Past Landscape Dynamics as a Guide for Conservation Interventions in Bardia National Park, Nepal

The Terai Arc Landscape is a unique subtropical landscape at the foot of the Himalayas, that sustains many keystone species, including the continental tiger (Panthera tigris). Conservation efforts have led to an increase of this species, increasing human-wildlife conflict significantly. To optimize the habitat suitability and reduce conflict, conservationists aim to implement various interventions in Bardia District. However, this ecologically and geomorphologically complex landscape is understudied, making it difficult to estimate the potential impact of different interventions.

Therefore, this study aims to reconstruct past ecosystem states and drivers of  the Bardia landscape to help estimate the outcomes of conservation measures. To achieve this, sediment cores were collected and analyzed for sedimentary ancient DNA, combining shotgun sequencing with mitochondrial mammalian capture, providing a vegetation- and land use history. In addition, the fluvial history of the sampling sites was investigated using grainsize analysis and x-ray fluorescence.

The results from these cores indicate consistent, low-intensity human land use over the last centuries. Only in the last few decades, does the intensity increase, likely due to a confirmed migration wave of people from the hill regions of Nepal to the lowlands after the eradication of Malaria. However, before this, changes in vegetation composition appear more so due to geomorphological change. Namely, one lake is an oxbow lake that was shaped from a past channel of the Karnali river. The combination of past vegetation and fluvial history shows how the severing of the meander from the river led to a fairly fast transition of riverine grassland and forest to a wetland-environment with denser vegetation.

This finding is particularly relevant for Bardia National Park, as the river branch that currently determines its western boundary, the Geruwa, appears to be undergoing a process of disconnection from the Karnali and thus becoming ephemeral or even drying up. Our outcomes show that such a transition can rather quickly affect the presence of riverine grasslands, which are seen as crucial for the tiger, thus affecting habitat suitability. A potential outcome of such a habitat change could be the movement of tigers towards other riverine grasslands nearby, which have a higher human population density, thus increasing the risk of human-wildlife conflict.

One of the interventions proposed by park managers is to artificially keep the Geruwa branch of the Karnali open by removing gravel from blocked channels. This study demonstrates that although this is a somewhat controversial measure, it could actually be desirable in terms of maintaining the tiger population within the National park rather than outside of it. This highlights how assessing past environments can meaningfully contribute to making optimal conservation decisions in challenging contexts.