zonal transition of evergreen, deciduous, and coniferous forests along the altitudinal gradient on a...

Plant Ecology 133: 63–78, 1997. 63c 1997 Kluwer Academic Publishers. Printed in Belgium.

Zonal transition of evergreen, deciduous, and coniferous forests along thealtitudinal gradient on a humid subtropical mountain, Mt. Emei, Sichuan,China

Cindy Q. Tang & Masahiko OhsawaLaboratory of Ecology, Chiba University, Yayoi Cho 1-33, Chiba 263, Japan

Received 3 December 1996; accepted in revised form 4 July 1997

Key words: Altitudinal gradient, Community structure, Diversity, Dominance, Floristic composition, Physiognomy,Topographic factor

Abstract

Altitudinal zonation of evergreen, deciduous and coniferous forests on Mt. Emei (3099 m asl, 29�34.50 N,103�21.50 E), Sichuan, China was studied to understand the transition of vegetation zonation from tropical totemperate mountains in humid Asia. On the basis of quantitative data on floristic composition and communitystructure sampled at ten plots selected in different altitudes on the eastern slope of the mountain, forest zonationand the inter-relationships among different life-forms of trees in each zonal forest community were studied quant-itatively. Three forest zones were identified physiognomically along the altitudinal gradient, viz. (i) the evergreenbroad-leaved forest zone (660–1500 m asl), (ii) the mixed forest zone (1500–2500 m asl), and (iii) the coniferousforest zone (2500–3099 m asl). Great compositional changes were observed along elevation, and the zonal forestcommunities were characterized by their dominants and floristic composition. Maximum tree height decreased from33 m at lower middle altitude (965 m asl) to 13 m near the summit (2945 m asl). There was no apparent deciduousforest zone along the altitudinal gradient, but true mixed forests of three life-forms (evergreen, deciduous, andconiferous) were formed around 2000–2500 m asl. Patches of deciduous forest were found in a lower part of themixed forest zone, particularly on scree slopes, between 1450 m and 1900 m asl. These patches were dominated bythe Tertiary relic deciduous trees, such as Davidia involucrata, Tetracentron sinense, and Cercidiphyllum japonicumvar. sinense. High species diversity in the mixed forest zone resulted from the overlapping of different life-formsat middle altitudes, which is partly due to wider variety of temperature-altitude correlations. A comparison of thealtitudinal zonation with the other east Asian mountain vegetation clarified that Mt. Emei is located exactly at theecotone between tropical and temperate zonation types in eastern Asia.

Abbreviations: asl-above sea level, BA-basal area, DBH-diameter at breast height, RBA-relative basal area, Mt.-Mount.

Introduction

The mountain forests in eastern Asia are attractive forthe comparative study of vegetation zonation in humidmonsoonal climates because of their essentially con-tinuous extension of mountain topography from trop-ical to temperate regions. Vegetation in relation to themountains in China have been described variously byearlier researchers. Wang (1961) studied the generalcharacteristics of the forests in China; in particular,

his concept of the mixed mesophytic forest is helpfulto understand differentiation of various forest types inChina. Wolfe (1979) analyzed altitudinal zonation offorests relative to latitude in eastern Asia based onclimatic properties. The vegetation zonation of theTibetan Plateau (Chang 1981), and the geographic-al distribution of the coniferous forest in China (Li& Chou 1984) were studied. Ohsawa et al. (1985)and Ohsawa (1993) analyzed the zonation patterns ofmountain forest vegetation along latitudes in eastern

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Asia. Fang & Yoda (1988) reported the relationshipbetween climate and vegetation in China. Song (1988)described the main types of the broad-leaved evergreenforest in China. Although it has been clarified thatthe tropical and temperate vegetations have their lim-its at middle latitudes in China by Chang & Chiang(1973), Zheng & Chen (1981), and Liu & Qiu (1986),the interaction between the tropical and temperate ele-ments around their boundary both along altitudinal andlatitudinal gradients in China has not been widely sub-stantiated with quantitative data.

Mt. Emei is situated in the transitional zonebetween tropical and temperate zonation types onmountain vegetation template in eastern Asia. There-fore, it is well suited to investigate how tropical andtemperate elements interact along altitudinal gradi-ents. To understand this phenomenon, it is essen-tial to investigate the relationships among the zonalvegetation types, the community structure and the spe-cies behavior on Mt. Emei. The altitudinal distributionranges of evergreen trees extend widely on Mt. Emeicompared with other subtropical mountain forests inChina (Li 1984), and abundant ancient remnants occuron this mountain (Yang & Li 1989). The structure,types and zonation pattern of the forests; however, havenot been made clear. Moreover, no study in relation tooverall structure of altitudinal zonation of mountainforest vegetation in eastern Asia has been conductedso far.

The main objectives of the present study are to (1)describe and examine the structure of the zonal forestvegetation on Mt. Emei, and (2) compare the altitudinalvegetation zonation with the other mountains in easternAsia.

Study area

Study site

Mt. Emei (3099 m asl, 29�34.5’ N, 103�21.5’ E), loc-ated in the southwestern part of the Emeishan city ofSichuan, China, is 20 km from north to south and upto 5 km from east to west. The foothill is 551 m aslwhich gradually rises to 3099 m asl (Figure 1). Mt.Emei has a rich flora. The vegetation changes greatlywith altitude and geomorphological factors. The veget-ation on Mt. Emei was not greatly affected by the lastglaciation during the Quaternary Period. The plantsmigrated and escaped extinction while the glacier wasadvancing and retreating, because both the mountain

Figure 1. The study area, Mt. Emei. Contours at 200 m intervals.

and its riverine tributaries had a north–south orienta-tion (Guan 1982). Therefore, the mountain became asanctuary for many Tertiary deciduous elements, likeDavidia, Tetracentron, Cercidiphyllum, and Euptelea.

The topographic features of Mt. Emei are not wellclarified. It is old relative to nearby mountain systemssuch as Mt. Gongga and the Himalayas. It has stoodin Sichuan basin area since the late Cretaceous Peri-od, about 70 million years ago. Due to the glaciationduring the Quaternary, the valley bottom is ‘U’ shapedaround 710–1020 m asl. The mountain is made upof steep slopes leading into very narrow valleys. Theparent rocks mainly consist of shale, dolomite, basalt,sandstone, etc. (Zhao & Chen 1980).

Climatic conditions

This area is influenced by the southeast monsoon dur-ing summer. There are two climatic stations of themountain area: at 447 m asl (Emeishan city) and at3047 m asl (Jinding in one peak of this mountain).According to climatic records during 1981 and 1993,the mean annual temperature is 17 �C and 3.1 �C forEmeishan city and Jinding, respectively; and the aver-age annual precipitation is 1528 mm and 1756 mm,respectively. The temperature lapse rate between the

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Figure 2. Ecological climatic diagram for Emeishan City (447 m asl)and Jinding (3047 m asl). The temperature lapse rate is estimated onMt. Emei. Data sources are Sichuan Meteorological Agency (1981–1993), and Yang Yu Pou (1985).

two climatic stations is 0.54 �C/100 m in mean annu-al with a maximum of 0.6 �C/100 m in May and aminimum of 0.45 �C/100 m in December. To general-ize the lapse rate relevance, we incorporated additionaltemperature data along altitudes in the basin area:Wen-chuan, Baoxing and Yaan (Yang 1985), the mean annu-al temperature lapse rate is 0.49oC/100 m, the largesttemperature lapse rate is in May (0.58 �C/100 m), andthe lowest is in December (0.45 �C/100 m) on Mt.Emei (Figure 2). The trend on Mt. Emei is similar tothe most other parts of China (Fang & Yoda 1988) withthe altitudinal lapse rate of temperature low in winterand high in summer. Additionally, Li (1990) studiedthe altitudinal changes of precipitation: it progressivelyincreased by 49.6 mm/100 m and 36.5 mm/100 mbelow 1200 m asl and between 1200–2300 m asl,respectively; however, it decreases progressively by58.7 mm/100 m above 2300 m asl, and the highest aver-age annual precipitation was approximately 2300 mmaround 2300 m asl.

Methods

Data

The mountain forests are subjected to factors such asclimatic conditions, topographic situations, and humanactivities; thus, forests are structurally and floristic-ally heterogeneous. We selected ten plots to invest-igate altitudinal changes of floristic composition andcommunity structure in the following altitudes alongeastern slope: 660 (Plot 1), 780 (Plot 2), 965 (Plot3), 1160 (Plot 4), 1620 (Plot 5), 1660 (Plot 6), 2210(Plot 7), 2425 (Plot 8), 2825 (Plot 9), and 2945 (Plot10) m (see Figure 1). One at the lowest altitude (Plot1) was a secondary forest, because there was no veget-ation without human disturbance, and the other ninewere relatively less human disturbed plots. The plotsize was from 10 � 20 m2 to 40 � 40 m2, and the sizewas the maximum available size within homogeneoustopographic habitats. At each site, general informationabout each plot was noted, such as altitude, exposure,and inclination. The plot was established on a relat-ively gentle slope which was accessible from the path.Except in the case of Plot 1, the sites with the signs ofdisturbance of cutting or some other human activitieswere carefully avoided.

All stems taller than 1.3 m in height were tagged,the species identified, their diameters at breast height(DBHs) measured, and tree heights measured. Thelocation of each individual was mapped. The coverageand maximum height of the species of herb layer wererecorded. Each tree seedling was identified, measuredby height, and counted for further analyses.

Nomenclature follows Flora Sichuanica EditorialBoard (1981–1992) and Editorial Board of ChineseMedical Botany on Mt. Emei (1981).

The field work was carried out in November of1994, from late August to early October of 1995, andOctober of 1996.

Analyses

The cross-sectional area of every stem (cm2) was cal-culated from DBH, and all the basal areas of the specieswere summed to obtain species basal area (BA, cm2).In each plot, relative BA (RBA, %) of each specieswas used as abundance of the species, and the domin-ant species were determined based on the dominanceanalysis (Ohsawa 1984a). In a community dominatedby a single species, its relative dominance may bestated at 100%. If, however, two species share dom-

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inance the relative dominance of each should ideallybe 50%, or if there are three co-dominants, 33.3%,and so on. The number of dominant species is thatwhich shows the least deviation between the actual rel-ative dominance values and the expected percent shareof the corresponding co-dominant-number model. Thedeviation (d) is calculated by the following equation:

d = 1=NfX

i2T

(xi � x0)2+

X

j2U

x2jg,

where xi is the actual percent share (here relative basalarea is adopted) of the top species (T), i.e., in the topdominant in the one-dominant model, or the two topdominants in the two-dominants model, and so on;x0 is the ideal percent share based on the model asmentioned above, and xj is the percent share of theremaining species (U). N is total number of species.

Species diversity was shown by using the Shannon-Wiener Index (Pielou 1969).

Community physiognomy was described by per-centage composition of the life forms: evergreen,deciduous and coniferous trees. Structural paramet-ers of the vegetation, i.e., height, stem density, basalarea, diversity, etc., each emphasized different aspectsof the community structure. Size distribution of eachcomponent species was used to elucidate regenerationpattern of the species.

Results

Floristic composition and the life-form distributionalong the altitudinal gradient

The total of 122 tree species in 69 genera and 51 fam-ilies were recorded in the ten plots, these included 40evergreen broad-leaved, 75 deciduous broad-leaved,and 7 coniferous species. For the pooled data ofall plots, the relative basal area of each tree lifeform was nearly equal: 39.3, 27.8, and 32.9% forevergreen broad-leaved, deciduous broad-leaved, andconiferous species, respectively (Table 1). The ever-green broad-leaved trees were dominantly composedof Fagaceae, Lauraceae, Magnoliaceae, Illiciaceae andSymplocaceae. The deciduous broad-leaved trees weremainly constituted by Aceraceae, Caprifoliaceae, Dav-idiaceae, Eupteleaceae, Juglandaceae, Styracaceae andRosaceae. The coniferous trees consisted exclusivelyof Pinaceae and Taxaceae. The general trend of the life-form distribution along altitudes is illustrated in Fig-

ure 3, in which Plot 1 (660 m asl) and Plot 5 (1620 masl) were omitted, because Plot 1 was a secondaryforest and Plot 5 was a topography-controlled com-munity developed on a scree slope. It clearly indicatesthat evergreen broad-leaved trees were distributed inlow and middle altitudes up to 2300 m, then deciduousbroad-leaved trees mixed with evergreen broad-leavedtrees between 1500–2500 m asl, and coniferous treeswere mainly distributed above 2000 m asl, finally con-iferous trees dominated exclusively above 2500 m asl.In this instance, three zones could be supposedly dis-tinguished along altitudes, e.g., (i) the evergreen broad-leaved forest zone (below 1500 m asl), (ii) the mixedforest zone, (a) the evergreen/deciduous broad-leavedmixed forests (1500–2000 m asl), and (b) the broad-leaved and coniferous mixed forests (2000–2500 masl), and (iii) the coniferous forest zone (2500–3099 masl).

Life-form transition patterns along the altitudin-al gradient were analyzed on the basis of three treelife-forms and their partitioning in height class dis-tribution (Figure 4a, b). Figure 4a clearly indicates agradual shift of the tallest tree life-forms in the com-munity along altitudes; that is, the uppermost storeyof forest was taken by evergreen broad-leaved treesbelow 1200 m asl, deciduous broad-leaved trees around1200–2000 m asl, and finally coniferous trees above2000 m asl. The altitudinal ranges roughly coincidedwith the transition of the physiognomic zones amongevergreen, deciduous, and coniferous as shown in Fig-ure 3. The tree height of each life-form changed withaltitudes (Figure 4b). In Plot 2 (780 m asl), most of thelayers were composed of evergreen trees, though therewere a few deciduous species, such as Acer catalpifoli-um and Euscaphis japonica up to 10 m and 13 m in treeheight, respectively. At increasing altitudes, deciduoustrees gradually replaced evergreen trees from lowerstrata of the forest. In Plot 6 (1660 m asl), both the can-opy and shrub layers were a mixture of evergreen anddeciduous trees. Some deciduous trees such as Acersinense, reached a height of 24 m in the uppermoststorey, and evergreen trees such as Machilus pingii,constituted subcanopy of ca. 20 m in height. Abovethis altitude, coniferous trees appeared in all the layers(Plot 7) or in upper layers (Plot 8). In Plot 7 at 2210 masl, the forest was co-dominated by evergreen, decidu-ous and coniferous trees. Coniferous Abies reacheda height of 26 m in the uppermost storey. EvergreenLithocarpus and deciduous Acer reached a height of14 m, respectively. Sequentially, evergreen trees dis-appeared, except some shrubs, such as Eurya fangil,

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Table 1. Floristic composition of the trees in the sample plots. RBA = relative percent of basal area. Dominant species (see the text) of each plotare indicated by asterisk.

Plot number 1 2 3 4 5 6 7 8 9 10Altitude (m) 660 780 965 1160 1620 1660 2210 2425 2825 2945Exposure (degree) S80W N68E S9W N62W N58W N19W N32W N59E N58W S52WInclination (degree) 17 27 54 35 20 16 29 25 16–21 14–22Maximum height (m) 27 22 33 20 23 27 30 18 24.5 13Maximum dbh (cm) 52 44 135 38 63 103.8 93 42 44.3 34 TotalPlot size (m2) 20�20 20�20 30�10 20�10 20�20 30�20 40�40 20�20 30�20 20�10 value ofDiversity index 1.875 1.621 1.674 2.068 2186 3.152 3.386 3.141 0.284 0.229 10 plotsTotal BA 2415.0 2844.5 7297 3064.9 4790.8 5103.4 2908.5 1828.6 4798.1 3809.9 38860.7Total stem number 133 153 109 100 55 118 239 141 142 82 1272Total species number 9 18 20 13 18 22 31 25 9 11 122

RBA(%) RBA(%) RBA(%) RBA(%) RBA(%) RBA(%) RBA(%) RBA(%) RBA(%) RBA(%) RBA(%)

Evergreen broad-leaved treesCastanopis hystrix �48.7 11.0Symplocos laurin 4.1 1.1Eurya semiserrulata 3.5 +

Lindera nacusua 0.1Machilus pingii �64.5 �19.2Phoebe zhennan �17.7 1.5Eurya loquizna 1.1Symplocos botryantha 0.3Camellia yunnanensis 0.1Cinnamomum argenteum 0.1Camellia sp. 0.03Ficus henryi 0.02 0.02Pittosporum formosana 0.01Eurya sp. 0.007 0.01Ilex latifolia 0.002Ficus carica +

Acer laevigatum 0.1Michelia martinii �65.8 0.2Illicium henryi �19.7Lindera pulcherrima 6.6 �15.7Sloanea hemsleyana 1.9Aucuba emeiensis 1.1 0.17Pittosporum adaphniphylloides 0.2Actinodaphne emeiensis 0.03 �48.7Ligustrum compactum 0.002Lindera megaphylla �10.8Schefflera delavayi 0.7Stachyurus yunnanensis 0.02Ilex chinensis 0.008Lithocarpus cleistocarpus 0.02 �7.3 �27.2Castanopsis platyacantha 0.001 1.6Symplocos caudata �5.8 0.02Camellia oleifera 3.1Rhododendron argyrophyllum 1.2 0.5 0.05Rhododendron vernicosum 0.09Rhododendron strigillosum 1.8Rhododendron calophytum 0.5Eurya fangil 0.1Symplocos ernestii 0.02Rhododendron monanthum 0.003 0.3Subtotal 56.4 95.969 95.952 76.128 0.021 38.47 29.64 0.5 0.003 0.35 393

Deciduous broad-leaved treesMallotus tenuifolius 0.5Vaccinium carlesii +

Euscaphis japonica 2.9Prunus padus 0.7 0.6 2.6 1.2 4.2 �5.8Acer catalpifolium 0.3Viburnum punctatum 2.4Debregeasia edulis 0.5Choerospondias axillaris 0.4 �28.6Nothapodytes pittosporoides 0.01Celtis bungeana 0.004Meliosma cuneifolia 0.004Vaccinium petelotti 0.002Euptelea pleiospermum �17.2Toona sureni 6.2Cornus capitata 0.3Prunus dielsiana 0.1Perrottetia racemosa 0.03Cornus controversa 0.001 0.009 0.1Davidia involucrata �52.2 �5.7

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Table 1. Continued.



Cercidiphyllum japonucum var. sinense �20.1Aesculus wilsonii 6.6 0.04Prunus brachypoda 6.2Tetracentron sinense 4.6 1.5Prunus grayana 4.2 �6.5 4.7Staphylea holocarpa 3.2Pterocarya insignis 0.1Acer sinense 0.09 �8.6Viburnum erubescens 0.04 2.7Acer flabellatum 0.03 �10.5 �7.6Decaisnea fargesii 0.001 0.04Alangium chinensis 0.001Euonymus porphyreus + 0.07Pterostyrax psilophylla �9.1Juglans cathayensis 0.1Cornus macrophylla 0.05Viburnum betulifolium 0.02 0.7Acanthopanax setchuenensis 0.003Enkianthus chinensis 4.1Prunus pilosiuscula 3.2 1.1 0.2 0.008Acanthopanax evodiaefolius 1.9Acer caudatum var. prattii 1.2Lyonia ovalifolia 1.1Salix hypoleuca 0.8 0.5Corylus ferox 0.8Litsea veitchiana 0.6 0.007Hydrangea macrophylla 0.5 1.8Ilex micrococca var. pilosa 0.4Betula utilis 0.3Litsea cubeba 0.3Viburnum sympodiale 0.2Hydrangea xanthoneura 0.2Sorbus folgneri 0.08 0.1Deutzia pilosa 0.04Cotoneaster moupinensis 0.007Acer maximowiczii �7.6Viburnum sympodiale var. cordifolium �6.8Enkianthus deflexus 3.0Litsea ichangensis 2.0Acanthopanax leucorrhizus 1.8Betula luminifera 1.5Lonicera nervosa 0.6Lonicera lanceolata 0.5 0.2Rubus eucalyptus 0.3Lonicera tatsienensis 0.3 0.2Rosa spinosissima 0.1 0.03Lonicera tangutica 0.1Aralia chinensis 0.07Viburnum dilatatum 0.03Euonymus szechuanensis 0.01Acer caudatum 2.1Ribes tenue 0.7 0.005Sorbus prattii 0.07Spiraea mongolia 0.3Salix luctuosa 0.09Salix dunnii 0.02Subtotal 0.5 3.9 3.92 23.831 99.971 61.513 33.867 45.817 3.54 0.953 278

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Table 1. Continued.



Coniferous TreesPinus massoniana �22.0Cunninghamia lanceolata �21.0Cryptomeria fortunei 0.1Taxus chinensis 0.04 �5.4Abies fabri �18 �29.1 �96.597 �97.4Tsuga chinensis �13.2 �24.7Sabina squamata 1.3Subtotal 43.1 0 0.04 0 0 0 36.6 53.8 96.597 98.7 329

Total 100 100 100 100 100 100 100 100 100 100 1000

Symplocos ernestii and Rhododendron monanthum inthe ground layer. In Plot 8 at 2425 m asl, the can-opy layer was characterized by coniferous trees whiledeciduous trees prevailed in the subcanopy and shrublayers. Above 2500 m asl (Plots 9 and 10), the canopylayer was represented only by coniferous species, andthe maximum tree height decreased from 18 m to 13m. Deciduous broad-leaved trees occurred only in thelower strata. Thus, the deciduous trees occupied lowerstrata of evergreen or coniferous canopy layer exceptPlot 6, in which emergent deciduous trees toweringabove evergreen trees.

Forest structural features along the altitudinalgradient

Six structural features are illustrated in Figure 5a–f.The maximum tree height was 33 m at Plot 3 (965 masl), while it was 13 m at Plot 10 (2945 m asl) near thesummit. The maximum tree height with some addition-al data from the trees nearby each plot (closed circles)overall exhibited a step-wise decreasing pattern, an ini-tial steep decrease (from 31 m to 20 m) up to 1200 masl, then nearly flat, non-decreasing pattern (about22 m) between 1200 m and 2000 m asl, and again steepdecrease (from 26 m to 13 m) above 2000 m asl (Fig-ure 5a). The maximum diameter at breast height alsotogether with the additional tree data (closed circles)fluctuated greatly, i.e., from DBH 135 cm (Plot 3 at

965 m asl) to 34 cm (Plot 10 at 2945 m) along altitudes(Figure 5b). The BA of 0.7% of land area was highestat Plot 3 (965 m asl). At low altitudes, the BA valuewas relatively low but fluctuated greatly, partly due toheterogeneity of community structure, tree size, indi-vidual dispersion, etc. (Figure 5c). Stem density variedalong gradients showing roughly an inverse trend toBA. The plots around 1600–2210 m asl had low stemdensities with more large trees (Figure 5d). Remark-ably, the number of tree species showed an unimodalpattern along altitudinal gradients, and high speciesnumbers were around upper intermediate altitudes: 31species at Plot 7 (2210 m asl), 25 species at Plot 8(2425 m asl) and 22 species at Plot 6 (1660 m asl)(Figure 5e). The diversity index also showed a patternsimilar to species number, i.e., an unimodal pattern,the higher index 3.386 at Plot 7, 3.152 at Plot 6, 3.141at Plot 8 (Figure 5f).

Dominance-diversity relationship

To ascertain diversity structure in relation to tree life-forms of all zonal communities, dominance-diversitycurves are drawn in Figure 6. The abundance of eachspecies was plotted on a logarithmic scale from themost abundant to the least abundant species. In Plot7 (2210 m asl), many species had similar RBA, therewere no remarkably dominant species in RBA. Hence,five species were co-dominants, and the diversity was

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Figure 3. Altitudinal distribution ranges of dominant species and RBA distribution pattern of three life forms. P and circle mean the plot. Theline indicates the distribution range of dominant species.

the highest (see Figure 5f). Towards both high and lowaltitudes the pattern became steeper: to higher altitudesthe top dominant became conspicuous while towardslow altitudes several groups of equally dominant spe-cies shared the same abundance.

The diversity curves could represent the relativeimportance of the species in the community as well asillustrated the role of certain species played in determ-ining community structure. And the interrelationshipsamong species distribution in each community couldbe inferred quantitatively by diversity curves, i.e., geo-metric, log-normal and random niche-boundary types(Whittaker 1975). Based on the diversity curve types,indeed, three groups of forests could be discrimin-ated along altitudes: (i) Plots 1 to 4, the evergreenbroad-leaved forest zone (660–1500 m asl), havingthe dominance-diversity curves of a geometric to log-normal distribution, mostly by evergreen trees, (ii)Plots 5 to 8, the mixed forest zone (1500–2500 m asl),

having the log-normal and random niche-boundarycurves, predominantly by deciduous trees (Plot 5) orby both evergreen and deciduous trees (Plot 6), orby broad-leaved and coniferous trees (Plots 7 and 8),and (iii) Plots 9 and 10, the coniferous forest zone(2500–3099 m asl), having the monopolized geomet-ric curves with the top of coniferous species. Thisconcurred with the physiognomic classification in Fig-ure 3, and it is clearly indicated that the transitionalnature of the forest zonation, from the low altitud-inal evergreen broad-leaved forest to the transitional,middle-altitudinal mixed forest of evergreen/deciduousbroad-leaved and coniferous trees, and to uppermostconiferous forest near the mountain top along the steepslopes.

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Figure 4. Maximum height of three life-forms along the altitudinal gradient (a) and height class frequency distribution (b). P means the plot.

Size structure of population and regenerativemechanism in the zonal forest

The population structures of 38 of 122 species with asufficiently large population were analyzed (Figure 7).In general, the following three tree size-class distribu-tion patterns, suggesting different regenerative mech-anisms of species (Ohsawa 1991), were found. Theinverse-J type is formed by species having the highestfrequency in the small DBH classes with a gradualdecrease in the number of individuals towards the lar-ger classes (e.g., Phoebe zhennan). The sporadic typeindicates that the adjacent classes are badly repres-ented, frequency rises again more or less sharply inintermediate classes (e.g., Lithocarpus cleistocarpus).The emergent type is only represented by large sizeones with unimodal distribution in a mature community(e.g., Prunus grayana). Here, representative forests

were selected to describe the size structure of theirpopulations. Forests were named by their principaldominant species and were referred to by the genusname only.

(1) Evergreen broad-leaved forest zone at 660–1500 masl (Plots 1, 2, 3 and 4)This is a zone of various forest types belonging tothe evergreen broad-leaved forest zone. Below 750 masl, the secondary forest of Castanopsis hystrix, Pinusmassoniana, and Cunninghamia lanceolata existed.Castanopsis hystrix was an apparent dominant at lowaltitudes. The natural forest occurred from 750 m aslupwards. The prevalent evergreen genera were of theLauraceae such as Machilus, Phoebe, Actinodaphne,Lindera, Magnoliaceae such as Michelia, Illiciaceaesuch as Illicium and Fagaceae such as Castanopsis, andseveral others such as Symplocos (see Table 1). Not-

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Figure 5. Structural features of forest along the altitudinal gradient.P means the plot. The closed circles for (a) and (b) indicate the dataobtained from tree individuals nearby the plots.

ably, outside of Plots 1 to 4 in this zone, Ficus henryiwas common around 750–900 m asl, Quercus (Cyc-lobalanopsis) myrsinaefolia, Cinnamomum longepan-iculatum, Daphniphyllum macropodum, Lithocarpus

Figure 6. Dominance-diversity curves of all the plots. Tree life-forms are distinguished with the marks. P means the plot.

spicatus, and Manglietia fordiana were found around1000–1500 m asl.Machilus-Phoebe forest at 780 m asl (Plot 2)

The forest canopy was constituted by 18 species,and was dominated by evergreen broad-leaved species,such as Machilus pingii and Phoebe zhennan, whichwere components of the climax forest in this region,while Phoebe zhennan was represented in all sizeclasses. The seedlings of Phoebe and Machilus wereabundantly present in both shaded and well-lit places.Some evergreen genera, like Castanopsis, Symplocos,Eurya, Camellia and Ilex, were found in the subcan-opy and shrub layers. The understory with a coverageof 30% was mainly formed by Plagiogyria euphle-bia, Abacopteris simplex, Lysimachia trientaloides,and Bredia tuberculata.

(2) Mixed forest zone at 1500–2500 m asl (Plots 5, 6,7 and 8)(i) Evergreen/deciduous broad-leaved mixed forestzone at 1500–2000 m asl (Plot 6)

Choerospondias-Machilus-Pterostyrax-Acer-Litho-carpus-Prunus-Symplocos-Davidia forest at 1660 masl (Plot6)

This is a part of wide-ranging mixed forest zone,evergreen species mixed with some deciduous species.The forest canopy was nearly closed with 22 spe-cies. Evergreen elements of Machilus, Lithocarpus,Symplocos and Castanopsis were found in the can-opy, subcanopy and shrub layers, there were someMachilus and Symplocos seedlings in the understory,Camellia and Eurya were found in the shrub layer.Of the deciduous elements which had pioneer or seral

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nature, Choerospondias sporadically ranged 104 cmDBH, Pterostyrax and Acer were presented in discon-tinuous size-class distribution. Prunus was representedas the emergent type. Both Davidia and Tetracentronsporadically occurred on rocks or small heaps of earth,probably escaped from the deep shade of the herb layer.Juglans was found only in shrub layer. The understoryvegetation with a coverage of 96%, was dominatedby Impatiens sp., Oxalis griffithii, Asarun himalaicum,Sinarundiaria chungii, and Asplenium trichomanes.

Besides the above mentioned species, both Quer-cus (Cyclobalanopsis) multinervis and Quercus (Cyc-lobalanopsis) oxyodon reached to 50–65 cm DBH, andoccurred around 1500–1900 m asl outside the plots.

However, some patches of deciduous forests com-posed of Davidia, Tetracentron, and others wereencountered on scree slopes around 1450–1900 m asl.They were regarded as a kind of topographic climax.(ii) Broad-leaved and coniferous mixed forest zone at2000–2500 m asl (Plots 7 and 8)

This zone reached to around 2500 m asl, the forestswere distinctively co-dominated by two or three life-forms of the evergreen, deciduous and coniferous trees,such as Lithocarpus, Acer, Prunus, Abies, Tsuga, andTaxus. Lithocarpus-Abies-Tsuga-Acer-Taxus forest at2210 m asl (Plot 7)

The forest had a closed canopy supported by arich species assemblage was composed of 31 species.There were five co-dominants of three life-forms, i.e.,Lithocarpus, Acer, Abies, Tsuga, and Taxus. Of theco-dominants, Lithocarpus present in nearly all sizeclasses, but many stems had large sizes (30–34 cm).Acer was found sporadically in all size classes, whileEnkianthus had a comparatively good regeneration.Abies and Tsuga had large DBH, and some Tsuga grewon ridges. Though Abies and Tsuga were the emergenttype, there were some seedlings of them in the rel-atively exposed sites of the understory. Some Taxusoccurred on small heaps of earth suggesting regen-eration on the sites escaped from the dense bamboounderstory, stems were more common in the 5–14 cmsize classes. Rhododendron, Litsea and Symplocosoccurred by sporadic or inverse-J type in the shrublayer. The understory vegetation with a coverage of90% was dominated by dwarf bamboo of 80–100 cmin height, Sinarundinaria fangiana, Chimonobambusasp., Impatiens sp. etc.

Lithocarpus could be extended to 2300 m asl inthis zone. An altitude of 2300 m was the upper limitfor canopy trees of evergreen broad-leaved species.

Abies-Tsuga-Acer (flabellatum and maximowiczii)-Viburnum-Prunus forest at 2425 m asl (Plot 8)

The forest with an open canopy composed of 25species. Of six co-dominants, Abies and Tsuga weresporadically present in various size classes, and manyof their seedlings were noticed. Regeneration occurredon small heaps of earth to escape from the shade ofthe ground layer. Two species of Acer were of thesporadic type. Viburnum with some seedlings showedthe inverse-J type. Prunus was continuously distrib-uted in small and middle size classes. Enkianthus andLitsea were found in the understory. Liana Actinidiawas in the shrub layer. The understory vegetation witha coverage of 80% was mainly composed of Rubus sp.,Polygonum suffultum, and Sinarundinaria sp.

(3) Coniferous forest zone at 2500–3099 m asl (Plots9 and 10)The coniferous forest zone was exclusively dominatedby one conifer, i.e., Abies fabri. The forests were dis-tributed as patches among the grasslands or shrubscomposed of Salix, Spiraea, Sorbus, Ribes, Rhodo-dendron, etc.Abies forest at 2945 m asl (Plot 10)

Most stems of Abies fabri were in 25–30 cmDBH. Obviously, there were some Abies seedlingsin the understory and it had the sporadic type ofsize distribution. Regeneration on the exposed sitesescaped from the deep shade of the shrub and herblayers. A few Sabina squamata were discovered insmall size classes. The shrub layer was dominatedbyRhododendron, Spiraea, etc. The understory cover-age was 98%, which was occupied by Sinarundinariasp. and Polygonum viviparum.

Discussion

Temperature influence on forest vegetation

The climatic condition is often an important variablecontrolling forest distribution on mountains. The tem-perature conditions at different altitudes on Mt. Emeiwere examined in comparison with the well studied andsimilar scale temperate mountain of Mt. Fuji, centralJapan (Figure 8). The decreasing temperature with alti-tude must explain important vegetational boundaries.

Along altitudes, the decreasing rate of temperat-ure sum WI (Kira 1948) is high on Mt. Emei com-pared with that on Mt. Fuji. As for the upper limitsof evergreen broad-leaved forests, and the limits for

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Figure 7. DBH class frequency distribution for the selected plots of each zonal forests. Dominant species are indicated by asterisk.

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Figure 8. Temperature conditions related to Mt. Emei (solid lines) and Mt. Fuji (broken lines). The coldest (CMT) and the warmest (WMT)monthly mean temperatures are separately indicated. The temperature sum is indicated by warmth-index (WI). The closed and open dots referto the meteorological observatories along altitudes on Mt. Fuji, Mt. Emei and in Sichuan basin area (Wenchuan, Baoxing, Yaan) respectively.

the individual trees, the two temperature conditions,i.e., the temperature sum of 85� �months and the cold-est monthly mean temperature of –1 �C, are decisive,respectively (Ohsawa 1990). The temperature sum of85� � months is at ca. 1600 m asl on Mt. Emei, whileit is at ca. 715 m asl on Mt. Fuji (see Figure 8). Thecoldest monthly mean temperature of –1 �C is at ca.2200 m asl on Mt. Emei, while that is at ca. 800 m aslon Mt. Fuji. The altitude of coldest monthly mean tem-perature of –1 �C almost coincides with that of the WIof 85� �months around 800 m asl on Mt. Fuji; however,on Mt. Emei, the altitude of 2200 m with the coldestmonthly mean temperature of �1 �C is much higherthan that with the WI of 85� �months (ca. 1600 m). Thisexplains why the altitudinal distribution of some ever-green broad-leaved species can exceed the upper limitof evergreen broad-leaved forest. Thus, on Mt. Emei,though the evergreen broad-leaved forest is distributedup to 1500 m asl, some of the component canopy spe-cies, e.g., Lithocarpus cleistocarpus, can extend up to2300 m asl to mix with deciduous and coniferous trees.Ohsawa (1991) showed that in tropical mountains twotemperature conditions (i.e., WI = 85� � months andcoldest monthly mean temperature of –1 �C) occur atdifferent altitudes, while the two temperature condi-tions fall on nearly the same altitude due to the strong

seasonality in temperate mountains. Our results arein accord with the latitudinal trend and the relationbetween the two temperature conditions is intermedi-ate on Mt. Emei as it is intermediate between tropicaland temperate mountains.

The difference of temperature conditions betweenMt. Emei and Mt. Fuji is more pronounced in winterthan in summer. The mean annual range of temper-ature along altitudes is 17–19 �C and 21–25 �C onMt. Emei and Mt. Fuji, respectively. Generally, thedeciduous forest can occur where the mean annualrange of temperature exceeds 20 �C (Wolfe 1979). Thetwo mountains are nearly at the southern boundary ofthe distribution of deciduous forests along latitudinalgradients. Mt. Fuji with more than 20 �C mean annualrange of temperature has a typical deciduous broad-leaved forest zone dominated by Fagus crenata, Tiliajaponica, Quercus mongolica var. grosseserrata andAcer spp. around 800–1600 m asl. Mt. Emei, withless than 20 �C mean annual range of temperature,lacks of the distinctive deciduous forest zone, and theequivalent zone of deciduous forest is occupied by themixed forest zone with dominants, such as Machilus,Lithocarpus, Davidia, Acer, Prunus, Taxus, Tsuga, andAbies. This is probably why the various forest types of

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deciduous, evergreen and coniferous trees, can co-existon Mt. Emei.

Latitudinal comparison of forest zonation

The vertical profile of vegetation zones in southeast-ern to eastern Asia and the characteristics of altitud-inal vegetation zonation on Mt. Emei are given inFigure 9a, b. The evergreen broad-leaved forest zonebelow 1500 m asl on Mt. Emei is closely related tothose on the tropical and subtropical mountains of Mt.Kerinci (Sumatra), Mt. Kinabalu (Borneo), Mt. Yush-an (Taiwan) and Mt. Namshila (Bhutan Himalaya) asexemplified by the occurrence of common characterist-ic species, such as the subtropical elements of Castan-opsis and some lauraceous genera ofPhoebe,Machilus,and Lindera. In contrast, because of human activities,there is no primary evergreen forest under 750 m aslon Mt. Emei. More often, they appear in mixed standswith some seral or introduced conifers, such as Pinusmassoniana, Cunninghamia lanceolata and Crypto-meria fortunei. This is a characteristic of eastern andsouthwestern China (Wang 1961).

In the evergreen/deciduous broad-leaved mixedforest zone at the lower part (1500–2000 m asl) ofthe mixed forest zone on Mt. Emei, though manydeciduous species including some canopy species suchas Choerospondias, Pterostyrax, Acer, Prunus, etc.occur in the emergent layer of the forests around 1500–2000 m asl. Most of them are colonizing or seral spe-cies with shade-intolerant nature and having relativelylong life spans and large sizes. Nevertheless, somepatches of deciduous forest which are mostly domin-ated by the Tertiary relic plants, such as Davidia, Tetra-centron, and Cercidiphyllum, occurred on scree slopesaround 1450–1900 m asl. Many Tertiary relic plantsseem to require very particular habitats, these includeTetracentron sinense in the eastern Himalayas (Ohsawa1987a) and Euptelea polyandra on Mt. Kiyosumi,Japan (Sakai et al. 1995) that occur on scree slopesor deep ravines. Thus, they grow in unstable habitatswith limited competition from other evergreen broad-leaved trees (Guan & Chen 1986; Ohsawa 1987b).Davidia forest, which was considered as a kind ofthe evergreen/deciduous broad-leaved mixed forests,could develop into an evergreen broad-leaved forest aslong as the habitat was stable (Yang & Li 1989). Thus,the patches of deciduous forest on Mt. Emei shouldbe considered as a topographic climax maintained byunstable habitat conditions. The mixed mesophytictype of deciduous forest derived from the evergreen

broad-leaved formation (Wang 1961). Therefore, theTertiary relic deciduous forest on Mt. Emei is con-trolled by topographic habitat conditions. This situ-ation prevents the deciduous broad-leaved forest diffi-cult to establish a clear altitudinal zone on Mt. Emei.

The temperate coniferous forest (the broad-leavedand coniferous mixed forest) in the upper part (2000–2500 m asl) of the mixed forest zone on Mt. Emei issimilar to the equivalent zone on mountains at trans-itional areas between tropical and temperate moun-tains, in which the dominants are Tsuga and Piceain Taiwan (Su 1984) and Bhutan (Ohsawa 1987a),and Tsuga, Abies, and Cryptomeria in Japan such asMt. Miyanoura (Ohsawa 1984b) and Mt. Kirishima(Kitazawa et al. 1961) both in southern Japan. On Mt.Emei, it is characterized by a mixture of both tropic-al montane evergreen elements such as Lithocarpus,and temperate deciduous and coniferous elements likeAcer, Prunus, Abies, Taxus and Tsuga. The forestaround 2200 m asl exhibits a concentrated overlap ofthe tropical and the temperate elements. This explainsthe relatively high diversity in the mixed forest zonewhich is accurately located at the ecotone not only onthe horizontal zonation, but also on the vertical belt ofthis mountain. The diversity trend on Mt. Emei is inaccordance with the trend found on temperate moun-tains, in which lowland species diversity is alreadyrather low and the decrease with altitudes is not asprominent as in tropical mountains (Ohsawa 1995).There are still some possibilities that reduced humanimpacts which have species diversity in lowland.

Mt. Emei is located at the ecotone between tropicaland temperate types which enhances species richness.The mixture of the forest vegetation on this moun-tain was brought about by climatic changes and micro-topographic factors. In order to understand how theforest structure developed, and why some Tertiary rel-ic plants can grow in such unstable scree slopes orvalleys at certain altitudes, we must examine the com-munities in relation to topography as well as altitudes.Also, clarification of the high diversity in the ever-green/deciduous broad-leaved and coniferous mixedforest should clarify the subject.

Acknowledgements

We are indebted to Prof. Dr Marinus J.A. Wergerfor critically reading this paper. We also owe twoanonymous reviewers for their valuable suggestions.We acknowledge the help of Dr Da Liang-Jun of Asia

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Figure 9. The vertical profile of vegetation zones in southeastern to eastern Asia (a) modified from Ohsawa (1993), and the altitudinal vegetationzonation pattern on Mt. Emei (b).

Air Survey Limited Company, Dr Toshiyuki Ohtskaof Chiba University, Dr Wu Jian-Ye of Tokyo Uni-versity and Mr Naoya Yoshida of Chiba University foraccompanying us in field survey. We thank Vice Pro-

fessor Zhu Zheng-Yin and Assistant Luo Ming-Hua ofSichuan Chinese Medicine School for identifying spe-cimens and helping a great deal in the field work aswell.

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