iawa journal, vol. 25 (3), 2004: 273–282

IAWA Journal, Vol. 25 (3), 2004: 273–282

INFLUENCE OF PROVENANCE VARIATION ON WOOD PROPERTIES OF TEAK FROM THE WESTERN GHAT REGION IN INDIA*

K.M. Bhat & P.B. PriyaWood Science Division, Kerala Forest Research Institute, Peechi 680 653, India

[E-mail: [email protected]]

SUMMARY

The three major teak provenances of the Western Ghats in India were characterised in terms of mechanical and anatomical wood properties. Within the same age of 21-year-old plantations, teak from the North Kanara provenance, generally known to display slow growth, had the lower values of static bending (modulus of rupture and modulus of elasticity) and longitudinal compressive stresses than the Malabar provenance (Nilambur). The weaker timber of North Kanara provenance was attributed to its relatively high percentage of parenchyma and low percentage of fibres in the narrower rings, probably as an adaptation to nutrient-rich soil condition. Observations of 65-year-old plantations reveal that there was a trend for bending stiffness (modulus of elasticity) and maximum stress (modulus of rupture) of the timber to be highest towards the southernmost geographic location (Konni) within the lati-tudinal range of 9° to15° S with a greater percentage of cell wall (with higher lignification) despite the slower growth rate and well defined ring-porosity with wider bands of earlywood parenchyma tissue. The study thus underlines the need to recognise the provenance source of variation to explain the varied growth-structure-property relationships of teak and to utilise the Indian genetic resources to the optimum in future teak improvement programmes.

Key words: Tectona grandis, ring-porous tropical hardwood, growth rate, wood anatomy, mechanical properties.

INTRODUCTION

Teak (Tectona grandis L.f.) has been selected for sustainable production of high-quality timber in the tropics and the global plantations currently exceed 5.2 million ha. Earlier studies based on teak samples obtained from different countries such as Bangladesh, India and Myanmar indicate that the strongest wood is produced from a modest annual radial growth of 4–5 mm (Limaye 1942). Smeathers (1951) observed that the timber produced in plantations from Trinidad was not inferior in mechanical properties to that

*) Extended version of a paper presented at the IUFRO Division 5 Conference, Rotorua, New Zealand, March 2003.

Associate Editor: Ute Sass-Klaassen

Downloaded from Brill.com05/01/2022 06:03:24AMvia free access

IAWA Journal, Vol. 25 (3), 2004274 275Bhat & Priya — Provenance variation in teak

of Myanmar although the former had the mean ring width of 5 mm as against 2 mm of the latter. On the other hand, Myanmar provenances planted in Trinidad developed trees with lower specific gravity than the already existing plantations (Smeathers 1951). According to Bryce (1966), the mechanical properties of 51-year-old Tanzania-grown teak were 15% inferior to teak wood of the same age tested from Myanmar and Trinidad. Teak wood from West Africa was reported to be harder and heavier than teak from the Asian region (Sallenave 1958). Similarly, teak is known to exhibit wide geographic/provenance variations in India with regard to wood figure and strength properties (Tewari 1994). The Malabar teak (Nilambur, Kerala) from the Western Ghat region in India (Fig. 1), generally displaying good growth and log dimensions with desired wood figure (golden yellowish brown colour), has a wide reputation in the world trade for ship-building. The central Indian teak from the drier region is reputed for better tree form, deeper colour and twisted or wavy grain, although it is stated to be often 7–8% lighter than South Indian and Myanmar teak. However, recent study reported greater genetic diversity in the teak populations of the Western Ghats region than in Central India (Nicodemus et al. 2003). Without considering the provenance as a source of variation, earlier studies reported contradictory findings with regard to the relationship between growth rate and wood properties in teak (Bourdillon 1895; Chowdhury 1952; Mukherji & Bhattacharya 1963; Bryce 1966; Rao et al. 1966; Bhat 1998). The specific objectives of the present study are: (a) to adduce evidences for the dis-play of the varied relationship between growth rate (ring width) and wood properties in teak due to the provenances in the Western Ghat region in India, (b) to provide an

Fig. 1. Geographic locations (Konni: Location I – Nilambur: Location II – North Kanara: Loca-tion III) of trees sampled in the Western Ghat region in India.

0 180 360

N

III

II

I



anatomical explanation as to why fast grown teak with wider rings can be both me-chanically stronger and weaker, and (c) to characterise three main provenances of the Western Ghats in terms of structural wood quality attributes for optimum utilization of the Indian genetic resources in future teak improvement programmes.

MATERIAL AND METHODS

Study material originates from 24 trees sampled from the three major geographic locations/provenances of teak plantations of the Western Ghats in India (Fig. 1). These provenances are: Konni (geographic location I), Nilambur (geographic location II) and North Kanara (Karwar Forest Division – geographic location III), which represent the major wet zone teak plantations of the Indian West Coast region. The data on environ-mental conditions of the study locations are recorded in Table 1.

Table 1. The environmental factors of the geographic locations of tree sampling.

Factor Konni Nilambur North Kanara (Location I) (Location II) (Location III)

North latitude 9° 3'–9° 85' 11° 12'–11° 32' 15° 30'–15° 40' East longitude 76° 41'–77° 6' 75° 82'–76° 32' 74° 40'–74° 50' Temperature range (°C) 12–35 17–37 17–35 Mean annual rainfall (mm) 2900 2600 2900 Soil type sandy loam river alluvial sandy loam rich in organic matter Drainage good good good

To compare the effects of growth rate on wood properties in relatively young (juve-nile) and mature trees between the geographic locations, six dominant trees each (with-in the marked area of 40 × 40 m) from 21-year- and 65-year-old plantations were sampled. In teak, the age demarcation point between juvenile and mature wood was esti-mated around 20 years (Bhat et al. 2001). A basal log of about 1.5 m length was col-lected from each tree for wood property investigations. For the purpose of this study, young 21-year-old plantations were compared between Locations II and III while the mature 65-year-old plantations were compared between Location I and II. About 5 cm thick cross-sectional discs were removed from breast height level (1.37 m from stump level) to study anatomical and physical properties and adjacent basal billets to prepare the wood specimens for mechanical testing.

Laboratory investigationsAnatomy For wood anatomical study, 15–20 μm thick cross sections were cut with a sliding microtome, from pith to periphery including inner, middle and outer portion of the radial strip to cover radial variation. For 65-year-old trees, 4 to 5 radial positions from pith to bark were studied. Standard microtechnique procedure was followed to prepare the



sections for microscopic observation and anatomical quantification. Important anatomi-cal properties studied were ring width, vessel diameter, percentages of fibres, vessels, parenchyma (ray and axial parenchyma combined) respectively and cell wall per se. Leica Image Analysis System (Quantimet 500+) was employed for precise quantifica-tion of wood anatomical features.

Mechanical testing The basal billets of 1.4 m length were converted into scantlings of 3 × 3 cm cross section to prepare test samples from pith to periphery in one radial direction selected randomly just below breast height. From each radius, samples (2 × 2 × 30 cm) were tested for static bending (modulus of rupture: MOR; modulus of elasticity: MOE) and compression parallel to grain (maximum crushing stress: MCS) in accordance with the Indian Standards (IS: 1708, 1986). The sample size of 2 × 2 × 10 cm has been used for compression tests. Small pieces from tested samples were cut to determine the wood density in air-dried condition corresponding to the radial positions of anatomical ex-amination. Mechanical testing has been done using a Zwick Universal Testing Machine. The mean values of the properties were compared between the provenances by paired t-tests to confirm the significant differences. Simple correlation coefficients were estimated to indicate the linear relationships among the selected anatomical and mechanical properties.

RESULTS AND DISCUSSIONTree size Size of the sampled trees of three provenances can be assessed from the mean values of dbh presented in Table 2. It is evident that radial growth is slow and tree diameter small in Locations I and III as compared to the trees of the Nilambur plantation (Loca-tion II) which is reputed for good growth and greater tree dimensions. Generally, dbh increased with tree age and the rate of increase was more rapid in young trees below the age of 21 years than in mature trees of 65 years.

Wood properties Except wood density, all the strength properties (MOR, MOE and MCS) were inferior in slow grown trees of geographic Location III to those of Location II in 21-year-old trees. On the other hand, in mature wood (65-year-old) of slow grown trees of Location I, the average bending strength values (MOR and MOE) were significantly greater than in wood from Location II where trees displayed a significantly larger dbh (Table 2). These results are in agreement with the previous findings reporting on considerably lower suitability indices for North Kanara than Nilambur (Malabar) teak (Sekhar & Gulati 1972; Rajput & Gulati 1983). The anatomical investigation provides a probable explanation for these geographic differences in mechanical properties as the teak wood in North Kanara (Location III) had a significantly higher proportion of parenchyma and a lower proportion of fibre tissue. This could be seen as a provenance adaptation with the higher amount of storage parenchyma possibly being related to the generally rich soil conditions (sandy loam) in this geographic location (Tables 1 & 2 and Fig. 2).



However, it is not clear if the present finding of high wood density in teak from Location III is attributed to more abundant parenchyma with a relatively high extractive content (phenolic deposits) as reported for some hardwoods of tropical trees (Taylor 1969). In contrast, another slow growing provenance (Location I) exhibited greater bending strength (MOE and MOR) with slightly greater wood density than the fast growing trees of Nilambur provenance (Location II). This is attributed to significantly greater cell wall percentage with a higher degree of lignification in both juvenile and mature wood of the southernmost geographic Location II (Fig. 2) although longitudinal compressive stress was lower (Table 2) and the role of parenchyma was not clear. The role of cell wall thickness with microfibrillar angle, as the structural determinants of bending strength of teak, have already been established in an earlier study (Bhat et al. 2000).

Ring width vs. tissue proportions The results reveal that juvenile and mature teak wood from the slow growing prov-enances of Location I and III displayed more distinct ring porosity with larger earlywood

Table 2. Comparison of mean values with standard deviations in parentheses of selected anatomical and mechanical properties of 21- and 65-year-old trees of Konni (Location I),Nilambur (Location II), and North Kanara (Location III).

Property No. of Location I Location II Location III t-value1) samples

21-year-old plantation DBH in cm 6 20.9 (1.2) 15.0 (1.0) **

Ring width in mm 126 5.0 (3.9) 3.8 (2.8) **

Vessel % 18 9.1 (2.7) 9.8 (2.8) ns

Fibre % 18 66.7 (21.3) 59.7 (20.2) *

Parenchyma % 18 24.2 (4.5) 30.5 (5.2) **

Cell wall % 18 54.5 (6.9) 45.7 (6.0) ns

Modulus of rupture , N-mm2 18 133.2 (29.5) 91.8 (18.0) *

Modulus of elasticity, N-mm2 18 13643 (2106) 8436 (1858) **

Max. compressive stress , N-mm2 18 53.9 (3.8) 44.6 (3.3) *

Air dry density in kg-m3 18 618.7 (43.3) 681.5 (44.1) *

65-year-old plantation DBH in cm 6 34.4 42.2 **

Ring width in mm 390 2.6 (1.7) 3.2 (2.3) **

Vessel % 18 11.9 (4.6) 14.9 (5.0) ns

Fibre % 18 60.2 (8.1) 58.6 (6.3) ns

Parenchyma % 18 25.8 (10.1) 26.6 (9.8) ns

Cell wall % 18 54.4 (8.7) 48.6 (6.6) *

Modulus of rupture, N-mm2 18 136.1 (19.8) 103.8 (18.4) **

Modulus of elasticity, N-mm2 18 17580 (2637) 12512 (1752) **

Max. compressive stress, N-mm2 18 48.0 (3.5) 59 (4.1) *

Air dry density in kg-m3 18 665.0 (44.2) 655.0 (44.0) *

1) Significance of t-value: ns = not significant; * = significant at 5% level; ** = significant at 1% level.



a b

c d



vessels associated with a wider band of parenchyma tissue (Fig. 2). Teak from the rela-tively fast growing provenance (Location II) had wide rings with a gradual transition between early- and latewood while vessels become smaller towards the latewood region with more gradual changes in vessel size. This last pattern resulted in a relatively uniform and high fibre percentage which would explain the modest mechanical behaviour of relatively fast grown teak from the Nilambur provenance in comparison to fast grown teak from other locations in India (Bhat 1998). This condition also subscribes to the view that wider rings are generally associated with wider latewood while earlywood width remaining more or less constant as a typical condition of many ring-porous species (Wheeler 1987; Priya & Bhat 1997, 1998). It is also of interest to note that growth rings are less well defined in fast growing trees (Fig. 2); extremely fast growth in the juvenile phase may even lead to diffuse porosity as reported from irrigated and fertilised trees (Bhat 1998; Priya & Bhat 1999; Bhat et al. 2001). In contrast to the findings of Rao et al. (1966), who concluded that there was no definite relationship between ring width and tissue proportions, the present results adduce evidence for a provenance-related variability in the relationship between tissue proportions and ring width. For instance, the wider rings of young teak from Location II were associated with a higher fibre and a lower parenchyma percentage in comparison with teak from Location III while the reverse was noted when comparing with Location I, another slow growing provenance (Table 2). This underlines the need to consider the role of provenances when explaining the contradicting results on the mechanical properties of fast grown teak. The problem of timber quality of fast grown teak is not new and has been debated since 1895 when Bourdillon supported the arguments of the contemporary silviculturists who attempted to prove that fast grown teak was the strongest. The present findings throw more light on this issue by elucidating the provenance-related variation. Previous studies did not provide a satisfactory answer as to whether or not fast grown timber is stronger despite the suggestion that fast growing provenances/clones can be selected for teak management without adversely affecting wood density (Bhat 2000; Bhat et al. 2001). However, Bhat and Indira (1997) cautioned that choosing wood density alone in the overall genetic improvement programme of timber quality of teak for solid wood uses would be misleading. This is further strengthened by the present results that wood density is not always associated with strength properties among the three provenances probably due to differences in extractive contents (Table 2).

←Fig. 2. Transverse sections of Tectona grandis (× 25) displaying the wood structure of three prov-enances from the Western Ghat region in India (a & b displaying the structure of ring number 20 from pith of North Kanara (Location III) and Nilambur (Location II) provenances, respec-tively; note the relatively high percentage of parenchyma in the narrow ring of the slow grow-ing provenance; c displays the juvenile wood, ring number 20 –21 from pith, and d represents mature wood with ring number 60–65 from pith of the Konni provenance (Location I); note the relatively high cell wall proportion despite narrower rings and abundant parenchyma, making the timber stronger with higher modulus of rupture and bending stiffness.



Structure-property relationships The simple correlation coefficients presented in Table 3 elucidate the extent of linear relationships among various anatomical and mechanical property variables. As the age demarcation point between juvenile and mature wood in teak lies around 20 years (Bhat et al. 2001), some age-related changes in structure-property relationships are anticipated between 21- and 65-year-old plantations irrespective of provenances. It became obvious that in juvenile wood the negative association between parenchyma percentage and mechanical properties was pronounced while in mature wood vessel percentage as-sociated with generally larger vessels, mainly contributed to lower bending strength (Table 3). It is perhaps for this reason that the impact of parenchyma tissue was less on the strength of 65-year-old slow growing teak from the Konni provenance (Location I) where stronger wood with a higher cell-wall percentage was noticed. The vessel diam-eter /percentage in teak wood has also been identified as one of the best anatomical in-dicators of age demarcation between juvenile and mature wood, although maturation age varies depending on different anatomical properties (Bhat et al. 2001).

Table 3. Simple correlation coefficients indicating linear relationships among selected anatomical and mechanical properties (provenances combined).

Correlating wood properties 21-year-old 65-year-old

Vessel % vs fibre % -0.53* -0.85**

Vessel % vs parenchyma % 0.18 0.13 Vessel % vs cell wall % -0.73** -0.79**

Vessel % vs MOR -0.11 -0.38 Vessel % vs MOE -0.41 -0.57** Vessel % vs UCS -0.39 0.69** Fibre % vs parenchyma % -0.93** -0.45* Fibre % vs cell wall % 0.58** 0.70** Fibre % vs MOR 0.77** 0.09 Fibre % vs MOE 0.89* 0.25 Fibre % vs UCS 0.58** -0.76** Parenchyma % vs cell wall % -0.36 -0.41 Parenchyma % vs MOR -0.84** 0.01 Parenchyma % vs MOE -0.86** -0.21 Parenchyma % vs UCS -0.50* 0.55* Cell wall % vs MOR 0.44* 0.60* Cell wall % vs MOE 0.69** 0.71** Cell wall % vs UCS 0.64** -0.74** MOR vs MOE 0.93** 0.87**

MOR vs UCS 0.72** -0.14 MOE vs UCS 0..80** -0.38

* = significant at the 5% level; ** = significant at the 1% level.



CONCLUSIONS

The observations on provenance-related variation offer a probable explanation as to why the mechanical properties of wood from fast grown teak can be lower than those of wood from slower grown trees while many studies consider wide tree rings as indica-tors of mechanically strong timber. The results also suggest a geographical trend of increasing mechanical strength as associated with a greater cell wall percentage which is running latitudinally towards the southern geographic location (Konni) within a range of 9° to 15° S in the Western Ghat region in India. This source of geographic variation is also important to explain the varied relationship between (quantitative and qualita-tive) wood anatomy and mechanical wood properties displayed by teak even within the same age groups. The results also rule out the possibility of wide rings being always as-sociated with either stronger or weaker wood by underlining the need for considera-tion of different provenances/seed sources in the tree improvement programme for sustainable teak management.

ACKNOWLEDEGEMENTS

The present paper represents part of a research project sponsored by the Kerala Forest Department. The constant encouragement received from Dr. J.K. Sharma, Director, KFRI and the technical sup-port from Mr. A.G. Benny and Dr. Ancy Mathew are gratefully acknowledged. Sincere thanks are due to Dr. Ute Sass-Klaassen for her useful comments to improve the manuscript.

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