ELSEVIER

INDUSTRIALCROPS ANDPRODUCTS

ANINTERNATIONALJOURNAL

Industrial Crops and Products 3 (1994) 69-74

Fuelwood value index in components of ten tree species of arid region in India

Sunil Puri aq* , Shambhu Singh b, Bharat Bhushan b a Department of Forestry, I.G. Agricultural University, Raipur 492 012, India

b Department of Fores@ Havana Agrkultuml Universi& Hisar 125 004, India

Received 22 November 1993; accepted 10 May 1994

Abstract

Calorific values of six indigenous species and four exotics were determined for components such as stump, main stem, tree top, branches, foliage and bark. Tree species selected were: Acacia nilotica, Azadirachta indica, Casuarina equisetifolia, Dalbergia sissoo, Prosopis cineraria, Zizyphus mautitiana (all indigenous); Acacia auriculifonnis, A. tortilis, Eucalyptus camaldulensis and E. tereticomti (all exotics). Studies indicated that indigenous tree species are better suited as fuelwood species as they contain high-density wood, low ash content and low nitrogen percentage. The most promising species were A. nilotica, C. equisetifolia and Z. mauritiana. The tree components among the groups (indigenous and exotics) and within the species differed very significantly (P < 0.01) in calorific values. The calorific means ranged from 18.7 to 21.77 MJ/kg for the indigenous tree species, and 16.3 to 20.0 MJ/kg for the exotic tree species. The fuelwood value index (FVI) was also worked out, taking into account the calorific value and density of the wood as positive characteristics, and high water content and high ash content as negative characteristics. It was observed that the FVI of the indigenous tree species was high.

Keywords: Calorific value; Fuelwood; Multipurpose trees; Indigenous; Exotics; Energy plantation

1. Introduction

In India, biomass resources play a vital role in the domestic and commercial energy sec- tors. Population growth and increased exploita- tion of forests have resulted in severe shortages of fuelwood, charcoal and other wood-based fuels needed for cooking, heating and commercial uses. Efforts to increase energy self-sufficiency, pro- moted at local, national and international levels have included the development of high-density, short-rotation fuelwood plantations on public and

* Corresponding author.

private lands. All kinds of plants are used as fuel- wood. Fuelwood characteristics of some Indian trees and shrubs have been documented (Krish- na and Ramaswamy, 1979; Purohit and Nau- tiyal, 1987; Bhatt and Todaria, 1990). Harker et al. (1982) presented a statistical summary of the calorific values of 402 species of wood of 246 gen- era of the temperate region, based primarily on lit- erature surveys. The calorific values ranged from 15.584 to 23.723 MJ/kg for hardwoods and 18.608 to 28.447 MJlkg for softwoods. Much of the data reported in literature relate to calorific determina- tions of tree stem sections. Other components of the tree should also be studied to understand the

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70 S. Pun’ et al. /Industrial Crops and Products 3 (1994) 69-74

variations within a tree species. Moreover, both exotics and indigenous tree species are planted un- der afforestation and social forestry programmes, but there is no exact information available about their energy status.

The study presents the fuelwood characteristics of ten major tree species of the arid region and their variations for tree parts such as stump, stem, branches, foliage and bark.

2. Materials and methods

2.1. Study site

The site selected for the present study are plan- tations of the State Forest Department in the Hisar region. The area is arid and contiguous to the “Thar Desert”. It is situated at a height of 215 m above sea level. Its latitude is 29YO’N and lon- gitude 75’46’E. The climate of the study site is dry with intense hot and cool weather. The mean max- imum air temperature goes up to 42°C in June and the mean minimum temperature comes down to 52°C in January. Maximum rainfall (up to 70%) of the total of 510 mm p.a. is received in the months of July and August. During winter, some rainfall is received as light showers from west- erly depressions. The evaporation exceeds precip- itation. The potential evapo-transpiration during summer exceeds 12 mm/day and during winter 5 mm/day.

The ground-water table varies between a depth of 3 and 11 m (fluctuations in water table usu- ally coincide with the monsoon season) and its quality varied from 1 to 16 dS m-l (decisiemem metre). The region is covered by Indo-Gangetic alluvium having a sandy loam texture. The soil has been classified as a Typic Camborthids (U.S. tax- onomy) of the Kirtan Series (Puri and Bangarwa, 1992).

2.2. Field sampling

A total of ten tree species were sampled. These were: six indigenous - Acacia nilotica (Linn.) Willd. ex Del. (ssp. indica (Benth.) Brenan), Azadirachta indica A. Juss., Casuarina equisetifolia J.R. et G. Forst, Dalbergia sissoo Roxb., Prosopis

cineraria (L) Druce., Zizyphus mawitiana Lank; and four exotics -Acacia auriculifomzis A. Cunn. ex Benth., A. tortilis (Forsk.) Hayne., Eucalyptus camaldulensis Dehnhardt., E. tereticomis Sm. Four trees were sampled of a single species with diam- eter outside bark at breast height (dbhob) close to the midpoint of diameter classes O-10, 10-20, 20-30, and 30-40 cm for each species.

Field samples were taken as 4-mm-increment cores from stump and stem, as 2.5-cm-thick disks from treetop (stem section from 2 cm dbhob to the tip of the tree stem) and branches, and as foliage and bark. Each category of a sample was taken from four different positions/directions of a tree which were thoroughly mixed. Samples were wrapped in aluminium foil and collected in poly- thene bags. Direct sunshine and high temperatures were avoided while transporting the samples to the laboratory in ice boxes.

2.3. Laboratory procedure

Samples were air dried in a forced-air con- vection oven at 80°C. When sufficiently dry, the samples were ground (using a Wiley mill) to pass through No. 4 sieve (4.7 mm mesh), pelleted and burnt in an oxygen bomb calorimeter to determine the calorific value. Basic statistical parameters such as mean and standard error were determined for each tree species and component. Two-way and three-way nested analyses of variance were carried out to determine the significance of differ- ences in the calorific value of the tree species and their components. Duncan’s multiple-range test (Duncan, 1955) was performed to determine the significance of the differences among the calorific means of the tree components.

Moisture content (determined after drying to constant weight at 8o”C), density (by the water dis- placement method), ash (sample burnt in a muf- fle furnace at 600°C) and nitrogen (estimated by the micro-Kjeldahl method) were also determined from the branch cuttings. The fuelwood value in- dex (FVI) was calculated following the method of Purohit and Nautiyal(1987) as follows:

FVI = calorific value (MJ/kg) x density (g/cm3) ash content (g/g) x water content (g/g)

S. Pun’ et al. I Industrial Crops and Products 3 (1994) 69-74 71

3. Results and discussion

The mean calorific values for the indigenous and exotic tree species were 19.405 and 18.273 MJ/kg, respectively (Tables 1 and 2). In general, the calorific values for both indigenous and exotic tree species are well within range to be charac- terised as a fuelwood species. Among different tree components, the treetops had a maximum calorific value and ranged between 19.770 and 21.814 MJ/kg for indigenous species, and between 18.421 and 20.096 MJ/kg for exotic species.

On basis of the average calorific values, the tree species can be categorized into three groups. Group I (having a calorific value of > 19 MJ/ kg) includes: Casuarina equisetifolia, Dalbergia sis- soo, Prosopis cineraria, Acacia nilotica (all indige- nous), and A. auriculiformis (an exotic). Group II (calorific value ranged between 18 and 19 MJ/

kg) comprises: Zizyphus mauritiana, Azadirachta indica (both indigenous) and Eucalyptus camald- ulensis (exotic). Group III (calorific value < 18) includes the two exotics, i.e., Acacia tortilis and Eucalyptus tereticomis (Tables 1 and 2).

The three-way analysis of variance done collec- tively on all components (Table 3) showed that the calorific values were significantly different (P < 0.05) between indigenous and exotics as well as between tree species within the two groups. The individual components within a tree species dif- fered very significantly (P < 0.01). In most cases, the calorific values were lower for the main stem but increased towards the stump and branches, in- cluding foliage. Singh (1986) reported longitudinal gradients in bole density; the lowest values were in the midpoint of the tree bole and increased towards the top and the bottom. The density gra- dients of oven-dried wood of Dalbergia sissoo,

Table 1 Calorific a values (MJ/kg) of oven-dried tree components of indigenous tree species

Species h Stump Stem Treetop Bark Foliage Branches Mean

Acacia nilotica 19.474 19.709 20.724 19.467 17.660 Azadirachta indica 18.697 18.680 19.770 18.563 17.230 Casuarina equisetijolia 19.870 19.960 21.814 19.737 20.873 Dalbergia sissoo 19.334 19.018 20.771 18.030 20.558 Prosopis cineratia 18.744 18.669 20.934 19.509 18.804 Zizyphus mauritiana 18.464 17.702 20.500 18.487 17.615

Mean 19.097 18.956 20.752 19.132 18.790 Standard error 0.175 0.265 0.279 0.189 0.389 Confidence limit at 5% 0.357 0.540 0.569 0.385 0.793

19.100 19.355 19.455 18.732 21.620 20.645 19.144 19.475 19.905 19.427 19.025 18.798

19.708 19.405 0.276 0.563

a Average of determinations based on three diameter classes. b Diameter at breast height outside bark ranged from 4.6 to 36.7 cm.

Table 2 Calorific a values (MJ/kg) of oven-dried tree components of exotic tree species

Species b Stump Stem Treetop

Acacia auriculiformis 18.697 18.393 20.096 Acacia to&is 17.230 18.013 18.421 Eucalyptus camaldulensis 18.675 18.923 19.917 Eucalyptus tereticornis 17.697 17.680 18.840

Mean 18.074 18.252 19.318 Standard error 0.196 0.173 0.269 Confidence limit at 5% 0.399 0.352 0.548

a Average of determinations based on three diameter classes. b Diameter at breast height outside bark ranged from 4.6 to 34.7 cm,

Bark Foliage Branches

19.402 18.713 19.440 17.902 17.057 17.967 18.462 17.152 17.643 17.563 16.230 18.455

18.332 17.288 18.376 0.325 0.415 0.295 0.663 0.846 0.601

Mean

19.123 17.765 18.462 17.744

18.273

72 S. Puri et al. /Industrial Crops and Products 3 (1994) 69-74

Table 3 Table 5 A three-way analysis of variance for the calorific values (MJ/kg) of ten tree species

Duncan’s multiple-range test on the calorific means for com- ponents of ten tree species

Source of variation

Among groups a Among species within

d.f. SS MS F

1 71.83 71.83 10.17’

groups Among tree components

8 56.50 7.06 2.22 *

within species 50 158.90 3.17 3.86 ** Within tree components 180 148.44 0.82 Total 239 435.67

a Indigenous and exotics. * Significant at 5% level; ** significant at 1% level. SS: sum of squares; MS: mean of squares; F: Fischer value.

Component Mean (MJ/kg) Group ranking

Treetop 20.172 A Branches 19.184 B Bark 18.860 C Stem 18.713 C Stump 18.678 C Foliage 18.239 D

Means within the same letters are not significantly different.

value groups were: (i) branches (Group B); and (ii) stump, stem and bark (Group C).

Acacia aurkuliformis, A. nilotica, Azadirachta in- dica and Eucalyptus tereticomis growing in the Uttar Pradesh region were reported by Pathak et al. (1985); the lowest values came usually from the limbs and the highest of trunk wood.

A summary of two-way analysis of variance done separately for each tree component (Table 4) showed that between indigenous and exotics as main groups the calorific value variation was sig- nificant (P < 0.05) for all components except for bark and branches which did not show a statis- tically significant difference. The calorific value variation between species within indigenous and exotic groups was highly significant at P < 0.01 for foliage and branches and significant at P < 0.05 for stump, stem and treetop (Table 4).

Table 6 shows some of the other characteris- tics of fuelwood features of these species. Zizyphus mauritiana contained high-density wood but due to its high ash percentage and medium biomass/ ash ratio, is comparatively less suitable as com- pared to Casuarina equisetifolia and Acacia nilot- ica. Moreover, in the former species the wood den- sity is high while in the latter species it is medium. Among the exotic species, Acacia auricu1iformi.s seems to be most suitable firewood species due to its medium density, above-average biomass/ash ra- tio and below-average ash content. In general, the wood of exotic species is comparatively lower in density than that of indigenous species.

Duncan’s multiple-range test on the means showed the ranking of tree components to be rep- resented by four significancy groups (Table 5). The calorific value was highest (Group A) for treetop (20.172 MJ/kg) and lowest (Group D) for foliage (18.239 MJ/kg). Intermediary and similar calorific

The emission of nitrogen oxide during combus- tion reduces the acceptability of wood with a high nitrogen content as fuelwood. Dalbergia sissoo and Azadirachta indica, although having higher-than- average wood densities and high calorific values, have a high N and moisture content and are thus less acceptable as fuelwood. Moreover, the ash content in Azadirachta indica is the highest while in Dalbergia sissoo it is above average. Similarly,

‘fable 4 Summary of analysis of variance for individual components of tree species

Source of variation d.f. Mean souares of individual components

Stump Stem Treetop Bark Foliage Branches

Among groups a 1 15.7’ 10.5 * 9.75 * 1.2 ns 45.5 * 11.07 n.s Among species within groups 8 2.7 * 1.92* 1.75 * 3.5 n.s 5.4** 2.95 ** Within species 30 0.92 0.67 0.72 2.4 1.1 0.41

a Indigenous and exotics. * Significant at 5% level; ** significant at 1% level; n.s.: non-significant at 5% level.

S. Pun’ et al. I Industrial Crops and Products 3 (1994) 69-74 73

Table 6 Fuelwood characteristics of ten tree species

Species

Indigenous: Acacia nilotica Azadimchta indica Casuarina equisetifolia Dalbergia sissoo Prosopis cineraria Zizyphus mauritiana

Exotics: Acacia auriculifonnis Acacia tortilis Eucalyptus camaldulensis Eucalyptus tereticomis

Density Ash Biomass/ash Moisture (g/cm3) (%) ratio (%)

0.68 2.1 79.6 48.6 0.72 4.3 58.5 58.8 0.87 1.3 89.7 51.9 0.70 2.8 72.9 55.8 0.67 3.2 65.2 44.0 0.90 3.7 62.7 46.7

0.70 2.4 65.5 52.9 0.58 2.3 57.3 51.3 0.65 3.5 50.8 60.9 0.62 3.3 55.2 59.2

FVI

0.21 1289.5 0.29 533.4 0.17 2815.0 0.30 872.5 0.26 924.4 0.22 979.1

0.23 1054.3 0.28 873.2 0.32 562.9 0.35 563.1

Table 7 Decision table with final fuelwood ranking for the ten species investigated

Species Calorific value

Density Ash Moisture N FVI Total Rank

Acacia nilotica 4 5 2 3 2 2 18 2 Azadimchta indica 7 3 10 8 7 10 45 7 Casuarina equisetifolia 1 2 1 5 1 1 11 1 Dalbergia sissoo 2 4 5 7 8 7 33 5 Prosopis cineratia 3 6 6 1 5 5 26 4 Zizyphus mauritiana 6 1 9 2 3 4 25 3 Acacia auriculifonnis 5 4 4 6 4 3 26 4 Acacia tortilis 9 9 3 4 6 6 37 6 Eucalyptus camaldulensis 8 7 8 10 9 8 50 8 Eucalyptus tereticomis 10 8 7 9 10 9 53 9

The ranking ranges from 1 (best) to 10 (worst).

both species of Eucalyptus, in addition to their high Summarizing these findings, a table can be set N content, also have a high ash content and low- up to rank the species with respect to their fu- density wood which reduces their acceptability as elwood characteristics (Table 7). This table which fuelwood. For ideal fuelwood, the most desirable includes all the parameters studied, confirms the characteristics are a high calorific value, high den- above results and shows the indigenous species sity of wood, low ash content, low N percentage as the clear “winners”. The best three species for and low water content. On this basis the fuelwood fuelwood (among ten species studied) are: Cu- value index (FVI) was calculated, taking into ac- suarina equisetifolia > Acacia nilotica > Zizyphus count the calorific value and density of wood as mauritiana. Since the calorific value, density and positive characteristics, and high water content and ash content are the most important parameters in high ash content as negative characteristics. Of the this kind of study, they could be weighted more ten species analysed, Casuarina equisetifolia, Aca- heavily in the final decision. In the present study cia nilotica, A. auriculiformis, Zizyphus mauritiana this would not make any significant change with and Prosopis cineraria were found to have more respect to the final ranking of the first two species. than 900 FVI due to the high calorific value, high However, Dalbergia sissoo ranks equal to that of density of wood, and low ash and water content. Acacia nilotica. The important conclusion derived

14 S. Pun’ et al. I Industrial Crops and Products 3 (1994) 69-74

from this ranking is that most of the indigenous tree species outweigh the exotics and that these former should be encouraged for afforestation and social forestry programmes.

4. Conclusions

The important findings of the present studies can be summarized as follows:

(1) Individual tree components within tree species and main groups (indigenous and exotics) differed significantly in their calorific values.

(2) From highest to lowest calorific values, the order of the component groups was treetop, branches, bark, stem, stump and foliage.

(3) Indigenous tree species are better suited as fuelwood as compared to exotics.

(4) The order of merit as fuelwood for the tree species is: Casuarina equisetifolia > Acacia niloti- ca > Zizyphus mauritiana P Prosopis cineran’a = Acacia auriculifonnis > Dalbergia si~~oo > Acacia tortilis > Azadirachta indica > Eucalyptus camald- ulensis > E. tereticomis.

Acknowledgements

The authors are thankful to the Indian Council of Forestry Research and Education for financial

assistance. We also acknowledge thankfully the field and laboratory facilities provided by different organizations to successfully complete this work.

References

Bhatt, BP. and Todaria, N.F!, 1990. Fuelwood characteristics of some mountain trees and shrubs. Biomass, 21: 233-238.

Duncan, D.B., 1955. Multiple range test and multiple F-test. Biometrics, 11: l-48.

Harker, A.P., Sandels, A. and Burley, J., 1982. Calorific val- ues for wood and bark and a bibliography for fuelwood. England. Report G 162, Tropical Products Institute, Lon- don.

Krishna, S. and Ramaswamy, S., 1979. Calorific values of some Indian woods. Forest Bulletin No. 79, Chemistry Series, Central Publication Branch, Government of India, Calcutta.

Pathak, B.S., Jain, A.K. and Rajor, A., 1985. Characteristics of some firewood tree species. In: R.N. Sharma, 0.P Vimal and V Bakthavatsalam (Editors), Bioenergy for Rural Development. Department of Non-Conventional Energy Sources, New Delhi, pp. 103-108.

Puri, S. and Bangarwa, KS., 1992. Effect of trees on the yield of irrigated wheat crop in semi-arid regions. Agrofor. Syst., 20: 229-241.

Purohit, A.N. and Nautiyal, A.R., 1987. Fuelwood value index of Indian mountain tree species. Int. Tree Crops J., 4: 177-182.

Singh, T, 1986. Wood density variation of six major tree species of the Northwest Territories. Can. J. For. Res., 16: 127-129.