Mineralogical Transformations under Fire in the Montane Grassland Systems of the Southern Western Ghats, India

Forest systems in the Western Ghats region have undergone significant transformations over the past century and wild fires are considered as a major factor for such modifications. Apart from natural fires, prescribed fire is also adopted as a management strategy in some of the forest types in the region. The present study evaluated the impact of prescribed fires on soil components in the high-altitude montane grassland systems of the southern Western Ghats. Fireinduced mineral transformations were assessed using X-ray diffraction (XRD), thermogravimetry (TGA), differential thermogravimetry (DTA), differential scanning calorimetry (DSC) and thermodynamic parameters. Organic carbon content which determines key soil functions was found to reduce from 1.96% before fire and stabilize at 1.48% in soils following fire. XRD and TGA–DTA analyses indicated that major changes in soil during fire occurred between 70°C and 110°C, 250°C and 320°C as well as 430°C and 500°C, corresponding to loss of interlayer water from phyllosilicate minerals, modification of gibbsite to amorphous minerals and goethite to hematite, and transformation of kaolinite to metakaolinite respectively. Thermodynamic parameters (ΔH, ΔS and ΔG) estimated from the DSC curves showed that such transformation had positive enthalpy (ΔH) and Gibbs free energy change (ΔG) values; hence they are not spontaneous or reversible by themselves.