Juvenile Height Growth in the Subtropical Evergreen Broad- Title Leaved Forest at Chichijima in the Bonin (Ogasawara) Islands
Author(s) Shimizu, Yoshikazu
Memoirs of the Faculty of Science, Kyoto University. Series of Citation biology. New series (1985), 10(1): 63-72
Issue Date 1985-03
URL http://hdl.handle.net/2433/258871
Right
Type Departmental Bulletin Paper
Textversion publisher
Kyoto University lrV{EMoll(s ol? Tl¥IE FAcul,.Ty ol; SCrENcE, Kyorro UNIvERslTy, SERIEs oF BIoLoGy Vol. X, pp. 63-72, March 1985
Juvenile Height Growth in the Subtrepical Evergreen Broad-Leaved Forest at Chichijima in the Bonin (Ogasawara) Islands
By
YOSHIKA7..U SHIMIZV
Laboratory for Piant Ecological Studies, Faculty of Science, Kyoto University, Kyoto 606
(Received August 25, 1984¥)
Abstract. Juvenile height growth of l9 species (277 individuais in total) was measured annually fi'om 1977 to 1982 in a forest, 5-6 m high, dominated by Distylium lepidotttm, at Chichljima. Juveniles ofmain canopy trees showed the rate o{' height growth, not more than 2 cmfyear, which was lower than that of the shrub and the second-layer species. The death of terminal shoots and the occurrence of new leaders were frequently observed in a}most all species. The sharp decrease in the annual height growth and the increase in the death rate occurred in 198e or l981 in many species in parallel, which was attributed to the unusual drought in the sumrner of l980. An introduced pieneer species, Pintts ltttchnensis, has been invading the forest which is thought to be in the stable climax stage of succession. The height growth rate of the pine juveniles, l9.9 cmlyear, was much higher than any other native component species. This exceptionai phenomenon is ascribed to the good iight condition in the forest where the canopy is not fully closed in spite of the high stem density.
Introduction
The subtropical evergreen broad-leaved forest, 5-6 m high, located on Åíhe flat calied Chuosan-higashi-daira at Chichijima has the highest species diversity of all forest types in the Bonin lslands (Shimizu l983). This forest dominated by Dist.vli.um lepidotum was classified by the former researchers as one of the climax forests (Numata and Ohsawa i970) or the natural forests (Okutomi et al. 1983) in contrast with the secondary forests. But it consists of not only many shade-tolerant trees but also light-demanding species like Schinza mertensiana. Juveniles of an introduced species, Pinus lutchuensis, are also found growing in the ibrest (Shimizu 1983). If the forest is in the c}imax stage, the invasion of the {brest by sttch a pioneer species as the pine is not in accordance with the common sense of ecological successlon. . On the other hand, it is difficult to determine the annual shoot growth by counting the number ofannual rings or scars ofwinter bud scales because these marks are usually obscure in the subtropical region. Literature which deals with the field data ofjuvenile height growth in subtropical forests is scanty. So this paper reports a study oR the dynamics of the subtropical fbrest from the viewpoint ofjuvenile height growth oÅí the compoRent species. 64 YOSMKAZU SHIMIZU e
Chuosan- f higashi- daira ecg' S-
Fig. 1. Location of the quadrat in the forest (1) and the et7 E(}iliii sunny open place (e) studied. Thin lines of the map show " the IOO m contour.
1 km
Method
A quadrat (30 m Å~ 30 m) was placed in the forest located on the fiat calied Chuosan-higashi- daira at Chichijima (Fig. 1). Five strata were determined in the forest according to the height from the ground (I: 4-6m, II: 2-4m, HI:O.7-2m, IV: O.2-O.7m, V:
Results
Species comPosition of thelbrest
Table l shows the species composition of the forest studied in this paper. The forest includes 38 woody spec!es and it is mainly composed ofDist)lium lepidotum, Pouteria obovata, Schima mertensiana, S]aygium buxifolinm, etc. The understory of the forest is occupied by not only many juveniles of the canopy species but also some shrub species such as Boninia glabra, CallicarPaglabra, Pittosporum chichisimense, S"mplocos pergracilis, Stach)urus Praecox var. matsu.7yakii, etc. most of which are endemic to Chichijima and the distribution of which is concentrated on this forest. As the canopy ofthe forest is not fuIly closed in spite ofrather high stem density ofthe canoby ttees, it is fairly bright even in the forest. The relative light intensity was lI.20/o on the forest J uvenl . le Hei ght Growth in the Subtrop ical l?orest 6S
Table l. Species composltlon of' the forest and the number ofj uvenl les sampled in this study
No. of indivi duals (t900 .2) J uvenl ]es sampled Species name I II III IV v Sapling Seedling (4-6 m) (2-4 m) (O.7-2 m) (O.2-O.7 m) ( Clinostignta savor.yana 3 g, i ?¥ Dist]lium lePidetttm 108 396 1 ElaeecarPas Pftotiniaefolius 5 20 Evodia nishimurae 13 Fagara boninensis Ficus boninsimense 3 Gardenia boninetasis li Geniostoma .glabra Uibisctts glaber g Jlex matanoana Juniperus ta.vt:f;oiia* Ligustrecm micrantum : l ?gg 17;A 'ii 1; Machiltts boninensis l, Macltiltts kebu M]rsine maximowiciii g i, Areolitsea sericea i Osmanthus insutaris Osteomeles boninensis * ii Pandanus boninensis 37 il l, ii3 Photinia wrightiana* Pintts lutchuensis 2 PittosPorum chichisimense * Pauteria obovata 13416 Ps.),chotria homalosPerma 3 RhaPhiolePis indica var. integerri.ma yg ii ? 716 Schima mertensiana 430 Staclayarus Praecox var. matsuzakii * 4 Syniplocos Pergracilis * Svaygittm bttxt:flolium 57 579 g Tarenna subsessilis * 229 Vaccinium boninense * 1 1 Viburnunw'aPonicum 8 var. boninsimense* g l4,Iikstroemia Pseudoretusa 6 5 39 325 6 3 Total 520 518 933 3364 18766 !33 !44 * Undergrowth shrub sp ecles. 66 YosenKAzu S}iiMizu floor (the mean value of50 sampling spots). Juveniles ofthe canopy trees, especially ofDistylium lePidotum and Pouteria obovata, are abundant in the forest. Furthermore, it is characteristic of the Åíorest that a pioneer species, Pinus lutchuensis, has been invading the forest, though no individuals of the pine have become matured yet (field observation). Height groiz,th rate of the species Fig. 2 gives the height growth rate (mean annual growth in height, cmlyear) of the.juveniles which were cl.assified into seedlings ( 20 .Pi 19 lllii' AWk ABo Fig. 2. Height growth rate of the seedlings ( tt - o 1 2 3 4 5(cmiy) Height growth rate ot seedtings Juvenile Height Growth {n the Subtropical Forest 67 (G) (b) L 200 180 300 l60 ilg ;40 120 2 oo JX 100 x l E mo 80 1oo l 60 x ' ' 2oo 40 l 20 EA e ---, s 1oo 60 O l L, l I 40 E -st ,7J.s '7g.4 ¥so.t.t6o.12 'sl.12 '77¥8 '7g.4 'eo.1 tso.12 ,sl.12 20 U) Ye ar Fig. 3. Annual height growth of the saplings of Pinits lutcintensis (circle) and Schima ntertensiana (triangle) . (a) In the sunny open place; (b) In the Åíor'est. siana which was measured in the forest and in the sunny open place. The height growth rate of the pine, 45.8 cmlyear, was nearly the same as that of Schima mertensiana, 49.7 cm!year, in the open place, bLit the former was much higher than the latter in the forest. Height growth rate of tlze individuats Fig, 4 shows the height growth rate of all individuals studied in this work. rl"he growth of saplings was faster than that ofseedlings, as mentioned before, but there seems to be no positive correlation between the height growth rate and tlae stem height of saplings (O.2-2 m in height) at the beginning of the measurement. The death ofterminal shoots and the occurrence ofnew leaders at lower positions as indicated in Fig. 5 were observed in many individuals of almost all species. Especially Pouteria obovata, Callicarpa glabra and Ta?'enna subsessilis showed the frequent shoot exchange of this type (Fig. 4), But recognized were no such special trend as the higher rate of height growth after the shoot exchange than beÅíore, or vice versa. 68 YosHIKAzu SHIMIzu The high death rate was recorded in Distylium lepidotum, Ligttstrum micrantum, Pittosporum chichisimense, Svv.7..ygium buxz:fTolium, etc. On the other hand, only a few individuals died during the study period in Pouteria obovata, RhaPhiolePis indica var. integerrima, Ilex matanoana, etc. Dead individuals were concentrated on the seedlings and the sap!ings less than O.5 m in stem height (Fig. 4). Distylium lepidotum `ilil DR=50.0 x . FSE=5.9 t- . xXxex-. i A -xx-"x x /l Ligustrum rn!crantum N 50 1oo 1se . DR=4T6 Pouteria cbovata F5E=8.5 DR=2B,6 . FSE=15.0 L i . . lrr x " - . . . . xxi 20 1co 150 so . n- . x Schima rnertenssana o 1oo 150 DR=36,4 ro 50 FSE=1.1 . Pintss lutchuensis DR=28,O t- FSE=3.5 -- . . . . /1111 '111 ro 50 KX) 1so Rhaphiotepis lndica var. Integerrtma . . -- DR=14,3 . FSE=2.9 . -"- . . i . '"'ls; . . . -- t -- . x . x 11i se oo 150 ro so 1oo 150 am Syzygium buxlfolium Neolitsea sericea i . DR=45.5 FSE=9.1 'iilii . . . i 1oo 150 xx- x i 20 se ro se 1oo ISO Photinla wrightiana IEex fnatanoana i DR=27.3 x FSE=O.O . 1oo 150 . Gardenia 205 boninensis i 20 50 1 1so El.aeocarpus photiniaefoUus . 100 0R=66.7 ro 50 150 FSE=5,9 Stachyurus praec.o. x . sL2riiio:rEr-:g:i:Eso nsls vaa matsuzakri 2 x 1 1 . 20 se 1oo 150 chichisimense st:ffxx,ry,s Pittosporum Machi{us250 kobu DR=60,O i FSE=3,2 2 . -x btS:[lil,-irlrl;}:ls:. e . Xxxx 20 50 1oo 150 ro Stem height Ccm) Stem height (crn) Fig. 4 J uvenl ]e Height Growth in the Subtropical Forest 69 il ll/ Wikstroemia pseudoretusa ii Tarenna subsessilis . DR=33.3 i FSE=O.O DR=ILI . FSE=13,O . . . . kx -xx -- . 20 50 100 20 50 1oo Machi[us boninensis Boninia glabra DR=16.7 1io . FSE=5.3 - DR=50,O FSE=18.e . A '11i . . -i i -- . x . 20 50 1 20 ii, Calticarpa glabra so 1oo si DR=8.3 FSE=17.2 Pandanusboninensis lli' ORurO.O ii . . FSE=40 Xs . . -- . 2o so 1 ro 50 100 Geniostoma gtabra Fi c us boninstmae x . . . . 20 so 100 ro 50 1 Syrnplocos pergraei[is. Hibiscus glaber ii . x 1 20 co 1oo oo so Myrsme maxirnowiezii Ctinostigma saveryana . g . -- 20 so 1 po 50 loo Stem height (cm) Fig. 4. Relation between tlxe stem height at the beginning of tlie measurement and the hei ght growth rate of all juveniles studied. Those that died (Å~) or exchanged the leading shoot (A) during the study period are indicated differently. The death rate (DR, O/.) and the frequency ofshoot exchange (FSE, O/.) are also pvesented. r.s.x i. :t ; tt r" u. i -t--- i- .1 J -r -t t --l ts"'-i .¥-'r k---S #t ji t-t-- Fig. 5. Schematic presentation of the exchange of a leadiRg shoot. 70 YOSHIKAZU SHIMIZU Annual height groteth and death rate Fig. 6 presents the annual change of the height growth and the death rate of some main component species. The sharp decrease in the annual height growth was found in 1981 in Callicaipa glabra, Disl71ium lePidotum, Li.aitstrum micrantum, MachilzLs boninensis, RhaPhiolePis indica var. integerrima and P41ikstroemia pseudoretusa. On the other hand, the high death rate was observed in 1980 or l98i in almost all species presented in Fig. 6. These phenomena occurring in many species in parallel seem to have some relation with the unusual drought which attacked Chichljima in the summer of I980. Pouteria obovGtq Schi ma mertensiGna itex matanoGna 3 30 3 30 2 20 2 20 ..-4. A 32 it is". 30 20 ts,, 1 ..,.:?`:y)t::>. tl 10 l 10 ¥ s. 10 ss 3..A,---A' s . O '78' '79 '80 '81 }82 O o s- o o ' o '78 '79 'eo '81 '82 '78'79 .eo '81 '82 Pinus {utchensis Wikstroemia pseudoretusa Machilus boninensis i2I ,i'k ii ,,i/6 15 1 'g 10 il' /ti 5 A""-t x. .tAh. A k-' . k---A N - o x tr -s s Nt Is s ts '78 'N '80tt '81 '82 '78 '79 '80 '81 '82 78 79 80 81 8 tN tsiN Distylium tepidotum Ligustrum micrantum Syzygium buxifotium g, 4 40 4 40 4 40 ttt4 tsi l ..4, 3 30 3 ,1-- 30 3 ..A 30 x , 2 x 20 , 20 it it tt t 2 N/ mo 2¥ ¥, 10 1 ` , 10 1,, Il ,, IA 1 10 o tt o o A.s o O ¥rs Nkl iSg¥s6 tsl ¥s2 O '78 'N '80 '81 '62 ,ra 'N ,eo '81 '82 Rhaphiotepisinqicavarlntegernma 6 60 TGrennq subsessilis 5 50 CQI[icarpa gtabra . /tkti 4 40 4 40 4 t- 3 itll 30 3 30 3 -iJi 20 2 i tt tltttSsts 2 20 tt 101 .10 tt it .s o o IA '78'79'8e'81'82 '78 '79 '80 o'o'81 '82 O'78 '79 rs'eo '81 '82 Year Fig. 6. Annual change of the height growth (circle and solid line) and the death rate (triangle and broken line). Juvenile H]eight Growth in the Subtropical Forest 71 Discussion Seedlings and saplings of the main canopy species grew slowly in the forest, i.e. not more than 2 cm/year (Fig. 2). The exchange of the }eading shoot was frequently observed in many species (Fig. 4). Moreover, many sample individuals diecl during the 5-year study period (Fig. 6), though juveniles of the main canopy species are abundant in the forest (Tabie I). So the turnover of the canopy trees would be rather slow, unless the role of canopy gaps in regeneration ofthe forest is taken into account. On the other hand, there is no record that the trees of this Åíorest were cut before World War II. The forest has not received any human activity since the end ofWorld War II. The forest is characterized by the several undergrowth shrlib species whose distribution is centered on this forest at Chichljima (Shimizu l983). The regeneration mechanism of the forest of this type is thought to be a series of tree-by-tree replacement in conjunction with small gap formation by a single dead tree (Shimizu 1984). So the structure and the species composition of the forest are rather stable. The successional stage of the forest can be defined as the climax in the sense that the forest is in the terminal stable stage on the site (Lincoln et al. 1982). But a light-demanding species, Pinus lutchuensis, which was first introduced to the Bonin Islands in l899 (Toyoshima 1938), has been invading the forest (Table l). Its shoot growth is exceptiona}ly much faster than any other native component species in the forest (Fig. 2). The invasion ofa climax forest by a pioneer species is an unusual phenomenon from a commonsense standpoint ofecological sticcession. This occurs in the forest perhaps because the light condition ls good enough for the pinejuveniles to grow in the forest although the forest is in the ciimax stage. But the reason why the canopy of the forest is not fully closed has not been investigated. I.n addition, the phenomenon may be related to the island situation that the pine as a new comer to the Bonin Islands has not been adjusted to the stabie ecosystem in the islands which had been accompiished through the longtime history of the isiands. Crowns ofsome pine saplings which had been under the canopy at the beginning of this ,stticly in 1977 were located above the canopy in 1984 (field observation). It is speculated that they wi}1 become emergent trees in the forest in a near future. A severe drought attacked Chichljima in the summer of 1980. The damage to plants was concentrated on the dwarf scrubs, O.3-1.5 m high, Iocated on mountain ridges and edges of sea cliffs, whereas no ciear damage ofthe canopy trees was observed in the Åíorest studied in this paper at that time (Shimizu 1982). But the drought seems to have had seme influences on thejuveniles in the forest because the sharp decrease in the annual height growth in l981 and the increase in the death rate in I980 or 1981 were found in many species in parallel (Fig. 6). The delay of the drought influeBce on the height growth may be attributed to the fact that the height growth in i980 had almost finished before the summer, and the infiuence of the drought appeared in the height growth of the following year. Acknowledgments I wish to express my thanks to ProÅí M. Ono and Ogasawara Research CommitteeofTokyo Metropolitan University for allowing the use of the laboratory at Chichljima. 72 YOSHIKAZU SKIMrZU I extend my gratitude to the staff of Fruit fly Research I.aboratory and viliagers of Chichi- jima for much kindly support in the course of the work. References Lincoln, R.J., G.A. Boxshall and P.F. Clark (i982) A Dictionary of Ecology, Evolution and Systematics. Cambridge University Press, Cambridge. 298 pp. Numata, M. and M. Ohsawa (1970) Vegetation and succession iR Chichijima, Bonin Islands. In: The Nature of the Bonin and Volcano Islands. pp. I59-l97. Ministry of Education and Agency for Culturai Affairs, rlrokyo. Okutomi, K., T. Iseki, Y. Hioki, K. Kitayama and Y. Sumihiro (1983) Vegetation of the Bonin Islands. In: Endemic plants and vegetation of the Bonin Islands. pp. 97-262. Tokyo Metropolitan Government, Tokyo. Shimizu, Y. (l982) InfiLience of the unusual drought in the summer of 1980 on the vegetation ofChichijima. In: e Ogasawarashoto-Shizenkankyo-genkyochosa-hokokusho No. 3. pp. 31-37. Tokyo Metropolitan Government, Shimizu, Tokyo. Y. (l983) Plant ecological' studies ofthe forests in the Bonin (Ogasawara) Islands. Ph. D. Thesis. Kyoto University, Kyoto. Shimizu, Y. (1984) Regeneration oÅí the subtropical evergreen broad-leaved forest at Chichijima in the Bonin (Ogasawara) Islands with reference to an environmental gradient and canopy gaps. Japanese Journal of Ecoiogy 34: 87-100. Toyoshima, K. (1938> Vegetation and the usefu1 tropical plants in the Bonin Islands. Bulletin ofthe Forestry and Forest Products Research Institute 36: 1-251.