The Natural Distribution of Livistona chinensis Past and Present

Including Livistona chinensis var. subglobosa and Livistona chinensis var. boninensis

There are three natural forms of Livistona chinensis formally known as Livistona chinensis (Jacq.) R.Br. ex Mart., Hist. Nat. Palm. 3: 240 (1838). from the Chinese mainland, Livistona chinensis var. subglobosa (Hassk.) Becc., Webbia 5: 16 (1920). from the Ryukyu archipelago of Japan & Taiwan, and Livistona chinensis var. boninensis Becc., Webbia 5: 12 (1921). from the Bonin Islands of Japan. However, these names have recently been taxonomically revised where Livistona chinensis var. subglobosa has been reduced to the species level as Livistona chinensis (Jacq.) R.Br. ex Mart., Hist. Nat. Palm. 3: 240 (1838). and Livistona chinensis var. boninensis is now Livistona boninensis (Becc.) Nakai, J. Jap. Bot. 11: 222 (1935).

Livistona chinensis var. subglobosa

Livistona chinensis var. subglobosa

Livistona chinensis var. subglobosa is perhaps justifiably not deserved of subspecies status, as the morphological differences are slight when compared with the Chinese mainland form. The main noticeable difference is to be seen in the size and shape of the seeds. The mainland China form, which is the commonest form in cultivation around the world produces a typically elongate, smaller seed (15 – 9 mm) than the Japan/Taiwan form which produces a larger, more globose seed (18 – 12 mm).

Livistona boninensis has had a much longer natural isolation, and differs in the height of the trunk being 18 m or more tall compared to 12 m for L. chinensis. Livistona boninensis‘ seeds are also larger but seldom ever as globose as L. chinensis var. subglobosa.

As I mentioned the mainland China form is by far the commonest form in cultivation with the main sources of seed being India, Pakistan, the USA and Europe. Livistona chinensis var. subglobosa from Taiwan and Japan is quite uncommon in cultivation outside of Taiwan and Japan, but is by far the most widespread and commonest form in the wild today. The former name of L. chinensis var. subglobosa was most useful as the indicator of provenance of the two main forms, and therefore identifying it as the Japan/Taiwan form and the most cold-hardy of the two (Zone 8b) (-6.7 to – 9.4). L. boninensis is equally as hardy.

Natural distribution of Livistona chinensis today

Livistona boninensis a palm native to Ogasawara-shoto or Bonin Islands (typical oceanic islands, located 1,000 km south of Tokyo, Japan), is endemic to several of the islands and introduced to the nearby Iwo (or Volcano) Islands. The Bonin Islands is a scattered archipelago of 20 or more rugged volcanic islands with many additional islets and rocks. The archipelago extends from the island of Mukojima in the north to the Iwo Islands in the south. The Bonins can be divided into three main clusters of islands: the Mukojima, Chichijima, and Hahajima-rettos groups. The native range of L. boninensis today is the Hahajima-retto group.
bonin-islands

The climate of the islands is subtropical, with a marked seasonal temperature variation, ranging from a sea level mean of 18°C in February to 25°C in July and August. A regular dry season occurs from January through March; sometimes there is also a secondary dry season in July and August.

The basal rocks of the Bonins were formed during the Tertiary 65 to 1.8 million years ago by submarine volcanic activity. Boninite, an andesitic volcanic rock rich in magnesium oxide, chromium, and silicon dioxide, is widespread, and is overlain in some areas by volcanic breccia. Most of the islands drop sharply to the ocean, with sea cliffs ranging from 50 to 100 meters in height.

The primary subtropical broad-leaved evergreen forest that remains on the islands can be classified into 3 major types. The palms occupy a dry forest on rocky slopes where the palm is a second dominant and is associated with Pandanus boninensis and Ochrosia nakaiana.

Livistona chinensis on the mainland of China no-longer has any truly natural wild stands of trees in any number. Small populations can still be found around Guangdong and on the island of Hainan. Although naturalised populations of the palm can be found in other areas of China and other South-East Asian countries, as well as some South Asian countries and Hawaii. The palm is commonly planted as a street ornamental throughout warm-temperate regions of the world.

Livistona chinensis var. subglobosa is naturally distributed from Taiwan through the islands of Okinawa and as far north as Kyushu, Japan, where it grows along shores washed by the warm Kuroshio current. However, due to it’s lowland habitat no wild populations exist in Taiwan today. In Japan, so called virgin L. chinensis forest is now found only on the islets of Aoshima and Tsukishima in the Miyazaki prefecture, Kyushu, Japan. The islet of the gods on Aoshima is the extreme northern limit of the species, and this is also officially recognised as the largest single population of the species in Japan consisting of 4000 individuals.

However, I report here, for the first time that by far the largest virgin population of Livistona chinensis var. subglobosa is to be found on a tiny island called Uotsurijima (Japanese) or Diaoyudao (Chinese). This is the largest island of the Senkaku Islands (钓鱼岛及其附属岛屿) or what we know as the Pinnacle Islands. Uotsurijima or Diaoyudao Island located at 25°44’39”N 123°28’26”E has an area of 4.3 square kilometres (1.7 sq mi) and a highest elevation of 383 metres (1,260 ft). L. chinensis is the dominant tree species on this island and I estimate this population to be over 100,000 individuals.

The Pinnacle Islands are a group of disputed, uninhabited islands currently controlled by Japan, but also claimed by both the Republic of China on Taiwan and the People’s Republic of China as part of Taiwan Province. The island group is made up of five small non-volcanic islands which sit on the edge of the continental shelf of mainland China, and are geologically separated from the Ryukyu Islands by the Okinawa Trough. Japan argues that these islets are part of the Ryukyu Islands. They are 170 kilometers (106 mi) north of Ishigaki Island, Japan; 186 km (116 mi) northeast of Keelung, Taiwan; and 410 km (255 mi) west of Okinawa Island.

The dispute appears to date from the 1968 announcement by two Japanese scientists that there may be large reservoirs of oil under the continental shelf below the islands. From the end of World War II until 1972, the United States occupied Okinawa, and controlled the islands, whose ownership was undisputed until 1970, when both China and Taiwan began to claim that the disputed islands were given to Japan in the Treaty of Shimonoseki in 1895 and should therefore be returned to Taiwan (after the end of World War II in 1945, all “unequal treaties” forced on China were declared void, including the Treaty of Shimonoseki, concluded in 1895). In 1971, the US expressed its intention to hand over the occupied territories, including the disputed islands, to Japan. Both the China and Taiwan governments protested and reiterated their claim to sovereignty over the islands. Taiwan made the official announcement on 11 June 1971, followed by China on 30 December. However, the United States handed over the disputed islands to Japan in 1972, even though they have not taken a definitive position on the sovereignty of the territory, considering the islands an “administrative territory” of Japan.

After losing the First Sino-Japanese War, Qing China signed the Treaty of Shimonoseki on 17 April 1895. This Unequal Treaty ceded Taiwan, Okinawa and its surrounding islands to Japan. The Chinese governments see the disputed islands as having been included in the islands ceded to Japan by the treaty, even though the Treaty did not explicitly enumerate all the islands ceded under it. On this basis, they argue for Chinese sovereignty over the islands for two reasons. First, that all the Unequal Treaties are null and void and thus the islands are still part of Taiwan Province of China. Secondly, that since the disputed islands were ceded along with Taiwan in 1895, therefore when Japan returned to China all territories it had obtained from China since the First Sino-Japanese War at the end of World War II, the disputed islands were returned along with Taiwan to China.

The first frustrating issue regarding this dispute is that no scientist can get anywhere near the island to evaluate the palm population or any of the other flora & forna. The Senkaku mole (Nesoscaptor uchidai) is an endemic mammal to the island and could, for all we know be extinct now. The second frustrating issue is regarding the feral goat population on the island, which is totally out of control. A sum total of 3 domestic goats were deliberately introduced to the island in 1978. There is now an estimated 300+ animals devastating the juvenile palm population, and due to the dispute over the island no government is prepared to send in hunters to eradicate the goats.

Distribution map for Livistona chinensis

Distribution map for Livistona chinensis

Natural distribution of Livistona chinensis in the past

The historical distribution of Livistona chinensis was certainly much more widespread than it is today. It is known to have occurred on Tsushima island (at latitude 34°N) located to the south of the Korean Peninsula. Evidence also points to the species being much more numerous on all the islands it occurs on today.

When haplotypes from the amplified DNA band patterns of the Japanese distribution of the species were compared by Japanese scientists they concluded the true origin of the species points to northern Taiwan, Iriomotejima, Ishigakijima and Okinawa in Japan. These same scientists also supported the hypothesis that natural distribution throughout its range in the islands occurred through oceanic drift of seeds on the Kuroshio current. I totally disregard this hypothesis based on the facts that viable seeds do not float even on salt-water, and that salt-water quickly kills the developing embryo within the seed.

Therefore, we need to look for lower sea-levels during the ice ages to see how distribution of this palm occurred. The current interglacial that we are currently enjoying started about 12,000 – 10,000 years ago when the planet warmed and the ice-caps started to melt making the sea-level rise. That last glaciation lasted roughly 100,000 years, where the Glacial Maximum occurred about 20,000 – 18,000 years ago, and it was at this time that the sea level was at its lowest, roughly 120-150 m lower than it is today.

China - Japan sea-levels during last Glacial Maximum

China - Japan sea-levels during last Glacial Maximum

As you can see from the map the lower sea-level explains how Livistona chinensis extended from Taiwan to Japan and Korea in the north, and to Hainan China in the south. However, this does not explain how the palm spread throughout the islands of the Ryukyu Archipelago of Japan. Nor does it explain how Livistona boninensis reached the Bonin Islands of Japan. For the palm to be able to reach, and spread through the Ryukyu from Taiwan the sea-level would have needed to be at least 400 m lower than today. To reach the Bonin Islands would have required a sea-level at least 1500 m lower than today. If we go back even further in time to evaluate even earlier Ice Ages then the Ice Age preceding the last occurred about 145 million years ago between the Jurassic and Cretaceous. But this Ice Age was not as cold, and did not produce very low sea-levels. Besides, we have not been able to find any palm relatives in the fossil record which date older than about 115 – 120 million years.

We have already mentioned that the Bonin Islands were formed during the Tertiary 65 to 1.8 million years ago by submarine volcanic activity. This same is true for the entire Philippine Arc of volcanic islands, which includes the Batan Islands of the Philippines and the Ryukyu Archipelago. The island of Taiwan is even younger and was formed less than 6.5 million years ago by the Luzon Volcanic Arc crashing into the Chinese continental margin and in doing so forced the land mass of Taiwan up from the sea bed.

The Pacific Rim, of which the Ryukyu is part was much hotter and far more active in the past, and during the last 1.8 million years has been rapidly cooling. With this the Ryukyu Archipelago and the Bonin Islands of Ogasawara-shoto have been sinking in a process called Ridge Subduction. Newly created, hot rocks are buoyant on the mantle, and therefore rise, displacing the seawater above it. Thus making shallow seas. As the rocks cool over time they sink further into the mantle. Making deep water above them. The full extent of the elevation they once were and the amount they have sunk is too difficult to quantify. But 1000 – 2000 m is not impossible, and this could be the answer we are looking for. Failing this the only explanation could be that seeds have been carried there by humans or birds, or that the seeds got there by floating on oceanic debris.

Conclusion: Livistona chinensis possibly occurred in the northern Taiwan area around 1.8 to 20 mya., but could have arrived there as late as 20,000 – 90,000 years ago. The species reached its maximum around 20,000 years ago when the sea-levels were 120 m lower than they are today. During this time its distribution stretched from southern China to Korea and as far north-east as Tokyo Japan. We assume that the islands of Ogasawara-shoto and Ryukyu Archipelago were much higher than they are today, and that 20,000 years ago they were still high enough to form a land bridge. Livistona boninensis became isolated at a very early stage, and Livistona chinensis has been slowly declining in numbers in recent times.