Joumal of Tropical Fmest Sciznce 17 (3) : 399-4 I 5 ( 2005 ) 399

GrRTH GROWTH OF RUBBER (HEVEA BRASIL/ENSIS)TREES DURING THE IMT\{ATURE PHASE

T. R. Chandrasekhar*, J. Nice, Y. A. Varghese, C. IL Saraswathyamma &I{. R. Vijayakumar

Rubbr fusearch Institute of India, Kottayam - 685 009, Krala State, India

fuceiaed Septembr 2003

GIIANDRASEKIIA& T. R., ALICE,J., VARGHESE, y. A_, SARASWAII-IYAMMA C.IC & VIJAYAKUMA& I{" R. 2005. Girth growth of rubber (Hanea brasikensis\ treesduring the immature phase. Growth and performance of rubber trees (Heveabrasilbnsis) during the immature phase were studied in a tropical humid climate.Monthly girth growth of the main stem from 25 clones, between ages three and eightyears, was monitored. Monthly girth increments, seasonal and annual absolute andrelative girth rates were the analysis p.rrameters. Three seasons, aiz. SI (April tillJuly),52 (August till November) and 53 (December till March) were demarcated for seasonalcomparisons. All clones followed a broadly similar pattern of growth. Monthly girthincrement varied from 0 to 2 cm month-r. Girth growth began in April/May, peakedinJuly/August, declined fiom October and terminated by December. In the subsequentperiod up to March, no growth was observed. Most of the growth occurred in 51 and52 with values of43 and 5370 respectively. Based on growth attributes, four groupingsof clones were obtained. The results indicated an annual growth period of seven toeight months with an annual mean girth increment of 6.5 cm annum-r and a meanrelative increment rate of 2.5 mm cm-l annum-r.

Key words: Para rubber - immature growth - growth rate - growth duration - clonalvariation

CIIANDRASEIAIA& T. R., ALICE,J., VARGHESE, y. A., SARASWATI{YAMMA9 C.Ii & VIJAYAKUMAR, I( R. 2005. Pertumbuhan ukur lilit pokok getah (Haneabtrsilimsis\ semasa peringkat belum matang. Pertumbuhan dan prestasi pokok getah(Hatea brasilfunsis) semasa peringkat belum matang dik{i. Pokok ini tumbuh di kawasanberiklim tropika yang lembap. Pertumbuhan ukur lilit bulanan bagi batang utama 25klon getah berumur antara tiga tahun hingga lapan tahun direkodkan. Pertambahanukur lilit bulanan, kadar-kadar ukur lilit mutlak tahunan dan bermusim serta kadar-kadar ukur lilit relatif tahunan dan bermusim merupakan parameter untuk analisis.TigamusimiaituSl (AprilhinggaJulai),52 (OgoshinggaNovember) dan53 (Disemberhingga Mac) dipilih untuk perbandingan musim. Semua klon menunjukkan polapertumbuhan yang agak sama. Pertambahan ukur lilit bulanan berjulat dari 0 cmbulan-r hingga 2 cm bulan-r. Pertumbuhan ukur lilit bermula padaApril,/Mei mencapaimaksimum padaJulai/Ogos, menurun dari Oktober dan berhenti pada Disember.Tiada pertumbuhan diperhatikan selepas itu sehinggalah Mac. Kebanyakanpertumbuhan berlaku semasa Sl dan 52 dengan nilai masing-masing 43% dan 58%.Berdasarkan ciri-ciri pertumbuhan, empat kumpulan klon diperoleh. Keputusanmenunjukkan tempoh pertumbuhan tahunan pokok getah sebanyak rujuh bulanhingga lapan bulan dengan purata pertambahan ukur lilit tahunan sebanyak 6.5 cmdan purata kadar pertumbuhan relatif sebanyak 2.5 mm cm-r setahun.

*E-mail : chandratr@rubbub o ard. org. in

400 Journal of Tropical Forest Science 17 (3) : 399-41 5 ( 2005 )

Introduction

Rubber (Harca brasilimsis) is one of the major industrial crops grown mainly intropical climates between 12o latitude on either side of the equator. In India, it islargely cultivated in the humid tropical zone between 8o 15' N and 12o 52' N latitudes.Even though the environmental conditions here are comparativelymore congenialfor growth and producttity of Hnea,moderate soil moisture stress is experiencedannually. The planting material is routinelypropagated bybud grafting high-yieldingselections onto seedlings, producing many individuals of a clone. The trees reacha suitable girth for tapping after about seven to eightyears. During this period thetrunk girth measurements are widely used as attributes of growth. Although growthin Heuea can be measured in various parameters, girth or circumferencemeasurement of the main trunk (bole) remains the most important. It is a variableof major interest to planters and is the main factor taken into consideration forevaluating tree growth and attainment of maturity (about 50 cm girth at a heightof 150 cm from the bud union) for crop harvesting (called tapping). Girth andgirth increment of trees are used in experimental work to assess the growthperformance of new planting materials and the effects of cultural treatments ongrowth (Shorrocks etaL.7965, Chandrashekar et a/. 1998).

Studies on growth are of fundamental importance in understanding theinteraction between plant and their environmental conditions (Rose & Charles-Edwards 1981, Hunt 1982). ln Heaeatoo, girth increment can be related directly tothe accumulation of dry matter. Data relating changes in plant morphology toplant age can be useful in studies dealing with modelling long-term growth. Tothis end, growth analysis can provide useful insights into the influence of biotic as

well as abiotic factors on it.ln Heuea, although there is good amount of information on the annual growth

patterns, both during immature and mature phases of the trees (Webster & Baulkwill1989, Sethuraj & Mathew 1992, George &Jacob 2000), reports on growth analysisare scanty. The work of Templeton (1968) was the first major attempt. He studiedthe biomass accumulation during the immaturity period following destructivesampling. An analysis of immature growth by Chandrashekar et al. (1998) andVijayakumar et al. (1998) were the second important efforts. They analysedimmature growth of various clones growing in dry sub humid climate whereprolonged drought and high summer temperatures exist using trunk girthrecordings measured on a monthly basis. However, very little is known about thedetailed time-course of the growth of plants in humid tropical conditions(Chandrasel<har et al. 2002). The aim of this work was to present an analysis ofgrowth and its performance in Hanea trees during their immature phase in humidtropical climatic conditions.

Journal of Tropical Forest Science 17 (3): 399-415 (2005) 401

Materials and methods

Study location, f.eld, planting and crop managernmt

This study was conducted at the Rubber Research Institute of India at Kottayam(9" 32'N, 76o 36' E, altitude 73 m asl), Kerala State, South India. Two trials werelaid out as part of the ongoing programme for evaluation of modern clones. Theexperimental site of the first trial (trial I) was west facing slope (32.5 to 46.6Vo) andthat of the second (trial II) was mostly north facing slope (32.5 to 55.4Vo) with asmall part on a hillock top. The soil is Ustic Kanhaplohumults with a bulk densityof 1.25 Mg --', permanentwilting point atl9.7Vo and field capacity at27.8 Vo.

The clones used in the trials and their basic details are given in Table 1. Eachtrial consisted of 1 3 clones with RRII 105 included in both the trials. Three whorledbud grafted plants raised in polythene baskets (55 x25 cm, lay flat dimension) for

Table I Clones and their basic details

Clone Parentage Country of origin

Haiken ISCATC 88 - 13

SCATC 93 . I14

RRII 5

RRII IO5

RRII 118

RRII 208

RRII 3OO

RRII 308

PR 255

PR 26I

PB 217

PB 235

PB 255

PB 260

PB 280

PB 3IO

PB 3IIPB 312

PB 3I4

RRIM 600

RRTM 703

KRS 25

KRS I28

KRS 163

Primary clone

RRIM 600 x Pil B84

TR31 -45xHK3-11Primary clone

Tji. lxGllMil3/2 x Hil 28

Mil3/2 x AVROS 255

TjirlxPRl0TGllxPB6/50

Tji. 1xPRl07TjirlxPRl0TPB 5/51 x PB 6/9

PB 5/51 x PB S/78

PB 5/5L x PB 32/36

PB 5/51 x PB 49

Primary clone

PB 5/51x RRIM 600

RRIM 600 x PB 235

RRIM 600 x PB 235

RRIM 600 x PB 235

TjitlxPB36RRIM 600 x RRIM 500

Primary clone

PB 5/63 x KRS 13

PB 6/63 x RRIM 501

China

China

China

India

India

India

India

India

India

Indonesia

Indonesia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Malaysia

Thailand

Thailand

Thailand

402 Journal of Tropical Forest Science 17 (3): 399-415 (2005)

five months were used for planting. Field planting of the trials was carried out in

Juty and August 1989. The design adopted was randomized complete block designwith seven replications in trial I and five replications in trial II. The experimentalplots consisted of seven plants in a row in contour planting at a spacing of 3.4 x 6.7 mgiving a planting density of 445 plants ha. 1. Standard cultural practices such as

manuring, weeding, mulching and sun scorch prevention were all part of theagro-management of the crop.

Plant and weather data

Girths of the main stem, measured at monthly intervals from March 1991 tillMarch 1997 (third to eighth year after planting), were the primary data fromwhich growth analysis quantitieswere derived. Girth measurementswere measuredfrom all trees at a fixed height of 1.5 m from the bud union (collar region). Treesunder observation were numbered and all recurring girth measurements weremade on these trees at the same position marked with paint (renewed every year)and the girth was always measured exactly along the paint mark. Every month,measurements were taken on the first three days and were considered as

representing the girth of the trees at the end of the previous month. Meteorologicaldata, i.e. rainfall, minimum and maximum temperatures, and sunshine durationfor the respective study periods and the preceding 10 years were collected fromthe observatory maintained at the station.

Growth analy sis p aramtters

Derivatives of the girth, uiz. monthly girth increment (absolute girth rate),seasonal and annual absolute and relative girth rates, and their means are thegrowth analysis attributes. The attribute, relative girth increment rate (\), thatindicates new girth per unit plant girth per time step was used to study the rate ofvariations in clones due to seasons and age. It was calculated as (ln @, -ln Gl) x 10,

where Gl and G2 are the girth in cm at time 71 and 72 respectively. Themultiplication constant 10 was used to convert the R, values to mm as theunmultiplied values were very small.

Monthly, seasonal and annual growth trmds

Monthly increases in trunk girth were studied. In each trial and clone, girths oftrees were used to work out trunk girth averages and monthly increments. Tocompare growth differences between the clones at different seasons, the l2-monthperiod from April till March was divided into three seasons, i.e. S1, 52 and S3.April tillJuly is the S1 season characterized by adequate soil moisture in the firsthalf of the season and excess soil moisture in the second half, August till Novemberis the 52 seasonwith excess soil moisture in the first haHof the season and good toadequate soil moisture in the second half, and December till March is the S3 seasonwhich is mostly rainless with low soil moisture. In order to match the growth ofclones with the designated seasons, the seasonal growth of each clone was obtained

Journal of Tropical Forest Science 17 (3): 399-415 (2005) 403

by subtracting the girth value of March with that ofJuly, the value ofJulywith thatof November and the value of November with that of subsequent March to represent51, 52 and S3 seasons respectively. Percentage contribution of the seasons to theannual growth and changes in annual girth increments and the rate as well as theprogress of tappability percentage of each clone six years after planting were workedout.

Clustuing of clones based on growth parameters

Clustering pattern of the clones was studied by using initial girth, seasonal andannual mean absolute and relative girth rates, mean culmination of absolute growthrate (Ir) absolute girth and percentage tappability of clones up to the end of sixyears after planting as phenotlpic characters in estimating dissimilarity betweenclones following squared Euclidian distance. Six years after planting was chosenbecause of maximum variability between the clones in tappability percentages as itis the variable of major interest to planters and is the main factor taken intoconsideration for evaluating the progress of tree growth and attainmentof maturityfor crop harvesting. By subjecting the dissimilarity matrix to UPGMA clusteringalgorithm (Sneath & Sokal 7973) a dendrogram was constructed to depict thegrouping structure of clones. A mean distance of 10 was set for truncating clustersof similar growth characteristics.

Statistical analysis

In each trial and clone, girths of plants of all the replications were used tocalculate trunk girth averages. Data of plants that became discontinuous due todiseases and wind damages were excluded from analysis. Wherever appropriate,the datawere subjected to analysis ofvariance. Statistical features of trial-wise,year-wise pooled seasonal and clone-wise annual I, and \ were calculated. Data analysis

and lattice plots of the monthly variations in I, of the clones were done using R-

package (Ihaka & Gentleman 1996).

Results

Weather conditions

The region received an annual rainfall ranging from 2000 to 4000 mm. The rainfallperiod was from April till November and could be distinguished into two moderateseasons and one major season. The first moderate rainfall season was in April andMay. Rains during this season started from pre-monsoon thunderstorm activitythat brought relief showers, recharging the soil with adequate soil moisture. Thiswas succeeded inJune by the arrival of the south-west monsoon that continued tillSeptember, and this was the major season. These rains resulted in excess soilmoisture. Occasional periods of monsoon cloud cover extended for 7-10 days,

severely restricting the direct-beam solar radiation. Maximum precipitation (about

404 Journal of TropicalForest Science l7(3):399-415 (2005)

65Vo of t!r'e total) occurred in this season and a large portion of itwas lost as runoff.The October-November period was the second moderate rainfall season that was

dominated by post-monsoon northeast rains. Itwas comparatively weak but broughtin good rainfall before withdrawing by mid-November. Thereafter, from Decembertill March, the region did not usually receive rains, resulting in stressful soil moisflrredeficits. During this season diurnal variation in air temperatures was sporadicallypunctuated by daily extremes stressful to plant growth.

Monthly mean maximum temperature varied from 28 to 35 oC and that of meanminimum temperature, from 20 to25 oC. Variation in maximum temperature was

not much. Mean maximum temperanfe in the summer season was around 34 oC butoccasionally reached 38 oC. In the remaining months, it was around 31 oC.

Mean sunshine duration (SSD) in the summer was around nine hours per day andevaporation was around 5 mm per day. In the monsoon months, mean SSD was4.4 hours a day while in post monsoon months it was around 5.7 hours a day. Bothseasons had similar evaporation values with slightly higher values in the latter season.Maximum humiditywas normally 80Vo reaching l00Vo during the rainy season.

Month$ growth patterns

Monthly Ig varied from 0 to 2 cm month-r (Figures 1 and 2). In both trials,acceleration phase in I* started from April and culminated inJuly in trial I, and inAugust in trial II. The deceleration phase in trial I was from August, while in trial IIitwas from September. In the deceleration phase of trial I, there was a small increase1n I, in October and thereafter it declined. In the acceleration phase of trial II, adecline in I* was observed inJuly in most of the clones. By Decembeq I* reachednegligible levels in both trials and thereafter till March very little growth wasobserved. From the fifth year onwards, inJanuary and March, a significant numberof trees representing most of the clones showed reduction in girth of about 0.2 to0.5 cm resulting in negative I*values. Maximum culmination I* in trial Iwas duringyear 3 and year 4, while in trial II it was during year 4 and year 5 (Table 2). Insubsequent years, culmination I, decreased in all clones.

Seasonal and annual trend,s

There was considerable variation in seasonal R, and progressive decline in growthwith age (Table 3). During year 3 (Its) andyear 4 (Y4), there was marked differencein growth of clones between trials. In '1|351, R* values of the trial I clones werehigher but in \8S2, R* was the reverse. During Y4S1, there was significant reductionin R, in both the trials, but was not so in Y4S2. In 53, a little growth was observedduring \E to \6, but in later years no growth was recorded. From 15 onwards, therewas progressive decline in seasonal R* in both trials. There was not much declinein annual I* from l3 to \5 but thereafter steadily declined (Table 4). On the otherhand R* steadily declined right from 16 in both trials. From lts to \5, most ofclones were growing at an I* of 8 to 10 cm yearr. In both trials most of the growthoccurred in Sl and S2 (Table 5). In all the seasons, higher girth group clones had

Journal of rropical Forest science 17 (3): zgg-415 (200b)

2

1.5

1

0.5

0

-0.5

AMJJASONDJFM

-EoE,r zEs) 1.5cg1E

E os

:05 -05

2

1.5

1

0.5

0

-0.5

405

2

1.5

1

0.5

0

-0.5

2

1.5

1

0.5

0

-0.5

o Apr 91-Mar 92

tl Apr 94-Mar 95

Month

C Apr 92-Mar 93

Apr 95-Mar 96

MJJASON

I Apr 93-Mar 94

A Apr 96-Mar 97

DJ

Figure I Monthly growth pattern of rubber clones in trial I

higher and lower girth group clones lower I, and R, respectively (Table 5). Growthin Sl was higher in trial I than in trial II. on the other hand, in s2 and s3, thetrend was reverse. Of the total growth in a year about 42.6Vo occurred in S1, 5l.2%in 52 and 4.7% inS3.

scATc 93-114

406 Journal of Tropical Forest Science 17 (3): 399-415 (2005)

I

coEEo

coEoC)

.E

.EC9

2

1.5

1

0.5

0

-0.5

2

1.5

1

0.5

0

-0.5

1

0.5

2

1.5

1

0.5

0

-0.5

2

1.5

1

0.5

0

-0.52

1.5

0

-0.5

AMJJASONDJFM

o Apr 91-Mar 92

;] Apr 94-Mar 95

Month

C Apr 92-Mar 93

A Apr 95-Mar 96

AMJJASONDJFM

I Apr 93-Mar 94

A Apr 96-Mar 97

Figure 2 Monthly growth pattern of rubber clones in trial II

Immature growth perfmmance

At the start of the study (Table 5), the largest girth observed in trial I was cloneRRII 118 (13.9 cm), followed byRRII208 and SCATC g&ll4with PR255 (10.3 cm)as the least vigorous of the clones, while in trial II the largest girth was noted forclonePB3l4 (15.0cm),followedbyPB 255 (14.2cm). KRS l28wastheleastvigorousclone. At the end of the study, RRII 118 recorded highest girth (62.2 cm) whileHaiken 1 the lowest in trial I. In trial II, highest girth was observed in PB 235 (61.3 cm),

Journal of Tropical Forest Science 17 (3): 399-415 (2005)

Table 2 Culmination girth increments (Ig, cm) of clones at different years

Trial/

Clone

Years after planting

407

3456(er-e2) (e2-e3) (e3-e4) (e4--e5)

78(e5-e6) (e6-e7)

Trial I

RRII 1I8

RRII 3OB

RRII 5

RRII 208

RRII IO5

RRII 3OO

PR 26I

SCATC 93 . 114

PR 255

RRIM 703

SCATC 88 - 13

RRIM 600

Haiken I

Trial IIPB 235

PB 280

PB 3I4

PB 312

PB 255

PB 3IO

RRII IO5

PB 311

KRS 163

PB 260

PB 217

KRS 25

KRS 128

1.94

1.64

r.94

l.8tr.64

1.7 4

r.67

1.40

1.63

1.36

r.57

1.53

1.63

t.44

1.80

1.60

t.44

1.40

1.36

1.50

1.38

1.38

r.44

1.40

1.36

t.26

1.93

r.7r

L.73

r.73

r.70

1.68

1.89

r.52

1.58

l.6l1.60

r.62

1.66

r.70

1.68

r.52

1.78

1.50

1.58

1.64

r.72

t.54

1.58

r.56

L.54

1.68

1.63

r.49

1.59

1.59

r.44

1.61

r.67

t.54

1.56

1.63

t.4lt.4L

r.r7

1.90

1.50

1.54

r.B0

1.46

1.62

l.B4

1.44

r.38

r.52

1.36

l.68

r.62

l.3lr.26

I .13

1.03

l.0lr.07

0.90

1.04

1.1 I0.91

1.01

0.99

0.91

l.l B

r.32

1.08

1.22

1.16

1.26

1.04

0.98

r.26

r.22

t.t41.04

r.06

l.l91.09

1.00

0.93

1.13

0.89

0.99

1.19

0.91

0.90

0.90

0.90

0.79

r.20

1.06

0.94

0.90

1.10

1.02

0.86

l.l00.98

1.04

0.80

0.98

0.82

0.96

0.80

0.77

0.81

0.77

0.77

0.7 4

0.66

0.69

0.51

0.77

0.76

0.53

0.84

0.90

0.78

0.78

0.78

0.86

0.68

0.80

0.78

0.80

0.54

0.94

0.96

followed by PB 280 and PB 314. KRS 128 recorded lowest girth (50.7 cm). By the sixthyear, only RRII 118 in trial I and PB 280, PB 235 and PB 314 in trial II had satisfactorypercentage of trees readyfor tapping (Thble 6).In subsequentyears mdorityof clones intrial II and four clones in trial I attained tappability. At the end of eightyears, all clones

attained tappability except Haiken 1.

Based on the growth attributes, four groupings of clones were obtained (Figure 3).The clones RRII 118, PB 235, PB 280 and PB 314with a mean girth of 60.3 clr,andg6%tappability formed the first group (Tables 5 and 6). The second group comprising sixclones had amean girth of 56.3 cm and91.1Vo tzppabrhtywhile the third group also hadsix clones with a mean girth of 53.5 cm and 8I.5Vo tappability. The fourth group hadnine clones with a mean girth of 50 cm and 56.3Vo tappability.

408 Journal of Tropical Forest Science 17 (3): 399415 (2005)

Table 3 Seasonal changes in Ig and Rs

Years after planting

Parameter

Apr 91-Mar 92 Apr 92-Mar 93 Apr 93-Mar 94

TI TII TI TII TI TIIApr 94-Mar 95 Apr 95-Mar 96 Apr 9LMar 97

TI TII TI TII TI TIIIs

Mean

Minimum

Mrurimum

C,/ (Vo)

&Mean

Minimum

Ma<imum

A,/(%)

Is

Mean

Minimum

Muimum

6{(7o)

&Mean

Minimum

Maximum

6{(Vo)

Is

Mean

Minimum

Ma:rimum

CtrVo)

&Mean

Minimum

Mru<imum

CY(Vo)

4.18 3.52

3.00 2.70

5.40 4.60

I I .41 13.88

2.94 2.33

2.25 1.87

3.88 3.51

r2.rr rt.57

3.92 4.41

1.40 3.00

5.90 5.70

21.16 16.10

2.r2 2.3r

0.80 r.70

2.86 2.95

17.42 9.98

3.29 2.07

1.7 4 I .30

4.50 3.80

L7.63 20.22

r.48 0.89

0.80 0.58

2.22 r.43

17.4t 15.30

4.30 5.32

2.66 4.r0

6.30 6.60

18.93 r0.66

1.65 2.01

1.05 1.30

2.57 2.53

17.50 13.52

0.24 0.76 0.51 1.38

-0.20 0.20 0.00 0.60

1.30 2.00 2.L0 2.60

88.96 53.83 71.17 34.73

0.12 0.34 0.18 0.45

-0.09 0.09 0.00 0.20

0.60 0.89 0.68 0.77

88.80 48.48 69.03 28.06

S1 (Apr-Jul)

3.05 2.96

r.80 2.00

4.70 4.20

17.5r 15.30

l.0l 0.92

0.63 0.56

L.74 r.2r

18.12 16.35

S2 (Aug-Nov)

3.73 4.r7

2.r0 2.70

5.30 6.10

15.69 15.93

1.11 L.t7

0.65 0.73

r.52 r.57

16.39 17.04

3.05 2.95

1.10 2.10

5.10 4.00

r 9.29 13.60

0.80 0.73

0.31 0.47

r.l2 0.99

r 6.15 15.59

3.34 3.39

2.30 1.80

4.60 4.70

12.96 16.51

0.81 0.78

0.57 0.39

1.t4 1.07

I 1.30 17 .57

53 (Dec-Mar)

0.83 1.01 -0.17 -0.31

-0.20 0.00 -0.60 -1.00

2.20 2.80 0.20 0.30

51.53 62.72 -57.68 -76.64

0.23 0.26 4.04 -0.07

-0.06 0.00 -0.13 -0.23

0.51 0.63 0.05 0.06

48.24 61.46 -56.14 -79.48

2.9r 2.56

1.60 1.60

5.30 3.40

20.24 L7.90

0.66 0.56

0.39 0.3r

0.98 0.80

L7.72 19.02

2.55 3.38

0.60 2.20

5.00 5.10

25.60 r8.97

0.54 0.69

0.13 0.43

0.92 0.97

2r.78 17 .7L

0.25 0.08

-0.30 -0.20

0.80 0.60

74.49 208.70

0.05 0.02

4.07 -0.04

0.15 0.11

72.51 21 1.51

1.77 2.0e

0.80 1.40

3.50 2.90

24.91 18.91

0.36 0.40

0.19 0.27

0.55 0.58

20.38 19.13

2.11 2.07

0.80 0.30

3.30 4.00

28.22 33.33

0.41 0.39

0.16 0.05

0.65 0.80

27.9L 35.49

-0.40 -0.40

-1.10 4.90

0.68 0.20

-76.96 -54.3r

-0.08 -0.07

-0.18 4.16

0.14 0.03

-73.94 -54.59

Ig = Girth increment (cm month-t), Rr = relative girth increment (mm cm-r season-l)CV = Coefficient of variation

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Table 5 Variations in abso_lute girth (cm) in March 1991 an_d 1997, seasonal and annual mean girthincrement rates (Ir) and relative increment rates (Rg) in various clones of Hanea

Clone Sl (Apr-Jul) 52 (Aug-Nov) 53 (Dec-Mar) AnnualGirth

March 9I t&I, &ir&& i*

Girth

March 97

Trial I

RRII 1I8

RRII 308

RRII 5

RRII 208

RRII IO5

RRII 3OO

PR 26I

SCATC 93 . 114

PR 255

RRIM 703

SCATC 88. 13

RRIM 600

Haiken I

Mean

SE

Trial II

PB 235

PB 280

PB 314

PB 3I2

PB 255

PB 310

RRII 105

PB 31I

KRS 163

PB 260

PB 217

KRS 25

KRS 128

Mean

SE

13.89

1 1.52

12.2r

12.93

12.09

1 1.98

rr.23

12.88

10.31

12.2r

12.33

12.86

12.61

12.24

0.52

13.98

13.90

14.98

12.8r

t4.23

13.27

12.88

13.39

t3.40

L2.52

t3.64

I 1.83

11.99

13.29

0.79

3.7L

3.33

3.32

2.97

3.00

3.05

3.00

2.95

2.92

2.99

2.83

2.96

2.52

3.04

0.1 I

2.92

3.00

2.66

2.65

2.82

2.67

2.64

2.74

2.58

2.73

2.42

2.58

2.58

2.69

0.01

L.24 4.00

1.28 3.65

r.29 3.57

r.l5 3.52

1.20 3.42

t.23 3.38

r.25 3.4r

I .18 2.98

1.29 3.37

L.t7 2.94

1 .15 3.15

1 .16 3.03

r.07 2.79

1.21 3.32

0.05 0.12

0.96 4.t3

1.01 3.97

0.90 3.67

0.98 3.98

0.97 3.79

0.95 4.04

0.97 3.77

0.99 3.69

0.95 3.78

r.02 3.78

0.89 3.42

r.04 3.66

1.01 3.58

0.97 3.79

0.05 0.r7

| .L7 0.18

r.zL 0.31

t.r4 0.22

r.r2 0.13

I .15 0.14

r.11 0.22

1.20 0.r7

0.98 0.26

L.20 0.34

1.03 0.35

1.09 0.20

I .03 0.10

0.99 0.1 I

I .l I 0.21

0.04 0.07

L.24 0.64

1.20 0.53

1.1 1 0.65

1.28 0.50

L.r7 0.39

1.30 0.30

L.25 0.34

1.19 0.39

l.2l 0.33

r.25 0.26

I .13 0.56

r.27 0.33

1.26 0.22

1.22 0.42

0.01 0.11

0.057 7.89

0.1 12 7 .28

0.077 7.rL

0.050 6.63

0.056 6.56

0.078 6.64

0.064 6.58

0.101 6.19

0.1l9 6.62

0.122 6.28

0.080 6.19

0.041 6.09

0.048 5.42

0.077 6.58

2.46 62.2

2.60 56.2

2.5L 56.0

2.32 53.6

2.4r 52.8

2.4r 52.6

2.51 51.3

2.27 50.7

2.61 50.6

2.33 50.0

2.32 50.0

2.23 49.9

2.11 45.4

2.39 52.4

2.4r 61.3

2.39 60.2

2.2r 57.6

2.44 57.5

2.27 57.3

2.37 56.1

2.35 55.0

2.32 55.0

2.29 54.8

2.39 53.9

2.20 52.6

2.46 5L.7

2.38 50.7

2.35 55.7

0.020 0.21 0.07

0.208 7.70

0.180 7.50

0. r98 6.98

0.187 7 .13

0.139 7.00

0.L24 7.01

0.L37 6.75

0.134 6.82

0. r 39 6.69

0.120 6.76

0.191 6.39

0.153 6.57

0.107 6.38

0.155 6.90

1.4

0.004 0.26 0.08 1.9

Journal of TropicalForest Science 17(3):399-415 (2005)

Table 6 Proportion of rubber trees attaining tappable girth

411

Clone

Total

no. of

trees

Years after planting

Number Percent Number Percent Number Percent

Trial I

RRII I 18

RRII 308

RRII 5

RRII 208

RRII 3OO

RRIM 703

SCATC 93 . 114

RRII IO5

PR 261

RRIM 600

SCATC 88. 13

PR 255

Haiken ITotal

Trial II

PB 280

PB 235

PB 3I4

PB 255

RRII 105

PB 312

KRS 163

PB 310

PB 217

PB 3IIPB 260

KRS 25

KRS I28

Total

49

47

47

49

49

47

46

48

49

49

49

47

45

62r

31

1l

10

6

4

3

2

2

9

II0

0

73

l920

IB

10

9

8

I

6

5

D

3

1

0

111

63.3

23.4

2r.3

12.2

8.2

6.4

4.3

4.2

4.L

2.0

2.0

0.0

0.0

1 1.8

45

32

32

26

24

r7

t4

15

l9

8

t3

l61

262

91.8

68. l68. I53.1

49.0

36.2

30.4

31.3

38.8

16.3

26.5

34.0

99

42.2

48

40

4l

4l

35

28

27

4l

31

30

27

28

I

424

98.0

85. I87.2

83.7

71.4

59.6

58.7

85.4

63.3

61.2

55.1

59.6

r5.6

68.3

97.0

100.0

88.6

88.2

94.1

100.0

88.2

97.0

75.8

85.7

82.9

70.6

62.s

86.8

33

35

35

34

34

31

34

33

33

35

35

34

35

44r

57.6

57.1

5L.4

29.4

26.5

25.8

20.6

18.2

15.2

t4.3

8.6

9q

0.0

25.2

31

31

2B

27

20

20

22

99

l923

20

I6

278

93.9

88.6

80.0

79.4

58.8

64.5

64.7

66.7

57.6

65.7

57.r

26.5

17.r

63.0

32

35

31

30

32

31

30

32

25

30

29

24

92

383

4L2

50

Lingkage distance40 10

RRil 1 18

PB 235

PB 280

PB 314

PB 312

PB 255

RRil 308

RRII 5

KRS 163

PB 310

RRil 208

RRil 105

P8311

PB 217

RRil 300

PB 260

RRIM 703

PR 261

scATc 93-114

scATc 88-13

RRIM 600

KRS 25

PR 255

KRS 128

Haiken 1

IV

50 40" 10 0

* Group designation is based on mean girth and tappability percentage at the end of study period.

Figure 3 UPGI\{A cluster pattern of the clones based on the growth attributes

Discussion

The study location is in the centre of the traditional rubbergrowing zone in India.Rainfall pattern is fairly well distributed. Initial growth observed for the clones inApril may not be due to the activity of cambium but largely due to the rehydrationof tissues resulting in complete restoration of turgor that was lost during thepreceding stress period. Appreciable increase in girth observed for all clones inthe following month, indicated that there had been no severe damage to thephotosynthetic machinery in the preceding stress period. Rapid increase in growthfrom May onwards was probably brought about by the decreise in the direci beamsolar radiation and increase in diffuse radiation. Maximum growth of all clonesobserved inJuly/Augustwas due to continuous accumulation of biomass occurringin spurts covering avariable number of days because of periodical changes in lighiand other environmental factors.

Journal of Tropical Forest Science 17 (3): 399-415 (2005)

0 Group *

I

Journal of Tropical Forest Science 17 (3) : 399-41 5 ( 2005 ) 4t3

The rate of growth declined progressively in all seasons. This trend was inagreementwith earlier reports (Templeton 1968, Chandrashekar et a\.7994,1998).Seasonal differences observed in growth rate between the trials could be due todifferential capture of radiation by the sites of the nvo trials. In the dry season,growth of all clones was reduced substantially. A small amount of growth observedcould be easily related with the pre-monsoon showers. In March 1995 and 1996there was reduction in girth in most of the clones due to the stress conditions.

It is well known that temperature and water availability are the two mostimportant constraints for growth and yield of plants. When ambient temperaturesare above optimum, substrates that could be used for growth are increasingly lostthrough excessive respiration (Hellmers & Warrington 1982). In the present study,the observed shrinkage of tree stems inJanuary and March could be due to soilmoisture stress conditions. This type of stem shrinkage resulting from drought hasbeen confirmed for many species of angiosperms and gymnosperms of thetemperate and the ropics (Kozlowski 1977, 7972). In the initial years of observationreduction in girth was negligible. Therefore, it can be presumed that increasedleaf area has also contributed to the reduction in girth during summer months.During the monsoon season, even though most part of many days was cloudy withlow sunshine hours, girth increase was good, indicating that the plants have receivedadequate photosynthetically-active radiation. It appears that Heaea prefersconditions of low light intensity for good growth.

In spite of no apparent limiting factors from October till December, the growthof plants started decreasing and in November it stopped completely. It is difficultto determine which environmental factor or factors that might have played a rolein the decline. One of the possible reasons could be the deciduous nature of Haneatrees. The trees shed leaves (wintering) annually during autumn with the onset ofcooler conditions, the biochemical signalling for which must set in much earlier.This signalling mayhave led to decreased photosynthetic activityin leaves, resultingin the progressive decline in terminal growth, leading to complete cessation ofgrowth by December.

Peak growth in trial I occurred when the sun was in the northern horizonswhile in trial II itwas observed when the sun was in the southern horizons. Thoughit is difficult to explain, possible reason could be differential capture of radiationby the sites of the two trials. The experimental site of trial I is west facing slope andthat of the second is mostly north facing slope with a small part on a hillock top. Itis well known that slope and aspect create variability in radiation climate mainlydue to the exposure of the sites to different time periods of direct sunlight andshade at any given season, resulting in seasonal as well as spatial variability in theradiation regimes (Rosenberg 1974,Lee 1978). This could have been the reasonfor the shifts in peak growth periods of the two trials.

From the growth curves, it is clear that in the tropical humid conditions, activegrowth period of Heueatrees is about seven to eight months fromApril till Novemberwith three months of grand period of growth fromJuly till September. Based onthe clustering patterns, group I clones can be termed as high, group II as aboveaverage, group III as average and group IV as below average vigour clones. Ingeneral, it could be said that the clones originated from China, Thailand and

4t4 Journal of Tropical Forest Science 17 (3) : 399-415 (2005)

Indonesia were of poor vigour, while those of Malaysia and India were of highvigour.

The main focus of the paper is to provide information on three important aspects

of growth of Hanea trees, namely, absolute girth rate, relative girth rate, growth

period and their age-related annual trends. Under ambient conditions of the

tropical humid climate experienced in the traditional rubbergrowing region inIndia, annual growth period of the trees was about seven to eight months with an

annual I, of 6.5 cm yearr and Ik of 2.5 mm cm-l yearr. Of late, a major stress inHweaimprovement is on breeding latex timber clones that are superior in bothlatex as well as timber production. In this direction, SrouP I clones appear to be

promising.

Acknowledgements

We thank N. M. Mathew, Director of the Rubber Research Institute of India, forencouragement in this study. Thanks are also due to the agro-meteorology section

for meteorological data.

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