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In the Himalaya, forests converted into farmlands might be beneficial for winter birds

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3 Jun 2020
In the Himalaya, forests converted into farmlands might be beneficial for winter birds

Vast swathes of forests in many countries are being converted into agricultural lands to meet the ever-increasing food demand. India has increased its croplands by 56% from 1880 to 2010 while losing a whopping 26 million hectares of forest land during the same period. While such changes in land-use patterns have devastating effects on wildlife, recent studies show that some agricultural areas can harbour greater biodiversity than forests. So, what factors related to cropland expansion drive this trend?

In a study, researchers from Princeton University, USA, have tried to understand how temperature variations in forested and agricultural lands affect winter birds in the eastern and western Himalaya. This study, published in the journal Ecography, found that in the Himalaya, croplands may benefit the conservation of some bird species, in contrast to the popularly held belief.

The biodiversity of any habitat depends on factors like the vegetation, light conditions, temperature, humidity and rainfall in the region. Those species that adapt well to these factors survive and thrive. However, when habitats are modified, it alters critical factors like the temperature. Since agricultural lands are, on average, warmer than forests, the current study focused on the differences in how bird species tolerate temperature variation between forested and agricultural land.

The researchers carried out their study in the Great Himalayan National Park in the western Himalaya and the Singchung Bugun Village Community Reserve in the eastern Himalaya. The eastern Himalaya receives significantly more rainfall and has lower annual temperature variations than the western Himalaya. The different environmental conditions in these regions host a varied composition of species. The researchers studied winter birds in the western Himalaya between November and December 2013, and in the eastern Himalaya between December 2017 and January 2018.

The study found about 1.6 times the number of species in the eastern Himalayan region than the west. Interestingly, the agricultural lands in the western Himalaya, where crops like cabbage, potato, tomato and garlic are grown, had more bird species than its forests. Since these birds have a broader thermal tolerance, they are distributed across forests and agricultural lands, say the researchers. On the contrary, eastern Himalaya had more bird species in the woods than in croplands. These birds, which do not tolerate wide temperature variations, depended on forests for foraging.

"For the western Himalayan birds, it appears as if mosaic landscapes of forest patches, interspersed with low-intensity agriculture is valuable as winter habitats," reasons Dr Umesh Srinivasan, one of the researchers involved in the study. "In the eastern Himalaya, however, while agricultural lands do hold many bird species, the retention of forests appears to be far more important for bird conservation."

The researchers also found that the agricultural bird community was more diverse than the forest bird community in the west. In contrast, the two eastern bird communities were equally varied. However, there is a word of caution on these agricultural lands being havens for birds.

"The conversion of low-intensity agriculture to more intensive uses such as grazing pastures should be discouraged to maintain winter birds in the west," warns Dr Srinivasan.

The debate on the effects of agricultural expansion on biodiversity has many sides to it. The findings of this study emphasise the need to analyse the impacts of farm areas while formulating conservation and management strategies for the expansion.

"Conserving a species in different parts of its geographic range might need different strategies, depending on how environmental conditions change across its range," says Dr Srinivasan. This study provides some insights into the effects of such changes in the birds' habitats. "We are now beginning to understand how bird species adapt to their environment, and how this influences their response to landscape changes due to human activities," he signs off.

This article has been run past the researchers, whose work is covered, to ensure accuracy.