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Fuelwood quality of promising tree species for alkaline soil sites in relation to tree age
Biomassand Eioenergy Vol. 10. No. 1, pp. 57-61, 1996 Copyright 0 1996 Else& Science Ltd 0961-9534(!)5poo53-4 Printed in Great Britain. All rights resewed 0961-9534/96$15.00+ 0.00
Pergamon
FUELWOOD QUALITY OF PROMISING TREE SPECIES FOR ALKALINE SOIL SITES IN RELATION TO TREE AGE* V. L. GOEL and H. M. BEHL Biomass Research Center, National Botanical Research Institute, Lucknow 226 001, India (Received I7 September 1993; in revised form 20 April 1995; accepted 10 June 1995)
Abstract-The fuelwood quality of five tree species suitable for alforestation of alkaline soil sites was investigated in relation to tree age for establishing harvest rotation cycles. Prosopis jrdipora and Acacia nilotica were found to be the most suitable species for short rotation fuel wood forestry programmes because of their high wood density, biomass yield, low ash and moisture content, and good heat of combustion at the juvenile stage. The performance of other species like Acacia auriculiformis, Terminalia arjuna and Sesbaniu formosa is discussed. Copyright 0 1996 Elsevier Science Ltd. Keywords-Fuelwood
tree species; fuel value index; age-wood quality relationship.
1. INTRODUCTION
2. MATERIALS AND METHODS
Energy plantations on degraded or substandard sites are a viable option to meet the fuelwood challenge. Fuelwood consumption in India has been estimated to be at least 235 Mm3/yr and industrial requirements to be 27.6 Mm3/yr against the availabilities of 40 Mm3 and 12 Mm3/yr, respectively.’ The gap between demand and production is being met through pilferage from managed and unmanaged forests’ and through imports.’ Although many multipurpose (MP) tree species are being studied worldwide, it is imperative to identify and evaluate the available species capable of providing high quality fuel, fodder and timber on underutilized lands in short rotations which can also ameliorate the soil. Wood quality plays a crucial role in selecting a species for fuelwood production and establishing harvest rotation cycles. However, such information on the fuelwood quality of juvenile and mature wood for species selection is not abundant.“’ In the present study, the wood quality of selected fuelwood (FW) tree species in relation to tree age has been investigated in order to establish harvest rotation cycles in plantations on degraded sites such as alkaline soil sites.
2.1. Site details and trials Site x species trials for 12 FW tree species were laid in 1982 at the Biomass Research Centre of this institute situated at Banthra, Lucknow (longitude 80”45’-80”53’E and latitude 26”40’-26”45’N). The species under investigation (Acacia auriculiformis A. Cunn. ex Benth., Acacia nilotica Wild. ex Del., Prosopis julifora Swartz, Terminalia arjuna Bedd.) were a part of that trial. Another trial of the same species and an exotic species trial were laid five years later in 1987. The soils of the experimental site are silty clay loam, non-saline sodic, heavy with high pH (8.5-10.6) and bulk density (> 1.7 g/cm’). The plants suffer anaerobic stress during monsoon months when the fields remain waterlogged. Low porosity and the non-availability of existing nutrients limit the growth and establishment of trees. The experiment was designed as a complete randomized block with three replicates, each measuring 40 m x 40 m. Planting was done at a square spacing of 1.5 m x 1.5 m corresponding to a density of 4444 plants/ha. The total above-ground biomass was estimated on the basis of linear regression equations defining the relationship between biomass as a dependent variable (JJ)
*NBRI Publication # 443 (NS). 57
V. L.
58
GOEL and
H. M.
BEHL
Table 1. Growth, establishment and productivity of species under investigation Species P. .i&flora . A. nilotica
Age (yrs) 5 10 5
10 A. auriculiformis T. arjuna
S. formosa
5
10 5 10 5
Height (dm)
Basal area (mYha)
Establishment (%I
Biomass (t/ha)
83 91 64 90 69 98 41 69 97
14.0 19.0 7.3 14.5 11.7 18.7 8.8 25.0 34.6
94.38 51.05 76.02 49.63 91.32 52.88 92.97 86.76 51.00
75.09 103.32 27.74 65.32 26.60 55.95 8.41 68.00 64.94
and height x diameter (d2h) as an independent variable. The mean annual increment (m.a.i.) in productivity was calculated for each species.
has been worked out9 The formula used for computation of the FVZ is as below: FVZ =
2.2. Sampling and analysis
Calorific value (kJ/g) x Density (g/cc) Ash content (g/g) x Moisture content (g/g)
Wood samples were cut at breast height (130 cm) after destructive felling of three candidate trees in each species. Cubes of 5 cm’ 3. RESULTS were oven dried to a constant weight and On the basis of mean plant height, basal area, analyzed for fuel quality studies. Samples of establishment and total above-ground dry 15year-old trees were collected from the biomass (Table l), and m.a.i. (Fig. l), P. primary limbs of naturally growing trees juliJora, A. nilotica and A. auriculiformis had adjacent to the experimental site, while those of S. formosa were taken from 5-year-old trees of outstanding performance. T. arjuna, though, had very high establishment and tolerance to an exotic species screening trial; lo- and 15-year-old trees were not available for this stress, but was moderate with respect to species. All the samples were collected in productivity. Table 2 shows the moisture content, density, December. The thermochemical properties calorific value and ash content of five tree (density, moisture, calorific value, ash and other species in relation to tree age (5, 10 and 15 elements) of the wood samples of different years). There were characteristic differences in species were determined. The density was these parameters among the various tree species. determined by the weight loss method for 1 cm The wood density in 5-, lo- and 15-year-old thick discs using glycerin. Part of the oven dried sample was ground to pass through a 30 mm trees varied only marginally in P. juliJora (0.80-0.89 g/cc) and A. nilotica (0.80-0.84 g/cc), sieve and was used for analysis. For determination of calorific value, powdered samples were again dried at 70°C for 24 hours and pressed into pellets. A Parr oxygen bomb calorimeter, model 1341, was used for determination of heat of combustion. The ash content was determined by burning 2 g of air dried and ground sample in a platinum crucible in a muffle furnace at 550°C for 5 h. The carbon content was determined in accordance with the Tyurin method. Nitrogen was estimated on a Kjeltec Auto 1030 N-analyzer after sulfuric acid digestion.8 All analyses were done in triplicate and the results were expressed on a dry weight basis, For comparing fuelwood characteristics of Fig. 1. Mean annual increment in various FW species under various species, a ‘fuelwood value index’, FVZ) study.
Fuelwood quality of promising tree species for alkaline soil sites in relation to tree age
59
Table 2. Thermal and elemental analysis of wood in relation to age Species A
auricull~ormis
A. nilotica
P. juiipora
T. arjuna
S. formosa
Tree age (YN
C.V. @J/g)
Ash (%I
(G,
5 10 15 5 10 15 5 10 15 5 10 15 5
18.60 20.66 20.58 19.57 20.46 23.68 20.33 21.42 23.90 20.59 20.01 21.03 24.11
3.00 2.95 2.80 2.42 2.00 1.40 3.10 2.70 1.50 4.60 4.00 3.80 4.00
47.56 52.33 61.55 53.48 55.92 66.00 54.18 58.53 66.81 50.50 54.83 62.97 54.01
however, in other species it increased with increasing tree age (Fig. 2). It was 0.50.78 g/cc in T. arjuna and 0.63-0.82 g/cc in A. auriculiformis. S. formosa, a fast growing species (average height: 97 dm) had the lowest wood density (0.39 g/cc) at the age of five years. The moisture content ranged from 31.7 to 5 1% among the various species, being highest in S. formosa. The variation in moisture percentage due to age was 24% in 5- and lo-year-old trees and 598.3% in lo- and lEyear-old trees (Fig. 3). The calorific value of wood samples varied from 18.6 to 24.11 kJ/g in different species. 5-year-old trees of S. formosa had the highest calorific value compared with the other tree species of similar age (18.6 kJ/g in A. auriculiformis against 20.6 kJ/g in T. arjuna). However, no relationship between calorific value and age of the tree was evident. The ash content differed in the five species investigated. It also varied in relation to the age of the tree. The highest wood ash was observed DENSITY
m
Si (%) 1.90 1.10 0.46 1.70 1.30 0.50 2.30 1.70 0.35 2.10 1.60
1.06 0.76
in all the treatments in T. arjuna (5, lo- and 15-year-old trees) as compared with that in other tree species in respective ages. The ash content decreased by 1% and 1.6% in A. nilotica and P. jt@ora, respectively for 15year-old trees as compared to 5-year-old trees. The total carbon content varied a little in the different species. The silica content, like the wood ash, was lower in mature trees of all the species (Table 2). It was only 0.35% in P. jz.difEora in 15-year-old trees as compared to 1.06% in T. arjuna of the same age. It was in the range l.l-1.7% in lo-year-old trees of all the species. In general, the nitrogen content was highest in P. juliflora followed by A. nilotica. It was nearly the same in T. arjuna and A. auriculiformis. The nitrogen content of the wood decreased with increasing age in all the species. The results showed marked differences in the fuelwood properties as indicated by the fuel value index (FVZ) of the different species at
(g/cc)
5-yr
0.59 0.42 0.39 0.71 0.57 0.52 0.82 0.79 0.64 0.65 0.42 0.38 0.83
lo-yr
m
15-yr
Fig. 2. Wood density of various fuelwood tree species at different ages.
60
V. L. Moisture
GOEL
and H. M. BEHL
(46)
60 50 40 30 20
10 0 S. formosa
A. auriculiformis m
T. srjuna
15-yr
P. jutiflora
A. nilotica
lo-yr
m
5-yr
Fig. 3. Moisture content of wood at different ages.
various ages (Fig. 4). Promising tree species like P. julijlora and A. nilotica had high FVZ values, whereas A. auriculiformis, T. arjuna and S. formosa were poor with respect to their FVZ. 4. DISCUSSION
High density, high heat of combustion, low ash and moisture content are desirable characteristics of quality fuelwood. Wood density varies with the species, age, geographical location, climate, planting density and growth rate.‘O Heinsdijk reported that in E. globulus, l-year-old plants ‘showed a density of 0.541 while in 26year-old plants it was 0.773.’ Similarly, he found that in E. camaldulensis, the wood density was 0.538 at the age of 5 years which increased to 0.765 at the age of 26 years. However, the difference in E. verminilis wood
density between 5- and 15-year-old trees was marginal (0.613 compared with 0.659). In the present study, the differences in wood density of certain species like A. nilotica and P. julifora were marginal while in others, density increased with the age of the tree. On the basis of m.a.i. and productivity, it can be suggested that P. julzflora should be harvested after five years and A. nilotica after six years. Data on the wood density of juvenile wood support the above recommendation. On the other hand, the density was too low in 5-year-old trees of A. auriculiformis and T. arjuna. It is not advisable to harvest trees of these species at an early stage. The study suggests that harvest operations in A. auriculiformis and T. arjuna should begin after 10 years. Sesbania formosa had poor wood density (0.39 g/cc); accordingly, it is not suitable for fuelwood purposes.
FVI (Thousands)
J
D
5-yr
lo-yr
m
15-yr
Fig. 4. Fuel value index of various fuelwood tree species in relation to tree age.
Fuelwood quality of promising tree species for alkaline soil sites in relation to tree age
Wood density can be used as a useful parameter to fix harvest rotation cycles, particularly for short rotation plantations. However, decisions would be specific for each tree species on a given site. Siren et al. observed that both biomass production and quality are important considerations to fix the optimum age for harvesting in Sulix.” Juvenile and mature wood formation are related to the maturity of cambial cells as influenced by hormone balance. Fast growing FW species like P. julifrora and A. niloticu make better fuelwood in short rotations than other species. The high moisture content and low density in the early stage can be attributed to the higher amount of sap wood in the juvenile stage. Zobel and Talbert have reported that there is a strong negative relation between specific gravity and moisture content” Low specific gravity in juvenile wood results from thin cell walls and a low amount of summer wood cells.13 Sir@ reported that tree age and girth had no apparent influence on calorific value in Pinus species.14 High wood ash is less desirable for fuelwood as it is noncombustible and reduces the heat of combustion.15 T. arjuna has a high ash content and a low nitrogen content as compared to P. juliforu and A. nilotica. Reduced nitrogen content is also a desirable trait as it indicates low emission of nitrous oxide which otherwise causes environmental pollution. The present study suggests that density is an important trait to consider when making selections among tree species. However, a combination of more than one parameter such as FVZ, m.a.i. and other characteristics should govern harvest operations. Acknowledgements-The authors are grateful to Dr P. V. Sane, Director of the Institute for guidance and provision of facilities. The research was a part of the Biomass Research Center programme which is funded by the Ministry of Non-conventional Energy Sources. Assistance
61
rendered by Shri R. K. Chaudhary in analyzing the samples is also acknowledged.
REFERENCES 1. Anonymous, Country update: India. How India can achieve self sufficiency in timber. A& Pacific Foresf Industries, pp. 22-29 (1993). 2. ITTO, Elements for the 1992 annual review and assessment of the world tropical timber situation. ITTC (XIV)/3, p. 98. International Tropical Timber Organization, Kuala Lumpur, Malaysia, 11-29 May (1993). of logged over forests in 3. ITTO, Rehabilitation Asia/Pacific region. Country studies. Annex I. India. PCF (VI)/9, p. 60. International Tropical Timber Organization, benpasar, Bali. 16-23 May (1990). 4. B. P. Bhatt and N. P. Todaria. Fuelwood characteristics of some mountain trees and shrubs. Biomass 21, 233-238 (1990). 5. D. Heinsdijk, Forest inventory. In Foresr Assessment, Book Distributors, PP. 173-217. International Dehradun, India (1987). 6. T. Tietema, M. Ditlhogo, C. Tibone and N. Mathalaza, Characteristics of eight firewood species of Botswana. Biomass and Bioenergy l(l), 41-46 (1991). I. D. M. Ranasinghe and G. L. Mayhead, Dry matter content in an age series of Eucalyptus camaldulensis (Dhen) nlantation in Sri Lanka. For. Ecol. Manure I 41. i37-142 (1991). 8. Y. P. Kalra and D. G. Maynard, Methods manual for forest soil and plant analysis. Information Report NOR-X-319, Forestry, Canada, Northwest Region, Northern Forestry Center, Edmonton, Alberta (1991). 9. V. L. Goel and H. M. Behl, Wood quality for fuelwood rotation cycles. Proc. IUFRO All Division V Conf. 23-28 August, Nancy, Paris (1992). 10. J. S. Gongalez, Wood density of Canadian tree species. Information Report NOR-X-315 Forestry, pp. 14. Canada. Northwest Region. Northern Forestrv Center _ (1990). 11 G. Siren, F. L. Sennerby and S. Ledin, Energy plantations-short rotation forestry in Sweden. In Biomass, Regenerable Energy (Eds D. 0. Hall and R. P. Overend), pp. 119-143. Wiley, Singapore (1987). I? .a. B. Zobel and J. Talbert, Wood and Tree Improvement. In Applied Forest Tree Improvement, pp. 376413. Wiley, New York (1984). 13. L. Basley, Importance, variation and measurement of wood density and moisture. Proc. Wood Measurement Con& pp. 112-143. University of Toronto (1967). 14. B. Singh, Conservation and fixation of solar energy in Pinus per& plantations of Darjeeling Himalaya. Biomass 5, 43-54 (1984). 15. B. Singh, and S. D. Khanduja. Wood properties of some timwood shrubs in Northern India. Biomass 4,235-238
(1984).
Pergamon
FUELWOOD QUALITY OF PROMISING TREE SPECIES FOR ALKALINE SOIL SITES IN RELATION TO TREE AGE* V. L. GOEL and H. M. BEHL Biomass Research Center, National Botanical Research Institute, Lucknow 226 001, India (Received I7 September 1993; in revised form 20 April 1995; accepted 10 June 1995)
Abstract-The fuelwood quality of five tree species suitable for alforestation of alkaline soil sites was investigated in relation to tree age for establishing harvest rotation cycles. Prosopis jrdipora and Acacia nilotica were found to be the most suitable species for short rotation fuel wood forestry programmes because of their high wood density, biomass yield, low ash and moisture content, and good heat of combustion at the juvenile stage. The performance of other species like Acacia auriculiformis, Terminalia arjuna and Sesbaniu formosa is discussed. Copyright 0 1996 Elsevier Science Ltd. Keywords-Fuelwood
tree species; fuel value index; age-wood quality relationship.
1. INTRODUCTION
2. MATERIALS AND METHODS
Energy plantations on degraded or substandard sites are a viable option to meet the fuelwood challenge. Fuelwood consumption in India has been estimated to be at least 235 Mm3/yr and industrial requirements to be 27.6 Mm3/yr against the availabilities of 40 Mm3 and 12 Mm3/yr, respectively.’ The gap between demand and production is being met through pilferage from managed and unmanaged forests’ and through imports.’ Although many multipurpose (MP) tree species are being studied worldwide, it is imperative to identify and evaluate the available species capable of providing high quality fuel, fodder and timber on underutilized lands in short rotations which can also ameliorate the soil. Wood quality plays a crucial role in selecting a species for fuelwood production and establishing harvest rotation cycles. However, such information on the fuelwood quality of juvenile and mature wood for species selection is not abundant.“’ In the present study, the wood quality of selected fuelwood (FW) tree species in relation to tree age has been investigated in order to establish harvest rotation cycles in plantations on degraded sites such as alkaline soil sites.
2.1. Site details and trials Site x species trials for 12 FW tree species were laid in 1982 at the Biomass Research Centre of this institute situated at Banthra, Lucknow (longitude 80”45’-80”53’E and latitude 26”40’-26”45’N). The species under investigation (Acacia auriculiformis A. Cunn. ex Benth., Acacia nilotica Wild. ex Del., Prosopis julifora Swartz, Terminalia arjuna Bedd.) were a part of that trial. Another trial of the same species and an exotic species trial were laid five years later in 1987. The soils of the experimental site are silty clay loam, non-saline sodic, heavy with high pH (8.5-10.6) and bulk density (> 1.7 g/cm’). The plants suffer anaerobic stress during monsoon months when the fields remain waterlogged. Low porosity and the non-availability of existing nutrients limit the growth and establishment of trees. The experiment was designed as a complete randomized block with three replicates, each measuring 40 m x 40 m. Planting was done at a square spacing of 1.5 m x 1.5 m corresponding to a density of 4444 plants/ha. The total above-ground biomass was estimated on the basis of linear regression equations defining the relationship between biomass as a dependent variable (JJ)
*NBRI Publication # 443 (NS). 57
V. L.
58
GOEL and
H. M.
BEHL
Table 1. Growth, establishment and productivity of species under investigation Species P. .i&flora . A. nilotica
Age (yrs) 5 10 5
10 A. auriculiformis T. arjuna
S. formosa
5
10 5 10 5
Height (dm)
Basal area (mYha)
Establishment (%I
Biomass (t/ha)
83 91 64 90 69 98 41 69 97
14.0 19.0 7.3 14.5 11.7 18.7 8.8 25.0 34.6
94.38 51.05 76.02 49.63 91.32 52.88 92.97 86.76 51.00
75.09 103.32 27.74 65.32 26.60 55.95 8.41 68.00 64.94
and height x diameter (d2h) as an independent variable. The mean annual increment (m.a.i.) in productivity was calculated for each species.
has been worked out9 The formula used for computation of the FVZ is as below: FVZ =
2.2. Sampling and analysis
Calorific value (kJ/g) x Density (g/cc) Ash content (g/g) x Moisture content (g/g)
Wood samples were cut at breast height (130 cm) after destructive felling of three candidate trees in each species. Cubes of 5 cm’ 3. RESULTS were oven dried to a constant weight and On the basis of mean plant height, basal area, analyzed for fuel quality studies. Samples of establishment and total above-ground dry 15year-old trees were collected from the biomass (Table l), and m.a.i. (Fig. l), P. primary limbs of naturally growing trees juliJora, A. nilotica and A. auriculiformis had adjacent to the experimental site, while those of S. formosa were taken from 5-year-old trees of outstanding performance. T. arjuna, though, had very high establishment and tolerance to an exotic species screening trial; lo- and 15-year-old trees were not available for this stress, but was moderate with respect to species. All the samples were collected in productivity. Table 2 shows the moisture content, density, December. The thermochemical properties calorific value and ash content of five tree (density, moisture, calorific value, ash and other species in relation to tree age (5, 10 and 15 elements) of the wood samples of different years). There were characteristic differences in species were determined. The density was these parameters among the various tree species. determined by the weight loss method for 1 cm The wood density in 5-, lo- and 15-year-old thick discs using glycerin. Part of the oven dried sample was ground to pass through a 30 mm trees varied only marginally in P. juliJora (0.80-0.89 g/cc) and A. nilotica (0.80-0.84 g/cc), sieve and was used for analysis. For determination of calorific value, powdered samples were again dried at 70°C for 24 hours and pressed into pellets. A Parr oxygen bomb calorimeter, model 1341, was used for determination of heat of combustion. The ash content was determined by burning 2 g of air dried and ground sample in a platinum crucible in a muffle furnace at 550°C for 5 h. The carbon content was determined in accordance with the Tyurin method. Nitrogen was estimated on a Kjeltec Auto 1030 N-analyzer after sulfuric acid digestion.8 All analyses were done in triplicate and the results were expressed on a dry weight basis, For comparing fuelwood characteristics of Fig. 1. Mean annual increment in various FW species under various species, a ‘fuelwood value index’, FVZ) study.
Fuelwood quality of promising tree species for alkaline soil sites in relation to tree age
59
Table 2. Thermal and elemental analysis of wood in relation to age Species A
auricull~ormis
A. nilotica
P. juiipora
T. arjuna
S. formosa
Tree age (YN
C.V. @J/g)
Ash (%I
(G,
5 10 15 5 10 15 5 10 15 5 10 15 5
18.60 20.66 20.58 19.57 20.46 23.68 20.33 21.42 23.90 20.59 20.01 21.03 24.11
3.00 2.95 2.80 2.42 2.00 1.40 3.10 2.70 1.50 4.60 4.00 3.80 4.00
47.56 52.33 61.55 53.48 55.92 66.00 54.18 58.53 66.81 50.50 54.83 62.97 54.01
however, in other species it increased with increasing tree age (Fig. 2). It was 0.50.78 g/cc in T. arjuna and 0.63-0.82 g/cc in A. auriculiformis. S. formosa, a fast growing species (average height: 97 dm) had the lowest wood density (0.39 g/cc) at the age of five years. The moisture content ranged from 31.7 to 5 1% among the various species, being highest in S. formosa. The variation in moisture percentage due to age was 24% in 5- and lo-year-old trees and 598.3% in lo- and lEyear-old trees (Fig. 3). The calorific value of wood samples varied from 18.6 to 24.11 kJ/g in different species. 5-year-old trees of S. formosa had the highest calorific value compared with the other tree species of similar age (18.6 kJ/g in A. auriculiformis against 20.6 kJ/g in T. arjuna). However, no relationship between calorific value and age of the tree was evident. The ash content differed in the five species investigated. It also varied in relation to the age of the tree. The highest wood ash was observed DENSITY
m
Si (%) 1.90 1.10 0.46 1.70 1.30 0.50 2.30 1.70 0.35 2.10 1.60
1.06 0.76
in all the treatments in T. arjuna (5, lo- and 15-year-old trees) as compared with that in other tree species in respective ages. The ash content decreased by 1% and 1.6% in A. nilotica and P. jt@ora, respectively for 15year-old trees as compared to 5-year-old trees. The total carbon content varied a little in the different species. The silica content, like the wood ash, was lower in mature trees of all the species (Table 2). It was only 0.35% in P. jz.difEora in 15-year-old trees as compared to 1.06% in T. arjuna of the same age. It was in the range l.l-1.7% in lo-year-old trees of all the species. In general, the nitrogen content was highest in P. juliflora followed by A. nilotica. It was nearly the same in T. arjuna and A. auriculiformis. The nitrogen content of the wood decreased with increasing age in all the species. The results showed marked differences in the fuelwood properties as indicated by the fuel value index (FVZ) of the different species at
(g/cc)
5-yr
0.59 0.42 0.39 0.71 0.57 0.52 0.82 0.79 0.64 0.65 0.42 0.38 0.83
lo-yr
m
15-yr
Fig. 2. Wood density of various fuelwood tree species at different ages.
60
V. L. Moisture
GOEL
and H. M. BEHL
(46)
60 50 40 30 20
10 0 S. formosa
A. auriculiformis m
T. srjuna
15-yr
P. jutiflora
A. nilotica
lo-yr
m
5-yr
Fig. 3. Moisture content of wood at different ages.
various ages (Fig. 4). Promising tree species like P. julijlora and A. nilotica had high FVZ values, whereas A. auriculiformis, T. arjuna and S. formosa were poor with respect to their FVZ. 4. DISCUSSION
High density, high heat of combustion, low ash and moisture content are desirable characteristics of quality fuelwood. Wood density varies with the species, age, geographical location, climate, planting density and growth rate.‘O Heinsdijk reported that in E. globulus, l-year-old plants ‘showed a density of 0.541 while in 26year-old plants it was 0.773.’ Similarly, he found that in E. camaldulensis, the wood density was 0.538 at the age of 5 years which increased to 0.765 at the age of 26 years. However, the difference in E. verminilis wood
density between 5- and 15-year-old trees was marginal (0.613 compared with 0.659). In the present study, the differences in wood density of certain species like A. nilotica and P. julifora were marginal while in others, density increased with the age of the tree. On the basis of m.a.i. and productivity, it can be suggested that P. julzflora should be harvested after five years and A. nilotica after six years. Data on the wood density of juvenile wood support the above recommendation. On the other hand, the density was too low in 5-year-old trees of A. auriculiformis and T. arjuna. It is not advisable to harvest trees of these species at an early stage. The study suggests that harvest operations in A. auriculiformis and T. arjuna should begin after 10 years. Sesbania formosa had poor wood density (0.39 g/cc); accordingly, it is not suitable for fuelwood purposes.
FVI (Thousands)
J
D
5-yr
lo-yr
m
15-yr
Fig. 4. Fuel value index of various fuelwood tree species in relation to tree age.
Fuelwood quality of promising tree species for alkaline soil sites in relation to tree age
Wood density can be used as a useful parameter to fix harvest rotation cycles, particularly for short rotation plantations. However, decisions would be specific for each tree species on a given site. Siren et al. observed that both biomass production and quality are important considerations to fix the optimum age for harvesting in Sulix.” Juvenile and mature wood formation are related to the maturity of cambial cells as influenced by hormone balance. Fast growing FW species like P. julifrora and A. niloticu make better fuelwood in short rotations than other species. The high moisture content and low density in the early stage can be attributed to the higher amount of sap wood in the juvenile stage. Zobel and Talbert have reported that there is a strong negative relation between specific gravity and moisture content” Low specific gravity in juvenile wood results from thin cell walls and a low amount of summer wood cells.13 Sir@ reported that tree age and girth had no apparent influence on calorific value in Pinus species.14 High wood ash is less desirable for fuelwood as it is noncombustible and reduces the heat of combustion.15 T. arjuna has a high ash content and a low nitrogen content as compared to P. juliforu and A. nilotica. Reduced nitrogen content is also a desirable trait as it indicates low emission of nitrous oxide which otherwise causes environmental pollution. The present study suggests that density is an important trait to consider when making selections among tree species. However, a combination of more than one parameter such as FVZ, m.a.i. and other characteristics should govern harvest operations. Acknowledgements-The authors are grateful to Dr P. V. Sane, Director of the Institute for guidance and provision of facilities. The research was a part of the Biomass Research Center programme which is funded by the Ministry of Non-conventional Energy Sources. Assistance
61
rendered by Shri R. K. Chaudhary in analyzing the samples is also acknowledged.
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