Tropics 16-1.Indb

TROPICS Vol. 16 (1) Issued January 31, 2007 Leaf demography and growth pattern of the tree fern Cyathea spinulosa in Yakushima Island ＊＋ Toru NAGANO and Eizi SUZUKI ＊ Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890−0065, Japan ＊ +Faculty of Science, Kagoshima University, Kagoshima 890−0065, Japan ＊＊ Tel.: +81−99−285−8942, Fax: +81−99−285−8942, E-mail: [email protected] ABSTRACT We studied the growth and leaf species. Cyathea species are important component to demography of tree fern Cyathea spinulosa Wall. ex give the subtropical characteristics to Yakushima. This Hook at a 40 m × 100 m plot with 163 tree ferns island is famous as the World Heritage Area, more than in lowland of Yakushima Island, southern Kyushu 2500 reports have been made about the island (Data base to clarify its life history. The 70 healthy individuals of Yakushima World Heritage Conservation Center). were periodically observed (16 times) from March There are only five short reports about geographic 1997 to March 2000. The numbers and lengths distribution of Cyathea in Yakushima. The ecology of of leaves on a stem increased with stem length up Cyathea has never been studied in Yakushima, and also to 20 leaves of a maximum of 3 m in length. Most in Japan. How long does it live? How big does it become? sporophylls flushed in spring and most trophophylls How is the phenology of the evergreen leaves? There is flushed in summer, although a few leaves emerged no study to answer for these questions for C. spinulosa. continuously all year around. Leaf death followed In the world, tree ferns have been studied for these the annual pattern of emergence with some delay. questions by several authors. Seiler (1981) studied leaf Leaf longevity was greater on leaves that emerged demography of Alsophila salvinii in El Salvador. From in summer than those in other seasons; the average leaf production rate and number of leaf scar on trunk leaf longevity was 7.1 months. The growth rate surface, he estimated longevity of individual. Tanner of the stem decreased gradually as stem length (1983) studied demography and survivorship of leaf increased; the average annual growth in stem length about Jamaican tree fern Cyathea pubescens. He also was 8.9 cm/year. The lifespan of individual tree estimated tree fern age using the same method with ferns in Yakushima Island were estimated less than Seiler (1981). Bittner and Breckle (1995) studied tree 50 years. The pattern of continuous leaf emergence ferns in Costa Rica and reported that the growth rate of and the short leaf longevity may result from its tree fern trunks is influenced by habitat. Ash (1986, 1987) pioneer habit in the successional stage. studied Leptopteris wilkesiana and C. hornei in Fiji. In addition to leaf production rate, leaf longevity and stem Keywords: Cyathea spinulosa , tree fern, leaf growth, he reported spore production rate and biomass demography, leaf longevity, Yakushima Island. allocation. Ough and Murphy (1996) studied the effect of clear fell logging on tree ferns, Dicksonia antarctica and C. australis in Australia. They suggested the reduction of INTRODUCTION tree ferns affected to flora and fauna widely. Medeiros et Ferns with erect, arboreal trunks are called tree ferns. al. (1992) report on population structure and vegetation Most tree ferns belong to the family Cyatheaceae and cover rate of invasive Australian tree fern C. cooperi into comprise about 900 species in the tropical and subtropical Hawaii. Walker (1994) studied the growth of Hawaiian zones of the world, with a few species extending into the tree fern Cibotium glaucum in different stage of forest lower latitudes of the warm temperate zones (Large and succession and reported that nitrogen set limit to growth Braggins, 2004). Yakushima Island, southern Kyushu in the early stages of primary succession. There is locates in warm temperate zone near boundary with no study about life history about Cyathea in Asia. The subtropical zone, and has three native species of Cyathea. purpose of this study is to clarify growth of C. spinulosa, Cyathea spinulosa is most common among the three on Yakushima Island through the monitoring of its stem 48 Toru NAGANO and Eizi SUZUKI elongation and leaf demography. to be facing extinction in various parts of the world Tree ferns have a single meristem at the top of their (Fu, 1992). In Japan, it has become a rare and precious stem, no branches, and no cambium to increase their species, especially on the islands of Kyushu and Honshu. diameter; hence they show a palm-like growth pattern. On Yakushima Island in southern Kyushu, however, C. Having a stem that can only elongate without lateral spinulosa is common in open habitats at elevations mainly growth limits the life of the plants. The oldest recorded below 400 m; the highest point was 700 m (personal age of a palm is only about 150 years for a species of the observation). genus Roystonea (Thomlinson, 1990), a much shorter lifespan than trees that are capable of living many Study site hundreds of years. Though C. spinulosa may have a A study plot was set up in Anbo (lat. 30˚18 ′31 ″N, long. similarly limited lifespan, the stem growth and life span of 130˚38′08″E) on the eastern coast of Yakushima in March this species has never been studied. 1997. The plot lies in the warm-temperate zone near the The characteristics of leaves, such as their shape, border of the subtropics; at Koseda, 8 km north-northeast arrangement, and phenology, are critically important of the plot, the annual mean rainfall was 4358.8 mm and for plants. For the umbrella-shaped evergreen crowns the annual mean temperature is 19.2˚C determined from of tree ferns, the leaf number and sizes are important 1971 to 2000 data from the Japan Meteorological Agency. in determining the most effective arrangement of the The monthly changes in climate during the study period photosynthetic organs. The leaves are dynamically are shown in Figure 1. maintained, with the emergence of new leaves and the The plot was 40 m × 100 m and set on a moderate death of old leaves. The longevity and phenology of the to steep slope (0 to 45 degrees) at an elevation from leaves are thus important in developing the most effective 150 to 170 m. A small stream flowed from west to east crown shape. In evergreen trees, there are many types of dividing the plot into two strips. The northern strip (about leaf phenology and longevity, which are strongly related 70% of the plot area) was in a plantation of Cryptomeria to the life-history strategy of the plant. For example, the japonica about 40 years old and the southern strip was in leaves of pioneer species tend to be shorter lived than a secondary broadleaved forest of Castanopsis cuspidata those of late-successional species (Kikuzawa, 1986). var. siebolidii. Although the conifer forest in the northern strip was managed as a plantation with periodic cutting of weeds, the southern side had been neglected for METHODS a long time and the floor was densely covered with 2 The tree fern species of Gleicheniaceae fern, Gleichenia japonica and Cyathea spinulosa Wall. ex Hook. is a common tree fern Dicranopteris linearis. Other tree ferns C. metteniana and in mid-latitudinal Asia, mainly living in wet forests. It is C. hancockii are found on Yakushima Island, but they are distributed from southern Japan, through South China, to rare and were absent from this plot. the northeastern Himalayas (Iwatsuki, 1992). In southern In March 1997, all leaves and stems of tree ferns Japan, it lives in the subtropics and the southern parts of with stems > 5 cm in length were numbered with plastic warm temperate forests. The maximum height is usually tags and aluminum wire, and the number of leaves (NL), 3 m although it occasionally reaches 5 m. Bi-pinnate length of the longest leaf (LL), stem length (SL), and evergreen leaves extend radially from the stem apex; position were recorded for each tree fern. They were these leaves can be up to 3 m long and 1.2 m wide. After periodically monitored (16 times) until March 2000. , leaves died, the leaf stalk bases don t shed and remain At each monitoring time, newly emerged leaves on attached on stem for long time: leaf scars are not found each plant were tagged with new numbers, and their on trunk surface. The diameter of the stem is as large lengths (from July 1998) were measured. The lamina as 20 cm in the upper part and 40 cm at the base when gradually changed from green to brown on the old leaves; covered with adventitious roots. when the whole of the lamina had turned brown we The populations of tree ferns are diminishing considered that the leaves had died and removed them rapidly in various regions. In 1975, the genus Cyathea, from the stem. From the numbers of dead and newly include most of Cyatheaceae species, became listed in emerged leaves, we can know the number of living leaves Appendices II by CITES (the Convention on International and their longevity. Trade in Endangered Species), are under restrictive trade We measured stem length every March. We (Large and Braggins, 2004). Cyathea spinulosa appears measured stem length rather than vertical height Leaf demography and growth pattern of the tree fern Cyathea spinulosa in Yakushima Island 49 because many of the tree ferns were grown on slopes respectively. Bigger ferns tended to have longer and and their stems often became inclined during the 3−year much more leaves.

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