Nirav Mehta1, J. Dinakaran1,2, Abi T. Vanak1 and Ankila J. Hiremath1
1Ashoka Trust for Research in Ecology and the Environment, Royal Enclave, Sriramapura,>Jakkur Post, Bangalore – 560 064, Karnataka, India
2Department of Botany, University of Delhi, Delhi, India
Prosopis juliflora (Sw.) DC., a tree introduced to India in the 19th century from Central and South America, is now one of the most widespread invasive species across arid and semiarid grasslands and scrublands in India. Prosopis juliflora (hereafter, Prosopis) was introduced to the Banni grasslands, a ~2500 km2 arid grassland region in Gujarat, western India, in the 1960s. Since then, it has swiftly become the major vegetation cover, having spread to about 60% of the landscape, and has come to be known locally as ‘gaando bawal’ (the mad babool). Prosopis has replaced grasslands and reduced fodder availability for milk-yielding livestock, thereby affecting livelihoods of traditional pastoralists who have historically used this landscape. In response to Prosopis invasion, local pastoralists have developed a parallel economy of harvesting this tree for fuel wood and for making wood charcoal. We assessed the rate of growth of Prosopis and measured the time for the plant to reach harvestable size, in 8 replicate plots (20 × 20 m) across Banni. We lopped all trees to ground level (as is done by Prosopis harvesters locally). Tree regrowth in lopped plots was monitored annually for 3 years to measure increment in stem diameter and height. We separately developed allometric equations by harvesting 55 Prosopis trees of various stem diameters and heights; these allometric equations were used to estimate annual biomass increments in the lopped plots. The total aboveground biomass of re-grown stems was of the order of 40 Mg/ha within 2 years post-lopping, and the stems reached harvestable size in about 3 years. This system of lopping allows for rapid re-growth and harvest, thus resulting in sustainable management of invasive Prosopis in the study area. Such management-by-utilization has helped mitigate the negative impacts of Prosopis on Banni’s pastoralists, while simultaneously yielding a renewable source of energy and income.