• Summary
  • Objectives
  • Status
  • Project Publications
Summary

Invasive plants are a pervasive problem of most ecosystems, reducing biodiversity and changing ecosystem functioning in irreversible ways. However, little is known about the impacts of terrestrial invasive plants on stream hydrology, especially during the dry season when their effect at the catchment scale is more pronounced. Water availability during the dry season is crucial for ecosystem functioning and human well being. In the Western Ghats, the dry season precedes the South West Monsoon and is the warmest part of the year. Preliminary investigations suggest that the spread of black wattle (Acacia mearnsii), and a mix of Scotch broom (Cytisus scoparius) and Gorse (Ulex europaeus), together referred to as broom, into natural grasslands in the Upper Nilgiris has significantly increased evapotranspiration and reduced dry-season streamflow. This study will attempt to measure the hydrologic footprint of wattle and broom in the Nilgiris South Range in the Upper Nilgiris. 

Understanding the relative impact of different land covers on dry season flows can therefore inform land use policy in India, particularly in headwaters of important basins which are under the control of the government and where large scale land-cover modifications can and are being implemented. Reduction in invasive plants are a pervasive problem globally. Across ecosystems, they have been linked to reducing biodiversity and changing ecosystem functioning in irreversible ways. However there is very little information available on the impacts of terrestrial invasive plants on stream hydrology. 

Government initiatives to restore natural grasslands entail large scale removal of wattle, even as a rapid spread of broom into grassland catchments has been observed. This provides an opportunity to measure the hydrologic impacts of these changes with a focus on dry season evapotranspiration, soil moisture availability, streamflow and water quality. Installation of limited equipment will allow us to conduct catchment level experiments which are rarely undertaken in India.

Objectives

1. To determine the impact of black wattle and a mix of Scotch broom and Gorse, on the water budget when compared with natural grasslands in the Upper Nilgiris in terms of (i) dry season streamflows, (ii) evapotranspiration demands, and (iii) soil moisture.
2. To quantify impacts of large scale removal of black wattle on sediment loads in streams.
3. To investigate decadal trends in areas under major land cover and natural grasslands and forests and their contribution to evapotranspiration at a landscape scale.

Status
  • Our results suggest a greater mean daily discharge in streams during dry periods in grassland-dominated catchments compared to catchments invaded by wattle. This decline in stream flows in wattle-invaded catchments is directly linked to greater water loss through evapotranspiration.
  • The results from the soil moisture study in the different land cover types suggest less soil moisture in young and old wattle stands compared to natural grasslands. This indicates greater water loss in wattle-invaded catchments compared to grasslands.
  • Analysis of land-use/land-cover trends using satellite images suggests an increasing trend in wattle-cover since the 2000s in the Nilgiris, which increased by 7% in area between 2000 and 2017. We found that grasslands were predominantly converted into wattle and other forest plantations (1700 ha) suggesting the invasion of natural grasslands by woody shrubs and trees in this landscape.
  • The generalised model of evapotranspiration revealed an increase of 8% - 12% in evapotranspiration due to conversion of grasslands into wattle plantations.
  • Reduced stream-flows as a result of excessive evapotranspiration losses by woody-invasive has a greater impact on the water availability for wildlife, drinking-water for humans, and water for power-generation in drier-periods.
  • Restoration of native montane-grasslands is crucial for sustaining the hydrological-cycle and increasing stream-flows in the Nilgiris.
  • In addition
    • Three papers in peer reviewed high impact journals
    • Two policy briefs
    • Completed two presentations/posters at international conferences and one poster in a national conference
    • Conducted one stakeholder workshop
    • Two PhD students and one MSc student were trained
    • Continued collaborations with Lancaster University and National Center for Biological Studies as well as with WWF India, Wildlife Conservation Trust and BIT Sathu Tamil Nadu.