IAWA Journal, Vol. 18 (3),1997: 311-317

WOOD ANATOMICAL CHANGES IN JUVENILE DUE TO INSECT DEFOLIATION by P. B. Priya & K. M. Bhat

Wood Science Division, Kerala Research Institute, Peechi 680 653,

SUMMARY

Selected anatomical characteristics and wood specific gravity of 8-year­ old teak protected from insect defoliation were compared with those from an unprotected population. Trees during the protection period of four years showed considerable increase in ring width (growth rate). Although latewood width was more c10sely correlated with ring width than earlywood width, no significant differences were found in specific gravity, cell wall percentage and diameter and percentage of vessels, probably due to juvenility. Furthermore, no intrinsic relationship could be established between the insect defoliation and the formation of false rings. Key words: Tectona grandis, ring width, specific gravity, tissue percen­ tage, growth rate, false rings.

INTRODUCTION

Radial growth of trees is influenced by numerous factors such as c1imate, site and dis­ turbances like defoliation. It has been shown by many workers (Stark & Cook 1957; Williams 1967) that acute insect defoliation may induce reduetion in the radial inere­ ment oftrees. The defoliation caused by two species of caterpillars, eommonly known as teak defoliator and teak skeletonizer, is one of the major reasons for low yield in several teak plantations in India (Beeson 1941; Nair et al. 1985). Aecording to Nair et.al.( 1985), in the teak plantations of Nilambur (India), the defoliation eaused by the former is more intense, often leading to eomplete stripping of young leaves, and is of regular annual occurrence with one or two waves of epidemie defoliations between late April and July followed at times by another lighter defoliation between August and Oetober. The effeets of inseet defoliation on the radial growth and ring width variation pat­ tern offorest trees have been discussed in detail by Mott et al. (1957). Rose (1958) reported complete or partial cessation of radial growth in tremuloides Michx., depending upon varying intensities of defoliation. Simi1ar impacts of inseet defo1ia­ tion on reduction in the radial inerement have been reported for jack and Doug- 1as- (Kuiman et al. 1963; Alfaro 1982; Alfaro & Shepherd 1991; Brubaker & Greene 1979). Champion (1934) conducted artificial defoliation experiments in teak and con­ cluded that three eomplete stripping of leaves in the same season eaused a 10ss of 65%

Downloaded from Brill.com09/25/2021 07:34:16PM via free access 312 IAWA Journal, Vol. 18 (3), 1997 of the normal increment. Recently, protection against insect defoliation was shown to increase heartwood percentage (decrease of sapwood proportion) with enhanced ra­ dial increment in 8-year-old teak (Bhat 1995b). Yet, the pattern of wood anatomical variation, due to insect defoliation, is not known in plantations of tropical although several control measures were included in plantation management plans. This is probably because of the fact that field investigations are confronted with the prob­ lems of uncontrolled conditions such as non-clonal material and extremely sensitive juvenile trees. The present study attempts to assess the effects of insect defoliation, during a short treatment period of four years, on wood anatomy and specific gravity of 8-year-old juvenile teak (Tectona grandis L. f.), a ring-porous tropical .

MATERIALS AND METHODS

The materials for the study were obtained from 8-year-old teak plantations in Nilam­

0 0 bur (11 0 12'-11 0 32' N and 75 82' - 76 32' E), India. The plantations of assorted age were established in the year 1974 and extended over an area of 2,500 ha, part of which represented the second rotation plantations. When the trees were four years old, some of the experimental plots were artificially protected against insect defoliation by spray­ ing an insecticide ('protected' trees), while other plots were left unprotected ('control' trees) (Nair et al. 1985). Artificial protective measurements were taken for four years during the period 1979-1982. At the end of the eighth year, the trees were felled. About 10 cm thick discs were cut at breast height level (1.37 m from stump level) from 102 trees representing 51 'protected' as weIl as 51 'control' trees. Ten discs were se­ lected at random from each treatment for the study. Specific gravity was determined in all the sampies. A wedge-shaped block of wood was cut from the discs which included all the rings from pith to bark. The blocks were then cut along the tangential to separate the first four rings from the second block of four rings formed during the age between 5-8 years. Specific gravity was deter­ mined separately for the two halves of the blocks so that it can be compared between the first four rings as weIl as the last four rings separately, for the 'protected' and 'con­ trol' sampies, since the trees were protected artificially against insect defoliation only after four years growth. Green volume of the sampies was determined by the water displacement method. Specific gravity of the individual sampies was then calculated as oven dry weight over green volume. For anatomical observations, ten trees each of the 'protected' and 'control' popu­ lations, showing no sign of eccentric growth, were selected. The sampies were sec­ tioned using a sliding microtome at 15-20 micrometre thickness. The sections were stained, dehydrated and made permanent for image analysis by a video image analyser (Leica, Quantimet 500+). Various parameters such as vessel diameter, vessel percent­ age, cell wall percentage and ring width were measured by image analysis for the peripheral three rings individually. While determining ring width, earlywood and latewood widths were measured after making an arbitrary demarcation between the two, by identifying the earlywood with wide vessels, parenchyma and thin-walled

Downloaded from Brill.com09/25/2021 07:34:16PM via free access Priya & Bhat -- Insect defoliation in teak 313 fibres and latewood with narrower vessels and more thick-walled fibres. The quantita­ tive features were compared between the two treatments using the 't' -test. With the help of a stereo rnicroscope ring width was measured in all the discs col­ lected from the 102 trees from two opposite radii covering the eccentricity if any. Ring-wise microscopic examination was carried out in samples of both the 'control' and 'protected' trees so as to determine whether insect defoliation had induced false ring formation.

RESULTS AND DISCUSSION

No significant difference was found in the wood specific gravity between the 'control' and 'protected' trees. It was evident that protection from insect defoliation at the age of four years accelerated the growth rate in the following year with an increase of about 28% ring width (Fig. 1). The extent of growth acceleration (increased ring width) due to protection remained more or less constant for the rest of the period up to the eighth year. This supports the hypothesis that radial growth is dependent on the newly formed assimilates of the leaves and defoliation leads to reduced girth increment of the trees (Busgen et al. 1929). Evidently, insect defoliation reduced the growth rate ofthe trees in the corresponding years appreciably, without altering the specific gravity. This is in agreement with the observation of Zhang and Zhong (1991) in ring-porous East­ Liaoning wood where growth rate showed little effect on specific gravity of juve­ nile wood. Our findings on reduced growth rate reflect the results of N air et al. (1985)

12r,------,------, --- Contro! ...... Protected

10

~ 8 ~ -5 ~ 6 9 4~~~~~~~~~~~~~~~~~~~~~~~~~~~

2

o 'L-______~ 1 2 3 4 5 6 7 8 Rings from pith Fig. 1. Ring width in relation to cambial age (ring number from pith) in 51 'contral' and 51 'protected' teak trees.

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Table 1. Comparison of mean values of anatomical properties in 10 'control' and 10 'pro- tected' trees.

Parameters Growth ring Control Protected t-value no. from pith Mean Mean

Specific gravity 1-4 0.539 0.548 -0.63 ns 5-8 0.553 0.563 -1.03 ns

Vessel diameter (mm) 6 0.178 0.180 0.48 ns 7 0.187 0.176 1.67 ns 8 0.170 0.176 -1.62 ns

Vessel area (%) 6 23.6 23.8 -0.19 ns 7 21.9 19.1 2.18 ns 8 22.4 19.9 1.67 ns

Cell wall area (%) 6 44.3 44.9 -0.67 ns 7 45.2 45.5 -0.33 ns 8 45.4 47.4 -1.91 ns

Ring width (mm) 6 2.5 3.5 -2.57 * 7 2.6 3.7 -2.68 * 8 2.5 3.6 -3.33 **

Earlywood width (mm) 6 0.927 0.775 -0.28 ns 7 0.809 0.898 -1.81 ns 8 0.735 0.939 1.40 ns

Latewood width (mm) 6 1.604 2.732 -2.29 * 7 1.821 2.807 -2.77 * 8 1.807 2.637 -3.56 ** * = significant at 5% level; ** = significant at 1% level; ns = not significant. that the loss of volume increment was the most serious impact of defoliation, about 44% of the potential increment (i.e., increment in the absence of defoliation) in vol­ urne was lost due to defoliation, whereas the gain in volume due to protection amounted to 80% of the increment of unprotected trees. The mean values of the quantitative anatomical features and 't' -test values are pre­ sented in Table 1. No significant differences were found in vesse1 diameter, vessel per­ centage and cell wall percentage between the 'control' and 'protected' trees. There was a significant increase in the latewood width of the 'protected' trees corresponding to the increase in ring width, while earlywood width remained fairly constant (Table 1). However, the effects of wider latewood on other anatomical features were too little to cauSe anychange in specific gravity. This is probably because the relative proportions of latewood arid fibre-wall substance are smaller in wider rings of juvenile wood than

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Tab1e 2. Corre1ation coefficients for the interre1ationships between se1ected pairs of ana- tomica1 parameters.

Cell wall Vessel Vessel Ring Specific Earlywood Latewood percentage diameter percentage width gravity width width (1) (2) (3) (4) (5) (6) (7)

(2) -.278 (3) -.802** .309 (4) .258 .271 -.239 (5) .297 -.099 -.327 .266 (6) -.395* .417* .413* .151 .005 (7) .260 .251 -.225 .981 ** .214 .276

n = 60; * = significant at 5% level; ** = significant at 1% level. in mature wood. Similarly, Zhang and Zhong (1991, 1992) reported in East-Liaoning oak that specific gravity was hardly related to the latewood percentage in juvenile wood, but the relationship was found to be rather complex in mature wood, where specific gravity and cell wall percentage increased with growth rate (ring width). They concluded that latewood percentage was not always a good indicator of specific grav­ ity. Age (ring number from pith) is a decisive factor in controlling specific gravity of wood, while growth rate is statistically less important. The same trend is observed here in juvenile teakwhich is in conformity with the earlier reports (Bhat 1995a, b) although vessel diameter and vessel percentage were positively correlated with earlywood width (Table 2). Prom Table 2 it is also clear that ring width was significantly positively correlated with latewood width, whereas earlywood width remained fairly eonstant regardless of growth rate as reported in other ring-porous hardwoods (Zobel & Van Buijtenen 1989; Haygreen & Bowyer 1989). No relationship could be established between insect defoliation and the formation of false rings in sampled trees, although insect defoliation has been stated to be one of the causes of the latter (Haygreen & Bowyer 1989; Panshin & De Zeeuw 1980). Ac­ cording to Chowdhury and Rao (1949), juvenile wood produced in teak trees usually shows diseontinuous or often continuous false rings. About 80% of the dises observed in this investigation had false rings in any one of the eight annual rings. The trees whieh were artifieially protected against inseet defoliation also displayed false rings in the wood formed during the proteetion period. Therefore, some physiologieal distur­ banee other than defoliation must have led to rhythmie growth and false ring forma­ tion. Also we made observations on trees from another loeation (Peeehi), whieh had lost their foliage soon after flushing due to aeute insect defoliation and resurgence of new foliage after abrief period of one week. When the growth ring of that year was observed microseopieally, no false ring was found. Probably this was beeause either the eessation of radial growth may not be of sufficient duration to produce cells ehar-

Downloaded from Brill.com09/25/2021 07:34:16PM via free access 316 IAWA Journal, Vol. 18 (3),1997 aeteristie of latewood or the resumption of growth may not be intense enough to pro­ duee an auxin gradient favourable for the formation of the earlywood type of eells (panshin & De Zeeuw 1980; Haygreen & Bowyer 1989). Another probable explana­ tion is that there might have been only slight resumption of radial growth whieh might have led to the formation of earlywood eells eharaeteristie of a false ring only in the upper reaehes of the erown without extending up to the base of the , although eam­ bial reaetivation is known to be almost simultaneous throughout the tree of ring­ porous speeies (Wareing 1951).

ACKNOWLEDGEMENTS

We are grateful to Drs. K. S. S. Nair and v.v. Sudheendrakumar, Entomology Division of Kerala Forest Research Institute for the supply of sampie material from the experimental teak plantations for the insect defoliation study.

REFERENCES

Alfaro, R L. 1982. Tree mortality and radial growth los ses eaused by the western spruee budworm in a Douglas-fir stand in British Columbia. Can. J. For. Res. 12: 780-787. Alfaro, RL. & RF. Shepherd. 1991. Tree-ring growth of interior Douglas-fir after one year's defoliation by Douglas-fir tussoek moth. For. Sei. 37: 959-964. Beeson, C. F. C. 1941. The eeology and eontrol of the forest inseets of India and the neighbouring countries. (Reprint 1961). New Delhi, Govt. of India. Bhat, KM. 1995a. Properties of fast-grown teak wood: the impact on end-user's requirements. Paper presented in IUFRO XX World Congress, Tampere, Finland. Bhat, KM. 1995b. A note on heartwood proportion and wood density of 8-year-old teak. Indian For. 121: 514-517. Brubaker, L. B. & S. K Greene. 1979. Differential effeets of Douglas-fir tussoek moth and west­ ern spruee budworm defoliation on radial growth of grand fir and Douglas-fir. Can. J. For. Res. 9: 95-105. Busgen, M., E. Muneh & T. Thomson. 1929. The strueture and life of forest trees. Chapman & Hall Ud., London. Champion, H.G. 1934. The effeet of defoliation on the inerement of teak saplings. For. BuH. (Silv. Serv.) 89, FRI, Govt. of India Publ., Delhi. Chowdhury, KA. & K.R. Rao. 1949. The formation of growth rings in Indian trees. IV. False growth rings in saplings ofteak (Teetona grandis) and (Swietenia maerophylla). Indian For. Ree. (n.s.) Wood Teehnology 1: 1-15. Haygreen, G.l & L.l Bowyer. 1989. Forest produets and wood seience, an introduction. Iowa State University Press. Kulman, H.M., A.c. Hodson & D.P. Duncan. 1963. Distribution and effeets of jaek-pine bud­ worm defoliation. For. Sei. 9: 146-157. Mott, D.G., L.D. Nairn & lA. Cook. 1957. Radial growth in forest trees and effeets of inseet defoliation. For. Sei. 3: 286-304. Nair, KS.S., V.v. Sudheendrakumar, R.V. Varma& KC. Chaeko. 1985. Studies on the seasonal ineidenee of defoliators and the effeet of defoliation on volume inerement of teak. KFRI Res. Report 30. Peeehi. Panshin, A.J. & C. de Zeeuw. 1980. Text book of wood teehnology. EdA. MeGraw Hill, New York.

Downloaded from Brill.com09/25/2021 07:34:16PM via free access Priya & Bhat - Inseet defoliation in teak 317

Rose, A.H. 1958. The effeet of defoliation on foliage produetion and radial growth of Quaking . For.Sei. 4: 335-342. Stark, R.w. & J.A. Cook. 1957. The effeets of defoliation by the Lodgepo1e Need1e miner. For. Sei. 3: 376-396. Wareing, P.F. 1951. Growth studies in woody speeies. IV. The initiation of eambial aetivity in ring-porous speeies. Physiol. . 4: 546-562. Williams, C.B. Jr. 1967. Spruee budworrn damage symptoms related to radial growth of grand fir, Douglas-fir and Enge1mann Spruee. For. Sei. 13: 274-285. Zhang, S.Y. & Y. Zhong. 1991. Effeet of growth rate on wood speeifie gravity ofEast-Liaoning oak wood. Can. J. For. Res. 21: 255-260. Zhang, S.Y. & Y. Zhong. 1992. Strueture-property relationship of wood in East- Liaoning oak. Wood Sei. Teehnol. 26: 139-149. Zobel, RJ. & lP. van Buijtenen. 1989. Wood variation, its eauses and control. Springer-Verlag, Berlin, Heidelberg.

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