Western Ghats: Native habitats reduced to one-third and hydrological regulation disrupted, says review article

The Western Ghats, the most densely populated global biodiversity hotspot, not only harbours 30% of India’s plant and animal species, but is a “museum” of ancient plant and animal lineages and a “cradle” of more recently evolved species, endemic to the region.

Yet, two centuries of plantation expansion, dams, roads and infrastructure development, now compounded by climate extremes, accelerating invasive species spread, and urbanisation and infrastructure, have reduced native habitats to one-third of their original extent, disrupted hydrological regulation critical to peninsular India’s water security, and driven range contractions among narrow-ranged endemics, says a new review article published on Wednesday in Nature Reviews Biodiversity.

The article, “Biodiversity origins, threats and conservation in the Western Ghats” is authored by Kamaljit S. Bawa, Jagdish Krishnaswamy, Jahnavi Joshi, Ayyappan Narayanan, Kiran Mathramkot Chandrasekharan, and Lokesh Bagepalli Subramanyam. from the Department of Biology, University of Massachusetts, Boston, MA, USA, School of Environment and Sustainability, Indian Institute for Human Settlements, Bengaluru, CSIR-Centre for Cellular and Molecular Biology, Hyderabad, India/Academy of Scientific and Innovative Research, Ghaziabad, India, Department of Ecology, French Institute of Pondicherry (IFP), UMIFRE 21 CNRS-MEAE, Puducherry, and Geo-spatial Laboratory, Indian Institute for Human Settlements, Bengaluru, respectively.

Incidentally, the review is dedicated to the late Madhav Gadgil amid the deeply divided debate over the conservation measures for the Western Ghats, including provisions of the Gadgil and Kasturirangan committee reports and the Centre’s latest draft notification on the proposed Ecologically Sensitive Area (ESA) in the Western Ghats.

Threats

Speaking about the threats to the Western Ghats, the article says several of these pressures began during the expansion of coffee and tea plantations under the British colonial rule and have continued since then.

“Plantation of woody cash crops is a major driver of land-use change in the region. Coffee plantations started around 1860, and tea and rubber at the beginning of the 19th Century. Coffee now occupies about 3,000 sq km and tea occupies 1,134 sq km in mid-elevation, high-rainfall zones, mainly in Kerala, Tamil Nadu and Karnataka, overlapping with biodiversity-rich ecosystems.,” it says. It further says that cardamom covers over 730 sq km between 600 and 1,200 m above sea level, areas traditionally comprised of natural forests. Rubber spans 5,000 sq km, mainly in the west-facing valleys, including 3,226 sq km in Kerala, with over 600% expansion during the last 70 years. Cashew, introduced by the Portuguese, has expanded nearly 53,500 ha in the Northern Western Ghats alone, posing a threat to lateritic plateaus and their ecosystems. The arecanut, once restricted to humid uplands, has now spread into irrigated drier regions, it adds.

As a result of land-use change, the Western Ghats lost an estimated 40% of its natural forest cover between 1920 and 2010, with steeper declines in northern areas and shallower declines in southern areas, it said.

Apart from direct land conversion, linear infrastructure is a major driver of fragmentation, says the article, pointing out that the Western Ghats have 26,400 km of roads, 10,042 km of railways, 2,621 km of canals, and 132 km of power lines, which disrupt ecological connectivity and wildlife movement and cause wildlife mortality.

Climate change

It also warns of rapidly changing climate dynamics, in particular, the future of the monsoon in the Western Ghats remaining uncertain, with historical observations showing that total rainfall has been declining since the 1950s, whereas most climate models simulated and projected increases in the recent past and in the future.

Despite the complexity of trends in annual rainfall, one of the consequences of global warming, an increase in extreme rain events is already occurring in the Western Ghats and thus, in the areas that have seen a moderate decrease in annual rainfall totals, a greater proportion of the rainfall was being received as more intense rain, it says.

“Extreme rain events (over 900 mm per day and over 100 mm/h) in the Western Ghats can trigger landslides, even in forested zones. Some future projections indicate that annual maximum rainfall will increase substantially at lower elevations and more modestly at middle elevations, consistent with heightening flood risks. Furthermore, rainfall and warming anomalies are projected to be the highest in the north,” it added.

The review article says systematic conservation planning, apart from considering expansion of protected areas, community reserves and enabling connectivity among landscapes, must take into account patterns of endemism, phylogenetic distinctiveness, and evolutionary refugia.

“...Current protection is disproportionately focused on charismatic megafauna and does not reflect the spatial distribution of unique evolutionary lineages or data-deficient taxa,” it says. “Effective conservation requires three mutually reinforcing elements: spatial prioritization anchored in biogeographic gradients, climate-resilient management and habitat restoration, especially for sky-islands, lateritic plateaus and freshwater ecosystems, and inclusive governance of both land-sparing and land-sharing conservation interventions,” the study adds.