Status, Aspects and Environmental Considerations of Eucalyptus Planting in Bangladesh - Mohammad Ali

Assistant Professor, Institute of Forestry

Chittagong University, Bangladesh

ABSTRACT

It is concluded that eucalypt planting can be vastly expanded in Bangladesh without a serious impact on the environment and that environmental confusions of the use of eucalypts can be minimised in stand management with appropriate techniques. Eucalypts are favoured due to their high productive potential, and found superior to other species. Some 456,000 ha is assessed as suitable for eucalypt planting which on short rotations can produce 6-8 times more stem wood than present forest crops; highway and feeder road planting area are available, equivalent to 988,000 ha, and could produce energy roughly 20 times more than present crude oil imports ($200 million/yr). No negative reaction to eucalypt planting were noted by village people, a review showed 80% in favour of short rotation species with emphasis on cash crop objectives of fuel production. It is considered that further extension and explanation of [land] resource allocation and management inputs would increase choice of eucalypts because the crown structure is suitable for combination with agricultural crops. Problems of allelopathy, nutrient depletion and water use are considered together with appropriate management techniques. The lack of in country improved seed/plant sources is noted as is the need to develop markets and uses to increase the economic importance of eucalypt wood production.

Key words: Eucalyptus, Bangladesh, production potential, environment degrade.

INTRODUCTION

Though eucalypts have become important industrial species in many countries, debate still remains about their effect on the environment; objection to large scale planting is very intense in India (Shiva and Bandyopadhyay, 1983; Karanth and Singh, 1983). However, the current expansion rate of eucalypt around the world shows not all countries embarking in large scale plantations are convinced by concerns raised in India.

This controversy has resulted in confusion about the suitability of eucalypt plantations in Bangladesh. Research results suggest that some provenances of several species of the genus are suitable for the country in terms of growth and site adaptability. As a result the country has undertaken a large scale eucalypt planting program and to date 6,500 ha have been brought under plantations to supply domestic fuelwood. No specific research project has yet been under-taken to verify objections under Bangladesh conditions. In some cases, it is assumed that the effects in Bangladesh are the same as those in India; as a result, a confused/negative attitude towards eucalypt planting has developed among policy makers, politicians and elites.

However the mass of rural people, who plant eucalypt on their homesteads have not shown any negative reaction to these environmental whims. These people participate in tree planting in small rural woodlots, agroforests and marginal land rural areas. An early return of a handsome volume of wood is very important to them. They are in crucial need of fuelwood, poles and posts for domestic uses. So a sharp divergence of opinion exists between different groups of people in society.

Literature, experiences, environmental issues, environmental controversy are discussed in Bangladesh relevance; conditions are discussed. Policy status, trends in eucalypt planting are addressed and research priorities highlighted.

HISTORY OF EUCALYPT IN BANGLADESH

In the 1930’s Eucalyptus citriodora Hood was haphazardly introduced into eastern Bangladesh by tea estates as an ornamental (Davidson and Das, 1985; Zabala, 1990). The species was spread widely by botanists, foresters and gardeners but no plantation was established. First interest on other species of eucalypt was recorded in 1963 when germination tests of three species E. citriodora, E. tereticornis and E. botryoides were made in the silvicultural research stations at Mymensingh and Chittagong (Davidson and Das, 1985). From then on until 1984 about 37 species were introduced and tried (Islam and Neven, 1989). After five years of experimentation, the Bangladesh Forest Research Institute in Chittagong arrived at the conclusion that E. camaldulensis Dehnh, E. tereticornis, E. brassiana S.T. Blake, could be profitably grown in the soil and climatic conditions of Bangladesh (Das, 1984). Since then small scale planting on degraded lands and roadside have been initiated. Initially spacing was 3m x 3m, later reduced to 1m x 1m to maximize production. Actually eucalypt were introduced in this subcontinent much earlier than Bangladesh, for instance, in 1867 in Pakistan, in 1919 in India (Chaturvedi, 1983). At present eucalypt planting around the world extends to about 80 countries and another 50 countries are in trial phases.

NEED FOR EUCALYPTS

Bangladesh, with more than 110 million population over an area of 14.3 million (mil.) ha is highly populated, 764 persons per square km. About 83% of the total population live in rural areas. The country is mostly composed of flood plains except some hilly areas along the eastern and north eastern boundaries and upland terraces on the central and north western regions. Of the total land area 0.93 mil. ha are waterways, 8.5 mil. ha cropped area, 2.67 mil. ha uncultivated land and 2.2 mil. ha declared Forest Land. However, only 0.93 mil. ha (6.5%) is under tree cover, some 40% of the Government controlled forests (UNDP/FAO, Global Environmental Monitoring System 1983-84; Huq and Banik, 1992). The remaining 60% Government forest includes denuded grasslands, scrub and encroached lands. The forests are unevenly distributed and of low productivity types because of their heterogeneous character.

The regional disparities of forest resources and population distribution reflect the highly populated areas, central and northern regions, have practically no natural forest or plantations, while least populated areas, eastern and south western, contain almost all the natural forests and plantations (Figure 1).

Figure 1. Population distribution and regional disparities in respect of forest resources

Source: Davidson (1984); Huq and Banik (1992)

Figure 1 highlights the problem of mal-distribution of public forests on one hand, and the importance of highly productive people oriented forest activities in particular areas, on the other. The possibility of horizontal expansion of forestry activities is limited. A comparative statement of change of land use pattern from 1973 to 1987 (Figure 2) indicates the potential of horizontal expansion of forests.

Figure 2. Comparison of land utilization (x 1000 ha) in Bangladesh from 1973 to 1987

Source: FMP, 1992 (landuse)

The homestead village woodlots currently supply 53% of annual consumption of timber, fuelwood and bamboo in Bangladesh (FMP, 1992). Dependence for this produce on the village woodlots is almost 100% in non forested areas (Figure 1). As a result, a substantial decline in tree cover is also common in rural areas.

Though there are several causes of forest decline, over exploitation to meet industrial and domestic demand is the most important. A large tract of forest land, Unclassed State Forests (USF) of Chittagong Hill Tracts, has become barren and degraded due to shifting cultivation and over exploitation. Reserve Forests of Rangkheong, Chittagong were depleted by 61% between the years 1963 to 1983 (Chowdhury and Hossain, 1989) promoting further deterioration of the environment. As eucalypts have adaptation potential to degraded areas and grow faster than many native species, the country has been raising eucalypt plantations largely on degraded sites.

PRESENT STATUS OF EUCALYPTS

Three species, E. camaldulensis, E. tereticornis and E. brassiana have proved superior to over 30 others tried in the country (Davidson, 1985). With these species Petford, Mt. Garnet and Coen provenances respectively are the best ones. After 5 years of growth, mean annual increment per ha ranged from 11.7 to 95.6 m³ for Petford, 4.9 to 66.6 m³ for Mt. Garnet and 7.3 to 34.2 m³ for Coen (Figure 3).

Figure 3. MAI in m³/ha/yr of three superior provenances at different research stations at the age of 5 years

Source: Davidson et al (1985)

The Petford provenance of E. camaldulensis has been planted widely in Bangladesh to supply fuelwood at a rotation of 6 years and, poles and posts at a rotation age of 12-18 years. Block plantations with eucalypt currently cover an area of 6,500 ha (Figure 5). These plantations were established mainly on accessible lands of three hill Districts of Chittagong, Chittagong Hill Tracts and Sylhet in the east. Seed for plantations are collected from provenance and growth trials of the Bangladesh Forest Research Institute.

Keen interest is shown in raising eucalypts along roadsides, homestead agroforests and rural marginal lands (Figure 4). The Forest Department, NGOs and rural population are mainly involved in these plantings. About 10,000 ha of land are in agroforests, mostly eucalypt and acacias (Figure 4). The proportion of eucalypts in these plantings is unknown but it may be assumed to be not less than 60% of the planted area.

In the hill Districts of Bangladesh of Chittagong, Coxs Bazar and Sylhet, where most of the forest areas are located, some eucalypt plantations have been established; areas established from 1985-92 are shown in Figure 5.

Figure 4. Statement of yearwise plantation area in hectare

Source: TANDP, Bana Bhavan, Dhaka

Table 5. Plantation (ha) raised under second forestry project from 1985-1992

Source: Latif (1993): long rotation over 30 years, short rotation 12-18 years and fuel wood rotation is 6 years.

PROSPECTS FOR EXPANSION

Eucalypt planting objectives are restricted to production of fuelwood, poles and posts only. The species have potential for the production of raw materials for industries, pulp wood industries; plenty of land is still available for tree planting.

The central and the NW regions contain 50,181 ha of tree cover though the total notified forest areas in these regions are estimated as 113,654 ha (Chowdhury, 1993). These forest areas are scattered, small patches and they are under heavy exploitation pressure. As a result the areas are ecologically fragile and need restocking and proper management to balance extraction with planting. Planting on these areas alone will not lessen the pressure on natural tree cover; planting in marginal lands is also important and some 31,573 km of road and highways are still available for strip plantations in 61 non forested Districts in Bangladesh (Figure 6).

These marginal lands are suitable for eucalypt planting. Marginal lands in some cases can be planted in multiple rows whereas feeder roads cannot be planted by more than one row. Karim (1991) has calculated that Bangladesh can establish energy plantings along highway and feeder roads which are equivalent to 988,000 ha and thereby produce energy which is roughly 20 times more than crude oil imported annually. Moreover, 140,000 ha of land are available for energy plantations in the unclassed state forests of the south east

Figure 6. Marginal lands available for plantation

Source: Chowdhury (1993)

Richards and Hassan (1989) studied the suitability of Bangladesh soil for growing eucalypt on land capability classes. About 456,000 ha were found suitable for eucalypt (Figure 7). These areas could produce 3-4 times more biomass and 6-8 times more stem wood on short rotations with eucalypt than the present forest crops (Munshi, 1986). Chowdhury (1993) studied growth potential of E. camaldulensis, Acacia auriculiformis and A. mangium by a site index method of growth and showed eucalypt better than acacias (Figure 8).

Figure 7. District wise area of land in 1,000 ha suitable for raising eucalypts

Source: Richards and Hassan (1989

Figure 8. Average site index of main species planted in woodlot and agroforests

Source: Chowdhury (1993).
*1 means study area one: Dhaka, Tangail, Mymensing, Comilla.
*2 means study area two: Rangpur, Dinajpur, Rajshahi.

PEOPLES’ ATTITUDES TO EUCALYPTS

The future of eucalypts in Bangladesh depends on their acceptability in society among different groups of people. To indicate the degree of acceptability, it is relevant to understand how people react with participatory forestry practices specially in woodlot and agroforestry plantations where eucalypts are the major components of the systems. Peoples’ participation is so far, encouraging in such plantation activity. The average participants in woodlot and agroforestry plantations are about one family per ha and peoples’ participation is increasing day by day (Figure 9).

Figure 9. Statement of number of participants in plantations of the years from 1988 to 1992

Source: TANDP, Bana Bhavan, Dhaka

Social surveys can also be a indicator of social acceptance of eucalypts. Chowdhury (1993) interviewed people living in and near the forest and plantation areas to understand their preference in choosing species. Among the interviewee, 80% favoured short rotation species, 15% favoured combination of short and medium rotation species, whereas less than 2% respondents favoured long rotation species; the rest did not have any choice or they did not understand about the choice. However, none mentioned fuelwood as the first priority but the majority advocated cash returns. It was found the majority prefer E. camaldulensis to A. auriculiformis.

The Swiss Development Corporation has been conducting research from 1986 on tree growing in the ‘khet’ (abandoned area) and has the experience of farmers favouring E. camaldulensis. In the D & D (Diagnosis and Design) survey, conducted by BARI, BRAC and ICRAF in 1991, it was reported that the tendency was to give lowest priority to trees in terms of resource allocation and management inputs, as farmers have little knowledge of production potential and management of trees. However, if they are motivated and provided with technology, they would prefer eucalypts as their first priority species in agroforestry because of its better crown architecture suitable to their agricultural crops.

A third approach could be users’ preference. With the increase in alternative uses of eucalypt, acceptability will increase. For instance, cottage industry where about 75% of total industrial labour forces are employed (Chowdhury, 1993), depends on local timber species, bamboo, canes, and murta. Exotic species like acacias and eucalypt are yet to be exploited in this sector. Though eucalypt can be used in many secondary timber based industries as pulp, veneer, hardboard, particle board, matches and furniture it are not used for such purposes in Bangladesh. If the uses of eucalypt are fully explored, and management techniques to increase production rate per unit land area are adopted, their acceptability will increase further in society.

POLICY ISSUES ON EUCALYPTS

There has been a lot of interest in the forestry sector to cover the barren and marginal lands with plantations of rapid growing species. A Thana Afforestation and Nursery Development Project has aimed at the establishment of short rotation plantations over an area of more than 20,000 ha (Figure 10). In addition there is a target to train about 75,157 individuals and the development of 91 forest extension nurseries to promote extension activities in the rural areas.

Figure 10. Plantation target of Thana Afforestation and Nursery Project, Bangladesh

This year arrangements are made to plant about 85 million seedlings and the Government has instructed nurseries to raise 100 million (15 million excess) seedlings so mortality filling can be made with comparatively older seedlings. The Prime Minister has urged the people to plant and grow at least one tree for each individual in their marginal land. So far 22 large NGO organizations have planted 12.5 million seedlings. At present some 676 numbers of NGOs and their 125,000 workers are engaged in plantation activities. There are poor statistics available concerning the species composition of those activities.

From field observation, my general impression is that most of the NGO people are engaged in short rotation crops with exotic fuelwood species with an emphasis on eucalypts. In the last few years Government organizations have also preferred fuelwood crops. This year the Government is especially giving advice to plant more fruit trees. Probably poor performance (maybe due to an inbreeding problem) of some eucalypt plantations in the hill areas of Chittagong Forest Division have created some confusion. It is possible a negative attitude may have developed within the Government concerning eucalypts. The minutes of a Government meeting on plantation programs in January 1993 proposed action to discourage eucalypt plantings but no specific reason was outlined. Perhaps environmental confusion, resulting from eucalypt controversies in some countries may have led the Government to develop this attitude. These eucalypt environmental issues have yet to be justified by indigenous study.

CRITICISM OF EUCALYPTS

Eucalypt planting is a controversial issue in some countries where it has been planted extensively. Critics assert that: i) it has deleterious effect on the hydrological balance; ii) it depletes the soil nutrients; iii) it has an allelopathic effect leading to inhibition of growth of other plants; and iv) it has a deleterious effect on native animals. This may be disputed by the reasoning that it is highly unlikely that a genus with outstanding evolutionary adaptation to infertile soils and a dry climate of Australia will use excessive water and nutrients.

Eucalypt as a single entity failed to take account of the great climatic and edaphic diversity of the Australian continent. There are more than 600 eucalypt species differing in inherent growth rates, environmental adaptation to low nutrient soils, and dry climates. Within the Australian forests site factors exert a strong control on species composition, stand structure, leaf area index and productivity. As each unit of forest in Australia is in balance with the particular characteristics of the site, the eucalypts are not making excessive demands on the resources of that site.

Where a eucalypt is planted in countries other than Australia, it is removed from it’s regulated environmental context, and the checks and balances imposed by site no longer apply. For example, E. camaldulensis occurs naturally as a woodland in dry areas over most of the Australian continent where the rate of water use is hardly an issue in the Australian circumstances (Florence, 1992), it could become an issue where it is established elsewhere as a forest on moderately fertile soil with good rooting depth and access to a water table.

ATTRIBUTES OF INTRODUCED EUCALYPTS

It is important to understand the attributes of eucalypts planted in Bangladesh to understand their environmental consequences. The most outstanding eucalypts introduced are E. tereticornis and E. camaldulensis. These species, including others introduced elsewhere as exotics, as E. grandis and E. urophylla in the Indo-Malaya region, tend to have a number of characteristics in common:

(a) They belong predominantly to the subgenus Symphyomyrtus - individual members of which may be characterized by a wider environmental tolerance than members of other subgenera.

(b) They are the more successful species capable of responding more positively to better soil conditions - particularly higher soil fertility.

(c) They are capable of rapid root development, particularly in depth. This may be a general attribute of eucalypts growing, or capable of growing, away from moist regions.

(d) The species usually reach early and strong peaks in current annual volume increment (CAI). This peak may be as early as 4 years in E. tereticornis, 6-7 years in E. grandis and 12-15 years in E. globulus. By the time the peak is reached wood volume production on high quality sites may be in the range of 24 m³/ha/yr for E. tereticornis to 50 m³/ha/yr for E. globulus (Florence, 1992).

The controversial effects of eucalypt on environment should be seen with respect to its attributes, and high productivity within a short duration.

ALLELOPATHY AND EUCALYPTS

It is widely held in some countries, notably India, that eucalypts are strongly allelopathic; that they produce foliar and root exudates directly toxic to other plants. This may not be true in all cases. It is more likely that the effect of eucalypt on understory plants or adjacent crops are the result of the very great capacity of eucalypts to compete for short supply soil resources (nutrients and water). Where soil resources are not in short supply the understory vegetation may be maintained under a vigorous tree canopy.

In India Dabral et al (1987) found an undergrowth vegetation of Lantana spp., Murraya koenigii, Carissa karonda, Jasminum officinale, Mallotus philippensis and Syzygium cumini under 16 year old Eucalyptus hybrid plantation, at spacing 2m x 2m, at an experimental site near Dehra Dun Forest Research Station. In our forest conditions undergrowth develops, especially if spacing is more than 1m (Bhuiyan, 1986). I have observed undergrowth under eucalypt plantings at 1.8m x 1.8m spacing but the diversity is less than of native forest types. The composition observed could have been disturbed by weeding, ground fire and shrub collection of local people and a confirmation study of the diversity of undergrowth needs to be made under suitably undisturbed eucalypt plantation.

Lisa and Michelsen (1993) reported in Ethiopia that eucalypt leaf exudates have some inhibitory effect on germination, and on reduction of shoot dry weight of four crops tested; they state an allelopathic potential rating from lower to higher as Cupressus lusitanica < E. globulus < E. saligna < E. camaldulensis. This type of exudate allelopathy may be controlled by management techniques under rainfall conditions of Bangladesh.

NUTRIENT DEPLETION BY EUCALYPTS

During the rapid biomass accumulation phase, fast growing eucalypts will accumulate a store of nutrients in the phloem and sapwood (7-10 years of growth). This nutrient is withdrawn very efficiently from the cells at heartwood formation and maintained in a mobile phloem - sapwood pool (Banks, 1992). As there is a very low residual concentration of nutrients in the heartwood, the mature stand in the natural environment manages on a much smaller biomass nutrient pool than in a forest of comparable productivity elsewhere. A large tree will have a thin shell of relatively nutrient rich active tissue surrounding an inert bole wood mass. The tree can be felled and removed at low nutrient cost to the site, i.e. a small amount of nutrient is exported per unit weight of wood.

Alternatively where the stand is grown in well stocked plantations and harvested on short rotations (e.g. 6-10 years), there may be a substantial nutrient cost to the site. Pande et al (1987) reported harvesting of utilizable biomass (bole, bark and branch) at age 10 years in Kerala Forest Division, India, results in the removal of 52% nitrogen (N), 70% phosphorus (P), 66% potassium (K), 78% calcium (Ca), and 67% magnesium (Mg); the removal of N, P, K, Ca and Mg will be 42%, 55%, 54%, 61% and 56% respectively in the Madhalli Afforestation Center at the age of 7 years. A major depletion of site nutrient is caused by early removal of the crop, rather than to deleterious effect of eucalypt plantations. The site nutrient depletion by early biomass removal may also vary from site to site and species to species at a particular age of harvest. Yet, scientific opinion is, that such cost may still be no greater than what of other fast growing tree species.

The nutrient accumulation is generally greater in species with a comparatively larger crown biomass relative to stem size. The ranges of nutrient accumulation in E. camaldulensis was established by Hopmans et al (1990) (Figure 11). A considerable amount of N accumulated in the leaves and twigs of eucalypt can be left in the forest environment, and would compensate for the loss to some extent but in case of other macro nutrients some corrective measures may have to be taken. This is very important, especially in the case of eucalypts, because nutrient content in the litter of eucalypt is lower than other species as they usually absorb nutrients before the shedding of litter (Banks, 1992). Sing et al (1989) state that the litter of Populus deltoides contains 1.3 times more N and 1.5 times P and K than of E. hybrid. Additions of N, P and K to the soil through litter decomposition was respectively 36.6%, 91.6% and 69.9% more in P. deltoides than the E. hybrid. Moreover, litter fall was 5 kg per tree per year for P. deltoides whereas for E. hybrid it was only 1.5 kg. Bahuguna (1991) reported that litter decomposition is faster under eucalypt than under ‘Sal’. In Bangladesh the loss of soil nutrient may be more severe as the litter layer and the leftover debris on the forest floor are regularly harvested. If we consider these human factors and the early harvesting of eucalypt, the depletion of soil nutrients by the deleterious effects of eucalypts is not an established fact under the social conditions of Bangladesh.

Figure 11. Range of nutrient content in gm/m² of leaf area depending on the crown size

Source: Hopmans et al (1990)

WATER USE BY EUCALYPTS

Claims are made that eucalypts use excessive amounts of ground water by developing a deep root system. In dry areas, though eucalypts develop long deep tap root in moist areas, they mostly develop fibrous roots (Zimmer and Grose, 1958). Dabral et al (1987) observed that the fibrous root of eucalypts extend up to 18 m within a soil depth of 30 to 60 cm in moist areas. When moisture content varies at different localities of a site, eucalypts may try to maintain growth by extending root systems in drier areas. An observation on height growth of E. camaldulensis at top hill and valley shows that first year growth was significantly different from the top to the valley but from the second year height growth was not significantly different (Figure 12). This adjustment could have taken place by differential expansion of the root system by eucalypts for enough moisture. A supportive statement to this effect is noted by Pal and Raturi (1991). They studied the dry biomass production of E. hybrid in a semiarid environment under rainfed condition. The stand was divided into three classes according to the height growth of the species and found that at the age of three, the lowest class produced 31.8% root biomass whereas the highest class and the middle class root biomass was 21.0% and 26.7% of the total biomass respectively. The higher root development of suppressed trees may be to capture more moisture from the soil to maintain the physiological need and hence growth potential to compete with the dominant trees. However, the following points can be made against the statement of excessive water use:

(a) Florence (1992) mentions that in a regrowth forest of E. regnans, a strong early peak in CAI (current annual increment) water yield declined for some 25 years before beginning to rise again. The pattern is closely related to the pattern of volume production for this species, that is, a peak in CAI occurs around 20 years.

(b) Some eucalypts which are widely planted as exotics, have even faster early growth rates than E. regnans, and a strong early peak in CAI, e.g. E. tereticornis, E. grandis, and E. camaldulensis. Where these species are planted on high quality sites with access to a good soil water resource, high rates of water use might be anticipated at an early age. This is expressed, for example in the rapid decline in stream flow as early as 6 years on an E. grandis catchment in South Africa (Florence, 1992).

(c) It is possible that where one of the more opportunistic of the faster growing eucalypts (e.g. E. camaldulensis) has access to a substantial water resource (e.g. a water table at 1 to 2 m), and where there is a prolonged dry period with high vapour pressure deficits, large amounts of water may be transpired. In this case, water use efficiency may be low. This may explain why E. camaldulensis has sometimes been planted to help drain or control swamps (Florence, 1992).

Figure 12. Height variation of eucalypt at different age between valley and hill top in Chittagong. Significance tested at p = 0.05 level.

Source: Anon (1992)

Alternatively where the same species does not have access to a substantial water resource, moderate level of wood production may still be obtained under rainfed conditions. In this case other attributes of the species may be important, for example, the capacity to maximize access to water supply through an extensive root system, and to tolerate relatively high levels of water stress. Again the species may not extract soil water to the same level of potential as other species, thus helping to maintain some contact between the root system and soil water under dry conditions. In these manner, site attributes, wood production and water use may be closely related.

Thus, while a species reputation for high water use may be justified under some conditions, it cannot be justified in others. It is difficult to accept in our condition where the plantation depends entirely on rainfall infiltration to the soil, that eucalypts should not be planted because of excessive water consumption. Indeed, eucalypts may not survive at all unless it can open stomata and transpire water daily. This means that eucalypts cannot dry out soil entirely but do it proportionately to the availability of moisture. A supportive statement may be mentioned from Lima et al (1990) who reported from the cerrado region of Brazil, where rainfall is usually 1,100 to 1,150 mm per year that establishment of forest plantation with the eucalypt and pines will not adversely affect the soil water regime. In Bangladesh annual rainfall ranges to about 3,000 mm and hence water use by eucalypt may not be a problem.

MANAGEMENT STRATEGY

Appropriate management techniques could improve the social and environmental consequences of the use of eucalypts in Bangladesh. For example, thinning a stand will reduce water use and increase stream flow at least temporarily. Thinning may remove those trees which are more inefficient user of water (e.g. transpiring but producing little wood). Indeed, in the jarrah forest of Western Australia, a heavy thinning to retain the better trees resulted in both increased wood production and increased stream flow (Florence, 1992). In our condition one option might be to thin early for fire wood production and maintain the residual trees over a longer rotation of pulpwood production. For fast growing eucalypts, it is surprising how small the stocking may be, yet, produce maximum site volume production.

Eastham (1990) studied the relationship between stem density and water use efficiency with 2,150, 304 and 82 stems per ha to relate transpiration with biomass production. Tree density modified biomass production and water use of trees, with both being consistently lower at the higher densities throughout the study. Values varied both with season and with year. This means that selection of a suitable stem density in a stand may help in water management for efficient use.

Crop improvement may be another strategy to minimize the consequences. In Bangladesh, though there were some provenance trials for selection, no seed orchard has been established. Local and rural nurseries use seed from provenance trial plots and distribute these for planting. As a result projected yields from the planting are not available in the field from these inbred seedlings, and lead to social disparities. A seed orchard designed to hybrid production, and clonal propagation from selections may improve the yield and protect land race formation.

The hybrids and clones can be planted in small patches with native species forming a mosaic of mixed stands may solve the problems of allelopathy and wildlife diversity, while at the same time, productivity can be maintained. Appropriate research should be taken on this line.

CONCLUSIONS

Eucalypts have been introduced into Bangladesh for a long time. But within a short period, a large degraded forest area has been planted with eucalypt. A lot of interest is shown in eucalypt planting in: agroforestry, marginal land afforestation and homestead forestry. There is some confusion within elite circles about eucalypts but this is not apparent in the rural people.

One of the reasons of wide acceptance of eucalypt is its high productivity. This productivity potential should be maintained through adopting appropriate technology to uphold the interest of rural mass. However the full use of eucalypt has not been tapped; introduction of alternative uses will increase the economic importance of the species.

Environmental confusion on eucalypts can be minimized by stand management and crop mixing. Considerations of environmental factors should have priority in crop rotations, whereas productivity should be maintained by improved technology. This review stresses that selection of appropriate provenances for specific sites is important for efficient output.

Horizontal and vertical expansion of eucalypt planting is possible in Bangladesh without a serious impact on the environment. The economic importance of the species can also be extended, support is extended to research to be undertaken to promote eucalypt planting in Bangladesh.

FUTURE RESEARCH NEEDS

In Bangladesh eucalypt research programs were limited to provenance and elimination trials. Priority should be given to research on the following characteristics of eucalypts:

• Eucalypt and other species interaction, particularly for species in mixed plantations;

• Eucalypt and undergrowth patterns under the monsoon climate of Bangladesh;

• Impact of eucalypt on wildlife habitat, particularly in mixed plantations;

• Interception of precipitation; soil moisture relationship; comparative studies of native species and eucalypts;

• Natural and chemical exudates of stem flow and infiltrates from eucalypts;

• Effect on soil chemicals and soil micro and macro fauna, due to litter and exudates;

• Nature of root development, nutrient retention and recycling process of eucalypts;

• Choice of species and provenance in specific sites;

• Genetic improvement study with efficient water use management objectives; and

• Stand management strategy for maximizing benefits.

Studies related to these fields are important before talking about eucalypts. Based on derived information we may expect that the rotation, intensity, scale and spacing of plantations, be adjusted for harvesting the best benefits - in terms of yield and of the environment.

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