Everyone who has ever lived in or around Lahore is probably familiar with the Chang Manga reserve. During my student days in the late ’50s/early 60s, my friends & I went a few times picnicking there. I remember that most of the trees there were Shisham, Kikar & white Mulberry (Shahtoot) nearly all of these are native to the region. This reserve was planted in 1866 and about a hundred years later it was still going strong, clear evidence that native species are best for reforestation.
Nevertheless, one cannot stop progress and I am aware of the growing popularity of the two non-native tree species in Punjab these being Eucalyptus & Poplar. Let us try to objectively look at these newly introduced species along with the good old Tali/Shisham (Dalbergia Sisso). Admittedly, Safeda/Eucalyptus has been around for quite a while but it was mostly limited to Rawalpindi & Potohar region and not very common in central & southern Punjab.
All three of these trees would prefer a minimum of 400mm of rainfall and ideally, a maximum temperature of around 30-35 deg C. However Shisham can tolerate up to 45 deg, understand that some Australian Eucalyptus species can tolerate high temperature & drought conditions. Don’t think Poplar is suitable for planting in semi-arid climates.
There are genuine reasons why these days Eucalyptus and Poplar are getting popular especially as 'Tree farming' alternative to the usual crops. The most important reason is being their fast growth rate. For example, while a Shisham tree needs about 15 to 20 years to reach biomass of 400-450 Kg (10-12 maunds); the Eucalyptus tree as well Poplar will reach about 400 Kg in about 7 years. Since Eucalyptus will also grow quite well in the saline soil, waterlogged & poor quality soils whereas Shisham & Poplar would not, indicates why Eucalyptus is very popular for forestation.
For long term forestation in Punjab, the region I am familiar with; one would normally go for Shisham & Kikar. For the mountainous areas and foothills of the mountains where there is plenty of rainfall (about 700-800 mm), Poplar is probably most suitable. And for the marshy, saline & other low-quality soils, I would make use of Eucalyptus.
In the lands good for agriculture, high yields of Eucalyptus may be quite tempting, but prudence requires that plantation of these trees should be limited to a couple of rows along the banks of the canals & irrigating water channels (khaals in Punjabi), these would help in the water seepage & soil erosion and also provide the farmer with additional income every 6 to 7 years but plantation of Eucalyptus en mass on agricultural land would definitely lower the underground water table. I remember reading somewhere that mass cultivation of Poplar in the Indian Punjab led to a steep price fall of its wood which has led many farmers to switch back to the traditional crops.
It would not be fair to Eucalyptus without mentioning that its wood is ideally suited for the electricity transmission poles and also for ‘match sticks’, fireboard and charcoal production. Essential oils are extracted from its leaves.
Since I have scant information about where and what kind of soil Eucalyptus has been planted en masse in the KPK ‘s billion tree project, I would refrain from commenting on it.