IAWA Journ al, Vol. 17 (1), 1996: 5-14
LONGITUDINAL VARIATION IN SELECTED WOOD PROPERTIES OF NATURALLY AND PLANTATION GROWN LIGHT RED MERANTI (SHOREA LEPROSULA AND S. PARVIFOLIA, DIPTEROCARPACEAE) by Monique T. M. Bosman
Rijksherbarium / Hortus Botanicus, Leiden University, P.O. Box 95 14, 2300 RA Leiden, The Netherlands
SUMMARY
Longitudinal variation in fibre wall percentage, area percentage of vessels and resin canals and specific gravity was studied at three to five height levels in three naturally and five plantation grown trees of Light Red Meranti (Shorea leprosula and S. parvifolia ). All three variables show considerable differences within and among the studied trees. The area percentage of vessels and resin canals increases from the base to the top of the bole, most prominently in the naturally grow n trees. The fibre wall percentage and the specific gravity in both the naturally grown and plantation grown trees show a decrease followe d by an increase towards the top of the bole, with the lowest values at heights of about 5-10 m. The average fibre wall percentages for planta• tion grown trees mostly fall within the same range as those of the naturally grown trees. The total-tree-averages for specific gravity of three plantation grow n trees and for the percentage of vessels and resin canals of two plantation grown trees are distinctly lower than those of the three naturally grow n trees. Keywords: Shorea leprosula, Shorea pa rvi folia , Light Red Meranti, tropi• cal hardwoods, fibre wall percentage, specificgravity,tissue proportions, longitudinal variatio n, wood quality, plantations.
INTRODUCTION
The study of variation in wood properties of plant ation grown tropical hardwoods in comparison with patterns found in naturally grow n trees of the same species contrib• utes to the understanding of the effects of plantation growth on wood quality. Under• standing of varia tion patterns in naturally grown and plantation grown trees is also relevant for the deve lopment of selection programmes of future planting material. Light Red Meranti, one of the major exported timbers of Malaysia and Indonesia, can now be propagated and grown in cultivation (Smits 1987) and some large-scale plantations have been developed in the past decade. The timber quality of these trees, however, is still uncertain as the rotation period for Shorea species is expected to be about 40 years (Tan et al. 1987).
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A pilot study on radial variation in two Light Red Meranti species , Shorea leprosula Miq. and S. parvifolia Dyer, already showed that only very minor differences in spe• cific gravity and selected wood anatomical properties existed between plantation grown and naturally grown trees (Bosman et al. 1994). However, radial variation patterns may be different at different height levels (Bhat et al. 1989). To supplement the data on radial variation an analysis of longitudinal variation in the same two species is presented here. Longitudinal variation has so far been less extensively studied than radial variation, involving fewer species and variables. For Shorea, only Sahri and Kadir (1994) and Sahri et al. (1995) recently studied this subject. Usually only specific gravity, the most important wood quality variable, and sometimes also fibre length are studied and often only one or a few trees have been sampled. Longitudinal variation has been studied in hardwoods by Alipon (1991), Kroll et al. (1992), Land & Lee (1981), Land et al. (1983), Omolodun et al. (1991), Phelps & Workman (1992), Rueda & Williamson (1992) , Sulaiman & Lim (1993), Wilkes (1988), Yanchuk et al. (1983) and others, and in soft• woods by, e.g., Keith & Chauret (1988) (for a survey of earlier literature: Panshin & De Zeeuw 1980). Patterns and extent of variation differ among and within species (Harzmann 1988; Zobel & Van Buijtenen 1989). In softwoods, specific gravity in about two thirds of all studied species decreases, often considerably, towards the top of the tree. In hardwoods, patterns are less pronounced and more variable : specific gravity may increase or decrease from the base to the top or it may decrea se from the base of the tree to halfway up the bole and then again increase towards the top (Panshin & De Zeeuw 1980; Tsoumis 1991; Zobel & Van Buijtenen 1989). Part of these variation patterns in specific gravity and related properties may be ex• plained by a) mechanical factors, such as greater stresses at the stem base, resulting in higher specific gravity, b) heartwood formation , usually in higher proportions at the stem base and c) the extent of juvenile wood, always in higher proportions near the top, with, especially in softwoods, a considerably lower specific gravity (Tsoumis 1991). However, as in other species, genetic factors may also play an important role in longi• tudinal variation (Land et al. 1983; Wilkes 1988). In this study not only specific gravity but also some related wood anatomical vari• ables, such as cell wall percentage and tissue proportions, have been studied to obtain a better understanding of the variation found within and among the studied trees.
MATERIAL AND METHODS
In general the same methods of sampling, sectioning and measuring were used as for the study on radial variation (Bosman et al. 1994). Of the 12 trees available for that study, 8 trees were selected for the present study: numbers 1-7 and 10. The samples came from different institutions and not all were sampled in the same way and at the same heights . Six of the studied trees were sampled at three different heights and two trees (no. 4 and 6) were sampled at five different heights (Table 1). At each height, samples of 1.5 cm in radial diameter were taken every 6 cm along the radius from pith
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Table I. Trees studied. For sampling heights marked with an asterisk (*) radial variation has been discussed in a previous study (Bosman et al. 1994) . Tree numbers follow those adopted in that study.
Tree Shorea Origin Age DBH Crown Sampling heights no. species years cm at m in m
S. parvifolia plantation Kalimantan 17 35 15.5 5*, 10, 15 2 S. parvifolia natural forest Kalimantan ? 32 14 8*, 12, 16 3 S. leprosula plantation Kalimantan 35 35 14 8*, 12, 16 4 S. leprosula plantation Java 34 77 22 1, 7*, 13, 19, 25 5 S. parvifolia natural forest Kalimantan ? 45 15.5 5*, 11, 16 6 S. leprosula natural forest Kalimantan ? 43 21 I, 6*, 11, 16, 21 7 S. leprosula FRIM campus Malaysia 62 38 13.9 1, 7*, 14 10 S. leprosula FRIM campus Malaysia 62 41 23.6 1, 12*, 22
to bark, the first sample adjacent to the pith. For the heights at which radial variation was already studied, more samples (every 3 ern) were available. Radial variation pat• terns may change abruptly in the first 5-10 em from the pith (Bosman et al. 1994). To exclude possible influences of juvenile wood it was therefore decided to discard the first 9 em near the pith in calculating average values per tree for each height (radius• averages) and total-tree-averages. Thus for each radius 1-8 samples were used . Be• cause radial variation in these middle and outer parts of the radius is relatively small, an initial weighting ofradius-averages to reflect differences in cross-sectional area did not or in some cases only slightly alter the unweighted averages and was therefore abandoned in further analysis. Three variables were studied: the basic specific gravity, the cell wall percentage within the fibre tissue ('fibre wall percentage') and the area percentage of vessels and resin canals.
RESULTS
No large differences in radial variation patterns were found for any of the investigated variables between trees of S. parvifolia and S. leprosula (Bosman et al. 1994) . There• fore, the two species are not separately indicated in the figures.
Variation patterns in the investigated variables Although considerable differences exist between trees, some general patterns of longitudinal variation can be distinguished for all three variables.
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[ 80 40 35 30 0 5 10 15 20 25 30 Height of sampling in metres (H) Fig. I. Average fibre wall percentage versus height of sampling in plantation grow n trees ( - ... - ) and naturally grown trees ( - - • - - ). The first 9 cm from pith are excluded from the radius averages. 0.57 0.55 0.53 0.51 6 0.49 Fig. 2. Average specific gravity versus height of samp ling in plantatio n grown trees ( - ..-) and naturally grown trees ( - - • - - ). The first 9 cm from pith are excluded from the radius averages. Downloaded from Brill.com10/07/2021 06:29:34AM via free access Bosman- Naturally and plantation grown Meranti 9 25 ~ 24 V> 23 20 vV> V> 19 0) ;> 18 '- 0 0) 17 OJ) .9 16 e 0) u 15 ...0) 0.. 14 ell ~ ell 13 0) OJ) 12 e 0) II ~ 10 0 5 10 15 20 25 30 Height of sampling in metres (H) Fig. 3. Average area percentage of vessels and resin canals vs height of sampling in plantation grown trees ( - &-) and naturally grown trees ( - - • - - ). The first 9 cm from pith are excluded from the radius averages. The average fibre wall percentage (Fig. 1) is initially high (64-81 %) near the base of the tree, i.e ., at a height of about 1 m (data from this height were only available for trees no. 4, 6, 7, and 10). After that it decreases to reach its lowest value (37-74%) at c. 5-10 m (excluding no. 10), and then again it increases towards the top of the bole (up to 57-78%), to be followed by a final decrease or levelling off at the crown base in most trees. The average specific gravity (Fig. 2) follow s approximately the same pattern: high• est value near the base (0.38-0.47), then a decre ase towards the lowest value at about 5-13 m (0.29-0.39), followed by an increase (up to 0.31-0.44) and, in some trees, a final decrease or levelling off near the top of the bole. The average area percentage of vessels and resin canals (Fig. 3) follow s a less con• sistent pattern, but most trees show an increase from the base of the tree (12-20%), to the top of the bole (12-25 %), although trees no. 3 and 7 show a dip at around 10m. However, the increase is significant in only two naturally grown trees and two plan• tation grown trees (Table 2). This is in part due to the low number of observations (3 to 5). The slope of the increase is distinctly steeper in the naturally grown trees than in the plantation grown trees. Only in tree no. 7 is the increase almost as strong as in the naturally grown trees. As stated in the study on radial variation (Bosman et al. 1994) the increase in relative amount of vessels and resin canals indicates a decrease in relative amount of fibre tissue. Downloaded from Brill.com10/07/2021 06:29:34AM via free access 10 IAWAJournal, Yol. 17 (1), 1996 Table 2. Correlation (regression formulas and correlation coefficients) between the area per• centage of vessels and resin canals (AY) and the height of sampling (H) in plantation grown (P) and naturally grown (N) trees. Tree numbering as in Table 1. Data are radius-averages per height level excluding the first 9cmfrom the pith (significance levels:***p < 0.01; **0.01 ~ P < 0.025; * 0.025 ~ P ~ 0.05; ns =not significant; n =number of observations). Tree No. Shorea species Origin Area percentageof vessels and canals (AY) n I S. parvifolia P 0.05 H + 11.41 ns 3 2 S. parvifolia N 0.33 H + 14.92 ns 3 3 S. leprosula P -0.02 H + 15.69 ns 3 4 S. leprosula P 0.12 H + 16.00 * 5 5 S. parvifolia N l.\9 H + 5.69 *** 3 6 S. leprosula N 0.37 H + 14.93 ** 5 7 S. leprosula P 0.31 H + 17.76 ns 3 10 S. leprosula P 0.19 H + 16.32 * 3 The radial variation patterns at the different height levels for all three variables and for most of the studied radii are the same as those described earlier (Bosman et al. 1994), i. e., a more or less distinct increase from pith to bark. Only in five radii (all at levels above 12 m) was a decrease in specific gravity and/or fibre wall percentage found (in trees no . 3,4,5, and 10). This decrease is caused by relatively high values near the pith at those heights. In trees no. 3 and 4, these higher values even lead to higher total-tree• averages of specific gravity and, respectively, fibre wall percentage, when the first 9 em from the pith are included (Table 3). Table 3. Total-tree-averages for fibre wall percentage (FW), specific gravity (SG) and area per- centage of vessels and resin canals (AY) in plantation grown (P) and naturally grown (N) trees. Tree numbering as in Table I. The first 9 em from pith are excluded from the total-tree-averages. The averages between parentheses include these first 9 em from the pith. Tree No. Shorea species Origin FW (in %) SG AY (in %) I S. parvifolia P 61 (SO) 0.29 (0.28) 12 (II) 2 S. parvifolia N 66 (57) 0.43 (0.37) 19 (IS) 3 S. leprosula P 59 (41) 0.31 (0.32) IS (13) 4 S. leprosula P 61 (66) 0.41 (0.41) 18 (IS) 5 S. parvifoli a N 55 (53) 0.37 (0.35) 18 (IS) 6 S. leprosula N 71 (60) 0.42 (0.36) 19 (IS) 7 S. leprosula P 60 (52) 0.35 (0.31) 20 (17) 10 S. leprosula P 61 (58) 0.41 (0.38) 19 (IS) Downloaded from Brill.com10/07/2021 06:29:34AM via free access Bosman - Naturally and plantation grown Meranti 11 Correlation between investigated variables When the averages from all investigated heights are considered the correlation be• tween the three studied variables is positive and highly significant (SG = 0.0036 FW + 0.14, r = 0.7 and SG = 0.0076 AV + 0.24, r = 0.48, both with P < 0.005). The variation in fibre wall percentage and area percentage of vessels and resin canals explains, re• spectively, (r 2 =) 53% and 23% of the variation in specific gravity. Thus, the variation in specific gravity is mainly explained by an increase in fibre wall percentage despite a decrease offibre area percentage. Positive significant correlation was also found in the earlier study on radial variation, and with even higher explanatory values of the ana• tomical variables (Bosman et al. 1994). Plantation grown versus naturally growing trees When naturally grown trees are compared with plantation grown trees, the longi• tudinal patterns of variation are approximately the same for all variables and trees studied. However, the ranges of radius-averages (Fig. 1-3) and the total-tree-averages (Table 3) are sometimes distinctly different between the two categories of trees. The radius-averages of fibre wall percentage in plantation grown trees vary from 37% in tree no. I (at 5 m) to 81% in tree no. 4 (at I m). This is a slightly wider range than observed in naturally grown trees: i.e., from 44% in tree no. 5 (at 5 m) to 75% in tree no. 6 (at II and 16 m). This difference may in part be due to the fact that more planta• tion grown trees (5) than naturally grown trees (3) have been examined. Total-tree• averages of this variable for plantation grown trees fall within the natural range as observed in the three naturally grown trees. For specific gravity, two plantation grown trees (no. I and 3) fall almost completely outside the range of radius-averages observed in the naturally grown trees, which is from 0.32 in tree no 5 (at 5 m) to 0.47 in tree no. 6 (at I m). Only the highest value, in tree no. 3 (at 16 m) reaches the lowest value of the naturally grown trees, i.e., 0.32. Also, when total-tree-averages are compared, tree no. I and 3, and also tree no.7, show distinctly lower values than those observed in the three naturally grown trees. The radius-averages of area percentage of vessels and resin canals in plantation grown trees vary from 12% in tree no. I (at 5 m) to 24% in tree no. 7 (at 14 m) and fall within the range of values found in the three naturally grown trees, i.e., from 12% in tree no. 5 (at 5 m) to 25% in tree no.5 (at 16 m). However, two trees (again, no. I and 3) have a distinctly lower total-tree-average for this variable. DISCUSSION AND CONCLUSION Although ranges of radius-averages and total-tree-averages may differ for some trees and some variables, the variation patterns found in plantation grown trees are com• parable with those found in naturally grown trees. The increase in area percentage of vessels and resin canals, however, tends to be steeper in naturally grown trees when compared with plantation grown trees. Apparently wood of the plantation grown trees is in this respect somewhat less variable than that of the naturally grown trees. A simi- Downloaded from Brill.com10/07/2021 06:29:34AM via free access 12 1AWAJournal, Vol. 17 (1), 1996 lar conclusion was drawn for radial variation ofspecific gravity and fibre wall percent• age (Bosman et al. 1994). Whether this difference between plantation grown trees and naturally grown trees is due to differences in growth rates cannot be concluded as the growth rates of the studied trees are not available. The typical variation pattern found for specific gravity (and with it, fibre wall per• centage), showing a decrease followed by an increase going upward in the stem, has been reported in about one third of the studies of longitudinal variation in hard• woods studied (Barrichelo et al. 1984: Eucalyptus; Briscoe et al. 1963: Swietenia; Hamilton 1961: Quercus;Sahri et al. 1995: Shorea ;Taylor 1979: Nyssa, Carya, Quercus, Liquidambar; Yanchuck et al. 1983: Populus) and a few softwoods. Although observ• ed frequently, the dip in specific gravity at a height of about 5-10 m has not yet been explained. Other hardwoods show a more or less steady increase or, as is most com• mon in softwoods, a decrease towards the top of the bole (Zobel & Van Buijtenen 1989). Some plantation grown trees show rather low values for all variables: tree no. I, 3, and to a lesser extent no. 7. Specific gravity in tree no. I is even below the natural range (0.3-0.8) for this species given by Martawijaya et al. (1986). The fact that these trees are relatively young (no. 1 and 3) or not very tall for their age (no. 3 and 7) may account, at least in part, for these low values (compare age, DBH and crown height in Table 1). The radial variation patterns as described earlier (Bosman et al. 1994) are here con• firmed for most trees. The relatively high values in four trees (no. 3, 4, 5, and 10) for fibre wall percentage and/or specific gravity, near the pith at heights above 12 m, which result in a decrease instead of an increase towards the bark, have not been re• ported before for this or any other hardwood species, and remain unexplained. It may be relevant to note that the two trees most prominently showing this phenomenon are the two largest (in height and DBH) plantation grown trees sampled for this study (trees no. 4 and 10). The considerable longitudinal variation within trees for all variables demonstrates the importance of careful selection of samples for wood anatomical research and wood quality tests. For the species studied, the most representative average values in large, full grown trees are found at heights above 10-15 rn, whereas in the basal 5-10 m differences in specific gravity and wood anatomical variables may be very large. As has been argued before (Bosman et al. 1994), the increase in area percentage of vessels and resin canals indicates a decrease in the relative amount of fibre tissue. Despite this decrease of fibre tissue towards the top of the bole, in general the fibre wall percentage increases to such an extent that specific gravity also increases with increasing height (Fig. 4a & b). The relatively high values for specific gravity and fibre wall percentage found in some plantation grown trees (no. 10, and especially the fast and vigorously grown no. 4) offer promising possibilities for selection programmes using indigenous species for sustainable forestry. More species, trees and variables have to be studied to fully comprehend and make use of the variation in structure and quality of tropical hardwoods. Downloaded from Brill.com10/07/2021 06:29:34AM via free access Bosman - Naturally and plantation grown Meranti 13 Fig. 4. Plantation grown Shorea: Transverse section of stem wood. - (a) S. leprosula: high specific gravity (0.4) sample showing fibre tissue with high percentage cell wall (67%) in combination with a high percentage of vessel and resin canal area (20%) (tree no. 10 at 12 m, 17 em from the pith). - (b) S. parvifolia: low specific gravity (0.3) sample showing fibre tissue with low percentage cell wall (36%) in combination with a low percentage of vessel and canal area (10%) (tree no. I at 5 m, 19 cm from the pith). - Scale bars =200 urn, ACKNOWLEDGEMENTS This study has been financed by the Tropenbos Foundation and was executed at the Rijksherbarium / Hortus Botanicus of Leiden University. I thank Mr.Willie Smits of the Wanariset in East Kalimantan, Dr. Nana Supriana of the Forest Products Research and Development Centre in Bogor, Java, and Mr. Wulf Killman and Dr. Mohammed Salleh Nor, director of the Forest Research Institute in Kepong, Malaysia for generously providing material for this research. The photographs were kindly made by Bertie Joan van Heuven. REFERENCES Alipon , M.A. 1991. Relative density and shrinkage of yemane (Gmelina arborea Roxb.) at dif• ferent ages and height levels. FPRDl 1. 20 (3/4): 50-60. Barrichelo, L.E.G., A.H. Nariyoshi, O. Beij & A.S. Diniz. 1984. Variations in the characteris• tics of eucalyptus wood due to differences in species age and location. In: ABCP Proc. 17th Annual Meeting, Nov. 19-23, Sao Paulo, Brazil. Vol. I: 389-399 (Abstract) . Bhat, KM., KV. Bhat & T.K. Dhamodaran. 1989. Radial pattern s of density variation in eleven tropical Indian hardwoods. Holzforschung 43: 45-48. 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