Forest resources in Pakistan are very limited. Out of the total 87.98 million hectare land-mass, only 4.28 million (4.8 per cent) are under forests, while out of 20.53 million hectare area of Punjab, only 0.572 million hectare (2.72 per cent) area is under forests.
More than 50 per cent of these forests are protective in nature while others are sparsely populated and are not producing to their full potential. As a result, there is a big gap between supply and demand of wood. To meet with this gap, the forest department mainly relies on trees growing on farmlands. The import of wood is mainly confined to pulp and paper with some share of industrial wood (plywood).
The farm-grown trees in Punjab are fulfil more than 90 per cent demand of fuel wood and about 80 per cent of timber. The Punjab forest department conscious of its limited resources motivates farmers for tree-planting on their farmlands through various agroforestry programmes, with limited research backing.
Consequently, the department is not able to suggest proper spacing, rotation age, suitable tree species for different soil types, silvi-cultural and cultural operations, compatible arable crops and economics of growing trees on farmlands under linear or block fashion. That is why, farmers plant trees on their farmlands only half-heartedly. They have reservations that trees may affect their agricultural crop yields adversely through competition for moisture, light and nutrients. They are source of pests and diseases, and above all, trees do not pay as against their damages to crops. These assumptions of farmers can only be removed through a scientific approach.
Farmers have been demanding fast-growing tree species with high economic returns and with minimum damaging effects to their arable crops. In the search of tree species having fast rate of growth, multifarious uses and compatibility with agricultural crops, different exotic tree species were introduced in the country during 20th century. Out of various tree species poplar (populus delloides) proved itself very fast growing, compatible with most of ‘rabi’ crops, highly economical commercial timber, having variety of uses like packing cases or crates, matches, shuttering material, light constructional material, ice-cream sticks, toothpicks, artificial limbs, fodder, fuel wood, chipboard, plywood, particle board, sports goods and ‘khas’ of desert coolers.
Hence a Ph. D research project was designed at the department of forestry, wildlife and range management, University of Agriculture, Faisalabad, and conducted by the Punjab Forestry Research Institute, using poplar and wheat-fodder-maize as intercrops. The objectives of the study were to evaluate the growth of poplar (populus deltoides clone AY-48) trees at different densities under wheat-fodder-maize agroforestry system. To determine the effect of poplar tree intercropping on growth, yield and quality of wheat-fodder-maize, and to compare the economics of agroforestry system with conventional arable farming.
In this connection, comparison of poplar trees growth under intercropping system at different tree densities was done with sole poplar tree crop. Similarly, growth and yield of wheat-fodder-maize under intercropping system was compared with sole crops to determine the effects of intercropping. Economics of agroforestry system at various tree densities was also compared with conventional farming practices. Similarly post-harvest soil fertility (organic matter, nitrogen, phosphorus and potassium) of experimental site was studied for determining effects of intercropping on soil nutrient status.
The salient findings of the study were:
1. Intercropping of wheat-fodder-maize crops and tree spacings has positive effect on poplar tree growth.
2. Wheat grain yield decreased under different poplar tree spacings, however, this decline in yield was not significant at tree spacing of 3.7 x 9m and 3.7 x 12m.
3. Poplar tree intercropping has no significant effect on wheat grain quality.
4. Poplar tree intercropping has some negative effect on grain weight and size but this effect decreased with the increase in tree spacing.
5. Poplar tree intercropping significantly decreased fodder maize fresh yield. However, this effect was diluted with increase in spacing amongst trees.
6. Land equivalent ratio (LER) studies revealed that there was overall 74-52 per cent yield advantage in agroforestry over conventional mono-cropping.
7. Soil fertility increased under agroforestry systems compared to conventional farming system.
8. Intercropping of poplar tree in wheat-fodder maize cropping system was economical at all tree densities in terms of net benefits, benefit-cost ratio and internal rate of return. However through marginal analyses it was found that intercropping in a tree density of 3.7 x 9m was most economical.
9. Rotation age of 8 years was found to be the best one for intercropping at the tree densities tested.
10. For pure forestry at the spacing of 3 x 3m, the rotation age of 4 years was found to be the best one as it was not economically viable after that age.
11. Intercropping of wheat-fodder maize in poplar trees at tested densities was economical at tree age of 7 and 8 years. So intercropping should continue throughout the rotation age of poplar trees.
Recommendations: a.Poplar tree spacing of 3.7 x 9m be adapted for intercropping wheat-fodder maize; b. Agroforestry is preferable than pure forestry to get better poplar tree growth; c. Agroforestry is an economically viable option; d. Poplar trees should be harvested at eight years rotation in agroforestry system at 3.7 x 9m density;and e. lnter-cropping should continue throughout the rotation age of trees.through agroforestry