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1 Tea Ecosystem and Climate Change
Tea (Camellia sinensis L.) is a global beverage and India is the largest producer and consumer of tea. Tea is grown in thirteen states of India, and north-eastern parts, particularly Assam (26°00'N 93°00'E) and West Bengal (23°00'N 87°00' E) states contribute over 65% of the total national production. Way back from 1891, tea growing areas were rapidly increasing and now it spread from Upper Assam (Dibrugarh district), South Bank (Sibasagar, Jorhat and Golaghat districts), North Bank (Sonitpur, Darrang and Nalbari districts), Cachar, Dooars (Jaipaiguri district) to Darjeeling districts of North Bengal (Figure 1); and contribute around 70 million kg of tea per month and earning 25 million US $ (data based on June 2010 report of Tea Board, India (http://www.teaboard. gov .in).
Being a plantation crop that too formed at the cost of tropical and subtropical forests of north-east India, tea ecosystem is under constant pressure from insect pests since time immemorial. With global warming resulting in climate change, tea growing environments are undergoing rapid changes and new challenges and pest outbreaks are arising every now and then. Analysis of 100 years weather data as recorded at different eco-regions of tea growing belt by Tocklai Experimental Station (http://www.tocklai.net), Jorhat (26o7'N 94o13'E) showed a deficit rainfall (6%~8% from the normal) resulted greater frequency of drought, elevated CO2 level (1.5 ppm per year) and rise in temperature for north-east India. The minimum temperature on an average has risen at many places from 1deg C to 1.2deg C over past 90 years, but at the same time a decrease in maximum temperature in the peak production phase has also been observed, and more than 200 mm of annual average rainfall has been lost. Winter temperature during past one decade has increased by 0.7oC from the past 30 year average (Refer:http://www.tocklai.net/Concept%20note%20on%20climate%20 change[1].2.pdf). The last one decade has particularly experienced extreme fluctuation in weather conditions in Dooars (26°32'N 88°46'E West Bengal). The year 2006 recorded 400 mm and 660 mm deficit rainfall compared to previous and successive years; 2008 and 2009 also experienced deficit rainfall in the same tune. 2010, however, recorded second highest rainfall in past 30 years, 5 129 mm. Meantime, a rise of 1.1deg C in minimum winter temperatures (November~January)...