Jhum cultivation or slash-and-burn agricultural system, also known as shifting cultivation is an age-old agricultural practice by the ethnic tribal communities of uplands and it is still prevalent in all the northeastern states. The existing practice of jhum cultivation in Tripura and other north-eastern states of India has been identified as one of the anthropogenic and unscientific form of land use which is influencing the biodiversity to impede the ecological balance of the region. Over the last few years emergence of a new class of shifting cultivators who reduced the earlier 15–20 year cycle of shifting cultivation on a particular land to 2–3 years now resulted in large-scale deforestation, soil and nutrient loss, and by the way affecting the indigenous biodiversity to a large extent.
For shifting cultivation farmers generally select a forest patch and clear fell the vegetation normally in December and January. Thereafter, they burn the vegetation. During this practice, small, cut-trunks portion and roots are normally not removed. The herbs, shrubs and twigs and branches (slashed vegetation) are burnt in February and March. Sowing of seeds is followed during April and May. They will continue the cultivation for a few years and abandon the cultivated site and shift to other forest sites. After that they will return to the former site, and once again practice shifting cultivation on it. From the erosion point of view, the second year of jhumming cycle is more hazardous than the first year
Shifting cultivation is prevalent in all the northeastern states. Chart 1 present the results of successive studies carried out by the Forest Survey of India, i.e. State of Forest Report, 1995 and 1997. It was noted that loss in forest cover in the northeastern states was mainly due to the shifting cultivation.Chart 2 presents total area affected by the shifting cultivation in the region, a study carried out by the RTFSC .
Chart-1: Loss of forest cover in NE India Due to shifting cultivation (in Sq. km)
Source: State of Forest Report (1995, 1997)
Chart 2: Annual area under shifting cultivation (in Sq. Km)
Source: RTFSC (1983), Basic Statistics of NER, 2002, Government of India, North Eastern Secretariat, Shillong. p. 42.
A comparison between the forest cover since 1987 onwards till 2003 is depicted in Table 1 below. Although it is improper to make a comparison in different assessments due to change in technology and scale of interpretation, however, it may still be observed that the forest cover of the country has remained between 19.5% to 20.5% in the last two decades.
Table 1: Forest Cover in Different Assessments (1987 to 2003) (Area in square km)
| Year of Assessment | 1987 | 1989 | 1991 | 1993 | 1995 | 1997 | 1999 | 2001 | 2003 |
| Forest Cover in India | 640,819 | 638,804 | 639,364 | 639,386 | 638,879 | 633,397 | 637,293 | 675,538 | 678,333 |
| Percent | 19.49 | 19.43 | 19.45 | 19.45 | 19.43 | 19.27 | 19.39 | 20.55 | 20.64 |
Source: FSI Reports, 1987-2003
Cumulative area affected by shifting cultivation during 10 years was found to be 1.73 m ha. State-wise details are given in Table 2.
Table 2: Area affected by the shifting cultivation (Area in ‘m ha’)
| States | Cumulative area of Shifting Cultivation (1987-89 to 1995-97) |
| Arunachal Pradesh (AP) | 0.23 |
| Manipur (MN) | 0.36 |
| Mizoram (MZ) | 0.38 |
| Tripura (TR) | 0.06 |
| Assam (AS) | 0.13 |
| Meghalaya (MG) | 0.18 |
| Nagaland (NG) | 0.39 |
| Total | 1.73 |
Source: FSI report on shifting cultivation (Between 1987 to 1997)
The extent of area under shifting cultivation is maximum (0.39 m ha) in Nagaland followed by Mizoram (0.38 m ha) and Manipur (0.36 m ha). These states together account for about 65% of the total area under shifting cultivation in the N-E.
Impact of shifting cultivation
Deforestation: Shifting cultivation was assessed by the FAO to be one of the causes of deforestation In Tripura, comparison of the current forest cover (Satellite data of Nov 2006-Jan 207) with the previous assessment (satellite data of Nov 2004) shows a loss of 100 sq. km of forest cover. The change matrix given in the table-3 reveals that there has been a decrease of 2 sq. km in the very dense forest, 46 sq. km in moderately dense forest and 52 sq. km in open forest..
Table 3: Forest cover change matrix (area in sq. km) in Tripura
| 2005 assessment (data of Nov-Dec 2004) | 2007 (data of Nov 2006-Jan 2007) | Total of 2005 | ||||
| VDF | MDF | OF | Scrub | NF | ||
| Very Dense Forest (VDF) | 110 | 1 | 1 | 0 | 1 | 113 |
| Moderately Dense Forest (MDF) | 0 | 4,754 | 9 | 9 | 43 | 4,816 |
| Open Forest (OF) | 0 | 13 | 3,152 | 25 | 54 | 3,244 |
| Scrub | 0 | 0 | 13 | 40 | 1 | 54 |
| Non-Forest (NF) | 0 | 2 | 17 | 1 | 2,244 | 2,264 |
| Total of 2007 | 111 | 4,770 | 3,192 | 75 | 2,343 | 10,491 |
| Net Change | -2 | -46 | -52 | 21 | 79 | |
Source: FSI Report (2009) on Forest and Tree Resources in States and Union Territories; Tripura.
On the basis of ground truthing by the official of FSI, main reasons for decrease of forest cover is shifting cultivation in all districts. Degradation of forest causes ecological imbalance, rapid drying up of small water sources, and loss of productivity of land causing reduction in family income and enhancement of poverty in absence of any subsidiary income.
Loss of nutrients and top soil: With reduction in jhum cycle from 20–30 years to 2–3 years, the land under shifting cultivation looses its nutrients and the top soil. With reduction in crop yield, the families start moving to other virgin areas. Now, a stage has come that it has already affected 2.7 million ha of land, and each year 0.45 ha of land fall under shifting cultivation, in northeast India. So long as the jhum cycle has duration of 10 years or more this type of cultivation did not pose any threat to the ecological stability and soils of the largely forested hill area. While studying jhum ecology in Meghalaya, it was reported that water and nutrient losses in shifting-cultivation areas were far greater than in the virgin areas, and areas left for 50 years after jhuming. Thus, reduction in the cycles of jhuming, adversely affects the recovery of soil fertility, and the nutrient conservation by the ecosystem. Repeated short-cycle jhuming has created forest-canopy gaps which are evident from the barren hills.
Other ecological consequences: Frequent shifting from one land to the other has affected the ecology of these regions. The area under natural forest has declined; the fragmentation of habitat, local disappearance of native species and invasion by exotic weeds and other plants are some of the other ecological consequences of shifting agriculture. The area having jhum cycle of 5 and 10 years is more vulnerable to weed invasion compared to jhum cycle of 15 years. The area with fifteen-year jhum cycle has more soil nutrients, larger number of species, and higher agronomic yield with ratio of energy output to input as 25.6 compared to jhum cycle of 10 and 5 years (4.6–9.8) .
Although jhuming has many benefits from livelihood point of view, but in long run it destroys the ecosystem balance because one inch soil formation in nature takes about 1000 years. But several inches of soil are washed out each year due to jhuming. Heavy siltation of Brahmaputra River from its tributaries and frequent breaking of embankments are caused by heavy soil erosion from hills of North East India. A study by ICAR institute of NEH region, Barapani, reported that the shifting cultivation on steep slopes (44-53%) has soil loss value of about 50 tones/ ha/ year with corresponding nutrient losses of 703 kg of organic carbon, 144 kg of phosphorus and 7 kg of potash annually. Major adverse effect of shifting cultivation apart from soil and nutrient losses are rapid siltation of river beds causing floods, denudation of forests which hardly gets regeneration time because after 3 to 5 years they have to be burnt for another jhuming due to population pressure. Previously this period was for 7 to 10 years.
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