Urban Trees for Combating Climate Change

By: Saibal Dasgupta, Rajesh Kumar and Prakash Lakhchaura,
The urban environment of modern India has undergone dramatic changes predominated by concrete structures, congested commercial spaces and incessant traffic. The degeneration of living environment in urban areas has severely disrupted the balance of urban climate as tree cover is eliminated to make way for ‘development’.
Forests

 

Between 1991 and 2011 urban population in India rose from 25.7 to 31.8 per cent as per the Census records. The annual urbanisation exponential growth rate of 2.76 per cent registered during 2001-2011 has in fact reversed the declining trend observed during 1981-91 and 1991-2001. Increase of 91.1 million persons to urban population during 2001-2011 is not only the highest registered thus far, it is also higher than the increase of 90 million persons to rural population. Faster urbanisation in terms of population and area coupled with developmental and industrial activities results in increase in gaseous and solid wastes causing serious threat to human and environmental health. Most of India’s urban areas are experiencing problems of deterioration of air quality, increased air temperature, increased noise levels etc. It is also a fact that the large proportion of population of the world now lives in cities and that further urbanisation cannot be stalled. The number of metropolitan cities in India (+1million) has risen sharply, from 35 to 53 during 2001-2011. According to a Report published by the UN titled ‘World Population Prospects: The 2005 Revision’ it was projected that by 2030, 60 per cent of world’s population will reside in urban areas.

Under such pressure, greening of cities is now recognised as one of the redressal mechanisms. With lack of green space, coupled with exponential population increase – physical, social, psychological and environmental hazards in third world countries will become acute.

Trees Combating Climate Change

In urban areas, plantation is ensured in parks, residential localities, streets, avenues and industrial sites as shelter belt plantation. Trees have multifunctional roles but their role in combating climate change has recently been recognised. Plant growth occurs through the process of photosynthesis, during which carbon is captured from the atmosphere and stored in plant cells as cellulose or polysaccharide. Trees, therefore, act as a carbon sink and their biomass in trunk, branches, leaves and roots serve as storehouse of carbon. Heartwood (inner darker part of the tree) contains about 48 per cent carbon in the form of cellulose and it is estimated that 2.2 tonnes of wood contains one tonne of carbon. The impact on climate change will depend on the quantum of per unit biomass accumulated by urban trees.

Out of a total of 583 species found in urban areas, analysis was carried out for 29 dominant species by the Forest Survey of India (FSI) in 2008 whose contribution is more than 0.5 per cent of the total estimated woody volume of urban trees at national level. The remaining species have been clubbed under ‘rest of species’. The top five species in urban area which contribute maximum to carbon stocking (in million tonnes-MT) are coconut palm – Cocos nucifera (3.6), Neem – Azadirachta indica (3.3), mango – Mangifera indica (2.2), tamarind – Tamarindus indica (2.0) and Eucalyptus (1.1). The total carbon stored by the urban trees is 23.89 MT from 7.79 million hectares urban area i.e., 3.01 tonnes of carbon per hectare (tC/ha). The total carbon stock in woody biomass of India’s forest has been estimated as 1083.81 MT from 63.34 million hectares of forest area, which works out to be 17.11 tC/ha. Thus, the urban trees contribute only about 2.21 per cent of total carbon stock of India’s forest. The study reveals that there is ample scope for the increase in green cover in
the urban areas of India and the importance of trees in urban environment needs wider recognition particularly in the role of mitigating atmospheric carbon.

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