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Status of exotic trees in Indian agroforestry


K.S. Bangarwa and M.S. Hooda (kulvirsb@yahoo.com)

If we continue to exploit the forests at the present rate, there will be no forests left by 2050, causing damage to the environment and biodiversity. Forests have a very low growing stock (65 m3/ha) and a mean annual increment of about 0.7 m3/ha. The condition of forest-based industries is not healthy in India. Therefore, promoting large-scale farm forestry/agroforestry plantations is essential.

Fig. 1. Wheat with poplar (Populus deltoides).

The National Forest Policy (1988) directed the wood-based industrial units to meet their future raw material requirements by developing partnerships with farmers. Some progressive industrial units have promoted farm forestry/agroforestry plantations through the supply of planting stocks, technical extension services and buy-back arrangements with varying degrees of success.

Fig. 2. Turmeric (Curcuma domestica) with poplar (Populus deltoides).

Short-rotation tree species having faster growth, multiple uses and wider adaptability were deemed desirable for agroforestry/farm forestry plantations. Moreover, some exotic tree species were introduced to contribute to the success of farm forestry plantations programs.

Poplar (Populus deltoides)

This tree was was introduced to India in the 1950s, from the United States of America. It is now widely grown all over northern India and is considered an agroforestry tree because of its desirable characteristics and multiple uses. It is widely grown on a rotation of six to eight years. A well-drained, deep and fertile soil is suitable for poplar. One-year-old bare-rooted saplings (4-5 m) are used for transplanting from January to February with spacings of 8 × 3 m2 or 7 × 3.5 m2, 6 × 4 m2 or 5 × 4 m2. Rows are planted in a north-south direction to provide maximum sunlight to agricultural crops. G3, G48, L34, S7C15, Uday, Kranti and Bahar are superior clones of poplar that are suitable for the different agroclimatic conditions of northern Indian states like Punjab, Haryana, Uttar Pradesh and Uttranchal.

Commercial-scale plantations of poplar have been expanding since the WIMCO-sponsored Farm Forestry Project was launched in 1984. The maximum production potential of a poplar plantation is 50 m3/ha per year and the average potential of a poplar plantation is 20 m3/ha per year. Because of its deciduous nature, poplar can support the growth of agricultural crops beneath it without adversely affecting yield (Fig. 1).

During the first two years, the maximum returns can be obtained from a sugarcane + poplar combination. From the third year onwards, shade-loving crops like turmeric can be grown successfully (Fig. 2). During the winter season, wheat can be grown.

Poplar replaced Eucalyptus tereticornis when the latter's market prices declined in the 1990s. Ten million trees used to be planted annually in 0.02 million ha with an average density of 400-500 trees per hectare. The advantages of integrating poplar trees in farms are as follows:

Today, however, market prices for poplar are at their lowest. Hence, farmers have started to prematurely fell poplar trees. But six- to eight-year-old poplar trees, with a girth of 1 m, could not even be sold at Rs.600 per tree, when a tree would cost Rs.1 500 before 1996.

Eucalyptus tereticornis

This tree was introduced to India from Australia around 1790. Now, its cultivation has spread to nearly the whole of the Indian subcontinent. Large-scale plantations of E. tereticornis were established between 1970 and 1985. Nearly 2% of the cultivable land in northwestern India is planted with E. tereticornis (Fig. 3).

Under rainfed conditions, the cultivation of E. tereticornis is a safer investment than that of agricultural crops. However, market prices declined in the 1980s due to poor-quality wood as a result of closely spaced planting.

Poplar and E. tereticornis complement one another as the latter thrives in medium-quality soil and plantation requirements are favorable for absentee landowners. Poplar trees, on the other hand, thrive in highly fertile soil and require irrigation. The average productivity of E. tereticornis plantations is 10 m3/ha per year on forestlands and 15 m3/ha per year on farmlands. The average productivity of commercial clones is about 20-25 m3/ha per year and many farmers have achieved up to 50 m3/ha per year. Hence, the judicious mixture of clonal E. tereticornis and poplar cultivation on farmlands will keep tree farming profitable.

Prosopis juliflora

Introduced a century ago from South America, this tree (Fig. 4) is locally known as "kabuli kikar." It has successfully established itself on almost all the habitats including saline lands, alkali lands, wastelands, road sides, field boundaries and common lands. It is an evergreen tree, generally 3-4 m high, with long, drooping branches and a spreading crown. It is an ideal tree to use to reclaim deserts and an important source of food, fodder, fuelwood, charcoal, timber and gum. It is very easy to establish and grows fast even in adverse conditions. Large-scale plantations reduce the pressure on forests and other useful indigenous tree species.

Fig. 3. Eucalyptus tereticornis in block plantation.

Fig. 4. Prosopis juliflora.

However, P. juliflora is also becoming an aggressive weed in several states of India. It has become so widespread in grasslands, protected forests and nature reserves that it is alarming ecologists. It is now considered a serious threat to the existence of indigenous trees and shrubs in India.

Leucaena leucocephala

This tree (Fig. 5) is an exotic tree introduced from Hawaii, USA. Indians perceived it as a miracle tree as it provides fodder, fuel, pulpwood and timber. Its fodder contains 25.6% of crude protein and is considered essential during the lean months of green fodder. L. leucocephala alleys produce about 8 t/ha per year and 4.5 t/ha per year of fodder and dry fuel, respectively. It also easily spreads like a weed.

Acacia tortilis

This tree was introduced in India from Israel in 1958 to help establish large-scale plantations in the sandy areas of Rajasthan and Haryana. Desert-loving, the tree (Fig. 6) has undesirable wood quality and is thus priced low in the market. Therefore, its establishment on a plantation scale was ultimately discouraged.

Conclusion

Farmers in India may need to be careful in integrating exotic trees into their agroforestry farms. Aside from looking at market prices, farmers should also consider the trees' capability to be efficient and effective suppliers of food, fodder and fuelwood. More importantly, they should also check how the tree of choice complements the other crops, including its maintenance requirements. (The authors work at the Department of Forestry, CCS Haryana Agricultural University, Hisar-125 004, India.)

Fig. 5. Acacia tortilis.

Fig. 6. Leucaena leucocephala.


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