Impact of soil conservation measures on vegetation recovery in the catchment of a rapidly silting recreational lake at Chandigarh

Sukhna, a recreational lake developed in 1958 at Chandigarh (North India) by constructing a 12.8 m high earthen dam across three ferocious Shivalik torrents, suffered from pre-mature siltation due to heavy soil erosion from its 4207 ha catchment area. Intensive soil conservation measures were initiated but after 16 years of lake construction which included effective closure imposed by fencing 2540 ha forest area, large scale plantation, construction of more than 180 silt detention earthen dams and equal number of masonry check dams supported by vegetative conservation measures. These measures, carried over a long time, led to vegetation cover development and ecological recovery which formed the subject matter of a comprehensive study conducted during 2008–09 in the catchment of a representative 560 ha micro-watershed. Assessment of vegetation recovery, abundance and species distribution was carried out by physical measurements in plots of different sizes -10000, 100 and 1 sq m for trees, bushes and grasses spread over three landscape regions and slope classes.

The overall tree density in treated area over control improved in a period of 35 years from 162 to 450 and bush density from 5977 to 8984 ha⁻¹. However, the shade provided by large number of trees and aggressive bushes like Lantana camara reduced the number of grass clumps from 173 to 55 sq m⁻¹. Recovery was attributed to improvement in moisture regime, control of biotic pressure and forest fires.

Natural regeneration of tree species was affected by wildlife browsing, invasion of weeds, and at places by shade. The prominent tree species were Acacia catechu, Acacia nilotica, Dalbergia sissoo, Acacia modesta, Prosopis juliflora, Acacia latifolia and bush species of Lantana camara, Murraya koenigii, Carrisa carandus, Adhatoda vasica and Ziziphus nummularia.

Limited manipulation of the bush cover like removal of Lantana from safer slopes to promote growth of palatable grasses for wild life is recommended. The vertical cliffs which continue to trigger landslides should be stabilised with location specific bio-mechanical measures. Sukhna lake catchment demonstrate the extent of ecological recovery of degraded forest eco-system within 35 years of integrated soil conservation measures and effective closure.