Achyut Tiwari

Pines are evergreen conifers woody plants that bear seed cones and which have bundles of needles rather than the broad leaves commonly found on deciduous trees.
In Nepal, there are two native species of Pinus; Pinus roxburghii (chir pine) and Pinus wallichiana (blue pine), the former constitute 8.45% and 3.37%, respectively, of total forest area in Nepal according to the then Department of Forest Research and Survey (DFRS), Kathmandu, Nepal. The two species are also the major constituents of forests in the mid-hills of Nepal where households largely depend on forest resources for their livelihoods and subsistence.

Faster Growth
The third pine- Pinus patula (native to Mexico) is later introduced to Nepal during the 1970s, grows considerably faster than other two indigenous pine species, is likely to be sustainable on most sites where good standard silviculture practices are carried out.
Chir pine is one of the most common conifers in the sub-tropical region of Nepal and is distributed in all aspects of western Himalaya but is generally found in well-exposed southern slopes in Central and Eastern Nepal.
It can grow reasonably well in almost all types of soil and has been proved to be a successful pioneer species even at most degraded sites due to its high survival rate. Chir pine occupies 8.54% of total forest cover, being the fifth most dense tree species in Nepal with 7.05% of total volume in the forest, and has also been an important planted tree species linked with highly successful community forestry program in Nepal (DFRS).
It is reported that it possesses a biomass of 9.09 t/ha in Nepal which accounts for 5.09% of total woody biomass.
Although chir pine is also one of the most important tree species for the local people for its multipurpose uses such as timber, resins, firewood. Studies indicated that chir pine natural forests are highly sensitive to moisture availability in the early growing season in relatively drier regions of western Nepal, hence we could expect more moisture-related physiological stress to chir pine forests in mid-hills, as central Nepal is experiencing intensified spring drought.
Initially, pine was favoured for plantation development as it is less vulnerable than other species to damage by grazing animals and can grow in degraded areas with poor soils.
Nowadays the local people in the mid-hills of Nepal blame chir pine for transforming the hills to drier condition with the drying spells and suppression of species turnover, and of course, the blame is louder for the planted population. However, we do not have strong scientific evidence to support the blame and to address the controversial issue regarding the impact of chir pine for drying of the ecosystem.
Nepal has substantial areas of pine plantation with significant potential that is largely untapped. With basic management interventions, these plantations could be used to improve rural livelihoods, alleviate poverty, and support the development of wood-processing industries.

Limited Knowledge
We have limited knowledge about the impacts of rapid environmental changes on the health of our forests including the key species like chir pine, and about effective management plan for forest restoration and securing maximum forest products.
Particularly we do not have clear ideas on proper harvestable age/size prescribed so far, although it has been mentioned that 55 years' rotation was found to be effective for chir pine from central Nepal, however, some of the over matured pine trees still exist in the forest, thereby causing loss of forest quality and economy.
The overall Himalayan region is experiencing warmer temperatures, particularly day temperature responsible for a higher rate of evapotranspiration, early melting snow and substantial decrease in snowfall.
It has already been warned that the Himalayan region is moving towards the incipient stage of desertification, threatening the sustenance of the mountain ecosystem. Long—glacier-fed rivers are becoming non-glacial, overland flows on hill slopes are increasing, groundwater recharge is reducing drastically, natural springs were fast drying up, the base flow of rivers was dwindling rapidly, perennial rivers had become non-perennial and the lakes too were drying up for the entire Himalayan region. Yet there have been little studies on the causes for this desertification. Pine forests are expanding at a rapid rate and at the cost of the broad-leaved forests of oak, rhododendron and alder in Nepalese hills, both by plantation of pine as well by replacement of broadleaved forest due to thermophilisation.
Pine forests have been blamed to be one of the key drivers for depleting the underground water. Recent studies carried out in Western Himalaya indicated that the groundwater recharge rate in oak forests is 23 per cent, compared to a measly 8 per cent in pine forests.

Water Resource Depletion
As the recharge rate of pine forest is only one-third of the oak forest, the pine forest has triggered an overwhelming reduction in the net recharge rate. So, it is clear that the most potent and the most devastating agent for the depletion of natural water resources are the pine forests.
A pine tree sheds copious amounts of pine needles (pirul), which due to its toxicity is neither consumed by animals nor decomposed by microbes to convert it into humus and soil. Every year, the annual production of pine needles is overlaid by the next year's leaf fall. Thus, the pine needles keep accumulating year after year in the absence of a natural decaying process. The pine needle cover functions like an impermeable plastic sheet, which accelerates the rainfall-runoff all over the area.
Pine is an aggressive species in terms of its physiological mechanism related to growth and regeneration. It does not require much soil to germinate; hence it keeps expanding its distribution range through the natural process. The forest fires near the oak forests dry up their soil thus making them suitable only for the germination of pine, as it can grow even without much moisture.
Pine plantations were encouraged in India by the forest departments during and even after the British rule for its commercial production of resin, which was used for turpentine oil used in the paint industry. It was stopped only in 1993 after local people protested that pine trees were found to be drying up underground aquifers.
Some hydrologists have made valuable suggestions—both mechanical and biological—to help replenish the water resources, we need to reverse the ratio of pine and oak forests. Some of the measures that can help arrest the devastating reduction of natural water resources by pine forests include banning the plantation of pine and systematic removal of pine needles.
We could encourage large-scale efforts to plant broadleaved trees like oak, utis, kafal and gurans to replace pine monoculture forests. And we could promote the use of pine needles to make charcoal and mattress stuffing. Local forest users can be given incentives to collect and sell pine needles, and a systematic plan is also needed to cut pine trees to be used in the furniture industries.
These measures can go a long way to rejuvenate and replenish natural water resources. Moreover, systematic study of the physiological response of chir pine in response to water utilising strategies is essential before blaming pine to be responsible for the drying of landscapes.

(Tiwari is an assistant professor at Botany Department, TU)