The role that shade trees play in tea gardens of Assam — by Amrita Ghosh and Aravinda Anantharaman
The lush green valley of the Brahmaputra river in Assam is decked up with many tea gardens adding to its beauty. Tourists and travellers stop by these tea gardens to click a picture or two. The play of light and darkness offered by these shade tree plants and sunlight forms a sight to behold! But the shade tree canopy of the tea gardens of Assam has a more important role to play in the production of a great cup of Assam tea.
Sau Shade Trees form a canopy over the tea bushes and an elephant corridor (📸 Nirajmani Chourasia)
The Camellia Sinensis var. Assamica tea plants thrive best in humid and warm temperatures. The best ambient temperatures for tea in Assam, in general, is within 13°C to 32°C, while 28ºC to 32ºC is most conducive for the ideal growth of tea leaves.
Recent global warming phenomena has also had an impact on the ambient temperature of Assam’s tea gardens, where recently the state has recorded an increasing trend in temperature, averaging up to 38ºC for long periods in the northern summer.
If the ambient temperature is above 32°C, it becomes unfavourable for optimum photosynthesis, more so if it is accompanied by low humidity.
Dr Devajit Borthakur, a plant breeder and advisor at our Aideobarie tea farm, says that “When the temperature soars above 32ºC, the tea leaves can get sunburnt. This yields a bitter taste owing to the higher production of significantly more polyphenols in the tea leaves”.
A scientific analysis of the impact of higher temperatures on tea production levels has implied that exposure to warmer temperatures can lead to negative impacts on yield. One degree of warming of monthly temperatures above 26.6°C would result in a 3.8% reduction in tea yield.
Other tea growing regions, like China, Taiwan, Japan and the African highlands, do not experience such high temperatures, like in Assam. Shade trees are in that way, very unique to Assam and act as the natural sunscreen for the tea bushes of Assam.
Albizzia Chinensis provide good shade to tea bushes (📸 Boroon Mahanta)
Initially, Albizzia Chinensis or the “Sau-tree” was most commonly used as a shade tree in Assam. Some other leguminous trees (Albizzia Odoratissima, Dalbergia Assamica and Erythrina India) were also added for nitrogen fixation of the soil. These shade trees tower over the tea bushes at a height of 10 to 80 feet.
Interestingly, the indigenous tea plant of Assam was discovered under the great canopy of a forest, as an under storied plant species.
In the tea gardens of Assam, shade trees reduce sunlight exposure to half and also absorb harmful radiation from the sun. This stops the leaf from getting sunburnt and the natural levels of polyphenols are controlled. With deep roots, the trees hold the soil from eroding during the heavy monsoon season in Assam and also helps in maintaining soil moisture. The leaves, twigs, seedpods, etc. that are shed by these trees provide around 2500–5000 kilograms of organic manure per hectare in a year, adding to the soil’s fertility.
Hoolock Gibbons of Assam (📸 Udayan Borthakur)
Assam is not just the largest contiguous tea-growing area in the world. It is also a refuge for many endangered and vulnerable animal species like the one-horned Rhino, red-headed vulture, the hoolock gibbon and many bird species. Wild elephants roam the breadth of the state, with many herds wading through the tea gardens, through what is called, “elephant corridors”. The shade trees provide a natural habitat for many of these native birds across the state and also indigenous hoolock gibbons in some smaller areas of Assam.
To obtain the optimum benefit of our Sau trees, we use an eco-friendly, chemical-free pest control method, These are Yellow Sticky Roll Traps that are wrapped around the Sau shade trees. These two feet wide traps attract the tea pests with their organic odour. We rely on the wind to blow them towards the bands where the glue acts as a trap. These traps are replaced periodically.
Yellow Sticky Roll Traps that are wrapped around the Sau trees at Aideobarie (📸 Boroon Mahanta)
At Aideobaire, these shade trees are a kind of guardian, the strong and silent pillars of our tea farm. We have about 13,000 of them on our tea farm of 200+ hectares. Some of the shade trees protecting our tea bushes are as old as the 124-year-old farm. We have active re-plantation practices with new shade trees, to maintain the right temperature conducive for tea production for years to come.
Acting as the tea farm’s natural umbrella, the tea made from the tea bushes grown under the adequate shade of these Sau trees at Aideobarie, is another step we take for a cup of tea that is just right — from our farm to your cup.