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. This tendency was similar at every observation period. Because the boundary between the observation time. The relationship between length of stem base and the ground is usually indistinct in big longest leaf (LL) and stem length (SL) is expressed by a tree ferns as a result of the accumulation of roots, we saturation curve, as the expanded allometric equation (2): hammered a nail 50 cm from the base of the stem in May 1/LL=1/(9.03 × SL0.87) +1/2.94 (R2 = 0.55) (4). 1997 to use as a reference point for measuring length. We At first, leaves become large quickly as the stem considered tree ferns that had at least one leaf with sori elongated, but the increment rate gradually diminished. (sporophylls) during the 3 years to be fertile. As a result, tree ferns with stems longer than 1 m usually bore leaves from 2 to 3 m in length (Fig. 3a). On the other Allometric analysis hand, the number of leaves (NL) increased proportionally The relationship between sizes of various plant parts (X with stem length throughout the range of observed stem and Y) was regressed by 2 allometric equations using lengths (Fig. 3b), expressed by the following simple least-squares regression: a simple allometric equation (1) allometric equation (1): and an expanded allometric equation (2): NL = 2.13 × SL0.24 (R2 = 0.52) (5). Y = aXb (1) Although Fig. 3a suggests that fertile tree ferns and have longer leaves than infertile ones, they do not 1/Y = 1/[aXb]+1/c (2), mean the sporophylls are longer than trophophylls on where a, b, and c are regression constants. Equation (2) the same stem. The comparison between sporophyll is derived from equation (1) based on the assumption and trophophylls on the same stem showed that the that the relative growth rate of Y decreases linearly as X former was significantly larger than the latter (t-test, P increases up to its upper limit of c (Ogawa et al. 1965). < 0.01). The leaf length changed seasonally: (longer in Relative growth rate summer and shorter in winter) even in infertile trees To determine the relative growth rate (RGR) of a plant ferns. Because most sporophylls emerged in summer part, we used the following equation: while trophophylls did in other seasons, the difference in

RGR = (ln Lf − ln Li)/T (3), length can be affected by the change of environment with where Li is the initial length [m], Lf is the final length [m], season. and T is the span of the measurement period [years]. Leaf phenology The numbers of newly emerged and dying leaves over RESULTS the 3-year study period with average 2.21 months interval Population structure are shown in Figure 4 (observations were conducted in In March 2000, there were 163 tree ferns with stems > the marked months). The numbers of dead and newly 5 cm in length in the plot (Fig. 2). Fifty-four individuals emerged leaves divided by the lengths of the observation (33%) of them had sporophylls at least one during the intervals are the values of the monthly rates of dead and study period of three years. The number of individuals newly emerged leaves, respectively, shown in Figure 4. decreased as stem length increased. The longest stem Leaves emerged throughout the year; but leaf emergence reached 3.33 m in March 2000, and 60% of them were was vigorous from spring to autumn. Old leaves also shorter than 50 cm. The tree ferns with stems longer died in an annual pattern similar to that of emergence than 1 m (24% of population) were fertile in most case. though the pattern of death was a little delayed than Many individuals were damaged by weed cutting in the that of emergence. As a result, the number of leaves per plantation during the study period. Then we analyzed the individual increased in spring and the end of summer. growth of 70 tree ferns that suffered little damage and Comparison between the climate data in Fig. 1 and leaf survived throughout the period. More than half of these phenology in Fig. 4 indicates that the leaf phenology had were larger than 1 m, and 70% of them were fertile. a pattern similar to that of temperature but not rainfall. Although leaves emerged through out the year, Length of leaves and stems trophophylls emerged mainly in summer, and sporophylls The relationships between stem length and longest leaf emerged from March to July. The sporophylls accounted length and between stem length and the number of for 26.4% of all leaves in the 3-year observation period. leaves in the individual are shown in Figure 3a and 3b, Spores were dispersed mainly from July to August. 50 Toru NAGANO and Eizi SUZUKI

��℃� 30 �� 1200

25 1000 �

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15 600

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0 0 �� 1997 1998 1999 2000 Fig. 1. Climate of Yakushima Island (Koseda) from March 1997 to March 2000.

80 �� 70 �� 60

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0 25 50 75 00 25 50 75 00 25 50 75 00 25 50 � � � � � � � � � � � � � � 0 0 0 1 1 1 1 2 2 2 2 3 3 3 ��

Fig. 2. The numbers of C. spinulosa in stem length size classes longer than 5 cm in March 2000. Leaf demography and growth pattern of the tree fern Cyathea spinulosa in Yakushima Island 51

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Fig. 3. Relationships between stem length and the longest leaf length (a) and between stem length and number of leaves per plant (b) in March 2000.

Leaf longevity months. We designated the leaves that had newly emerged at a The relationship between the half-life and emergence particular observation time as a cohort, and observed time of a cohort changed seasonally: those cohorts that their survival rates. Survival rate was relatively high emerged in winter to spring tended to have shorter during the first 4 months, but decreased rapidly in longevity than those of the emerged in summer to the following 6 months (Fig. 5). Between the 6th and autumn (Fig. 6). By comparison in the same cohort, 9th month, survivorship in all cohorts fell to less than sporophylls died an average of 0.9 months earlier than half. The average longevity of leaves in all cohorts was trophophylls (t-test, P < 0.01). No relationship between 7.12 months over this study period; the longest was 14 stem length and average leaf longevity for each individual 52 Toru NAGANO and Eizi SUZUKI

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Fig. 4. Numbers of emerging and dead leaves each month on 70 tree ferns from March 1997 to March 2000. Each mark indicates observation times.

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0 0 2 4 6 8 10 12 14 16 �� Fig. 5. Survivorship curves of leaves in 12 cohorts with different emergence times, which were observed completely from emergence to all death. Leaf demography and growth pattern of the tree fern Cyathea spinulosa in Yakushima Island 53

6 �� 5

4 � � � � � � � � � � � � � � � � � � � � � � � � � 1997 1998 1999 �� Fig. 6. Relationship between emergence time of leaves and the half-life of the cohort from March 1997 to March 1999.

300

250

200

150 ��

100 � � � � � � � � � � � � � � � � � � � � � � � 1998 1999 2000 �� Fig. 7. Seasonal change in mean length of newly emerged leaves of the 70 tree ferns from July 1998 to May 2000. Bars show standard deviation. 54 Toru NAGANO and Eizi SUZUKI

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Fig. 8. Relationship between stem elongation per leaf emergence and initial stem length over the 3-year study period.

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Fig. 9. Relationship between initial stem length (SLi) and relative growth rate of stem length (RGRSL) over the 3−year study period. Leaf demography and growth pattern of the tree fern Cyathea spinulosa in Yakushima Island 55 over the 3-year observation period (R2 = 0.0002). and SLi is initial stem length in March 1997. From the equation (6), if the environmental Leaf length conditions have been constant during the study period: Figure 7 shows the seasonal shift of average length of tree ferns of 5 cm in length will need 20 years to reach newly emerged leaves. The average leaf length over 1 m, 37 years to reach 3 m, and more than 100 years to the whole period was 207.6 ± 52.0 cm. Although the become 7 m length. difference was not clear, leaves emerging from winter to spring tended to be shorter. DISCUSSION Leaf emergence and stem elongation Leaf demography Because tree ferns show a palm-like growth form, the In C. spinulosa, although new leaves emerged mainly stems elongation and emergence of new leaves occurs in spring and summer, leaves emerged continuously together. The stem elongation per leaf was more variable throughout the year (Fig. 4). This pattern of leaves among small plants than among big ones (Fig. 8). On emerging throughout the year is found only in a few tree average, the stem elongated by 0.69 cm every time a new fern species, such as C. pubescens in the Jamaican cloud leaf emerged. forest (Tanner, 1983). Many tree ferns have a single leaf-ﬂush period in a year (Seiler, 1981; Ash, 1986, 1987; Stem growth Medeiros et al. 1992; Bittner and Breckle, 1995). Most Among the 70 tree ferns, an average of stem elongation tree fern species grow in areas of lower latitude with was 8.9 cm/year over the 3-year observation period. The less annual change in temperature than in Yakushima annual growth rate of stem length derived from equation Island. C. spinulosa growing on Yakushima Island with (3) showed an inverse relationship to length, because clearer seasonality has a more continuous leaf emergence smaller plants showed a higher growth rate (Fig. 9), pattern. The seasonality of phenology can be affected by expressed as two factors: climate and habitat. Areas with a signiﬁcant 2 RGRSL = –0.051ln(SLi) + 0.097 (R = 0.27) (6), seasonal climate change will support plants with a clear where RGRSL is the relative growth rate of stem length, seasonal phenology. An open habitat supports trees

Table 1. Growth rate and estimated age of stems and leaf longevity in tree ferns. Stem length Growth rate Leaf longevity Habitat (m) (cm/yr) (months) (forest type) Source Cyathea spinulosa 5 8.9 7.1 secondary this study

Cyathea contaminans 20 5.5−7 secondary Holttum (1963) Cyathea furfuracea 4 10.9 primary Tanner (1983) Cyathea pubescens 10 6.6 17.5 primary Tanner (1983) Cyathea woodwardioides 9 24.3 primary Tanner (1983) Cyathea hornei 4 16.8 primary Ash (1987) Leptopteris wilkesiana 2 24−30 primary Ash (1986) Alsophila salvinii 9 8.3 24.0 primary？ Seiler (1981) Alsophila bryophila 7 5.0 primary Tryon and Tryon (1982) Cyathea arborea 10 28.6 secondary Conant (1976) Alsophila erinacea 15 13.6 primary Bittner and Breckle (1995) Alsophila polystichoides 35 18.8 primary Bittner and Breckle (1995) Cyathea delgadii 5 21.3 primary Bittner and Breckle (1995) Cyathea delgadii 5 81.9 secondary Bittner and Breckle (1995) Cyathea nigripes 8 17.1 primary Bittner and Breckle (1995) Cyathea pinnula 2 10.1 primary Bittner and Breckle (1995) Cyathea trichiata 10 89.7 secondary Bittner and Breckle (1995) 56 Toru NAGANO and Eizi SUZUKI growing for longer periods than in a closed climax forest Individuals in good condition may share more resources (Kikuzawa, 1986). Some Cyathea species are conspicuous to stem elongation. As a result, they will become during secondary succession in tropical mountain successive individuals. The stem elongation is not only vegetation (for example, C. contaminans in Java and C. of advantage to C. spinulosa but also disadvantage. In elmeri in Mindanao (Whitmore, 1984)), although some tree ferns without secondary thickness of stems, the species seem to be adapted to life on the floor of mature stem elongation may be subject to break down. Though forest. C. spinulosa on Yakushima prefers sunny habitats adventitious roots on the stem increase with the stem such as small gaps in the forest. Hence, its continuous growth and may increase the strength,, they are soft and pattern of leaf phenology may be induced by its growing may not work as real stem. With the increase of stem habitat, not by climatic seasonality. height, the risk of break down increases. The advantage The average leaf longevity of 7.12 months is far of more light decreases with the increase of stem height shorter than that of the other tree fern species listed in because layer near ground is covered by small herbs Table 1 except C. contaminans (5.5−7 months, Holttum, but upper layer has less. Quick elongation of stem is 1963), a tall common tree fern growing open habitats in not needed or to be avoided for taller C. spinulosa. Then tropical mountains of Asia. Furthermore, it is shorter than the elongation of stem per leaf emergence converges the range of leaf longevity of 16 evergreen herbaceous to 0.7 cm. This is probably related to the increase in ferns in Japan (10−37 months), rather similar to 6 summer stem diameter (maximum of 20 cm): a thicker stem can green herbaceous ferns (6−7 months) (Yoshida and accommodate more leaves at the same height. Takasu, 1993). C. spinulosa and C. contaminans are living in secondary forests and prefer open habitats. The leaf Growth rate longevity seems to be strongly affected by the habitats. Bittner & Breckle (1995) reported that the height The leaf longevity and length also showed annual growth of secondary-forest species (80−90 cm/year) changes (Figs. 6 and 7). Leaves emerged in winter to were at least 4 times of the primary-forest species (10−20 spring tended to have shorter longevity and to be smaller cm/year) (Table 1). Although the growth rate of C. in length. The cold winter climate greatly decreased the spinulosa gradually decreased as stem length increased, number of emerged leaves and also affected the leaf the average annual growth in stem length was 8.9 cm/ length. The survivorship of leaves decreased sharply year. This is similar to the growth rates of primary- between the 4th and 7th months (Fig. 5). Many leaves forest species rather than secondary-forest species, that emerged in the late spring to summer were injured although the leaf phenology suggests that C. spinulosa is by strong winds (typhoons) in summer. This might be a secondary-forest species. The tree fern species studied the cause of the shorter longevity of sporophylls. Shorter in the cited reports here are all tropical species, and the leaf longevity requires the plant to make new leaves to maximum height of such Cyatheaceae is 35 m, whereas maintain its life. The leaf survival strategy of pioneer the maximum height of C. spinulosa is 5 m (Large & species is characterized by longer-term leaf emergence Braggins, 2004). Such difference of maximum height may and shorter leaf longevity compare to climax tree species be related the slow growth rate of C. spinulosa. (Kikuzawa, 1986, 2005). The shorter longevity of leaves The stem lengths of 80% of the individual tree ferns and their continuous emergence whole the year in C. found in the plot were less than 2 m. If these individuals spinulosa might be related to its preference for open grew at the above-mentioned rate of 8.9 cm/year, their habitats. age can be at most 30 years. Even the largest tree fern found in the plot is only about 40 years old, nearly Stems and leaves coinciding with the age of the conifer plantation. There For the mean leaf longevity of C. spinulosa was 7.12 are few individuals that grow larger than 4 m; thus, the months, its annual leaf production was more than existing lifespan of C. spinulosa might be less than 50 years on leaf number. Bigger individuals tended to have more Yakushima Island. leaves than smaller ones (Fig. 3) and need more leaf production. The production of new leaves accompanies Population structure the stem elongation. It is apparently of advantage to small In addition to the original 163 tree ferns shown in Figure individuals: Because such individuals may get more 2 there were many smaller ones (< 5 cm) inside and light as grow larger. Figure 8 shows great variation of around the plot. Most of these small tree ferns were stem elongation per leaf emergence in small individuals. living on the floor of the conifer plantation in the northern Leaf demography and growth pattern of the tree fern Cyathea spinulosa in Yakushima Island 57 strip of the plot; fewer were found in the secondary Fu, L.K. (ed.) 1992. China Plant Red Data Book: Rare and forest in the southern strip of the plot during the study Endangered Plants, Vol. 1 Science Press, Beijing period. The northern strip had denser canopy trees and New York. thinner understory vegetation than the southern strip. Holttum, R.E. 1963. Cyatheaceae. Flora Malesiana Ser.2− The environment of the former seemed to be suitable for Pteridophyta, Vol. 1(2): 65−169 N. V. Er ven P. establishment of small tree ferns. Noordhoff, Groningen. In this study, the smallest mature tree fern was 27 Iwatsuki, K. (ed.) 1992. Ferns and Fern Allies of Japan. cm in length, and it was estimated to be 9 years old since Heibonsha, Tokyo. (in Japanese). it started making its trunk from the equation (6). Not all Kikuzawa, K. 1986. Leaf survival strategy of forest tree ferns longer than 27 cm in length make sporophylls trees. Japanese Journal of Ecology, 36: 189−203 (in every year, but most tree ferns longer than 70 cm (ca. 15 Japanese). years old) did. Kikuzawa, K. 2005. Ecology of Leaf Longevity - from During the study, no tree ferns died naturally in Individuals to Ecosystems. Kyoritsu Publisher, the conifer plantation, but a few died in the secondary Tokyo (in Japanese). forest. On these tree ferns, the numbers and length Large, M.F. & Braggins, J.E. 2004. Tree Ferns. Timber of leaves gradually decreased until they had all died. Press, Cambridge. It might be due to decreases in light level caused by Medeiros, A.C., Loope, L.L., Flynn, T., Anderson, S.J., dense thickets of Gleicheniaceae ferns in the secondary Cuddihy, L.W. & Wilson, K.A. 1992. Notes on the forest. Our observation showed that C. spinulosa has the status of an invasive Australian tree fern (Cyathea characteristics of pioneer plants and that they preferred cooperi) in Hawaiian rain forests. American Fern relatively open sites such as along roadsides, stream Journal, 82: 27−33. sides, or valleys. The cutting of understory vegetation Ogawa, H., Yoda, K., Ogino, K. & Kira, T. 1965. in conifer plantations may contribute to maintaining Comparative ecological studies on three main types the open habitat. Because such sites do not persist in of forest vegetation in Thailand. II. Plant biomass. nature, tree ferns must spread to other sites by spore Nature and Life in Southeast Asia, 4: 49−80. dispersion. C. spinulosa makes small populations in new Ough, K. & Murphy, A. 1996. The effect of clear fell open habitats and they will vanish over a few decades, logging on tree-ferns in Victorian wet forest. but it will continue to exist moving from sites to sites on Australian Forestry, 59: 178−188. Yakushima Island. Seiler, R.S. 1981. Leaf turnover rates and natural history of the Central American tree fern Alsophila salvinii. ACKNOWLEDGMENTS We sincerely thank American Fern Journal, 71: 75−81. the staff of the Yakusugi Museum and students of the Tanner, E.V.J. 1983. Leaf demography and growth of Ecological laboratory of Kagoshima University for their the tree-fern Cyathea pubescens Mett. ex Kuhn in assistance in the field. We also thank Dr S. Aiba, Dr K. Jamaica. Botanical Journal of the Linnean Society, Tomiyama, and Dr Sk. Yamane of Kagoshima University 87: 213−227. for their comments on the manuscript. We also thank the Thomlinson, P.B. 1990. The Structural Biology of Palms. anonymous reviewers for their helpful criticism, useful Clarendon Press, Oxford. comments and suggestions. Walker, L.R. 1994. Growth and fertilization responses of Hawaiian tree ferns. Biotropica, 26: 378−383. Whitmore, T. C. 1984. Tropical Rain Forest of the Far REFERENCES East, 2nd ed. Clarendon Press, Oxford. Ash, J. 1986. Demography and production of Leptopteris Yoshida, C., Takasu, H. 1993. Leaf life-span in some wilkesiana (Osmundaceae), a tropical tree-fern from ferns of the Kii Peninsula I. Acta phytotaxonomica et Fiji. Australian Journal of Botany, 34: 207−215. geobotanica, 44: 59−66. (in Japanese) A s h , J . 1987. Demography of C y a t h e a h o r n e i (Cyatheaceae), a tropical tree-fern in Fiji. Australian Received 13th Sep. 2005 Journal of Botany, 35: 331−342. Accepted 09th Mar. 2006 Bittner, J. & Breckle, S.W. 1995. The growth rate and age of the tree-fern trunks in relation to habitat. American Fern Journal, 85: 37−42.