Impact of management practices on the tropical riverine grasslands of Brahmaputra floodplains: Implications for conservation

Abstract

Globally, the conservation value of tropical grasslands, unlike tropical forests, is underappreciated, and their degradation is widespread. Conservation of this vulnerable ecosystem requires scientifically validated management strategies. The present study examines the impact of flooding, herbivory, and other management practices on the riverine grasslands of Brahmaputra floodplains of Assam, India, for devising effective conservation strategies. Inundation period-based unsupervised classification was used to derive the types and extent of grasslands viz., short (SG) and tall (TG). Subsequently, the data on vegetation composition and nutrient status viz., soil carbon (C), nitrogen (N), phosphorus (P), and potassium (K), was collected from inside and outside of 15 exclosures that were subjected to different management regimes, including grazing (freely accessed by mega- and meso-herbivores), ungrazed (not accessed by mega- and meso-herbivores), ungrazed with controlled burning and ungrazed with invasive removal. A total of 1152 plots were monitored for two-year, from January 2014 to December 2015. The results of the study revealed that the areas inundated for a longer duration were dominated by SG and had higher species diversity, while areas inundated for the shorter duration were dominated by TG and had low species diversity. We further observed that grazing exclusion promoted heterogeneity, woody and invasive growth, and soil nutrient content. Burning and invasive removal reduced woody and invasive growth and enhanced soil nutrient conditions. Grazing and burning decreased heterogeneity, while invasive removal increased heterogeneity. Alteration of the flooding regime due to reduced water availability may affect the ratio of SG and TG extent in the long run, which may alter the vegetation composition and the productivity of these grasslands. We recommend short-term rotational grazing for SG and long-term for TG to promote heterogeneity and soil quality. Controlled burning can be carried out in dry and invaded areas post uprooting of invasives to mitigate the effect of succession.