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Sprout Demography and Intraclonal Conlpetition in Lycium barbarum, a Clonal Shrub, during an Early Phase of Revegetation

L;jciun~ b n r b a ~ t i n ~ , Clulial shrub, I'ost-h.? revcgetatio~i, Population of sprouts, Demography, Growth ilnalysis, Intrnclonnl compotition

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I'YSEK 1'. (1091): Sprout tlomogrclphy allcl ilitraclorial compotition in hjcium barbarum, u, clonal shrub, during i111 early phasc of rovegetation. - Folia Geobot. Phytotax., Praha, 26: 141-l(i9. - A demographic study of post-fire revogetntion in >L clonal shrub L y c i v m barba- r u m is prosontccl. Sponta~ioous clovclop~rient of the sprout population was estimated using both nonclcstrnctivo ant1 destructive mrthods lid compared to tho data from oxporirnentally thinnod plots. Relationships between growth pitramoters (height, biomass, leaf area) ;mtl thcir chnngos in the cowsc of clevolop~rici~t aro analysed. Doscrlptioii of the seasonal dyn:lmics of the sprout population is given. Intraclonal cocnpetition among individual sprouts was ohscrvotl. Rcsults uf thc growth analysis are prcsrnlcd for populwtlo~~s of tliffcrcnt age.

Shrubs represent an ecolop~cally i~ l rpo~~tan t group of plants nllich 111ay occur in a wide rnngo of habitats. The clonal habit is typical of l n a n shrubs. It nlay be favoured in estrclne habitats where the cllances of suocessful seedllng cstablish- lnerlt are low (SILVERTOWN 1982). Ur~f'ortl~nately delnographic studies on clonal shrubs arc few (see HARPER 1977, furthcr n~orc e.g. Annaira&~sox 1975, WEST et al. 1979, VASEIC 1980, ACLD 1987, H U E S ~ I C E 1987), ~llostly because of colnplica- ted lnodular construction (WHITE 1979, BEGOS et al. 1986), the different age structure of individual organs and generally difficult identification of single genets in clonal plants (KAYS et HARPER 1974, HARPER 1981, BELL 198-1, ~ ~ ' A T R I N S O N

et WHITE 1985, COOIE 1985). I n adclition, slow gronth ancl a long life span nlake shrubs notoriously difficult subjects for experirl~ontal cultiration for tho purposes of studying life cycles and testing hypo the.^^.

This paper presents a clei~iographic stndg of the revegetation in a clonal shrub Lycizlm bn?bn~unl folloniing the first year after burning. It acldrcsses following questions :

1. How do the relationships l~etween gronrth parameters (height, biomass, leafincss) vary as tlic 1)01)ulation gro~vs? IS it possible to use any easily iileasurable gron~tll parameter for- nonclcstructivc running obse~.vation?

2. What are the nlntual relationships among niodnlar units? Which is the appropriate i~iodular level for clenlogmphic studies at an early stage of tlevclop- ment ?

S T U D Y S I T E

The fioltl work was carried out in the town of f'lzeil (lat. 49.46 N, long. 13.24 E), West Bohemia. The mctnl imnui~l tcinperature of the area is 7.8 'C, annual precipitation is 495 inin (according to a 60-year avcrage, VESECI<~- ct al. 1961) .Tho study site was located along the railway line, 350 111 distant froin the central rrlilway station, on the right bank of the Radbuza river. L?jciwm baro ic~~tm preclominaterl on the esposetl (35-40") south-facing slope. The shrub layor i ~ t the locality consisted of L o ~ z i c e m batnrica, S y n ~ ~ ~ J ~ o r i c a r p o s r i v u l a ~ i s , Clernntis vitalba, Rosa subcanina, Berberis vulgaris and Rubus sp. div. Among trecs, Frazinzts exccl.<ior and Robinia pseudoacacia shodcl be rnentionecl. Herbs occurrcd only rilrcly in the undergrowth of the de~lse Lyci'um barbn- r u m stands (Bdloba ?aigra, Impntiens pcl?viflorcr, Pocc ?lernornlis, Urticn dioica ilnd Clrdidoniun~ majus ) .

The area of 20x 50 m covered by 14tjci1c.m barbartcm was completely burned in May 198S. Analyses of soil samples are presented in Table 1. The increase in the content of Cl-, SO:-, Ca?+ and I<+ is apparent whon burnt down places (samplos no. 6 , 7, 8) are co~nparcd with the old stand of L7jcium barbarum growing in the vicinity (no. 4, 5). The soil was claycy-sandy, loose, drying up, with n high content of ash in the surface layer.

S T U D Y S P E C I E S

h j c i u m b a r b a ~ u m (Solanaceae) is an adventive species (neophyte) in Czechoslovakit~. I t is a native of China, widely naturalized in Europe ( C n & ~ & r a s et al. 1987). I ts occurrence is duc to plantation in hedges and vineyards and subsequent escape from cultivation (DOST~L 1954). I t is frequently naturalized in hedges and on walls and waste ground, along railway lines and in fringe habitats.

Large monospecific thickets of Lqc ium barbarum ilre forincd by older leafloss branches covercd with horizontal and overhanging upper branches which bear leaves. Stcms aro up to 2.5-3 m, arching, greyish-white, often spiny (SCHROEDER 1964, CHAPIMAX et al. 1987).

The species spreads clont~lly through the horizontal root system, with clumps of sprouts growing from the root buds (Fig. 1). The individual sprouts bear alternate, shortly petiolate leavcs, up to 10 cm, varying from very narrowly elliptical to ntirrowly lanceolate in form. No seedling recruitment was observcd at the locality. Slight predation by aphids occurrcd at the locality throughout the year. Extensive stands of L?jc.ium barbnrun~ were infested by mildew after growth finished at the end of the vegetational period.

The species may serve as an example of modularity apparent a t more than one level (HARPER 1977, 1978, WHITE 1979, BEGOX et al. 1986, HUTCHINGS 1986a). One can thus recognize modules (a) at the level of clumps of sprouts growing close together from tho more or less horizontal root andlor (b) a t the level of individual sprouts. For roots lying relatively deep in the soil (more than 10 cm in some ctlses), sprouts can be rather distant from each other when they reach the ground surface. Moreover, tho clu~nps are ofton situated closc to each other. The sprouts of different clumps can thus grow neamr to each othor than those belonging to the same clu~np. For the resulting problems linked with the identification of clumps in tho field, tho sprouts aro more convenient units ant1 these are the focus of the present study.

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M E T H O D S

The study plots for detailed observation were located in May 1988, immctliately after burning. The following treatment regimes were ;rpplicd:

a) The plot 0.5 X 0.5 In was tlesignecl for running observation (plot R) in the course of the vegetationill period. Sprouts were recortlcd as thoy emerged. I numbered all ii~tlivitlual sprouts with plastic tags fastened around the stein with a wire (HUTCIIIXGS I986a). I t was necessary to transpose tags to the upper parts of steins during each meas~~rement in order to kocp interforcnce with growing sprouts t o a minimum. Othcrwisc, tags must be looked for with tliffculty in the lower parts of the stand. Measureinents of sprout height were made on tho plot wrokly at tho beginning of revegetation and monthly during the second half of the vegotationill period. The plot was harvesterl on Septernbor 16.

Fig. 1. Clump arrangelnent in L!/ciun~ bn~bn- rum. Soil s ~ u f ~ l c e is intlicatctl by il tiashatl line. Ilol. J. P ~ B ~ i o v b .

PYQEIC: S P R O U T DE3IOGRAPHl- IX L Y C I U M BARBARUM 145

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b) The clerlsity of cight sprouts per 0.25 m' was osperimentillly maintailled in the thinned plot (T) by regularly ro~noving nowly emerged sprouts. Onc sprout from each clump prcsent in the plot was retained. The running observation was conductecl as in the case of plot R.

c) Two quadrate plots 0.26 in2 wcre harvrsted, the first (plot A) on July 1 (aftcr 30 tlays of population tlcvclopment), ancl the second (plot B) on Scptembor 14 (74 d;tys olcl population).

Harvested sprouts w c ~ c divided according to clunlps. For each intliviclual sprout tho following characteristics were recorded: height, biomass, (scparatcly for stems, lcavcs, ant1 branches), leaf area, numbor of leaves, and basal diametor of stcm. For cstimstion of biomass, plunt ~natorial was driod up for 46 hours a t 85 "C. The leaf area assessnlont was mirdo by the drawing method ( R ~ c m - o v s ~ 6 e t al. 1967).

d) To estimate the maximum bio~nass produced by a sing10 clump, tho sprouts belonging to thc other clumps were romoved from its vicinity on five plots of 1 ni2. Variation in thc density of clumps and sprouts was also estimated.

e) I n addition, two plots of 0.5 X 0.6 m were harvested on Scptembcr 16 for estimation of the total biomass per plot.

For sunlmarization of the treatments applictl see Table 2. Parsmotors of growth analysis were calculated from the data obtained (H.u%r~n 1977, hloort~

ot CHAPXAN 1986, R Y C ~ O V S K L et al. 1987). The data were analysed using linear ~ c g r c s s i o ~ ~ accortli~lg to SOKAL at I~ORLB (19S1). Where

necessary, logarithmic transforzlliition was usrd for calculation.

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Fig. 2. Spi.out bio~nass plvttcd against sprout height. a) 30 days oltl populatioll (plot A) - full circlcs b) 74-87 tlays olti ~opulat ion (plots B, R) -empty circles Sprouts of thr tbiin~cd plot (T) - triangles. Numbers indicato percc~~tagc pl.oportior1 of thc bio- tmass of branches. Area delin~itated by the frame on Fig. 2a corresponds t o that indicated by the clashetl l i~ic on Fig. 2b.

PYQEK: SPROUT D E M O G R A P H Y I N L Y C I U N B A R B A R U N 147

RESULTS

P a r a m e t e r s of g r o w t h

A close relationship between sprout biomass and sprout height was found in the 30 day old population changing frotn linear t o a J-shapecl with increasing sprout height (Pig. 2a). Sinall morphological diversification within the rapidly growing

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Fig. 3. Proportion of loaf biomass in relation to sprout height. a) 30 days old population (plot A) b) 74 days old population (plot B). Plot T (not incluclod in statistical analysis) - triang1t.s.

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Fig. 4. Sp~out btonlttss plotted against basal dialnuter of the stem (74 days old population, plot B).

Fig. 5. Number of leaves plotted against sprout height. 30 days old population (plot A) - full circles, 74 days oId population (plot B) - empty circlcs. Plot T - triangles. Note the difforent scale in the uppm part of thc figure.

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population is reflected by lesser variance of data, increasing variance which'is apparent in plot B (Fig. 2b), can he explained by branching anci turning to woocl. Sprouts of the same height nlay possess a different bio~nass ancl pattern of bran- ching. The influence of branching is conspicuous in sprouts from the thinned plot T; branches may represent up to 78% of total sprout bioliiaes (Table 3). Less obvious correlation between bio~ilass and height has thus bcen found in d o t T.

Changes in the leaf proportion of sprout bionlass correspond to the allo~iietric rule (WALLER 1986). 30 days old sprouts hasre thus relatively more biolilass located in leaves than those of thc same height harvested a t the end of tlic veget,ztional period, which have already turned t o wood (Fig. 3).

Sprout biomass shosvs a linear relationship to the basal diameter of the steni (Fig. 4). However, an alloinetric relationship better fitted by the power function liiay be expected in the further development.

The number of loaves increased with sprout height (Fig. 5). For the lcaves falling from the lower parts of the stem, the number of leaves is fewer in older sprouts than in younger ones of comparable height. Linear relationship between t h e number of leaves and sprout height was found in smaller sprouts up to approxilnately 120 cm regt~rdless of population age. Howevcr, the curvo shows a rapid J-shaped

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Fig. 6. Leaf area of the sprout plotted against sprout; hoight. Solitary sprouts (30 days old) - squares, 30 days old population (plot A) - ft~ll circles, 74 clap old population (plot B) - empty circles.

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increase in taller sprouts. This is due to the large number of ne\v leaves en~erging on branches. A conspicuous increase in the number of leaves per sprout \vhich was observed in plot T is due to the salrie reason (see Table 3) .

The increase with sprout height is also apparent .when the leaf area of the sprout is taken into account (Fig. 6). Tlie steepest increase was observed in yoilng solitary spl'outs.

The increase of the total leaf area with increasing height is due ~.at,her to the increase in the nulnber of leaves than to the enlargement of indiridual leaves (Fig. 7). Distinct increase with increasing height in the inean l e d area was observed only in the 30 days old population. The highest, vigorously branched sprouts in the older population sho.ved even decrease in the mean leaf area because the leaves located on branches are usually sinaller than those growing on stems.

The leaves become thicker during development, whicl~ is seen fro111 t,he changes of the specific leaf area (Fig. 8) expressed as the ratio between leaf area and leaf bioinass (RYCHNOVSKA et al. 1987). However, regardless of sprout size: generally snlaller specific leaf area was recorded in the older population than in the younger one. This indicates a closer relationship of specific l e d area to the age of t,he sprout rather than to its size. The mean value calculated for one sprout was 384.8 cni"-l in plot A and 158.6 cin* g-1 in plot B, respectively.

Fig. 7. Mean leaf area plotted against sprout height. 30 days old population (plot A) - full circles. 74 days old population (plot B) - empty circles, b - intensively branched sprouts.

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Fig. S. Specific leaf aroa plotted against sprout biomwss. 30 tlnys old population (plot A) - full circles, 74 days old population (plot B) - e~llpty c.i:rlca.

Seasona l clynalllics

Unfortuaate1~-, the tiinc interval between the burning and the start of rcvegeta- tion can only be estinlated because the exact clate of thc stand damage is not " known. Revegetation did not start siinultaneous!g on the whole area; there was a time delay up to three nrcel;s (froin t,lle beginning of June to the beginning of its third decade). This was probably due to the cliffcrent clegree of damagc. It can be roughly cstiulatecl that the re~eget ,~ t ion process startccl within 2-5 weelrs after the fire.

Tlle iaitial rapid groxvth in height (up to 4.6 c;ii! . clay-', see Pig.. 9) was attended 1 1 ~ 7 the intcnse enlargement of leaf area (colupare \vitll Fig. 5s). In coiliparison to both these parameters, the increase in biolnass was slow (Pig. 2a) up to the height of 40-50 cl11 (which corresponds to approximately 10 days of growth in the niost r:apidlj. growing sprouts). A conspicuous increase in bionlass then appeared xvl~ich continued until the carrying capacity of t8he given environment was reached (see chapt,er Stand structure). After approximately 30 days of development (at the height, of doillinant spronts 90-120 cm) all the stenls regardless of height turned to wood and the growth in height slowed down (Fig. 9). Maxi~nuni value of LA1 was reached at $his point of development. This was 6.12 m2 111-2 in plot A and 6.32 in2 nl-' in plot B, respective1)-. Further emergence of new leaves, especially on branches, xias compensated bg t,he leaves falling off stems ancl so the t,otal leaf area reill~ins stable fro111 now on.

Branclling of the highest sprouts started witllin the next developmental phase, e.g. from the age of 30 days on. Sprouts \yere bowed bp their own weight and

branches prcxr- ul~n-ards frolu their horizontally oriented ternlinal parts ("Cham- pagnat" pattern of branching sensu HALL& ei al. 1978). In plot R, branching occurred in the six most vigorous sprouts which had all reac1;ed a co~lsiderable height ancl biolnass (112, iV/1, VlII/S, XI I l / l , 2, 7 ill Table -1). In tlie second half of August (after approximately 50 days of growth) the onset of flowering was recorded in several vigorously growing sprouts. However, the number of flowers - - per sprout was very low as co~npared withthe unburned stand.

hlortality of sprouts was 14.8 %. Sprouts which have lost all leaves in the course of the vegetational period were consiclercd cleacl.

Fig. 9. Ch;~ngrs in t h ~ Illcan spront hoigllt anrl in the n u ~ ~ l b e r of sprouts cl~uing the vegitatior~al pcriocl (plot It).

The clifferences between growth cl~aracterlatics calclilated for the initial develop- ~ilental phase ( i c. heforc the stellls turnecl to xvood) and those obtained in the seconcl half of the regetational period are presentecl in Table 5. NAR and E(+Ii vz~lues were 10 tinics greater in the e;~rl)- phase of popuintion growth. The totill productivity expressed as CGR relllaineci ~.oughl?- stable throughout the vcgela- tional period. However, if calculatecl separately for leaves and stems, respcctivcly, seasotlal cliffere~iues in hioinass allocation can be seen. The leaf nrowth rate " decreased ancl, on the contrary, the stem grolvtll rate increased obviously within the second half of the vegetational pel-iocl.

Fig. 10 illust,rates differences in tlle gro\vt,h of collorts in plot R. ,4 cohort was defined as a, set of sprouts comnlencing growth wit'hin a certain time iilterval (HUTCHTNGS 1986~2). All sprouts present in the plot e~nergecl within 18 days ancl mere divicletl into three cohorts. Nenlbers of t,he first cohort retained their adv;~n- tagc during the \\hole vegetational period and. moreover, the clistirictioil hecnnle even Inore profound. Jlc!ilbers of later cohorts shon-ecl less height incretnent wl~ich is exprcssecl in terms of c111 . day-' in Fig. 10. Differences ainoilg individual collo:.ts are p~esented in Table 6. The first cohort. wliich comprisecl 113 of the total nu1111)er of sprouts represented 55.9 %, of the total l>ionl,zss produced (Fig. 11).

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Fig. 10. Pcrfortnance of oohorts (plot R) expressed as an increase in the mean sprout hoight in the course of the vcgotational period (compare with Table 6). Numbers inhcate the rate of the growth in hoight (cm. dz~y-l) calculated for the time interval between observations. Cohorts are designated according to the d a b of emergence: A 21.-24. 6., B 26. 6-1. 7, C 2. 7.-8. 7. For comparison, d a t i ~ from thc thinned plot T are added (+).

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158 F O L I A GEOBOTAN1C.I E T P H Y T O T A X O S O X I C A , 2 6 , 1 9 0 1

C o n l p e t i t i o n a m o n g s p r o u t s

The coillparison of plot R with plot T where a low density of sprouts was lnain- tailled may serve as a conlparison of an overcrowded sprout population (total 54 sprouts . 0.26 with one not influenced by density dependent processes (S sul.outs . 0.25 m-'). \ L

Sprouts which did not suffer fro111 interference possessed conspicuously different habit and showed nlore rapid growth. Intensive branching started as early as 1-2 tveeks after the revegetation. Branching a t the very basis of sprouts was found in some cases. This resulted in rapid occupation of an open space. The growth in height was also faster, even in coinparison to the first cohort in plot R. (Fig. 10). However, the final height of sprouts in plot T did not surpass the height recorded in donlinant sprouts of plot R: The greater mean value presented on Fig. 10 is due to the absence of suppressed sprouts in plot T which lower the inean value obtained from plot R. Nevertheless, great differences between plots T and R in total biomass (Fig. "i, Table 3 vs. Table 4) and number of leaves per sprout (Fig. 5) were found. In addition, only the sprouts in plot T showecl a normal course of flowering which began in August and u as similar to that observed in unburned stands.

The above results indicate that conlpetition for light has taken place within the population of sprouts during revegetation. Due to the rapid development of the stand, the lower layers are overshadoxred in a short time. Sprouts suffering fro111 lack of light lose their leaves and eventually may die. Further developinental processes (branching, flowering) are presunlably conditioned by reaching the upper layers of the stand.

S t a n d s t r u c t u r e

The number of sprouts per 1 m h a r i e d from 188 t o 33G in a fully covered stand (87 days old), the mean value was 252.4 (n = 20).

Frequency distribution of biomass is presented in Fig. 12a. To express the diskinction from nornlal distribution, sBew gl was used (HUTCIIINGS 1986b). Skew indicates whether the distribution is negatively (g, < 0) or positively skewed (gl > 0) or whether the distribution is symetrically bell-shapccl (g, = 0). Frequency distribution of sprout biolnass is positively skewctl and g l value increased from 1.40 on June 1 to 4.80 on August 14.

Frecjuencg distribution of sprout height is approximately sq-~nu~ctrical a t the beginning and becollies negatively skewed in the course of the vegctational period (Fig. 12b). Sonic of the suppressed sprouts unclergo rapid height extension towards the light and so grow closer to the height of their neighbours. However, these sprouts increase very little in weight (cf. OGDEN 1970, HARPER 1977). Changes in thc height distribntion in the course of the vegetational period are illustrated in Fig. 13. RIore or less apparent bimodality of height clistributioil can be seen in both plcts (13 and R, Figs. 181) and U). ')

1) Howcvcr, one must kccp i n mind thc lilllitcd generality of conclusio~is clrawil frorn the . ~ ~ l u t u t ~ l comparison of plots resulting from a low n u n h e r of rcplicatos.

P Y S E K : S P R O U T D E h I O G R d P H Y I N L Y C I U M B X R D A B U N G 9

The structure of the stand a t the level of clunlps is presented in Fig. 14 where the position of individual clumps in the plot B was inapped (corresponding data see in Table 8). Different syillbols were used according to biomass estimated. The dominant clulllps are not distributed evenly in the plot. They are concentrated on the edge of the slope close t o the pathway froill where the shrub probably spread down the slope. The nuillber of clumps per 1 11i2 was relatively stable (40-56, mean value 16.4, n = 20). This holds true for the covered stands of Lyciunz bnrbn- rum whereas inore sparse dis t r ib~t~ion n.as found at the periphery of the area occupied.

Linear rclationship between clu~np bionlass and root dialneter can be seen in Fig. 15.

sprout biomass ( g )

sp rou t height Icm)

Fig. 12n. Frccl~~ency ilistribution of sprout biomass. Loft: 30 days old population (plot A) - va~iklnco 2.500, standard deviation s = 1.583, skew g, = 1.40. Itight: 74 days old popu- lr~tion (plot B) - s2 = 41.039, s = 6.46, g1 = 4.80. Fig. 12b. Frequency distribution of sprout height. Left: 30 clays old population - S' = 691.9, S = 26.30, g , = 0.12. Itight: 74 clays old populatioll - S' = 2786.4, s = 52.78, gl = -1.51. Mean values arc shown by arrows.

The stand structure espressetl as percentual proportion of individual clnn~ps on tlie total biomass of the harvested plot is presented on Fig. 16. Regardless of tlie age of the stand which is 30, 74, sncl 87 days (Table 7-g), respectively, there are usually 1-3 dominant clumps, each of thein forriling on average 13-20 7% of total bioniass of the plot. Maximunl hio!tlass produced by n clump was 70.73 g in plot B,

I J 2 L 6

,Q ,ao .20 L'

9' @'.~Q',~Q'.'~ sprout helght l cm)

d a t e

Fig. 13. Changes in the frequency clistribution of sprout height in the course of vegetational period (plot R). Prevailing height classcs are indicated by hatching. Mean sprout height is shown by a black arrow.

Fig. 14. 1)istribution of sprouts in thc plot B. Sprouts of the same clump are dolimitatecl by thc line. Nntnbers of clumps ant1 sprouts corl.cspond to Ti~blc 4. nifforent symbols are used to inclicatc sprouts according to thc biolnass protluucti: sln:~ll cirulcs - up to 15 g, large circles - morc than 15 g. Black ci~,cles inclicak rnxnbcrs of t'hc Ii~.st cohort (elnsrgsd on June 6).

PITSEP: S P R O U T DEMOC:BAPktY IS L Y C I C M B A R B - i R U X 161

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P Y ~ E K : SPROUT DE MOGRAPHY I N LYCIUM D A R D A R U M 163

and 82.59 g in plot R. Those clu~nps which were experinientally protected against the influence of neighbours did not exceed these values (mean bioniass 70.45 gj n = 6 ) . 2 )

Fig. 16. Clurnp biornrtss plottocl against root dialnetor (plot It). Numbers of clumps corraspond to tho Table 11.

Table 9. Performance of clumps in the plot R (harvestod at the p o p u l ~ t ~ o ~ l age of 87 days)

B~omass (g)

Number ~l locat ion of Numbor of Ioaves stoms total into sprouts Ioavos b~~ancllcs

I 5 I1 2

111 6 IV 6 v 4

v1 2 v11 2

VI I I 10 I S 2 X 3

X I 3

Plot-' 54 m-2 208

2) Thosc rcsults must bo treatccl wlth caut~on, howover, bocausc rcplicatc plots are lacking.

164 F O L I A G E O B O T A N I C d E T P H T T O T I S O N O J I I C A , 28. l991

Regarding total bioinass produced, there is very good accordance in the values obtained from both plots which were harvested a t the end of the vegetational period: 1386.9 and 1350.5 gmz, respectively. This is despite the localization of sampled plots in different parts of the slope, time delay in the start of the revege- tation (June 3 vs. June 21) ancl the different age of harvested populations. One oan thus consider the value obtained to correspond to the carrying capacity of the environment. This is confir~iied by additional samplings which n7erc used for the estiniation of total bioliiass only (1330.3 gnl2 and 1411.2 gtnz).

Fig. 16. Performance of clumps expressed as their share of tot:~l biomass produced in the plot. Numbers in bars represent tho numbers of sprouts presont in tho clump.

CONCLUSIONS AND DISCUSSION

Con cl us i on 1: Sprout height is a parameter convenient for l~ondestructive n~easarernent of the population growth in the early developmental phase when sprouts do not branch. It is more or less closely correlated with other growth characteristics (biomass, leaf area). Branching caused greater variance in data and weaker correlation of all paranleters observed. Biomass is thus consiclered the tliore appropriate characteristic for estimation of branched sprouts. However, these results indicate that the nondestructive estimation of further population deve1op:nent is problematic.

An inclirect ulethocl to estinlate the aerial bionlass based on its correlation with

height ivas proposed by FI'CZGERALD (1983) for sevei.al single-steiiiniecl woody plants. The use of the i~ietliocl is restrktecl t o young unbrilnohed slioots, Ilowever (e.g. Po l~u l tls tro~azJoi(1es).

Integration of plant clel~lograpliy 1~it.li sii:~ll>ling :.net,hods of productivity analysis seems t o be very useful ( E L o ~ ~ R - E L L I S 1980). Xo~v-aclays it represents a new levcl of clenlographic-ploducti~rit?; analysis and provides valuable infor~na- Lion on proportional biomass allocation (WHITE 1984). This allocation changes as the p!ant gro\irs. 1.esults arc in accordance v,iit,h those of SVEISB.J~~RSSSOS (1973) v7110 has fo~ulcl in Betztla pubesce~~s suhsp. torbuosi~ decrease of p r o p ~ ~ t i o n a l leaf 1)iouiass frolii about 50% of total plant dry ~veight for the sil~al!~st plants t o :tbcut 10% of total plant drj. weight for l111 tail plant,s, after which the proportion re1:~ains stable. In general, taller plants are forcetl to allocate proportionally more resources to supportive stelils ancl so usuallj- grow only as tall a s necesearj- to coiiipete ( \ % 7 7 4 ~ ~ ~ ~ 1986). There is evidonce given by ~ I E D V E (1987) that burning 11;~s no effect on allocat,ion of resources in sonle taws.

C o n c l u s i o n 2: Coinpetition for light took place among sprouts. Eotll gro~vth rate and branching were reducccl by intcrfejle~lcc from r~cighbours, ~vllioli resulted in the reduction of bio:nass produced per sprout. So~llc features of sprout popula- tion develop~nent ancl its changes in the course of thr: vcgetational pcriocl are similar t,o the behaviour of populations of genetically different indivicluals. A single sprout is tlie niost convenieiit module for the tleulographic study in L?jcr'rsm ~LL. I .~ (CI . I I ,~L - -

because it can be easily defined, countetl ancl nleasured. The typical response to the presence of neigh1)ours is ~~ccluction ill size w1:iali is

al~iiost inr7arial~lj- cxprc~ssccl in terms of hiot~tass (11-~IEPELE 1977, \YJIITE 1984). Change in luorphology due to interference - cspec;iallj~ the intensive brancl.~ing in spatially unlin~itccl conclit~ons - have been described both for herbs (NEW 1961) and trees ( 1 I T n 1 ~ ~ 1984). 11s a ConseqLIence of col~lpetition for' light, tnore rapid gro~vth in height was reportecl (GIVNISH 1982). Size hierarchies can also be causcd by interference from ~leighboitring plants. I t Illay be liiore likely t o occur for light, since cloniinant plants (or sprouts) lliay capture a clisproportionate share of inco- nliilg solar radiation (NITCTIELL-OLDS 1987). However. as enlphasized b j HUT- CIIINGS (1936b), the sole esistence of size hierarcliy in itself is not evidence that competition has taken place. It is verj dangerous to nleasure conlpetition simply by looking for correlatecl sizes of neighbours, since cornpetition cannot be measured when the effects of collipetition and local bite quality are confounded (MITCHELL- OLDS 1987). As discussed by HARPER (1981), one of the ways t o show competition is t o remove individuals ancl show that those tha t remain benefit fro111 the removal. I n the case of Lyciz~n~ balbnrim~, release from density dress caused conspicuous morphological changes and vigorous gro-t11 of sprouts that remained. Thc reasons for considering light t o be a decisive factor are as follo~vs:

1. Sprouts are genetioally uniform, so differences in the individual ability to capture resources are ~ilinilnized.

2. The root system is colninon t o a great estcnt ~vhich diniinishes differences resulting froin local site quality.

The structural differentiation of the population is thus conclitioned ~nost ly by relationships in the above ground space.

166 BOLI.4 G E O B O T A N I C A X T P H I ' T O T A S O N O ~ I I C A , 26, 1 0 9 1

The situation described represents competition on the level of individual organs or apical n~eristems, respectively (WHITE 1984, SILAWDER 1985). Cornpetition for light is in fact the interference among individual leaves which leads to the inutual shading of parts of the same genet ("narcissistic competitioi~" sensu HARPER 1981).

This study does not provide snfficient data to evaluate conceivable competition anlong clumps. Indiviclual cluillps vary considerably in total biomass and nuinher and size of sprouts. It seeilis that an individual clu~iip is capable of producing only a liillited biomass in a. givcil tiine interval. Clunips experiinentally freed froin the interference of neighbours did not produce illore bion~ass than clid the inost vigorous ones growing in fully developed stands. However, studies dealing with coinpetition among raiuets and with problc~us of intraspecific regulation of growth have been conducted exclusively on herbs so far (KAPS ct HARPER 1974, HARPER 1985, COOK 1985, ERIKSSON 1986).

The final wave of herbaceous reiteration in the top canopy of a tree has been compared to a population of herbs by HALLS e t al. (1978), WHITE (1979). The advantage of an early einergence of sprouts and the gradual exaggeration of differences in the course of development of the sprout population in Lycium barburunz corresponds to the res~zlts obtaincd froin investigations of herbaceous populations (Ross e t HARPER 1972 quoted by HARPER 1977, WALLER 1986). Frequency distribution of both biomass and height of sprouts is sirnilar t o that known for populations of genetically independellt indiviclusls (OGDEN 1970, HARPER 1977, HUTCHINGS 198613). The biinoclality typical of height clistribution of sprouts in Lycizcnz barba?um is suggested as more usual in circ~uiistances where conlpetition took place (FORD et NEWBOULD 1970 quoted hy HUTCI~INGS 1986b).

Conc lus ion 3: The capability of rapid ievegetation ancl the high growth rate enable Lycium bnrbarum to go throngh the critical herba~eous period in the deve- Iopinent of a woody plant quickly. Due to these characters as well as clue to the clonal habit of growth, Lycium barl)aru~n is tllus capable of successf~~l occupation of frequently clist~lrbed site:.

Fire is an itnyorta~lt inode of ecological c1ist~u.bance (RPI~IEL 1985). Clonal character of growth is typical of species of fire-disturbed habitats (COOK 1985, ICOOP 1987). Burning of above ground biou~ass stimulates vegetative growth from specialized undergro~ui~cl organs (KOJTAREK 1983, CRBWLEY 1986). There is a large body of literature on post-fire respronting from root buds (PELTON 1963 quoted by HARPER 1977, CRAWLEY 1986, T ~ E L E Y et ZEDLER 1978 clnoted by AULD 1987, BROWN et DEBYLE 1987) or lignotubers (AULD 1987, ICOOP 1957). This type of revegetation sfter burning was ohscrvecl even in nortnally nonsprouting species (DRISCOLL 1963). I n general, low seed production is typical of cloni~l shrubs and seedling recruit~~lent appears to be a rare event (SILVERTO\VN 1982, HUENNEICE 1987). From the point of view of life strategy, Lyciz~m barbarzinz belongs rather to the "phalanx" bypc (CLEGG 1978 quoted by HARPER 1981, LOVETT-DOUST 1981, BELL 1984, S~LANDER 1985).

The effects of fire bring about iluprovernent of habitat conclitions which inakes '

the site suitable for subsequent occupation. Breakdown of plant litter, breaking clorillancy in many species and the release of nutrients from accuniull~tecl standing dead biomass are the main consequences of fire (CRAWLEY 1986). Despite these

favourable circumstances, Lyciuyn bct~baruvz foriuecl exclusively illonospecific stands a t the locality investigated. Only rarely were seedlings of Robinia pseudo- acacia recorded.

CGR values calculated for Lycircyn bnrbarunz is 2-4 tilnes higher than those reported by R u c ~ ~ o \ ~ s n i i e t al. (1985) for lneadow conl~nunities. A comparable \ d u e was recorded only in the stancls of Glyceria n ~ a z i m l ~ . Similarly, the biomass procluced by Lyciunz ba~bnru?n in 70-85 days is coinparable with the whole vear's yielcl of the inost productive fertilized nleadows ( R y c ~ x o . i ~ s x i et al. 1985). However, one must keep in mind that such high procluctivity is restricted t o an early phase of developnlent in Lyciunl bc~rbrrrunz.

Provided tlle population is growing esponentidly, the RGR valuo can be for- inally identified with the intrinsic rato of natural increaso of a population (HARPEX 1977). However. even the value calculated on the base of data obtained on June 1 (30 days old population) was influenced by interference froin neighbouring sprouts. I n general, rapid growth is typical of root suckers since they can use a previously established root systeil~ (KOOP 1987).

Acknowlcclgomonts

My th:mnlcs aro duo to F. I i n a a u ~ n c and I<. I'RACH for their commnents on thr nlanuscript, V. J A R O ~ K for carrying out statistical analysis ancl nly wifo J. PYSKOV~ for (Irawirmng figures.

SUMMARY

1. Tlle dependence of sprout biomass, number of leaves and leaf area on sprout height was closer in the 30 clays old sprout population than in the 7-4 days old one. Increasing variance in data in the course of the vegetational period is clue to the spronts branching ancl turning to wood. Sprout height is thus a convenient parallletcl- for nondestructive ineasurenlent of population growt'll only until branching occurs.

2. Initial rapid growtll in height is attcncled by the intense enlargeincnt of loaf area. i\lIaximun~ value of LA1 (6.12-6.32 m2m-2) was reached aft'er approsin~ately 30 days of growth. Total bioniass harvcstecl a t the end of the veget,at,ional period varied froin 1 330.3 to 1411.2 g 111-2. Naximunl bioinass procluced by a single sprout was 28.18 g, the corresponding value for a single c lu~np was 82.59 g. Sumbcr of sprouts per 1 m2 varied fro111 188 to 336; number fo cluulps per 1 m2 was 40-56. Mortality of sprouts was 14.8 %.

3. NAR and lZGR values were 10 t i~nes greater in t l ~ e early phase of population growth than in the second half of the vegetational period. CGR reillailled stable throughout the vegetational season. Ho.i.irever, if calculated separately, t,he leaf growth rate decreased froin 7.16 to 4.17 g in-2 day-1 and, on the otller Ilancl, the stein growth rate increased from 9.84 to 15.57 g 111-2 day-l.

4. Coinpetition for light took place within the population of sprouts during revegctation. Growth rate and branching were reduced by interference from neighbours which resulted in the reduction of sprout biomass. Maximunl sprout bioinass producecl in thc experinlentally thinned plot, where the sprouts were freed fro111 conipetition, was 50.65 g.

5. The frequency distribution of sprout hioluasq ailtl sprollt height is sin~ilar to that known for populatio~is of geneticdly iridepentleilt individuals. The frecjuei~cp tlisiribution of s p r o ~ ~ t hio~nass vv1as positively slicn7ec1 and gL values increased from 1.10 in June to 4.80 in August. The frequency distribution of sprout lleigllt was approxi~~lately sy~ii~uctrical a t tho beginning and bccalne negatively slieweti (g1 = -,l 51) in thc course of the vegctational period.

6. Orv~ng to tllc high gro~vtli late and clo~ial sl)l*eading, Lycizirr, barbfit l c , / c is capable of successful occupation of freci1lently clistur1)cd sites.

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Roccivccl l 5 Ju ly 1989