縄島に多くの固有植物が分布しVJOO 16種、FR 15種、CLVFR 33種であった。ついで西表島で多くVJOO 13種、FR 10種、CLVFR9種、宮古島、石垣島では1～3種であった。