x020566shelf tinning

Received 26 Aug. 2003 Accepted 10 Feb. 2004Supported by the National Natural Science Foundation of China (30230030, 39800012) and Cooperative Project Futian-CityU MangroveResearch and Development Centre.

* Author for correspondence. E-mail: <[email protected]>.

http://www.chineseplantscience.com

Growth Dynamics and Self-Thinning of the Dominant Populationsin the Mangrove Community

LIAO Wen-Bo1*, LAN Chong-Yu 1, ZAN Qi-Jie1, WONG Yuk-Shan2, Nora Fung-Yee TAM2

(1. School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, China;2. City University of Hong Kong, Hong Kong, China)

Abstract : Consecutive investigations in 1994, 1996, 1998, and 2002 in the permanent plots establishedin Futian Mangrove Reserve of Shenzhen, Guangdong Province, revealed that the breaking, drying anddeath of the individual plants or branches in the mangrove communities were significant and the number ofplants in plots covering an area of 200 m2 was 417, 341, 196 and 132; the average density of population persquare meter is 2.08, 1.70, 0.98 and 0.66; the death rate between the interval of two investigations is18.2%, 42.5% and 32.6% respectively. The individuals of population exhibit an obvious diameter at breastheight (DBH) growth. For example, the maximum increment of individual DBH was up to 3.63, 2.45, and 4.52cm in the dominant populations Aegiceras corniculatum (L.) Blanco (Ac), Kandelia candel (L.) Druce (Kc),and Avicennia marina (Forsk.) Vierh. (Am), respectively. At the same time, growth of individual height wasalso prominent. In the second investigation, 233 out of the 341 individuals exhibit a height growth; whereasthe number under the third and fourth investigations was 127 out of 196 and 74 out of 132, respectively.During a 2-year interval, the maximum height growth was 1.5 m in Ac, 1.9 m in Kc, and 1.8 m in Am. Thebiomass also showed a relative change in the mangrove communities. The total biomass of stems andleaves decreased with time but occasionally an increase was found in the second and third investigationsand finally a decrease in the fourth investigation. However, the average biomass of the survived individualsusually increased with time. In terms of the total biomass, the results of the four investigations weresimilar to the previous research in which the data were calculated by the methods of standardized timbers,etc. being 7.57, 8.36, 5.15 and 7.71 kg/m2 during 1994, 1996, 1998 and 2002, respectively. The aboveanalysis indicates that self-thinning of mangrove communities is an important evolutionary process,characterized by drying, breaking, and death of individuals/ramifications. During the process of evolution,fewer new seedlings deve loped, and individual height growth, DBH growth , breaking and death fromdryness maybe closely related to the composition, structure and density of population in the mangrovecommunities.Key words : mangrove; Aegiceras corniculatum ; Kandelia candel ; Avicennia marina ; self-thinning;

growth dynamic

Despite the large body of materials and references con-cerning the research of seashore mangrove in China in theas pects of s pecies compos it ion and geograph icaldistribution, vegetation types, community structure, popu-lation patterns of mangrove plants , and ecological andphysiological feature of mangrove communities (Chang etal., 1957; Lin , 1987; 1997; Chen and Miao, 1994; Li et a l.,1994; Fang and Liang , 1995; Miao and Chen, 1997; Wongand Tam, 1997), very few studies have been reported on thepopulation and community dynamics, and evo lut ion ofmangrove.

Permanent plo ts can be used to study the dynamics ofplant communities because it is easy for observing the indi-vidual characters and life proces s in ecosystem, i.e. the

continuous changing process in time and space; as well asobserving the population change and development of com-munity in ecos ystem, and its environmental relation . Andmangrove is a community type with higher productivity andhigher recession rate, in which the species are of simplercomposition, higher ecological dominance, lower diversityindex and evenness; as well as with clumped pattern of domi-nant population distribution (Chen et al., 1994b; Li et a l.,1994). Therefore, it is o f importance to examine the dy-namic p roces s o f the dominant populat ions by des ign-ing permanent plots in the mangrove ecosys tem for long-term eco log ical research.

The authors designed a piece of permanen t plot cover-ing an area of 200 m2 and completed an eigh t-year’s

Acta Botanica Sinica植物学报 2004, 46 (5): 522-532

523LIAO Wen-Bo et al.: Growth Dynamics and Self-Thinning of the Dominant Populations in the Mangrove Community

observation. The chief objective of this study was to in-vestigate the biomass growth , individual plant growth inheight and diameter at breast heigh t (DBH), and demo-graph ic change in the mangrove communities, as a basisfor further inspection on the population dynamics o f thelocal mangrove.

1 Natural Geographical ConditionThe mangrove of Shenzhen Futian-Neilingding National

Nature Reserve of Guangdong Province, China, covers anarea of 300 hm2, including 13 mangrove plant species, morethan 100 semi-mangrove and seashore plant species, andmore than 190 bird species (Deng et a l., 1986; Yang andShen, 1992a; 1992b; Wang et al., 1993; Chen et al., 1994a;Chang et al., 1998). Especially, it is an important bird habitat,where sometimes there are as many as ten thousand birds.Based on Chen’s (1994b) and Li’s (1994) research, the spe-cies diversity index (Shannon-Wiener index) of Futian man-grove communities is 0.78, the evenness index is 0.49, theimportance value of the dominant population Aegicerascorniculatum (Ac), Kandelia candel (Kc) and Avicenniamarina (Am) is 0.72, 0.19 and 0.09 respectively. The simplecomposition and structure of the mangrove community areadvantageous for further inspecting and observing the re-lationship between species and community evolution (Chenet al., 1994b; Li et al., 1994).

Our selected permanent plot is situated in the northeastFutian Nature Reserve Mangrove in Shenzhen, with a geo-graphical position at about 22°32′N and 114°05′E, be-longing to an area of lower-subtropical oceanic monsoonclimate. The mean annual temperature is 22.55 ℃, meanmonthly temperature is 15.0 ℃ in January, and 28.72 ℃ inJu ly . The annual p recipitat ion is 1 794.14 mm, and annualdaily sunshine is 2 209 h exhibiting an obvious alternationof arid and humid seasons. In the Shenzhen bay and man-grove distribution area, the tide is the semi-diurnal with anaverage tidal range of 1.36 m, being maximal at about 2.8 m.The average salinity of seawater is < 1.5%, with a pH of 7.6.The physical and chemical properties of soil are as follows:organic compound, 22.3 g/kg; available N, 49.5 mg/kg; avail-able P, 50.9 mg/kg; available K, 951.2 mg/kg; so il salin ity,2.1%. Among the clunch deposit, 6.31% of the grain com-position is > 0.25 mm, 24.87% of which is 0.25-0.01 mm and67.35% of which is < 0.01 mm (Li et a l., 1994; Tam et a l.,1995a; Chang et al., 1998; Huang et al., 2000).

2 Materials and Methods2.1 Plot design

In 1994 we selected two zones, A and B, in a natural and

typical mangrove community in the south of Shazui villageof Shenzhen bay. Each zone was 10 m in width and 180 m inlength extending towards the beach. The zones were 150 mapart. A 0.3 m concrete bat was built on each side-border ofA-zone. A-zone was then irrigated and drained with livingwaste-water at the time after daily ebb-tide weekly for oneyear. B-zone was served as control. Four permanent plotsA-S1 to A-S4 and B-S1 to B-S4 were set up in A- and B-zonerespectively. In each zone the four plots (each plot cover-ing an area of 5 m× 5 m) extended in sequence from thebottomland towards the beach, the total plot area was 200m2. The first plot A-S1 in A-zone (likewise B-S1 in B-zone)was 20 m away from bottomland. A-S2, A-S3 and A-S4 in A-zone (B-S2, B-S3 and B-S4 in B-zone) were located in se-quence further away from the bottomland. The space be-tween the neighboring plots was identically 10 m.2.2 Plot investigation

Plants with height of over 1.3 m, including all brancheswith DBH over 1 cm, that had branched from the t runk atlevels below 1.3 m above-ground were accounted. Indi-vidual plant was identified with plastic-sealed ID (with thecode number). The ID cards were tagged on individual tree/branch at the height of 1.3 m. Measurements included thetree/branch height (H, or length (L)), trunk circumference atbreast height (expressed as DBH by divid ing the breastcircumference by 3.14), coord inate position of individuals(X, Y); and from which all data were computerized intodatabase (Li et al., 1987; Yu et al., 1993; Wang et al., 1996).The tree/branch height was measured at the highes t (thelongest) part and the breast circumference was measuredaround trunk at 1.3 m above-ground us ing a measuringtape. Four consecutive invest igations were carried out inJanuary of 1994, 1996, 1998 and 2002.

It is preferab le to take a 5 m× 5 m -s ized s ite as anindividual plot, since a plot with an area o f 25 m2 usuallyincludes three main dominant populations in the mangrovecommunity. In addition, the number of individual plants inthe eight plots, ranging from 41 to 65, represented a suit-able density fo r study. Moreover the population in thecommunity, being different from those in the land fo rest,grow in clusters with luxurian t branches from short andstout bases. During the developmental process, the basechanges much s lower than the b ranches. Therefore it ismuch easier to inspect the change of populations in man-grove community by measuring the total area at 1.3 m breast

height (ABH; ABH = π (DBH/2)2) of plants/branches thanthe total area at bas e, as the measurement of the latter isvery difficult and could be inaccurate. Furthermore, as thepermanent p lots were des igned in the core region of the

Acta Botanica Sinica 植物学报 Vol.46 No.5 2004524

mangrove community , they actually occupied only20+5+10+5+10+5+10+5 = 70 m among the 180 m from thebottomland extending to the beach. There was still a 30-40m conservation zone (of the same community), and another30-40 m zone o f annual herbaceous plan t Acanthusilicifolius L. (Ai), and also a 30 m zone of sporadic distribu-tion zone at the beach side (Wong et al., 1995a).2.3 Data analysis

The following equations were employed in analyses.Index of the area ABH: ABH-Index = Total of all indi-

vidual ABH in community or plots / Total area of all commu-nity or plots;

Biomass of mangrove community: W = a×DBH2 ×H×b (W is weight of total biomass; DBH is diameter at breastheigh t; H is tree height (length); a and b are constan ts),based on an analysis of Futian mangrove communities, thea and b values are confirmed by Tam et al. (1995b), i.e.:

Ac: LogW = 1.496+0.465 Log(DBH2×H)Kc: LogW = 2.814+1.053 Log(DBH2×H)Am: LogW = 2.092+0.529 Log(DBH2×H)

where W is the total b iomass of the above-ground parts(kg), DBH is diameter at breas t heigh t (m), H is height(length) (m).

3 Results and Analysis3.1 Characters of communities in the plots

In the eight plots A-S1, A-S2, A-S3, A-S4, B-S1, B-S2, B-S3 and B-S4, generally speaking, the vertical stratificationof communities was not significant with crown density ofabout 0.90-0.96. The dominant populations examined in1994 included Ac with a maximal DBH of 7.6 cm, Kc with amaximal DBH up to 12.1 cm, and Am with a maximal DBH of9.6 cm, and other biennial herbaceous species such as Ai.The number o f Kc and Ac were overwhelming in themangrove. And Am was a minor species, but it could be-come dominant in some sectional areas. Ai was particularlydominant in B-S3 and B-S4, d istributed s catteredly o r inclusters; As they exhibited a rapid life cycle only its heightand number were recorded.

In A- and B-zone, according to Chen’s (1994b) andLi’s (1994) research , the degree o f correlat ion amongthe dominan t populat ions (Ac, Kc and Am) was les ssign ifican t than their complexity, reflect ing a relativestab ility o f the mangrove community. In addit ion, thecalcu lat ing un it of total biomass in the mangrove com-munit ies approximated 12.14 kg/m2 (Tam et al ., 1995b).

Based on a detailed investigation in 1994, the main char-acters of the plot communities were as follows:

(1) Plo t A-S1 The Ac community, composed of Ac

solely, contained a total of 17 clusters with 54 main branches.Since Ac grows in clusters and all main branches usuallygrow directly from the root (or base), therefore they wererecorded as the same coordination, but for those branchesgrown above 1.3 m, from a main trunk they were accountedas the same individual plant.

(2) Plot A-S2 The Ac + Kc community contained fiveclusters of Ac with 41 branches and two clusters of Kc witheight branches.

(3) Plot A-S3 The Ac community contained 19 clusterswith 41 branches.

(4) Plot A-S4 The Ac + Kc community contained 21clusters of Ac with 43 branches and one cluster of Kc withfour branches.

(5) Plot B-S1 The Ac + Kc community contained 27clusters of Ac with 48 branches and four clusters of Kcwith 16 branches.

(6) Plot B-S2 The Ac + Kc + Am community contained16 clusters o f Ac with 50 branches, th ree clusters of Kcwith 10 branches, and one plant of Am (one branch).

(7) Plot B-S3 The Ac + Kc + Am community containedtwo clusters of Ac with 16 branches, six clusters of Kc with12 branches, six clusters of Am with nine branches, and theAi included nine clusters with height ca. 1.5 m and six clus-ters with height ca. 2 m.

(8) Plot B-S4 The Kc + Ac + Am community containednine clusters of Ac with 13 branches, 20 clusters of Kc with47 branches, two clusters of Am with six branches, and Aimore than 200 single branches.3.2 Growth dynamics of population3.2.1 Growth of population Based on the four consecu-tive investigations in January of 1994, 1996, 1998, and 2002,the individual change of A- and B-zone is shown in Table 1.

From Table 1, it is shown that in A-zone, the populationAc exhibited the highest branch death rate being 10.6% in1994 and up to 36.9% in 1998, and that of Kc was minimal asno death was found in 1996, and only one branch died(8.3%) in 1998.

In B-zone, the branch-death rate was still the highest inthe Ac population, accounted for 31.7% in 1996 and 73.2%in 1998. Eighty-six out of 126 individual plants survived in1996 and 23 survived in 1998. Branch death rate of Ampopulation ranked the second highest, being 31.2% in 1996,45.4% in 1998, and 33.3% in 2002. The death rate of Kc washigher than that in A-zone, accoun ted fo r 14.3% in 1996,23.6% in 1998 and 20.0% in 2002.3.2.2 DBH growth As shown in Table 2, in the 1994investigation o f A-zone, the DBH of the Ac populationranged 1.46-7.64 cm with an average increment of 0.37,


0.22 and 0.49 cm in 1996, 1998 and 2002 respectively. Com-paratively that of the Kc population ranged 3.66-12.10 cmwith an average increment of 0.76, 0.50 and 1.23 cmrespectively, indicat ing a more rapid g rowth o f the Kcpopulation.

In the B-zone, the average DBH of Ac, Kc and Am popu-lation in 1994 was 0.99-6.37 cm, 1.43-10.19 cm, and 3.03-9.55 cm, increasing 0.27, 0.74 and 1.00 cm in 1996, 0.11, 0.38and 0.31 cm in 1998, and 0.38, 1.01 and 1.42 cm in 2002respectively. Their growth was obviously increased in the

order of Am > Kc > Ac.3.2.3 Height growth There was an obvious growth inheight in the main population of the mangrove communityand that branch breaking, blight or death leading to nega-tive growth was also apparent (Table 3). From 1994 to 1996,the height growth of Ac increased 1.5 m in A-zone and thatof Kc increased 1.9 m in B-zone.

Further analys is showed significant growth differenceamong the dominant populations Kc, Ac and Am in A-zoneand B-zone. During the four invest igat ions , the to tal

Table 1 Demographic change in mangrove plots under different investigations* Year / Individuals 1994 1996 Second death rate** 1998 Third death rate** 2002 Fourth death rate**A-zone Ac 179 160 10.6% 101 36.9% 63 37.6%

Kc 12 12 0 11 8.3% 11 0TI 191 172 10.0% 112 34.9% 74 33.9%

B-zone Ac 126 86 31.7% 23 73.2% 10 56.5%Kc 84 72 14.3% 55 23.6% 44 20.0%Am 16 11 31.2% 6 45.4% 4 33.3%TI 226 169 25.2% 84 50.3% 58 31.0%

T I in A- and B-zone 417 341 18.2% 196 42.5% 132 32.6%*, number in 2000 not available; **, the death rate was calculated by using number of individuals in the former investigation as the cardinalnumber. Ac, Aegiceras corniculatum ; Am, Avicennia marina; Kc, Kandelia candel; T I, total individuals.

Table 2 Individual diameter at breast height (DBH) growth in mangrove plots under different investigations*

PopulationDBH

1994 1996Increment

1998Increment

2002Increment

(cm) (cm)** (cm)** (cm)**A-zone Ac TI 179 160 - 101 - 70 -

Maximum 7.64 8.82 3.63 9.49 1.43 10.35 4.68Minimum 1.46 1.43 -0.29 0.80 -0.35 2.99 -0.51Average 4.15 4.58 0.37 5.12 0.22 5.80 0.49SD 1.569 1.878 0.478 1.821 0.304 1.835 0.990

Kc TI 12 12 - 11 - 11 -Maximum 12.10 12.68 1.27 13.12 0.76 14.45 6.18Minimum 3.66 3.82 0.16 6.53 0.19 7.64 -0.92Average 7.42 8.18 0.76 9.08 0.50 10.31 1.23SD 2.215 2.331 0.276 2.059 0.208 2.262 0.789

B-zone Ac TI 126 86 - 23 - 10 -Maximum 6.37 7.80 2.55 8.12 0.70 9.04 0.96Minimum 0.99 1.27 -0.41 2.55 0 1.91 -0.80Average 3.02 3.46 0.27 4.35 0.11 4.28 0.38SD 1.075 1.262 0.416 1.437 0.160 1.892 0.764

Kc TI 84 72 - 55 - 43 -Maximum 10.19 10.99 2.45 11.78 1.46 14.01 11.46Minimum 1.43 2.23 -0.35 2.55 -0.06 3.92 -0.79Average 3.78 4.81 0.74 5.48 0.38 6.52 1.01SD 1.500 1.553 0.590 1.779 0.395 2.028 1.114

Am TI 16 11 - 6 - 3 -Maximum 9.55 14.08 4.52 14.65 1.27 16.15 2.55Minimum 3.03 3.09 -0.16 6.37 -0.06 9.14 0.70Average 5.10 6.66 1.00 9.55 0.31 12.21 1.42SD 2.066 3.602 0.825 3.233 0.527 3.181 0.819

*, all dead plants and branches were excluded from statistical analyses; **, positive increment > 0, zero increment = 0, negative increment <0 (That the stem of individuals dur ing the process of branch drying and breaking shrank slightly results in a negative increment of the DBHgrowth and leads to ultimate death). Abbreviations are the same as in Table 1.


number of individuals decreased from 417 to 341, 196 and132 res pectively. In the second investigation, among 341individuals 286 exhibited positive DBH growth, 22 individu-als had no growth and 33 had negative growth (DBHconst riction). However, in the third investigation, 137 ofthe 196 individuals exhibited positive DBH growth, 47 hadno growth and 12 had negative growth. As for the heightgrowth , in 1996, 233 of the 341 individuals had increasedheight growth, 20 had no growth and 88 had negative heightgrowth. From 1996 to 1998, 145 individuals died, including68 from the 88 with negative height growth counted in 1996.And among the rest 196 survived individuals, 127 had in-creased height growth, 39 ceased growth and 30 had nega-tive height growth.3.3 Self-thinning of population and succession of com-munities

Death of branches in mangrove plants initiated from theapex, expanded to the base and finally broke off. A commonphenomenon is that firstly the branch stopped growing inlength and then in DBH. Many of the breaking and dryingbranches migh t become s omewhat stouter near the t reecrown and then shrank and eventually died and broke off.

The process of branch-death could extend slowly down to1.3 m above ground.

The drying, breaking and dying of branches of man-grove population is a natural self-thinning process as wellas an ecological phenomenon of forest gap formation whichis closely related to population composition, communitycons truction, age construction and nature geograph icalposition. In the Futian mangrove region of Shenzhen City,the mangrove population was of a cluster growth. Both Acand Am had abundant branches, thus, their branch deathobviously could affect space change, although the basediameter o f the plants showed relat ively little change asbeing expressed in the disappearance of only nine coordi-nat ions in A-zone but 17 coordinations in B-zone whichwas inves tigated in 1996, reflecting a change of groundstratum indeed.

Moreover, the forest gap formation of mangrove com-munity was different from that of the land forest commu-nity such as the lower sub-tropic monsoon evergreen broad-leaved forest in South China, which generally resulted fromdeath of various populations. In contrast, the self-thinningproces s in the mangrove popu lat ion, becaus e of those

Table 3 Individual height growth in mangrove plots during eight years*

PopulationHeight

1994 1996Increment

1998Increment

2002Increment

(m) (m)** (m)** (m)**A-zone Ac TI 179 160 - 101 - 63 -

Maximum 5.800 6.500 1.500 6.500 1.300 6.200 0.800Minimum 1.400 0.800 -4.000 0.600 -3.800 1.300 -2.500Average 4.180 4.180 -0.044 4.470 -0.164 4.400 -0.230SD 0.992 1.565 0.884 1.480 0.726 1.465 0.259

Kc TI 12 12 - 11 - 11 -Maximum 5.500 6.300 1.100 6.400 0.200 6.500 0.600Minimum 4.400 5 0.300 5.100 0 5.100 -0.400Average 5.000 5.700 0.650 5.880 0.127 6.000 0.164SD 0.387 0.496 0.215 0.485 0.065 0.563 0.277

B-zone Ac TI 126 86 - 23 - 10 -Maximum 5.200 5.900 1.800 6.900 1.000 5.800 1.000Minimum 1.300 0.600 -3.900 2.600 -1.100 1.500 -3.900Average 3.570 3.630 -0.044 4.490 0.070 4.050 -0.590SD 0.933 1.332 0.959 0.903 0.370 1.283 1.500

Kc TI 84 72 - 55 - 44 -Maximum 5.100 5.400 1.900 6.400 1.200 6.700 3.000Minimum 2.200 0.600 -3.500 3.500 -0.500 1.300 -2.800Average 3.620 4.190 0.399 4.720 0.253 5.820 1.057SD 0.820 0.992 0.872 0.632 0.266 1.079 1.254

Am TI 16 11 - 6 - 4 -Maximum 5.700 6.700 1.800 6.900 0.600 6.200 0.500Minimum 1.300 1.400 -2.600 4.000 -2.500 4.500 -0.700Average 3.850 4.680 0.364 5.400 -0.717 5.700 -0.025SD 1.165 1.942 1.314 1.178 1.309 0.850 0.499

*, dead plants and branches were excluded from statistical analyses through all investigations; **, positive increment>0, zero increment = 0,negative increment <0. Abbreviations are the same as in Table 1.


plants with abundant branches and bigger base diameter,was usually carried out by continuous drying and breakingof branches.

The forest community in Shenzhen mangrove NatureRes erve, in part icular, has developed into a mature andstable one, where the young plants of the abundant popu-lations did not occur, and the seedlings were also seldomfound, it was likely that the natural renew may be attributedto the formation of forest gap after the death of individuals.Nevertheless, if the formation of forest gap and self-thin-n ing was related to ind iv idual death from naturalsenescence, the colon ized dist ribu tion of population inmangrove community would become randomized, and thecommunities will eventually undergo a stage of decay (Chenet a l., 1994b; Li et a l., 1994). An increas e of dry ing andbreaking branches and the sparsity of young trees andseedlings in the community indicate that this communitywas at a special stage, or a s ub-climax stage. On the otherhand, based on a recent research (Zhong et al., 1996), theage of Shenzhen mangrove community could rough ly beabout 20 years, and it was approved that the evolut ioncycle of mangrove community could be rather rapid andshort.3.4 Dominance of communities and their change inbiomass

The dominance of communities were usually expressedby the total ABH of the populations (Table 4).

From 1994 to 1996, the DBH of the main populations in

A- and B-zone was obviously increased, whereas muchmore decreased by 1998 indicating a marked strengtheningof self-thinn ing activity. In the development process ofmangrove community, the total individuals were obviouslydeceased, while the ABH of each individual was increasedduring the eight years, thus it was considered that the self-thinn ing was mainly res ulted from the individual diminu-tion and in turn reduction of population density. The self-thinning p rocess varied among three populations of thecommunity, characterized by an individual d iminution ofAc and increment of ABH (no obvious change of number)of Kc in the A-zone and apparent individual diminution ofboth Ac and Kc in the B-zone, as if there was less DBHchange of Ac and Kc in the B-zone than in A-zone. Appar-ently there was a negative correlation between the changeof ABH and individual number in Ac of A-zone as well as inAc and Kc of B-zone. As for the Am in B-zone, there was anincrease of ABH and no obvious decreas e of individualnumber, because unlike Ac, it has a major trunk with fewbranches.

Generally speaking, taking the land forest ecosystem asan example, a maximum ABH index and a minimum plant orbranch density may give rise to a higher community value.In fact, the evaluating index is related to various methodol-ogy and validation of the fo rest community. For example,an increase of the ABH and ABH-index indicates a growth-climax or -s ubclimax of the community fo llowed by adeclination trait and eventually an trend to decline, an

Table 4 Change of total area at breast height (ABH) in mangrove plots during the eight years Year / Individuals 1994 1996 1998 2002A-zone Ac Total individuals 179 160 101 64

TABH (cm2) 2 635.09 2 885.81 2 256.90 1 793.90AABH (cm2)* 14.72 18.04 22.35 28.51

Kc Total individuals 12 12 11 11TABH (cm2) 560.66 677.53 744.63 958.00AABH (cm2) 46.72 56.46 67.69 87.09

Subtotal Total individuals 191 172 112 75TABH (cm2) 3 195.76 3 563.34 3 001.54 2 753.90

B-zone Ac Total individuals 126 86 23 10TABH (cm2)** 1 014.87 913.49 317.84 169.54AABH (cm2)*** 8.05 10.62 16.43 16.95

Kc Total individuals 84 72 55 44TABH (cm2) 1 088.84 1 440.73 1 432.12 1 606.15AABH (cm2) 12.96 20.01 26.04 36.50

Am Total individuals 16 11 6 4TABH (cm2) 377.40 485.41 470.98 492.21AABH (cm2) 23.59 44.13 78.50 123.05

Subtotal Total individuals 226 169 84 58TABH (cm2) 2 481.11 2 839.63 2 280.94 2 267.90

*, negative corr elat ion of tota l indiv iduals (P < 0.05 ); **, sign ificant po sitive corr elat ion of tot al indiv iduals (P < 0.05 ); * **, high lysignificant negat ive co rrelation of tot al individuals (P < 0.0 1). AABH, average ABH; TABH, to tal ABH.


mangrove community. Comparing with the results in Table1, the death rate was positively related to the popu lationdensity.4.2 Dynamics of population growth in A-zone and B-zone

Based on the resu lts demonstrated in Tab les 1-4 andFig.4, the difference in the dynamics of population growthwas also obvious. In 1995, plots in A-zone was experimen-tally treated with living waste-water irrigation and drainageafter ebb-tide at weekly interval for one year, receiv ing atotal volume equaling 2 600 m3 in the plots o f ca. 1 800 m2

(A-zone, an area of 180 m× 10 m). B-zone was served ascontrol. By comparing the two kinds of plots, we might findsome evidence whether the mangrove forests and man-grove plants could develop some anti-pollution endurancethat is of important significance in ecological and environ-ment conservation.4.2.1 Comparison of population mortality (Table 1) InA-zone, the death rate was 10.0% in 1996 and 34.9% in1998, and was 25.2% and 50.3% in B-zone, indicating ahigher death rate in the latter. Furthermore, the treatment ofwaste-water irrigation and drainage in A-zone exerted noimpact on its population mortality. In further analysis, thedeath rate of population in A-S1, A-S2, A-S3 and A-S4 of A-zone in 1996 was 7.4%, 10.2%, 17.1% and 6.4% respectively,with an average of 10.0%; and that of B-S1, B-S2, B-S3 andB-S4 of B-zone was 21.9%, 26.2%, 25.0% and 27.7%respectively with an average of 25.2%. Noticeably, B-zone

had a higher and more even death rate among plots, whileA-zone showed great disparity in death rate of population,averaged from 6.4% to 17.1%. The analysis suggested thatthe death process could mainly be related to the s pecies,branch composition and population construction.4.2.2 Comparison of DBH growth The average DBHincrement of Ac in A-zone was 10.36% in 1996 and 11.79%in 1998; and that of Ac in B-zone was 14.09% in 1996 and22.65% in 1998 (Table 2). The average increment o f DBHgrowth of Kc in A-zone was 10.24% in 1996 and 11.00% in1998; and that o f B-zone was 26.56% and 13.99%respectively. Both Ac and Kc exhib ited a dominant DBHgrowth in B-zone. Moreover, in B-zone Am also showed aremarkable average increment of DBH growth of 30.59% in1996 and 43.39% in 1998.4.2.3 Comparison of height (length) growth The aver-age growth increment of heigh t o f Ac in A-zone was-0.95% (negative growth) in 1996, and 6.94% in 1998; andwas 1.69% and 22.72% respectively in B-zone. The averageincrement of height growth o f Kc was 13.10% in 1996 and3.16% in 1998 in A-zone and 14.80% and 12.65% res pec-tively in B-zone (Table 3). Obviously the height growth ofboth Ac and Kc in B-zone was more significant. Likewisethe Am population also had significant height growth in B-zone, being 21.56% and 15.38% respectively.

On the whole, the more obvious change in B-zone wasrelated to the original status (density, ABH, absolute height

Table 5 Comparison of population density in mangrove plots during eight years*

Year / Individuals 1994Population

1996Population

1998Population

2002Population

density density density densityA-S1 Ac 54 2.16 50 2.00 39 1.56 22 0.88A-S2 Ac 41

1.9636

1.3623

1.2420

1.12Kc 8 8 8 8

A-S3 Ac 41 1.64 34 1.36 14 0.56 7 0.28A-S4 Ac 43

1.8840

1.7625

1.6014

0.68Kc 4 4 3 3

B-S1 Ac 482.56

352.00

40.68

20.60

Kc 16 15 13 13B-S2 Ac 50 34 15 8

Kc 10 2.44 10 1.80 9 1.00 7 0.64Am 1 1 1 1

B-S3 Ac 16 8 4 0Kc 11 1.44 11 1.08 10 0.76 6 0.36Am 9 8 5 3

B-S4 Ac 12 9 0 0Kc 47 2.60 36 1.88 23 0.92 18 0.72Am 6 2 0 0

TI** in A- and 417 2.08 341 1.70 196 0.98 132 0.66 B-zone*, in the different plots of 5 m×5 m in A- and B-zone, density change (individuals/m2) was the result of population difference. Abbreviationsare the same as in Table 1.


of plant or branch, etc.) in the population and community.In the first investigation in 1994, the average DBH of Acwas 4.15 cm in A-zone and 3.02 cm in B-zone s howing adifference of 1.13 cm, and the latter was 37.42% less thanthe former. In respect of average height, Ac was 4.18 m inA-zone and 3.57m in B-zone respectively with a differenceof 0.61 m, then the height of Ac in B-zone was 17.09% lessthan that in A-zone. Ev idently populations of B-zone ex-hibited much more growth potential both in DBH and height.At the s ame time, the individual death rate in B-zone washigher, indicating that pollu tion may no t be the ess entialcause for the disparity between the two zones. On the otherhand , one might consider if was te-water irrigation mightprovide some nourishment for the vegetation could beconsidered. Some recent studies (Tam et al., 1995a; Wonget a l., 1995a; Huang et a l., 2000) have revealed that theto tal organic C and P in s oil had no sign ificant changebefore and after waste-water discharge in A-zone and theleaf conten ts of total organic C, P, and N were similar aswell.

5 ConclusionAn 8-year consecutive and comprehensive survey and

analysis of the typical mangrove plots in Shenzhen FutianMangrove Nature Reserve had demonstrated that the totalnumber of individuals and population density in mangrovecommunity decreased progres sively with relevant ind i-vidual death, branch-breaking and growth of DBH, heightas well as biomass. This indicates that this mangrove com-munity has been developing with a pos itive process ofevolution characterized by the following features:

(1) Self-thinning of the Shenzhen Futian mangrove com-munity is an important evolutionary process characterizedby frequent plant and branch death, drying and breaking.But the clustered development of mangrove plants hasmuch less impacts on positional change of ground surface.

(2) Growth in DBH and height of mangrove populationwas quite significant. Generally speaking, the total above-ground biomass usually decreased, nevertheless, the aver-age individual biomass was increased. For example, theaverage individual biomass of Ac in A-zone was 3.18, 3.50,4.98 and 4.46 kg /p lan t in 1994, 1996, 1998 and 2002res pectively ; that of Kc was 16.78, 23.2, 28.66 and 38.50kg/plant respect ively ; and that o f Am in B-zone was11.13, 17.06, 25.73 and 34.12 kg/plant respectively.

(3) The change in growth of height and DBH, individualand branch death is direct ly related to the original state(composition and st ructu re construction) of populat ionduring the evolutionary process of the community.

(4) Nonetheless, the potential physiological impacts ofthe environmental pollution to the mangrove communitymerits further consideration and investigation.

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(Managing editor: HAN Ya-Qin)

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