The government drive to axe trees that deplete groundwater is unlikely to yield significant results as the wrong species have been picked for felling. Plans are afoot to replace acacia and eucalyptus trees on government holdings with fruit-bearing trees to arrest depletion of ground water.
However, studies carried out by the Kerala Forest Research Institute (KFRI), Thrissur, a few years ago said cashew trees consume nearly double the quantity of water than acacia, eucalyptus and teak. Rubber trees also consume huge quantities of water.
The daily average water consumption of cashew trees was found to be around 48 litres during summer months, which is almost double that of eucalyptus. While eucalyptus used up to 24 litres a day, acacia consumed water in the range of 18 to 24 litres.
The water consumption of teak trees during summer months was almost zero as they shed leaves during the period.
Teak consumed more water during rainy season, said the study.
The research paper, 'water loss from tree plantations in the tropics,' was published by Jose Kallarackal and C.K. Somen of the Tree Physiology department of the KFRI.
The researchers looked into the water use characteristics of five species, including two varieties of eucalyptus, acacia, cashew and teak.
Factors like transpirational water loss (loss of water through leaf or stem) and evapotranspiration (the transfer of water from land to atmosphere by transpiration) were monitored during the pre- and post-monsoon seasons, said Dr. Somen.
Trees like teak and acacia showed better stomatal control (controlling the loss of water through the pores in leaves) which reduced the water loss.
Rooting depth (depth to which the roots travel) of cashew trees and eucalyptus was found to be higher than acacia.
Acacia being a shallow-rooted tree, its roots went down to the depth of 2.5 metres.
Eucalyptus and cashew had their roots even below 9 metres.
Trees with high rooting depth drew more ground water, explained Dr. Somen.
Jose Kallarakkal suggested focusing on water conservation programmes rather than axing trees if the government was keen on the saving water.
Rubber is farmed in 5.54 lakh hectare and cashew in 54,000 hectare.
The Kerala Forest department is the owner of the largest extent of teak plantations (76,734 hectare). It also has eucalyptus (6,566) Acacia auriculiformis (5,752) and Acacia mangium (3,589) farms.
T. N. Seema, vice-chairperson of the Haritha Keralam Mission, said the decision to axe the trees was taken after considering the public health issues associated with species like Acacia. The Social Forestry wing had earlier planted the trees at public places. The Mission has decided to replace them with fruit trees. Hence the decision, Dr. Seema said.
