Latitudinal and altitudinal variations across temperate to subtropical forests from southern Kyushu to the northern Ryukyu Archipelago, Japan

Abstract

We studied the latitudinal and altitudinal variations in composition and species richness of trees in 24 plots across temperate to subtropical regions from southern Kyushu to the northern Ryukyu Archipelago, Japan. Cluster analysis based on presence/absence of species in 0.25-ha segments of the plots identified three forest zones reflecting climate and geohistory: cool-temperate mixed conifer-broadleaf forest (MF) north of the Tokara Gap (Kyushu and Yakushima), warm-temperate evergreen broadleaf forest (EBF) north of the Tokara Gap, and subtropical EBF south of the Tokara Gap (Amami-Oshima, Tokunoshima, and Okinawajima). The MF zone corresponded to Kira's Warmth Index (WI) < 100°C. The two EBF zones overlapped in the range of WI, and thus their boundary was determined by geohistory rather than by climate. Plot-level species richness per 400 stems increased with increasing WI, with decreased values in Yakushima, suggesting that geohistory (isolations from Kyushu as well as by the Tokara Gap) depressed the species richness of Yakushima. Greater species richness in the subtropical EBF was explained by the presence of species whose distributions were restricted to the south of the Tokara Gap, indicating that the size of tree flora influences the plot-level species richness. By contrast, lower species richness of MF in Yakushima than in Kyushu was due to the absence of species whose distributions were restricted to Kyushu northward, indicating the impoverishment of the cool-temperate flora of Yakushima. In conclusion, climate and geohistory shape the tree-community composition and diversity of old-growth forests in this transitional zone from temperate to subtropical regions.

A dataset for vascular plant diversity monitoring for the natural World Heritage site on Amami‐Oshima Island, Tokunoshima Island, and the northern Okinawa Island

“…The study sites on Amami‐Oshima Island, Tokunoshima Island, and Okinawa Island are protected as the Amamigunto National Park and Yambaru National Park. The surveyed plots were established either in or beside the “Specific Plant Community” by Biodiversity Center of Japan (1978, 1988, 2000), and permanent forest plots by Aiba et al (2019, 2021); Ishihara et al (2011); Ugawa (2020) to complement the quantity of each species and the composition of herbaceous species as mentioned in Introduction. The sites in southern Kyushu were established in the protected area of National/Prefectural Park or Prefectural Nature Conservation Area except for Plot H.…”

“…The study sites on Amami-Oshima Island, Tokunoshima Island, and Okinawa Island are protected as the Amamigunto National Park and Yambaru National Park. The surveyed plots were established either in or beside the "Specific Plant Community" by Biodiversity Center of Japan (1978,1988,2000), and permanent forest plots by Aiba et al (2019Aiba et al ( , 2021…”

“…Two different datasets, the National Survey on the Natural Environment (Biodiversity Center of Japan, 1978Japan, , 1988Japan, , 2000 and individual research in permanent forest plots (Aiba et al, 2019(Aiba et al, , 2021Ishihara et al, 2011;Ugawa, 2020), are currently available in Amami-Oshima Island, Tokunoshima Island, and the northern part of Okinawa Island. The National Survey of Natural Environment provides the community composition with coverage and sociability for each species for each layer by Braun-Blanquet approach, but is less quantitative than the latter dataset because the abundances are scaled into nonlinearly ordinally classes and the estimate was varied among individual observers.…”

Further food for thought: higher tropical mountains revisited once again

“…Kira (1991) first coined the term warm-temperate evergreen lucidophyll forest for the warm temperate evergreen formation in southern part of mainland Japan, north of Okinawa. However, the distinction between subtropical and warm-temperate forests in Japan is accounted by geohistorical isolation, and the physiognomy (including lucidophylly) and overall species composition is similar between the two formations (Aiba 2016;Aiba et al 2021). Lucidophylly (lucidus, Latin: shiny; Phyllon, Greek: leaf), that is leaves with shiny upper leaves, often also coriaceous and with revolute margins, are characteristic of evergreen woody species which occur in humid lightly to moderately frost prone, that is tropical subalpine and warm temperate climates (Ashton 2014).…”

Ecological management of insular forests: conservation of endangered species and native ecosystems in Ryukyu Archipelago

“…This special feature starts off with a paper with a large biogeographical scope that provides detailed comparisons among forest vegetation in Ryukyu Archipelago. In the first paper of Aiba et al (2021), the characteristics of plant species richness in the old-growth forests are provided. They pointed out that the high diversity in the forests south of Amami-Oshima Island may be due to the climatic factor of a larger warm index and the geohistorical factor of the existence of the Tokara Gap.…”