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Wood factors affecting the variation in specific gravity of northern red oak (Quercus rubra) associated with soil origin
Forest Ecology and Management, 17 (1986) 129-136 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
129
Wood Factors Affecting the Variation in Specific Gravity of Northern Red Oak ( Quercus rubra) Associated with Soil Origin J.R. H A M I L T O N
and S.J. K N A U S S
Division of Forestry, Collegeof Agriculture and Forestry, West Virginia University, Morgantown, WV26506-6125 (U.S.A.) (Accepted 27 March 1986)
ABSTRACT Hamilton, J.R. and Knauss, S.J.,1986. Wood factors affectingthe variation in specificgravity of northern red oak (Quercus rubra) associated with soilorigin.For. Ecol. Manage., 17: 129-136.
Northern red oak (Quercus rubra L. ) specific gravity was shown to be significantly greater in wood produced on soils derived from limestone parent material than on soils derived from acid sandstone parent material. A number of wood factors were measured in order to determine the cause for the observed specific gravity differences. The factors were examined and their significance determined by both correlation and regression analyses where specific gravity was the dependent variable. The principal factors correlated with specific gravity on limestone lithologies were ring width, fiber wall thickness, and iron and magnesium in the wood ash. The major factors correlated with specific gravity on sandstone lithologies were percent vessels, percent total extractives, and mAanesium in the wood ash. Significant to both lithologies, were ring width, percent total extractive content and percent vessels. It was evident that wood specific gravity is influenced by a system of complex interacting variables and variation in specific gravity associated with soil origin cannot be explained by examination of simple site factors alone.
INTRODUCTION In recent years, with the advent of more intensive utilization of the timber r e s o u r c e , t h e r e h a s b e e n r e n e w e d i n t e r e s t in t h e v a r i a t i o n o f w o o d c h a r a c t e r istics a s s o c i a t e d w i t h generic a n d e n v i r o n m e n t a l f a c t o r s . I n t e r e s t h a s c e n t e r e d o n specific g r a v i t y b e c a u s e o f its g e n e r a l a c c e p t a n c e as a m e a s u r e o f w o o d quality. S e v e r a l s t u d i e s h a v e s h o w n t h a t soil c o m p o s i t i o n h a s a n effect on w o o d p h y s i c a l p r o p e r t i e s . V i h r o v (1954) r e p o r t e d t h a t t h e s t r e n g t h o f o a k wood, a n d Approved by the Director of the Agriculture and Forestry Experiment Station as Scientific Paper No. 1783.
0378-1127/86/$03.50
© 1986 Elsevier Science Publishers B.V.
130 by implication specific gravity, was influenced by soil type. Wilde and Paul {1959), in a study of factors affecting the specific gravity of quaking aspen, noted a small, but real, influence of soil type. Litwin (1969) reported a significant relationship between specific gravity and rock type where oak wood grown on limestone derived soils was significantly heavier than that grown on sandstone derived soils. An acceptable explanation for such associations has been elusive. Litwin (1969) suggested that ash content may contribute positively to the variation in specific gravity associated with parent material. Davis (1973) reported that the alcohol-benzene extractives were greater in wood from limestone soils than from sandstone soils. Hamilton et al. (1978) noted that the reported differences in specific gravity due to soil origin were not strongly influenced by either ring with or percentage latewood. They also observed that, even though parent material associated differences in ash and alcohol-benzene extractives content existed, neither property fully accounted for the observed difference in the specific gravity. They concluded that the explanation must lie in some uninvestigated factor or factors such as the relative proportion of the several tissue types, cell wall thickness or density or some other chemical property. This paper describes the results of recent research at West Virginia University into the effect of several wood properties on variation in specific gravity which is associated with soil parent material. METHODS Five areas were located which contained forests growing on both limestone and acid sandstone derived soilsin close proximity to one another. Each location on a sandstone soilor limestone soilis hereafter referred to as a lithology and each area contained a limestone and sandstone lithology.All areas were in the Appalachian Mountains of West Virginia with approximately 160 k m separating the northernmost and southernmost areas: Only Belmont and Frederick limestone soiltypes and Dekalb and C a m p sandstone soiltypes were included. The soiltype for each lithology was verified in the field.Thus, five pairs of study lithologies,within which there was minimal variation in precipitation,elevation,temperature regime and soiltype were selected for study. Ten northern red oak (Quercus rubra L. ) trees,free of visible defect, 50-75 years of age, with minimal lean and littletaper, were selected and permanently identified on each site. Small diameter increment cores were removed from each tree at breast height in order that tree age and bole wood quality could be assessed in the field.In the laboratory, a 10-year-period of uniform, defect-free growth, in the outer heartwood, which was c o m m o n to alltrees,was located on the cores. The 10-year-segment beginning with the 15th year and extending through the 24th year from the cambium was selected as the period to be used for all wood determinations. Five of the original ten trees on each lithology
131
were randomly selected for study. As a result of this location and selection process, the study included fifty trees which were equally distributed between the five areas and two lithologies within each area. A site index value (50 years) for each tree was determined from age and height data (Schnur, 1937). Wood for laboratory examination was obtained by removing three 25-ram diameter radial plugs of sufficient length to include the 10-year-study segment from each tree (Hamilton et al., 1984). They were taken one above the other at breast height from a point randomly located with respect to the tree's circumference, except in the case of leaning trees. In these, the plugs were taken from the neutral axis in an attempt to minimize the effect of tension wood. The plugs were placed in plastic bags and stored in a freezer after removal from trees. The wood factors studied were: specific gravity; latewood percentage; ring width; fiber length, diameter, and wall thickness; percentages of supportive tissue, axial parenchyma, rays, and vessels; total extractive content; and ash content and its elemental composition. Specific gravity, average percentage latewood, and average increment width were determined using intact 10-year segments. Specific gravity was determined using the maximum moisture content method detailed by Smith (1954). Ring width and percentage latewood were determined on a smoothed transverse surface using an optical micrometer to make linear measurements along three radii (Hamilton, 1963). The three measurements were averaged to obtain a representative value for each tree. Fiber 1ength, diameter, and wall thickness were measured on 25 fibers using a sample of macerated wood from a radial strip representing the entire 10-yearsegment. Alcohol-benzene and water soluble extractives and total ash were determined using ground wood samples from the entire 10-year-segment following the procedures detailed in ASTM D-1102, D-1105, D-1107, and D l l l 0 (ASTM, 1974a,b,c,d) and expressed as a percentage of dry wood. Total extractive content was obtained by combining the values for alcohol-benzene and water soluble extractives. Wood elemental concentrations were determined using wet-ashing and atomic adsorption spectrophotometric techniques ( Jackson, 1958; Perkins-Elmer Corporation, 1976 ) and expressed as ppm. The tissue type proportions were determined from projected photographic images of smooth transverse surfaces using a dot-grid sampling method {Hamilton and Bethel, 1961 ). They were estimated in three randomly selected increments from the 10-year-segments. An initial screening of the wood characteristics and their relationship to specific gravity was made using correlation and intuitive analysis. The most promising were joined in a composite model and the factors resulting from this analysis were further examined by means of linear regression analysis (Statistical Analysis System, 1979). Stepwise multiple regressions were computed using an addition-deletion procedure with specific gravity being the dependent
132 TABLE 1 Average specific gravity for five trees for limestone and sandstone lithologies in five areas - - the average difference between the two was highly significant (t = 4.20)
Site
Limestone Sandstone
Area 1
2
3
4
5
0.597 0.580 0.589
0.547 0.543 0.545
0.581 0.562 0.571
0.583 0.562 0.573
0.567 0.553 0.560
0.575 0.560
variable. This permitted identification of the variables contributing significantly to R 2 of the regression model. RESULTS AND DISCUSSION
Effect of lithology on specific gravity In each of the five study areas the specific gravity of wood in trees growing on limestone lithologies was higher t h a n that in trees growing on sandstone lithologies. The average difference was not large, 2.8%, but was consistent for each area. A paired t test indicated t h a t the difference was significant (Table 1 ). This difference in specific gravity associated with soil origin is in agreement with the results of previous studies (Litwin, 1969; Hamilton et ah, 1978). There was also an area difference but this was not unexpected since no a t t e m p t was made, nor was it possible, to closely match area as it was lithologies.
Relationships between specific gravity and other wood characteristics The wood characteristicsmeasured in an effortto identify those related to the observed variation in specificgravity are given in Table 2. As measured by site index, sandstone lithologieswere more productive of wood volume than were limestone lithologies.M e a n site index for limestone lithologieswas 20.7 and that for sandstone lithologieswas 22.5. O n average, ring width and percentage latewood were greater in wood from sandstone lithologies than from limestone lithologies (Table 2). Sandstone lithologieshaving trees with wider rings, greater percent latewood, larger site indices, and lower specificgravitythan trees on limestone lithologiessuggest the possibility of an inverse relationshipbetween siteproductivity and specificgravity.Some have reported that increased rate of growth whether occurring naturally (Guiher, 1965), as the result of fertilization (Saucier and Ike, 1969) or as the resultof the addition of sewerage effluent (Murphey et ah, 1973 ) is associated
133 TABLE 2 Means and standard deviations for the wood factors studied - - each mean is the average for 25 trees for each lithology Characteristics
Limestone lithology
Standstone lithology
Mean
Mean
s
s
Annual ring width (ram) latewood (%)
2.9 60.4
0.92 6.68
3.6 65.5
0.93 6.01
Tissue type ( % ) ray supportive axial parenchyma vessels
13.0 45.5 21.4 20.1
2.69 4.37 4.82 4.90
12.7 44.7 21.5 21.1
2.70 5.16 5.18 3.87
Fiber dimensions (mm) length diameter wall thickness Extraneous substances total extractive content (%) wood ash ( % ) maganese (ppm) zinc (ppm) copper (ppm) magnesium (ppm) iron (ppm) potassium (ppm) calcium (ppm) phosphorous (ppm) nitrogen (ppm)
1.42 0.02 0.006
20.0 0.30 2.43 8.56 2.15 7.62 19.81 501.36 273.14 362.12 854.80
0.054 0.001 0.001
1.89 0.076 2.399 5.007 0.834 6.216 10.816 127.900 128.360 139.450 168.110
1.42 0.02 0.006
19.2 0.23 10.94 10.15 2.13 8.28 16.39 505.16 152.25 363.96 780.40
0.069 0.001 0.001
1.89 0.093 8.797 5.344 0.575 7.269 8.705 103.280 119.790 113.420 112.640
with increased specific gravity. However, the relationship with site quality is more tenuous. Direct comparisons of specific gravity on poor and high quality sites irrespective of parent material, with quality being determined either by site index or soil moisture regimes, indicate that site quality has littlesignificant effect on specific gravity (Litwin, 1969; Hamilton et al.,1978). Most of the wood properties exhibited only small differences between lithologies. The largest differences were in the elemental composition of ash. These differences such as those for manganese, iron, and calcium probably reflect availability in the soil solution. The absence of major differences between lithologies for the wood properties, in addition to an examination of plots of the
134 TABLE 3 Significant ( P = 0.05 ) correlation coefficients b e t w e e n specific gravity a n d selected w o o d p r o p e r t i e s Wood Properties
Lithology
Limestone Ring width F i b e r wall t h i c k n e s s Vessel p e r c e n t a g e Fe ( a s h ) Mg (ash) Total extractives
0.5456 0.5245 --0.4136 0.5655 --
Sandstone
Combined
--- 0.3650 -0.3863 - 0.3945
-0.3314 - 0.2716 m ---
data and tests of homogenity of the slopes suggest that the two lithologies may be combined in some analyses in order to gain sensitivity. Significant correlations between specific gravity and the remaining wood properties are given in Table 3. Very few of the wood properties were correlated with specific gravity either by lithology or the combined values for the two. Ring width, fiber wall thickness and mineral content of the ash were important factors on limestone, whereas vessel percentage, mineral content of the ash and total extractives were important on sandstone. When data for the two lithologies are combined fiber wall thickness and vessel percentage were the only factors correlated with specific gravity. This correlation analysis suggests that the variation in specific gravity is controlled by only a few factors and their influence is different on the two lithologies. Wood ash content was not significantly correlated with specific gravity on either limestone or sandstone sites,although there was a greater amount of ash in wood from limestone sitesthan from sandstone sites (Table 2). Litwin (1969) also found high levelsof ash in the wood from limestone sitesand speculated a relationship between ash content and specific gravity. The results presented here question the existence of such a relationship. Examination of Table 2 reveals that for some elements in the wood there were rather large differences associated with lithology.Such was the case for Mn, Zn, Mg, Fe, Ca and N. T w o of these, M g and Fe, were significantlycorrelated with specificgravity (Table 3). The remaining elements exhibited no significantcorrelations.
Factors contributing to the regression on specific gravity The relationship between specific gravity and other wood factors was also examined using multiple regression. Those factors included in the regression analysis were selected from the correlation analysis as having a relatively high degree of correlation (although not necessarily significant, P < 0 . 1 5 0 ) , andby
135 TABLE 4 Wood propertyregressioncoefficientsand theirsignificancein the linearregressionmodel
.Parameter Ring width Total extractives limestone sandstone Percentvessels
Estimate 0.007106 0.005124 - 0.005013 - 0.002316
t value 2.23* 2.30* - 1.86Ns - 3.12*
NS,non-significant. *,significantat the 0.05levelofprobability. intuition. Multiple regressions were computed so that those factors making significant contribution to the regression R 2 could be identified. T h e factors included were ring width, latewood percentage, fiber wall thickness, percent vessels, percent ray area and the iron and magnesium content of w o o d ash. Of these, annual ring width, total extractive content and percent vessels were the only ones that had a significant contribution (Table 4). It appears that the percentage of annual increments m a d e up of vessels had the greatest influence and that the effect was not different on the two lithologies. Total extractive content was important on limestone lithologies but not on sandstone. Ring width had the least effect of the three factors.
SUMMARYAND CONCLUSIONS Upon initiation of the study it was anticipated that clearly defined relationships between specific gravity and some of the many factors examined would be revealed. For the most part such was not the case. The conclusion could be easily reached that wood specific gravity is influenced by a very complex series of interacting factors. On limestone lithologies specific gravity was correlated with Fe and Mg present in the wood ash, fiber wall thickness, and ring width. On sandstone lithologies specific gravity was correlated with wood Mg and total extractives, and the percentage of vessels. The factors making important and significant contribution to the regression were ring width, percent total extractives, and percent vessels. It is apparent that specific gravity is affected by different factors on the two lithologies studied. The only factor common to both was the relatively minor magnesium content of the wood ash. The low order of correlation and the lack of significant in the regression of broadly representative factors may be due to insufficient sample size. It is important to note however, that ring width, total extractive content and vessel percentage were significant factors in both the correlation and regression analysis.
136 REFERENCES ASTM, 1974a. Standard method of test for ash in wood. ASTM D-1102, American Society for Testing and Materials, Philadelphia, PA. ASTM, 1974b. Preparation of extractive free wood. ASTM D-1105, American Society for Testing and Materials, Philadelphia, PA. ASTM, 1974c. Standard method of test for alcohol-benzene solubility of wood. ASTM D-1107, American Society for Testing and Materials, Philadelphia, PA. ASTM, 1974d. Standard method of test for water solubility of wood. ASTM D-1110 (Method B), American Society for Testing and Materials, Philadelphia, PA. Davis, R.E., 1973. The effect of rock type on the chemical composition of red oak and yellow poplar. Master's Thesis, West Virginia University, Morgantown, WV. Guiher, J.K., 1965. Effect of rings-per-inch on specific gravity of red oak. For. Prod. J., 15: 409. Hamilton, J.R., 1963. A dual-linear micrometer. For. Prod. J., 13: 70. Hamilton, J.R. and Bethel, J.S., 1961. A photo-optical method for determining gross character istics of wood. J. For., 59: 373-374. Hamilton, J.R., Litwin, P.J. and Tryon, E.H., 1978. A note on the influence of soil parent material on northern red oak specific gravity. Wood Fiber, 10: 2-5. Hamilton, J.R., Cech, F.C. and Ammons, F.L., 1984. A tool for obtaining large cores from standing trees. For. Prod. J., 34 (11/12)" 33-34. Jackson, M.L., 1958. Soil Chemical Analysis. Prentice-Hall, Englewood Cliffs, NJ, 498 pp. Litwin, P.J., 1969. Effects of rock type and wood characteristics on the hardness of northern red oak wood. M.S. Thesis, School of Forestry, West Virginia University, Morgantown, WV, 107 pp. Murphey, W.L., Young, W.J. and Cutter, B.E., 1973. The effect of sewage effluent irrigation on various physicaland anatomical characteristicson northern red oak. Wood Sci.,6: 65-71. Perkin-Elmer Corporation, 1976.AnalyticalMethods for Atomic Adsorption Spectrophotometry. Norwalk, CT. StatisticalAnalysis System, 1979. SAS User's Guide. SAS InstituteInc.,Raleigh,NC, 494 pp. Saucier,J.R. and Ike, A.F., 1969. Effect of fertilizationon selectedwood propertiesof sycamore. For. Prod. J., 19: 93-96. Schnur, G.L., 1937. Yield, stand, and volume tables for evenagod upland oak forest.U.S. Dep. Agric. Tech. Bull.560, 87 pp. Smith, D.M., 1954. M a x i m u m moisture content method for determining specificgravityof small wood samples. U.S. Dep. Agric. For. Prod. Lab. Pep. 2014, 8 pp. Vihrov, V.E., 1954. The structureand physiomechanical propertiesof oak wood. InstituteLesa, Akademija Nauk, Moscow, U.S.S.R.,264 pp. From For. Abstr. 16: 4510. Wilde, S.A. and Paul, B.H., 1959. Growth specificgravity and chemical composition of quaking aspen on differentsoiltypes.U.S. Dep. Agric. For. Prod. Lab. Rep. 2144, 10 pp.
129
Wood Factors Affecting the Variation in Specific Gravity of Northern Red Oak ( Quercus rubra) Associated with Soil Origin J.R. H A M I L T O N
and S.J. K N A U S S
Division of Forestry, Collegeof Agriculture and Forestry, West Virginia University, Morgantown, WV26506-6125 (U.S.A.) (Accepted 27 March 1986)
ABSTRACT Hamilton, J.R. and Knauss, S.J.,1986. Wood factors affectingthe variation in specificgravity of northern red oak (Quercus rubra) associated with soilorigin.For. Ecol. Manage., 17: 129-136.
Northern red oak (Quercus rubra L. ) specific gravity was shown to be significantly greater in wood produced on soils derived from limestone parent material than on soils derived from acid sandstone parent material. A number of wood factors were measured in order to determine the cause for the observed specific gravity differences. The factors were examined and their significance determined by both correlation and regression analyses where specific gravity was the dependent variable. The principal factors correlated with specific gravity on limestone lithologies were ring width, fiber wall thickness, and iron and magnesium in the wood ash. The major factors correlated with specific gravity on sandstone lithologies were percent vessels, percent total extractives, and mAanesium in the wood ash. Significant to both lithologies, were ring width, percent total extractive content and percent vessels. It was evident that wood specific gravity is influenced by a system of complex interacting variables and variation in specific gravity associated with soil origin cannot be explained by examination of simple site factors alone.
INTRODUCTION In recent years, with the advent of more intensive utilization of the timber r e s o u r c e , t h e r e h a s b e e n r e n e w e d i n t e r e s t in t h e v a r i a t i o n o f w o o d c h a r a c t e r istics a s s o c i a t e d w i t h generic a n d e n v i r o n m e n t a l f a c t o r s . I n t e r e s t h a s c e n t e r e d o n specific g r a v i t y b e c a u s e o f its g e n e r a l a c c e p t a n c e as a m e a s u r e o f w o o d quality. S e v e r a l s t u d i e s h a v e s h o w n t h a t soil c o m p o s i t i o n h a s a n effect on w o o d p h y s i c a l p r o p e r t i e s . V i h r o v (1954) r e p o r t e d t h a t t h e s t r e n g t h o f o a k wood, a n d Approved by the Director of the Agriculture and Forestry Experiment Station as Scientific Paper No. 1783.
0378-1127/86/$03.50
© 1986 Elsevier Science Publishers B.V.
130 by implication specific gravity, was influenced by soil type. Wilde and Paul {1959), in a study of factors affecting the specific gravity of quaking aspen, noted a small, but real, influence of soil type. Litwin (1969) reported a significant relationship between specific gravity and rock type where oak wood grown on limestone derived soils was significantly heavier than that grown on sandstone derived soils. An acceptable explanation for such associations has been elusive. Litwin (1969) suggested that ash content may contribute positively to the variation in specific gravity associated with parent material. Davis (1973) reported that the alcohol-benzene extractives were greater in wood from limestone soils than from sandstone soils. Hamilton et al. (1978) noted that the reported differences in specific gravity due to soil origin were not strongly influenced by either ring with or percentage latewood. They also observed that, even though parent material associated differences in ash and alcohol-benzene extractives content existed, neither property fully accounted for the observed difference in the specific gravity. They concluded that the explanation must lie in some uninvestigated factor or factors such as the relative proportion of the several tissue types, cell wall thickness or density or some other chemical property. This paper describes the results of recent research at West Virginia University into the effect of several wood properties on variation in specific gravity which is associated with soil parent material. METHODS Five areas were located which contained forests growing on both limestone and acid sandstone derived soilsin close proximity to one another. Each location on a sandstone soilor limestone soilis hereafter referred to as a lithology and each area contained a limestone and sandstone lithology.All areas were in the Appalachian Mountains of West Virginia with approximately 160 k m separating the northernmost and southernmost areas: Only Belmont and Frederick limestone soiltypes and Dekalb and C a m p sandstone soiltypes were included. The soiltype for each lithology was verified in the field.Thus, five pairs of study lithologies,within which there was minimal variation in precipitation,elevation,temperature regime and soiltype were selected for study. Ten northern red oak (Quercus rubra L. ) trees,free of visible defect, 50-75 years of age, with minimal lean and littletaper, were selected and permanently identified on each site. Small diameter increment cores were removed from each tree at breast height in order that tree age and bole wood quality could be assessed in the field.In the laboratory, a 10-year-period of uniform, defect-free growth, in the outer heartwood, which was c o m m o n to alltrees,was located on the cores. The 10-year-segment beginning with the 15th year and extending through the 24th year from the cambium was selected as the period to be used for all wood determinations. Five of the original ten trees on each lithology
131
were randomly selected for study. As a result of this location and selection process, the study included fifty trees which were equally distributed between the five areas and two lithologies within each area. A site index value (50 years) for each tree was determined from age and height data (Schnur, 1937). Wood for laboratory examination was obtained by removing three 25-ram diameter radial plugs of sufficient length to include the 10-year-study segment from each tree (Hamilton et al., 1984). They were taken one above the other at breast height from a point randomly located with respect to the tree's circumference, except in the case of leaning trees. In these, the plugs were taken from the neutral axis in an attempt to minimize the effect of tension wood. The plugs were placed in plastic bags and stored in a freezer after removal from trees. The wood factors studied were: specific gravity; latewood percentage; ring width; fiber length, diameter, and wall thickness; percentages of supportive tissue, axial parenchyma, rays, and vessels; total extractive content; and ash content and its elemental composition. Specific gravity, average percentage latewood, and average increment width were determined using intact 10-year segments. Specific gravity was determined using the maximum moisture content method detailed by Smith (1954). Ring width and percentage latewood were determined on a smoothed transverse surface using an optical micrometer to make linear measurements along three radii (Hamilton, 1963). The three measurements were averaged to obtain a representative value for each tree. Fiber 1ength, diameter, and wall thickness were measured on 25 fibers using a sample of macerated wood from a radial strip representing the entire 10-yearsegment. Alcohol-benzene and water soluble extractives and total ash were determined using ground wood samples from the entire 10-year-segment following the procedures detailed in ASTM D-1102, D-1105, D-1107, and D l l l 0 (ASTM, 1974a,b,c,d) and expressed as a percentage of dry wood. Total extractive content was obtained by combining the values for alcohol-benzene and water soluble extractives. Wood elemental concentrations were determined using wet-ashing and atomic adsorption spectrophotometric techniques ( Jackson, 1958; Perkins-Elmer Corporation, 1976 ) and expressed as ppm. The tissue type proportions were determined from projected photographic images of smooth transverse surfaces using a dot-grid sampling method {Hamilton and Bethel, 1961 ). They were estimated in three randomly selected increments from the 10-year-segments. An initial screening of the wood characteristics and their relationship to specific gravity was made using correlation and intuitive analysis. The most promising were joined in a composite model and the factors resulting from this analysis were further examined by means of linear regression analysis (Statistical Analysis System, 1979). Stepwise multiple regressions were computed using an addition-deletion procedure with specific gravity being the dependent
132 TABLE 1 Average specific gravity for five trees for limestone and sandstone lithologies in five areas - - the average difference between the two was highly significant (t = 4.20)
Site
Limestone Sandstone
Area 1
2
3
4
5
0.597 0.580 0.589
0.547 0.543 0.545
0.581 0.562 0.571
0.583 0.562 0.573
0.567 0.553 0.560
0.575 0.560
variable. This permitted identification of the variables contributing significantly to R 2 of the regression model. RESULTS AND DISCUSSION
Effect of lithology on specific gravity In each of the five study areas the specific gravity of wood in trees growing on limestone lithologies was higher t h a n that in trees growing on sandstone lithologies. The average difference was not large, 2.8%, but was consistent for each area. A paired t test indicated t h a t the difference was significant (Table 1 ). This difference in specific gravity associated with soil origin is in agreement with the results of previous studies (Litwin, 1969; Hamilton et ah, 1978). There was also an area difference but this was not unexpected since no a t t e m p t was made, nor was it possible, to closely match area as it was lithologies.
Relationships between specific gravity and other wood characteristics The wood characteristicsmeasured in an effortto identify those related to the observed variation in specificgravity are given in Table 2. As measured by site index, sandstone lithologieswere more productive of wood volume than were limestone lithologies.M e a n site index for limestone lithologieswas 20.7 and that for sandstone lithologieswas 22.5. O n average, ring width and percentage latewood were greater in wood from sandstone lithologies than from limestone lithologies (Table 2). Sandstone lithologieshaving trees with wider rings, greater percent latewood, larger site indices, and lower specificgravitythan trees on limestone lithologiessuggest the possibility of an inverse relationshipbetween siteproductivity and specificgravity.Some have reported that increased rate of growth whether occurring naturally (Guiher, 1965), as the result of fertilization (Saucier and Ike, 1969) or as the resultof the addition of sewerage effluent (Murphey et ah, 1973 ) is associated
133 TABLE 2 Means and standard deviations for the wood factors studied - - each mean is the average for 25 trees for each lithology Characteristics
Limestone lithology
Standstone lithology
Mean
Mean
s
s
Annual ring width (ram) latewood (%)
2.9 60.4
0.92 6.68
3.6 65.5
0.93 6.01
Tissue type ( % ) ray supportive axial parenchyma vessels
13.0 45.5 21.4 20.1
2.69 4.37 4.82 4.90
12.7 44.7 21.5 21.1
2.70 5.16 5.18 3.87
Fiber dimensions (mm) length diameter wall thickness Extraneous substances total extractive content (%) wood ash ( % ) maganese (ppm) zinc (ppm) copper (ppm) magnesium (ppm) iron (ppm) potassium (ppm) calcium (ppm) phosphorous (ppm) nitrogen (ppm)
1.42 0.02 0.006
20.0 0.30 2.43 8.56 2.15 7.62 19.81 501.36 273.14 362.12 854.80
0.054 0.001 0.001
1.89 0.076 2.399 5.007 0.834 6.216 10.816 127.900 128.360 139.450 168.110
1.42 0.02 0.006
19.2 0.23 10.94 10.15 2.13 8.28 16.39 505.16 152.25 363.96 780.40
0.069 0.001 0.001
1.89 0.093 8.797 5.344 0.575 7.269 8.705 103.280 119.790 113.420 112.640
with increased specific gravity. However, the relationship with site quality is more tenuous. Direct comparisons of specific gravity on poor and high quality sites irrespective of parent material, with quality being determined either by site index or soil moisture regimes, indicate that site quality has littlesignificant effect on specific gravity (Litwin, 1969; Hamilton et al.,1978). Most of the wood properties exhibited only small differences between lithologies. The largest differences were in the elemental composition of ash. These differences such as those for manganese, iron, and calcium probably reflect availability in the soil solution. The absence of major differences between lithologies for the wood properties, in addition to an examination of plots of the
134 TABLE 3 Significant ( P = 0.05 ) correlation coefficients b e t w e e n specific gravity a n d selected w o o d p r o p e r t i e s Wood Properties
Lithology
Limestone Ring width F i b e r wall t h i c k n e s s Vessel p e r c e n t a g e Fe ( a s h ) Mg (ash) Total extractives
0.5456 0.5245 --0.4136 0.5655 --
Sandstone
Combined
--- 0.3650 -0.3863 - 0.3945
-0.3314 - 0.2716 m ---
data and tests of homogenity of the slopes suggest that the two lithologies may be combined in some analyses in order to gain sensitivity. Significant correlations between specific gravity and the remaining wood properties are given in Table 3. Very few of the wood properties were correlated with specific gravity either by lithology or the combined values for the two. Ring width, fiber wall thickness and mineral content of the ash were important factors on limestone, whereas vessel percentage, mineral content of the ash and total extractives were important on sandstone. When data for the two lithologies are combined fiber wall thickness and vessel percentage were the only factors correlated with specific gravity. This correlation analysis suggests that the variation in specific gravity is controlled by only a few factors and their influence is different on the two lithologies. Wood ash content was not significantly correlated with specific gravity on either limestone or sandstone sites,although there was a greater amount of ash in wood from limestone sitesthan from sandstone sites (Table 2). Litwin (1969) also found high levelsof ash in the wood from limestone sitesand speculated a relationship between ash content and specific gravity. The results presented here question the existence of such a relationship. Examination of Table 2 reveals that for some elements in the wood there were rather large differences associated with lithology.Such was the case for Mn, Zn, Mg, Fe, Ca and N. T w o of these, M g and Fe, were significantlycorrelated with specificgravity (Table 3). The remaining elements exhibited no significantcorrelations.
Factors contributing to the regression on specific gravity The relationship between specific gravity and other wood factors was also examined using multiple regression. Those factors included in the regression analysis were selected from the correlation analysis as having a relatively high degree of correlation (although not necessarily significant, P < 0 . 1 5 0 ) , andby
135 TABLE 4 Wood propertyregressioncoefficientsand theirsignificancein the linearregressionmodel
.Parameter Ring width Total extractives limestone sandstone Percentvessels
Estimate 0.007106 0.005124 - 0.005013 - 0.002316
t value 2.23* 2.30* - 1.86Ns - 3.12*
NS,non-significant. *,significantat the 0.05levelofprobability. intuition. Multiple regressions were computed so that those factors making significant contribution to the regression R 2 could be identified. T h e factors included were ring width, latewood percentage, fiber wall thickness, percent vessels, percent ray area and the iron and magnesium content of w o o d ash. Of these, annual ring width, total extractive content and percent vessels were the only ones that had a significant contribution (Table 4). It appears that the percentage of annual increments m a d e up of vessels had the greatest influence and that the effect was not different on the two lithologies. Total extractive content was important on limestone lithologies but not on sandstone. Ring width had the least effect of the three factors.
SUMMARYAND CONCLUSIONS Upon initiation of the study it was anticipated that clearly defined relationships between specific gravity and some of the many factors examined would be revealed. For the most part such was not the case. The conclusion could be easily reached that wood specific gravity is influenced by a very complex series of interacting factors. On limestone lithologies specific gravity was correlated with Fe and Mg present in the wood ash, fiber wall thickness, and ring width. On sandstone lithologies specific gravity was correlated with wood Mg and total extractives, and the percentage of vessels. The factors making important and significant contribution to the regression were ring width, percent total extractives, and percent vessels. It is apparent that specific gravity is affected by different factors on the two lithologies studied. The only factor common to both was the relatively minor magnesium content of the wood ash. The low order of correlation and the lack of significant in the regression of broadly representative factors may be due to insufficient sample size. It is important to note however, that ring width, total extractive content and vessel percentage were significant factors in both the correlation and regression analysis.
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