EUCALYPTUS A GOOD CHOICE IN THE ARID ZONE

SAIMA IBRAHIM
Mar 30 - Apr 05, 2009

The Punjab Forest Department and the Environmental Protection Department declared that eucalyptus trees are 'Environmentally Unfriendly'. Officially, they are pronouncing death sentence to this salinity-resistant plant in Pakistan's most populated province. The future planting of eucalyptus trees has also been prohibited.

The Parks and Horticulture Authority (PHA) in Lahore City had chopped down 1,200 trees for reason that eucalyptus trees deplete underground water at an alarming rate.

According to Punjab Forest Department, the tree was brought to Pakistan to deal with the countryÝs salinity and flooding problems. It was only later that it was realized that the tree absorbs too much water from the soil.

Environmentalists protested this drastic move. They said the government must not cut or uproot the eucalyptus trees without replacing them with other substitutes. World Wildlife Fund (WWF) Pakistan suggests eucalyptus trees should be phased out gradually. Local authorities should start planting indigenous trees or plants of similar girth beside the eucalyptus trees such as the Neem, Arjun, Peepul, Amaltas, Burma, Sukchain, among others, as good substitutes to the eucalyptus.

The tree's ability to survive adverse conditions and its fast growth rate make it the most suitable plant for reforestation.

Commercial and rural forestry is still based on variety of eucalyptus species including: E. grandis, E. camaldulensis, E. tereticornis, E. globulus, E. urophylla, E. viminalis, E. saligna, E. deglupta, E. exserta, and then either E. citriodora, E. paniculata or E. robusta.

There is a multitude of possible uses of eucalypts such as in construction timbers, furniture, farming tools, transmission poles, sleepers, fuel wood, honey, pulp and paper, rayon, fibreboard, and plywood. There are some less conventional uses such as in making essential oils, plant growth regulators, tannin extracts, industrial chemical additives, adhesives, fodder additives and fabrics (derivatives of rayon).

By further processing the eucalyptus oil, citronellol, menthol, thymol and roseol are obtained which are used widely in the pharmaceutical industry for the manufacturing of throat lozenges, candy for cough relief, oil balms, cooling ointments for burns, cold ointments, etc. They also are used in compositions for tooth paste, perfume, toilet soap and prickly heat powder, as well as for making of industrial solvents, insecticides and fungicides.

Eucalyptus has potentially high biomass production under low rainfall condition thus decision has to be made on how quickly the benefits from trees are required. A balance has to be struck between high water consumption and growing a large biomass quickly. Water consumption by eucalypts can be reduced by planting trees farther apart or by thinning existing plantations.

Thus by given proper planning and management, there is no need to exclude the eucalypts because of their perceived high rate of water consumption.

Results concerning ground water and catchment management show many inconsistencies. Site influences seem to be greater than species' influences. Drawing water from shallow and deep tube wells for high water demanding crops such as paddy rice, sunflower and cotton often has a greater effect on drawing down regional water tables than plantations of fast-growing trees.

But many times the trees are blamed when the underlying cause is an expanding population which has to be fed by growing more food and provided with water for drinking and washing. When compared with a range of crops, the eucalypts can achieve a high biomass production on a low nutrient uptake, as little as one-half to one-tenth that of most agricultural and estate tree crops. They can be successful on poor soils without fertilizer.

Neither a eucalypt, nor any other fast growing tree for that matter, is able to create biomass without using soil moisture and nutrients.

There are frequent questions about the impact of eucalyptus trees on the soil ˇ whether they exhaust soil fertility or cause erosion or compaction. The answer is that, with today's knowledge, environmental care and procedures, monitoring showed that soil losses in eucalyptus plantations are varied between 0.6- 1.0 t of soil/ha/year. These values were much below the estimated tolerance limits for the region (between 10-13 t/ha/year). They were also smaller than the losses for some of the main agricultural crops planted in the area.

BBC News in a story of Mali in West Africa describes how eucalyptus helps reverse erosion in Mali. In this region where the annual rainfall is less than 400mm, reforestation is essential to return nutrients to the soil, and to prevent erosion by the harsh desert winds.

In regard to soil erosion by water under trees, there is no evidence to single out eucalypts for special criticism. Erosive energy of rain under tree crowns depends much on the surface area of individual leaves-large leaves produce larger size droplets which have greater impact on energy on the ground.

Erosive energy of rain under the crowns would be least for Casuarina spp, with the acacias (e.g., A. auriculiformis) and narrow-leaved eucalypts (e.g., E. camaldulensis) occupying the mid-range and the broad-leaved eucalypts (e.g., E. globulus) at the top of the range for eucalypts, but even these have much smaller leaves than Anthocephalus spp and very much smaller leaves than Tectona grandis (Teak), the latter of which has been widely planted in tropical region, particularly in Asia.

Though some scientists are worried that the eucalyptus trees will drain large amounts of water out of the soil, Daouda Diarra from the World Food Program in Mali says they are a good choice in the desert environment.

"Eucalyptus is especially recommended for its rapid growth and the protection it gives against strong winds, in the more arid areas of Asia and Africa. Planting of eucalypts to provide windbreaks to protect crops and slow down the movement of soil and sand has been carried on for over a century. They have been found superior to other tree species based more on their ability to survive and grow under harsh conditions, rather than for any physical attribute.

Conclusions and Guidelines: Eucalypts can provide many benefits very quickly, ranging from industrial wood and fibre, poles and posts to nectar, oils, tannins and many other products. Several species are used for windbreaks and shelter.

Fast growth and high biomass production of eucalypts require the consumption of much water, even though these trees take up as little as one-half to one-tenth of the nutrients other agricultural crops. The soil nutrient reserve of a site also is finite and there is a nutrient cost for high biomass production of the trees.

Nevertheless, in most respects, the eucalypts cannot be singled out as being always bad or as being uniquely different from other kinds of fast-growing trees under the same management conditions. Planted eucalyptus trees will be successful only if they can grow well in the local conditions of climate and soil and only if they can provide the benefits required, either for industry or rural people in a sound land-use and environmental management programme. The tree planting project must be accepted by, and bring benefit to, the people both directly and indirectly affected.

The writer is lecturer at Jinnah University For Women
Karachi.